Coexistence and Impact of Limb Muscle and Diaphragm Weakness at Time of Liberation from Mechanical Ventilation in Medical Intensive Care Unit Patients

A physiological model of phrenic nerve excitation by electrical stimulation

Mechanical ventilation is essential in intensive care treatment but leads to diaphragmatic atrophy, which in turn contributes to prolonged weaning and increased mortality. One approach to prevent diaphragmatic atrophy while achieving pulmonary ventilation is electrical stimulation of the phrenic nerve. To automize phrenic nerve stimulation resulting in lung protective tidal volumes with lowest possible currents, mathematical models are required. Nerve stimulation models are often complex, so many parameters have to be identified prior to implementation. This paper presents a novel, simplified approach to model phrenic nerve excitation to obtain an individualized patient model using a few data points. The latter is based on the idea that nerve fibers are excited when the electric field exceeds a threshold. The effect of the geometry parameter on the model output was analyzed, and the model was validated with measurement data from a pig trial (RMSE in between 0.44 × 10-2and 1.64 × 10-2for parameterized models). The modeled phrenic nerve excitation behaved similarly to the measured tidal volumes, and thus could be used to develop automated phrenic nerve stimulation systems for lung protective ventilation.

Asymmetrical high-flow nasal cannula performs similarly to standard interface in patients with acute hypoxemic post-extubation respiratory failure: a pilot study

BACKGROUND

Standard high-flow nasal cannula (HFNC) is a respiratory support device widely used to manage post-extubation hypoxemic acute respiratory failure (hARF) due to greater comfort, oxygenation, alveolar recruitment, humidification, and reduction of dead space, as compared to conventional oxygen therapy. On the contrary, the effects of the new asymmetrical HFNC interface (Optiflow® Duet system (Fisher & Paykel, Healthcare, Auckland, New Zealand) is still under discussion. Our aim is investigating whether the use of asymmetrical HFNC interface presents any relevant difference, compared with the standard configuration, on lung aeration (as assessed by end-expiratory lung impedance (EELI) measured by electrical impedance tomography (EIT)), diaphragm ultrasound thickening fraction (TFdi) and excursion (DE), ventilatory efficiency (estimated by corrected minute ventilation (MV)), gas exchange, dyspnea, and comfort.

METHODS

Pilot physiological crossover randomized controlled study enrolling 20 adults admitted to the Intensive Care unit, invasively ventilated for at least 24 h, and developing post-extubation hARF, i.e., PaO2/set FiO2 < 300 mmHg during Venturi mask (VM) within 120 min after extubation. Each HFNC configuration was applied in a randomized 60 min sequence at a flow rate of 60 L/min.

RESULTS

Global EELI, TFdi, DE, ventilatory efficiency, gas exchange and dyspnea were not significantly different, while comfort was greater during asymmetrical HFNC support, as compared to standard interface (10 [7-10] and 8 [7-9], p-value 0.044).

CONCLUSIONS

In post-extubation hARF, the use of the asymmetrical HFNC, as compared to standard HFNC interface, slightly improved patient comfort without affecting lung aeration, diaphragm activity, ventilatory efficiency, dyspnea and gas exchange.

CLINICAL TRIAL NUMBER

ClinicalTrial.gov.

REGISTRATION NUMBER

NCT05838326 (01/05/2023).

NEW & NOTEWORTHY

The asymmetrical high-flow nasal cannula oxygen therapy (Optiflow® Duet system (Fisher & Paykel, Healthcare, Auckland, New Zealand) provides greater comfort as compared to standard interface; while their performance in term of lung aeration, diaphragm activity, ventilatory efficiency, dyspnea, and gas exchange is similar.

Diaphragm Dysfunction Predicts Weaning Outcome after Bilateral Lung Transplant

BACKGROUND

Diaphragm dysfunction and its effects on outcomes of ventilator weaning have been evaluated in mixed critical care populations using diaphragm thickening fraction (the ratio of the difference between ultrasound diaphragm thickness at end-inspiration and end-expiration to diaphragm thickness at end-expiration) or neuroventilatory efficiency (the ratio of tidal volume and peak electrical activity of the diaphragm). Such data are not available in bilateral-lung transplant recipients. The authors hypothesized that (1) diaphragm dysfunction, as defined by a diaphragm thickening fraction less than 29%, is more likely to occur in difficult weaning; (2) diaphragm thickening fraction and neuroventilatory efficiency predict weaning outcome; and (3) duration of mechanical ventilation before the first spontaneous breathing trial is associated with diaphragm dysfunction.

METHODS

Adult bilateral-lung transplant patients admitted to the intensive care unit were screened at the time of the first spontaneous breathing trial (pressure-support of 5 cm H2O and 0 positive end-expiratory pressure). At the fifth minute, diaphragm thickening fraction and neuroventilatory efficiency were measured during three respiratory cycles. Weaning was classified as simple, difficult, or prolonged (successful extubation at the first spontaneous breathing trial, within three or after three spontaneous breathing trials, respectively).

RESULTS

Forty-four subjects were enrolled. Diaphragm dysfunction occurred in 14 subjects (32%), all of whom had difficult weaning (78% of the subgroup of 18 patients experiencing difficult weaning). Both diaphragm thickening fraction (24 [20 to 29] vs. 39 [35 to 45]%) and neuroventilatory efficiency (34 [26 to 45] vs. 55 [43 to 62] ml/µV) were lower in difficult weaning (both P < 0.001). The areas under the receiver operator curve predicting difficult weaning were 0.88 (95% CI, 0.73 to 0.99) for diaphragm thickening fraction and 0.85 (95% CI, 0.71 to 0.95) for neuroventilatory efficiency. The duration of ventilation demonstrated a linear inverse correlation with both diaphragm thickening fraction and neuroventilatory efficiency.

CONCLUSIONS

Diaphragm dysfunction is common after bilateral-lung transplantation and associated with difficult weaning. In such patients, average values for diaphragm thickening fraction and neuroventilatory efficiency were reduced compared to patients with simple weaning. Both parameters showed similar accuracy for predicting success of ventilator weaning, demonstrating an inverse relationship with duration of ventilation.

EDITOR’S PERSPECTIVE

In vivocharacterization of the optical and hemodynamic properties of the human sternocleidomastoid muscle through ultrasound-guided hybrid near-infrared spectroscopies

Objective.In this paper, we present a detailedin vivocharacterization of the optical and hemodynamic properties of the human sternocleidomastoid muscle (SCM), obtained through ultrasound-guided near-infrared time-domain and diffuse correlation spectroscopies.Approach.A total of sixty-five subjects (forty-nine females, sixteen males) among healthy volunteers and thyroid nodule patients have been recruited for the study. Their SCM hemodynamic (oxy-, deoxy- and total hemoglobin concentrations, blood flow, blood oxygen saturation and metabolic rate of oxygen extraction) and optical properties (wavelength dependent absorption and reduced scattering coefficients) have been measured by the use of a novel hybrid device combining in a single unit time-domain near-infrared spectroscopy, diffuse correlation spectroscopy and simultaneous ultrasound imaging.Main results.We provide detailed tables of the results related to SCM baseline (i.e. muscle at rest) properties, and reveal significant differences on the measured parameters due to variables such as side of the neck, sex, age, body mass index, depth and thickness of the muscle, allowing future clinical studies to take into account such dependencies.Significance.The non-invasive monitoring of the hemodynamics and metabolism of the sternocleidomastoid muscle during respiration became a topic of increased interest partially due to the increased use of mechanical ventilation during the COVID-19 pandemic. Near-infrared diffuse optical spectroscopies were proposed as potential practical monitors of increased recruitment of SCM during respiratory distress. They can provide clinically relevant information on the degree of the patient's respiratory effort that is needed to maintain an optimal minute ventilation, with potential clinical application ranging from evaluating chronic pulmonary diseases to more acute settings, such as acute respiratory failure, or to determine the readiness to wean from invasive mechanical ventilation.

Phrenic nerve stimulation to prevent diaphragmatic dysfunction and ventilator-induced lung injury

Side effects of mechanical ventilation, such as ventilator-induced diaphragmatic dysfunction (VIDD) and ventilator-induced lung injury (VILI), occur frequently in critically ill patients. Phrenic nerve stimulation (PNS) has been a valuable tool for diagnosing VIDD by assessing respiratory muscle strength in response to magnetic PNS. The detection of pathophysiologically reduced respiratory muscle strength is correlated with weaning failure, longer mechanical ventilation time, and mortality. Non-invasive electromagnetic PNS designed for diagnostic use is a reference technique that allows clinicians to measure transdiaphragm pressure as a surrogate parameter for diaphragm strength and functionality. This helps to identify diaphragm-related issues that may impact weaning readiness and respiratory support requirements, although lack of lung volume measurement poses a challenge to interpretation. In recent years, therapeutic PNS has been demonstrated as feasible and safe in lung-healthy and critically ill patients. Effects on critically ill patients' VIDD or diaphragm atrophy outcomes are the subject of ongoing research. The currently investigated application forms are diverse and vary from invasive to non-invasive and from electrical to (electro)magnetic PNS, with most data available for electrical stimulation. Increased inspiratory muscle strength and improved diaphragm activity (e.g., excursion, thickening fraction, and thickness) indicate the potential of the technique for beneficial effects on clinical outcomes as it has been successfully used in spinal cord injured patients. Concerning the potential for electrophrenic respiration, the data obtained with non-invasive electromagnetic PNS suggest that the induced diaphragmatic contractions result in airway pressure swings and tidal volumes remaining within the thresholds of lung-protective mechanical ventilation. PNS holds significant promise as a therapeutic intervention in the critical care setting, with potential applications for ameliorating VIDD and the ability for diaphragm training in a safe lung-protective spectrum, thereby possibly reducing the risk of VILI indirectly. Outcomes of such diaphragm training have not been sufficiently explored to date but offer the perspective for enhanced patient care and reducing weaning failure. Future research might focus on using PNS in combination with invasive and non-invasive assisted ventilation with automatic synchronisation and the modulation of PNS with spontaneous breathing efforts. Explorative approaches may investigate the feasibility of long-term electrophrenic ventilation as an alternative to positive pressure-based ventilation.

Outcomes in critically ill patients after diaphragmatic stimulation on ventilator-induced diaphragmatic dysfunction: a systematic review

INTRODUCTION

Mechanical ventilation (MV) is a lifesaving procedure for critically ill patients. Diaphragm activation and stimulation may counteract side effects, such as ventilator-induced diaphragm dysfunction (VIDD). The effects of stimulation on diaphragm atrophy and patient outcomes are reported in this systematic review.

EVIDENCE ACQUISITION

Studies investigating diaphragmatic stimulation versus standard of care in critically ill patients and evaluating clinical outcomes were extracted from a Medline database last on January 23, 2023, after registration in Prospero (CRD42021259353). Selected studies included the investigation of diaphragmatic stimulation versus standard of care in critically ill patients, an evaluation of the clinical outcomes. These included muscle atrophy, VIDD, weaning failure, mortality, quality of life, ventilation time, diaphragmatic function, length of stay in the Intensive Care Unit (ICU), and length of hospital stay. All articles were independently evaluated by two reviewers according to their abstract and title and, secondly, a full texts evaluation by two independent reviewers was performed. To resolve diverging evaluations, a third reviewer was consulted to reach a final decision. Data were extracted by the reviewers following the Oxford 2011 levels of evidence guidelines and summarized accordingly.

EVIDENCE SYNTHESIS

Seven studies were extracted and descriptively synthesized, since a metanalysis was not feasible. Patients undergoing diaphragm stimulation had moderate evidence of higher maximal inspiratory pressure (MIP), less atrophy, less mitochondrial respiratory dysfunction, less oxidative stress, less molecular atrophy, shorter MV time, shorter ICU length of stay, longer survival, and better SF-36 scores than control.

CONCLUSIONS

Evidence of the molecular and histological benefits of diaphragmatic stimulation is limited. The results indicate positive clinical effects of diaphragm activation with a moderate level of evidence for MIP and a low level of evidence for other outcomes. Diaphragm activation could be a therapeutic solution to avoid diaphragm atrophy, accelerate weaning, shorten MV time, and counteract VIDD; however, better-powered studies are needed to increase the level of evidence.

Illness Weakness, Polyneuropathy and Myopathy: Diagnosis, treatment, and long-term outcomes

BACKGROUND

Severe weakness associated with critical illness (CIW) is common. This narrative review summarizes the latest scientific insights and proposes a guide for clinicians to optimize the diagnosis and management of the CIW during the various stages of the disease from the ICU to the community stage.

MAIN BODY

CIW arises as diffuse, symmetrical weakness after ICU admission, which is an important differentiating factor from other diseases causing non-symmetrical muscle weakness or paralysis. In patients with adequate cognitive function, CIW can be easily diagnosed at the bedside using manual muscle testing, which should be routinely conducted until ICU discharge. In patients with delirium or coma or those with prolonged, severe weakness, specific neurophysiological investigations and, in selected cases, muscle biopsy are recommended. With these exams, CIW can be differentiated into critical illness polyneuropathy or myopathy, which often coexist. On the general ward, CIW is seen in patients with prolonged previous ICU treatment, or in those developing a new sepsis. Respiratory muscle weakness can cause neuromuscular respiratory failure, which needs prompt recognition and rapid treatment to avoid life-threatening situations. Active rehabilitation should be reassessed and tailored to the new patient's condition to reduce the risk of disease progression. CIW is associated with long-term physical, cognitive and mental impairments, which emphasizes the need for a multidisciplinary model of care. Follow-up clinics for patients surviving critical illness may serve this purpose by providing direct clinical support to patients, managing referrals to other specialists and general practitioners, and serving as a platform for research to describe the natural history of post-intensive care syndrome and to identify new therapeutic interventions. This surveillance should include an assessment of the activities of daily living, mood, and functional mobility. Finally, nutritional status should be longitudinally assessed in all ICU survivors and incorporated into a patient-centered nutritional approach guided by a dietician.

CONCLUSIONS

Early ICU mobilization combined with the best evidence-based ICU practices can effectively reduce short-term weakness. Multi-professional collaborations are needed to guarantee a multi-dimensional evaluation and unitary community care programs for survivors of critical illnesses.

Early detection and assessment of intensive care unit-acquired weakness: a comprehensive review

Intensive care unit-acquired weakness (ICU-AW) is a serious complication in critically ill patients. Therefore, timely and accurate diagnosis and monitoring of ICU-AW are crucial for effectively preventing its associated morbidity and mortality. This article provides a comprehensive review of ICU-AW, focusing on the different methods used for its diagnosis and monitoring. Additionally, it highlights the role of bedside ultrasound in muscle assessment and early detection of ICU-AW. Furthermore, the article explores potential strategies for preventing ICU-AW. Healthcare providers who manage critically ill patients utilize diagnostic approaches such as physical exams, imaging, and assessment tools to identify ICU-AW. However, each method has its own limitations. The diagnosis of ICU-AW needs improvement due to the lack of a consensus on the appropriate approach for its detection. Nevertheless, bedside ultrasound has proven to be the most reliable and cost-effective tool for muscle assessment in the ICU. Combining the Sequential Organ Failure Assessment (SOFA) score, Acute Physiology and Chronic Health Evaluation (APACHE) II score assessment, and ultrasound can be a convenient approach for the early detection of ICU-AW. This approach can facilitate timely intervention and prevent catastrophic consequences. However, further studies are needed to strengthen the evidence.

Imaging of the Diaphragm Following Cardiac Surgery: Focus on Ultrasonographic Assessment

Diaphragm dysfunction is a common complication following cardiac surgery. Its clinical impact is variable, ranging from the absence of symptoms to the acute respiratory failure. Post-operative diaphragm dysfunction may negatively affect patients' prognosis delaying the weaning from the mechanical ventilation (MV), extending the time of hospitalization and increasing mortality. Ultrasonography is a valid tool to evaluate diaphragmatic impairment in different settings, like the Intensive Care Unit, to predict successful weaning from the MV, and the Cardiovascular Rehabilitation Unit, to stratify patients in terms of risk of functional recovery failure. The aim of this review is to describe the pathophysiology of post-cardiac surgery diaphragm dysfunction, the techniques used for its diagnosis and the potential applications of diaphragm ultrasound.

FT-GAT: Graph neural network for predicting spontaneous breathing trial success in patients with mechanical ventilation

BACKGROUND AND OBJECTIVES

Intensive care unit (ICU) physicians perform weaning procedures considering complex clinical situations and weaning protocols; however, liberating critical patients from mechanical ventilation (MV) remains challenging. Therefore, this study aims to aid physicians in deciding the early liberation of patients from MV by developing an artificial intelligence model that predicts the success of spontaneous breathing trials (SBT).

METHODS

We retrospectively collected data of 652 critical patients (SBT success: 641, SBT failure: 400) who received MV at the Chungbuk National University Hospital (CBNUH) ICU from July 2020 to July 2022, including mixed and trauma ICUs. Patients underwent SBTs according to the CBNUH weaning protocol or physician's decision, and SBT success was defined as extubation performed by the physician on the SBT day. Additionally, our dataset comprised 11 numerical and 2 categorical features that can be obtained for any ICU patient, such as vital signs and MV setting values. To predict SBT success, we analyzed tabular data using a graph neural network-based approach. Specifically, the graph structure was designed considering feature correlation, and a novel deep learning model, called feature tokenizer graph attention network (FT-GAT), was developed for graph analysis. FT-GAT transforms the input features into high-dimensional embeddings and analyzes the graph via the attention mechanism.

RESULTS

The quantitative evaluation results indicated that FT-GAT outperformed conventional models and clinical indicators by achieving the following model performance (AUROC): FT-GAT (0.80), conventional models (0.69-0.79), and clinical indicators (0.65-0.66) CONCLUSIONS: Through timely detection critical patients who can succeed in SBTs, FT-GAT can help prevent long-term use of MV and potentially lead to improvement in patient outcomes.

Diaphragm function in patients with Covid-19-related acute respiratory distress syndrome on venovenous extracorporeal membrane oxygenation

BACKGROUND

Venovenous extracorporeal membrane oxygenation (VV ECMO) is frequently associated with deep sedation and neuromuscular blockades, that may lead to diaphragm dysfunction. However, the prevalence, risk factors, and evolution of diaphragm dysfunction in patients with VV ECMO are unknown. We hypothesized that the prevalence of diaphragm dysfunction is high and that diaphragm activity influences diaphragm function changes.

METHODS

Patients with acute respiratory distress syndrome (ARDS) requiring VV ECMO were included in two centers. Diaphragm function was serially assessed by measuring the tracheal pressure in response to phrenic nerve stimulation (Ptr,stim) from ECMO initiation (Day 1) until ECMO weaning. Diaphragm activity was estimated from the percentage of spontaneous breathing ventilation and by measuring the diaphragm thickening fraction (TFdi) with ultrasound.

RESULTS

Sixty-three patients were included after a median of 4 days (3-6) of invasive mechanical ventilation. Diaphragm dysfunction, defined by Ptr, stim ≤ 11 cmH2O, was present in 39 patients (62%) on Day 1 of ECMO. Diaphragm function did not change over the study period and was not influenced by the percentage of spontaneous breathing ventilation or the TFdi during the 1 week. Among the 63 patients enrolled in the study, 24 (38%) were still alive at the end of the study period (60 days).

CONCLUSIONS

Sixty-two percent of patients undergoing ECMO for ARDS related to SARS CoV-2 infection had a diaphragm dysfunction on Day 1 of ECMO initiation. Diaphragm function remains stable over time and was not associated with the percentage of time with spontaneous breathing.

CLINICALTRIALS

gov Identifier NCT04613752 (date of registration February 15, 2021).

Modifiable risk factors for ventilator associated diaphragmatic dysfunction: a multicenter observational study

BACKGROUND

Diaphragmatic dysfunction is known to be associated with difficulties weaning from invasive mechanical ventilation and is related to worse patient outcomes yet our understanding of how to prevent diaphragmatic dysfunction remains incomplete. We examined potentially modifiable risk factors for diaphragmatic dysfunction and attempted to estimate benefits attributable to altering these modifiable risk factors.

METHODS

This prospective multicenter observational study was undertaken in the general ICUs of two tertiary care teaching hospitals. Critically ill adults expected to receive invasive mechanical ventilation for at least 48 h were enrolled. Diaphragm function was assessed by ultrasound each study day, with dysfunction defined as thickening fraction less than 20%.

RESULTS

From January to December 2019, 856 patients were screened and 126 patients were enrolled. Overall, 40.5% (51/126) of patients experienced diaphragmatic dysfunction during invasive mechanical ventilation. Patients with diaphragmatic dysfunction were more likely to develop ventilator associated pneumonia (risk difference [RD] + 12.9%, 95% Confidence Interval [CI] 1.4 to 24.4%, P = 0.028), were more likely to experience extubation failure (RD + 8.5%, 95% CI 0.4 to 16.6%, P = 0.039) and required a longer duration of invasive mechanical ventilation (RD + 1.3 days, 95% CI 0.1 to 2.5 days, P = 0.035). They also required a longer hospital stay (RD + 1.2 days, 95% CI 0.04 to 2.4 days, P = 0.041) and were more likely to die before hospital discharge (RD + 18.1%, 95% CI 3.7 to 32.5%, P = 0.014). Multivariable analysis considered the impact of age, sex, pre-existing nutritional status, caloric intake, amino acid intake, acute disease severity, modes of mechanical ventilation, measures of respiratory status, sedation, pain control and baseline diaphragm thickness. Only SOFA score (P = 0.008) and early amino acid intake (P = 0.001) remained significant independent risk factors for the onset of diaphragmatic dysfunction. Causal path modeling suggested early amino acid intake may significantly reduce diaphragmatic dysfunction (RRR 29%, 95% CI 10% to 48%, P = 0.003) and may also reduce mortality (RRR 49%, 95% CI 25% to 73%, P < 0.0001).

CONCLUSIONS

Amino acid intake during the first 24 h of ICU stay may represent an important, modifiable risk factor for diaphragmatic dysfunction and may have a direct causal effect on mortality. We recommend additional research on this topic.

Transcutaneous electrical diaphragmatic stimulation in mechanically ventilated patients: a randomised study

BACKGROUND

Few specific methods are available to reduce the risk of diaphragmatic dysfunction for patients under mechanical ventilation. The number of studies involving transcutaneous electrical stimulation of the diaphragm (TEDS) is increasing but none report results for diaphragmatic measurements, and they lack power. We hypothesised that the use of TEDS would decrease diaphragmatic dysfunction and improve respiratory muscle strength in patients in ICU.

METHODS

We conducted a controlled trial to assess the impact of daily active electrical stimulation versus sham stimulation on the prevention of diaphragm dysfunction during the weaning process from mechanical ventilation. The evaluation was based on ultrasound measurements of diaphragm thickening fraction during spontaneous breathing trials. We also measured maximal inspiratory muscle pressure (MIP), peak cough flow (PEF) and extubation failure.

RESULTS

Sixty-six patients were included and randomised using a 1:1 ratio. The mean number of days of mechanical ventilation was 10 ± 6.8. Diaphragm thickening fraction was > 30% at the SBT for 67% of participants in the TEDS group and 54% of the Sham group (OR1.55, 95% CI 0.47-5.1; p = 0.47). MIP and PEF were similar in the TEDS and Sham groups (respectively 35.5 ± 11.9 vs 29.7 ± 11.7 cmH20; p = 0.469 and 83.2 ± 39.5 vs. 75.3 ± 34.08 L/min; p = 0.83). Rate of extubation failure was not different between groups.

CONCLUSION

TEDS did not prevent diaphragm dysfunction or improve inspiratory muscle strength in mechanically ventilated patients.

TRIAL REGISTRATION

Prospectively registered on the 20th November 2019 on ClinicalTrials.gov Identifier NCT04171024.

Diaphragm Dysfunction and ICU-Acquired Weakness in Septic Shock Patients with or without Mechanical Ventilation: A Pilot Prospective Observational Study

Sepsis is a risk factor for diaphragm dysfunction and ICU-acquired weakness (ICU-AW); however, the impact of mechanical ventilation (MV) on these relationships has not been thoroughly investigated. This study aimed to compare the incidence of diaphragm dysfunction and ICU-AW in patients with septic shock, with and without MV. We conducted a single-center prospective observational study that included consecutive patients diagnosed with septic shock admitted to the ICU between March 2021 and February 2022. Ultrasound measurements of diaphragm thickness and manual measurements of limb muscle strength were repeated after ICU admission. The incidences of diaphragm dysfunction and ICU-AW, as well as their associations with clinical outcomes, were compared between patients with MV and without MV (non-MV). Twenty-four patients (11 in the MV group and 13 in the non-MV group) were analyzed. At the final measurements in the MV group, eight patients (72.7%) had diaphragm dysfunction, and six patients (54.5%) had ICU-AW. In the non-MV group, 10 patients (76.9%) had diaphragm dysfunction, and three (23.1%) had ICU-AW. No association was found between diaphragm dysfunction and clinical outcomes. Patients with ICU-AW in the MV group had longer ICU and hospital stays. Among patients with septic shock, the incidence of diaphragm dysfunction was higher than that of ICU-AW, irrespective of the use of MV. Further studies are warranted to examine the association between diaphragm dysfunction and clinical outcomes.

[Intensive care unit-acquired weakness-Diagnostic value of neuromuscular ultrasound]

Intensive care unit-acquired weakness (ICUAW) is one of the most common neuromuscular complications in intensive care medicine. The clinical diagnosis and assessment of the severity using established diagnostic methods (e.g., clinical examination using the Medical Research Council Sum Score or electrophysiological examination) can be difficult or even impossible, especially in sedated, ventilated and delirious patients. Neuromuscular ultrasound (NMUS) has increasingly been investigated in ICUAW as an easy to use noninvasive and mostly patient compliance-independent diagnostic alternative. It has been shown that NMUS appears to be a promising tool to detect ICUAW, to assess the severity of muscular weakness and to monitor the clinical progression. Further studies are needed to standardize the methodology, to evaluate the training effort and to optimize outcome predication. The formulation of an interdisciplinary neurological and anesthesiological training curriculum is warranted to establish NMUS as a complementary diagnostic method of ICUAW in daily clinical practice.

Evaluation of electric phrenic nerve stimulation patterns for mechanical ventilation: a pilot study

Diaphragm atrophy is a common side effect of mechanical ventilation and results in prolonged weaning. Electric phrenic nerve stimulation presents a possibility to avoid diaphragm atrophy by keeping the diaphragm conditioned in sedated patients. There is a need of further investigation on how to set stimulation parameters to achieve sufficient ventilation. A prototype system is presented with a systematic evaluation for stimulation pattern adjustments. The main indicator for efficient stimulation was the tidal volume. The evaluation was performed in two pig models. As a major finding, the results for biphasic pulses were more consistent than for alternating pulses. The tidal volume increased for a range of pulse frequency and pulse width until reaching a plateau at 80-120 Hz and 0.15 ms. Furthermore, the generated tidal volume and the stimulation pulse frequency were significantly correlated (0.42-0.84, [Formula: see text]). The results show which stimulation parameter combinations generate the highest tidal volume. We established a guideline on how to set stimulation parameters. The guideline is helpful for future clinical applications of phrenic nerve stimulation.

The metabolic cost of inspiratory muscle training in mechanically ventilated patients in critical care

BACKGROUND

Diaphragmatic dysfunction is well documented in patients receiving mechanical ventilation. Inspiratory muscle training (IMT) has been used to facilitate weaning by strengthening the inspiratory muscles, yet the optimal approach remains uncertain. Whilst some data on the metabolic response to whole body exercise in critical care exist, the metabolic response to IMT in critical care is yet to be investigated. This study aimed to quantify the metabolic response to IMT in critical care and its relationship to physiological variables.

METHODS

We conducted a prospective observational study on mechanically ventilated patients ventilated for ≥ 72 h and able to participate in IMT in a medical, surgical, and cardiothoracic intensive care unit. 76 measurements were taken on 26 patients performing IMT using an inspiratory threshold loading device at 4 cmH₂O, and at 30, 50 and 80% of their negative inspiratory force (NIF). Oxygen consumption (VO₂) was measured continuously using indirect calorimetry.

RESULTS

First session mean (SD) VO₂ was 276 (86) ml/min at baseline, significantly increasing to 321 (93) ml/min, 333 (92) ml/min, 351(101) ml/min and 388 (98) ml/min after IMT at 4 cmH₂O and 30, 50 and 80% NIF, respectively (p = 0.003). Post hoc comparisons revealed significant differences in VO₂ between baseline and 50% NIF and baseline and 80% NIF (p = 0.048 and p = 0.001, respectively). VO₂ increased by 9.3 ml/min for every 1 cmH₂O increase in inspiratory load from IMT. Every increase in P/F ratio of 1 decreased the intercept VO₂ by 0.41 ml/min (CI - 0.58 to - 0.24 p < 0.001). NIF had a significant effect on the intercept and slope, with every 1 cmH₂O increase in NIF increasing intercept VO₂ by 3.28 ml/min (CI 1.98-4.59 p < 0.001) and decreasing the dose-response slope by 0.15 ml/min/cmH₂O (CI - 0.24 to - 0.05 p = 0.002).

CONCLUSIONS

IMT causes a significant load-dependent increase in VO₂. P/F ratio and NIF impact baseline VO₂. The dose-response relationship of the applied respiratory load during IMT is modulated by respiratory strength. These data may offer a novel approach to prescription of IMT.

TAKE HOME MESSAGE

The optimal approach to IMT in ICU is uncertain; we measured VO₂ at different applied respiratory loads to assess whether VO₂ increased proportionally with load and found VO₂ increased by 9.3 ml/min for every 1 cmH₂O increase in inspiratory load from IMT. Baseline NIF has a significant effect on the intercept and slope, participants with a higher baseline NIF have a higher resting VO₂ but a less pronounced increase in VO₂ as the inspiratory load increases; this may offer a novel approach to IMT prescription. Trial registration ClinicalTrials.gov, registration number: NCT05101850. Registered on 28 September 2021, https://clinicaltrials.gov/ct2/show/NCT05101850.

Inspiratory Muscle Training While Hospitalized With Acute COVID-19 Respiratory Failure: A Randomized Controlled Trial

Although inspiratory muscle training (IMT) has been used in outpatient settings for patients who recovered from COVID-19 respiratory failure, little data exist to support earlier implementation in acute care hospitals. This study aimed to assess the safety and feasibility of IMT during the acute disease phase of COVID-19.

Design Setting and Patients

Sixty patients presenting with COVID-19 to a single academic medical center were randomized to control or intervention groups using systematic randomization.

Measurements

Participants in the control group had their maximal inspiratory pressure (MIP) measured at enrollment and hospital discharge. They were also asked for their rating of perceived exertion on the Revised Borg Scale for Grading Severity of Dyspnea and were scored by researchers on the Activity Measure for Post-Acute Care (AM-PAC) 6-Clicks Mobility Scale and the Intensive Care Unit Mobility Scale (IMS). Control group patients otherwise received standard care. Participants in the intervention group, in addition to the measures described previously, received inspiratory threshold trainers with the goal of doing 2 sessions daily with a physical therapist for the duration of their inpatient hospitalization. In these sessions, the patient completed 3 sets of 10 breaths with the trainer. Initial resistance was set at 30% of their MIP, with resistance increasing 1 level for the subsequent session if the patients rated their during-activity rating of perceived exertion as less than 2. Changes in functional outcome measures, amount of supplemental oxygen, hospital length of stay (LOS), discharge location, adverse events, and mortality were assessed in group comparisons.

Results

Of 60 enrolled patients, 41 (n = 19 in intervention and n = 22 in control) were included in the final data set, which required completion of the study, initial and discharge data points collected, and survival of hospitalization. Final groups were statistically similar. A total of 161 sessions of IMT were completed among the 19 patients in the intervention group. Mortality totaled 2 in the control group and 3 in the intervention group and adverse events during intervention occurred in only 3 (1.8%) sessions, all of which were minor oxygen desaturations. Sessions were unable to be completed for all potential reasons 11% of possible times. Dropout rate in the intervention group was 3 (10%). Both intervention and control groups demonstrated improved MIP, decreased supplemental oxygen requirements, improved function on the AM-PAC, and slightly decreased function on the IMS. Length of stay was shorter in the intervention group, and discharge disposition was similar between groups.

Conclusions

With a low number of recorded adverse events, similar mortality between groups, and successful completion of 161 exercise sessions, IMT may be a feasible and safe intervention for some hospitalized patients with COVID-19.

The Incidence of Diaphragmatic Dysfunction in Patients Presenting With Dyspnea in the Emergency Department

OBJECTIVES

Diaphragmatic dysfunction has been reported as a cause of dyspnea, and its diagnosis can be made using ultrasound. Diaphragmatic ultrasound is mainly used to predict respiratory failure in chronic conditions. The use of diaphragmatic ultrasound has also risen in acute settings, such as emergency departments (EDs). However, the number of studies on its use still needs to be increased. The present study aimed to find the incidence of diaphragmatic dysfunction in the ED.

METHODS

This prospective cohort study was conducted in an ED. We enrolled patients aged greater than 18 years who presented with dyspnea. Diaphragmatic excursion and diaphragmatic thickness techniques were performed. The primary outcome was the incidence of diaphragmatic dysfunction. The secondary outcomes were the associations between diaphragmatic dysfunction and the composition of respiratory therapies within 24 hours, intubation within 24 hours, and 7-day mortality.

RESULTS

A total of 237 patients were analyzed. The incidences of diaphragmatic dysfunction assessed by diaphragmatic excursion and diaphragm thickness were 22.4 and 32.1%, respectively. Patients with sepsis and cancer had the highest incidences. Diaphragmatic dysfunction assessed by both techniques was not associated with the composition of respiratory support therapies within 24 hours, intubation within 24 hours, or 7-day mortality.

CONCLUSIONS

The incidence of diaphragmatic dysfunction in dyspneic patients in the ED ranged from 22.4 to 32.1%, depending on the ultrasound technique. Diaphragmatic dysfunction was not associated with the composition of respiratory support therapies, intubation, or mortality.

Managing respiratory muscle weakness during weaning from invasive ventilation

Weaning is a critical stage of an intensive care unit (ICU) stay, in which the respiratory muscles play a major role. Weakness of the respiratory muscles, which is associated with significant morbidity in the ICU, is not limited to atrophy and subsequent dysfunction of the diaphragm; the extradiaphragmatic inspiratory and expiratory muscles also play important parts. In addition to the well-established deleterious effect of mechanical ventilation on the respiratory muscles, other risk factors such as sepsis may be involved. Weakness of the respiratory muscles can be suspected visually in a patient with paradoxical movement of the abdominal compartment. Measurement of maximal inspiratory pressure is the simplest way to assess respiratory muscle function, but it does not specifically take the diaphragm into account. A cut-off value of -30 cmH2O could identify patients at risk for prolonged ventilatory weaning; however, ultrasound may be better for assessing respiratory muscle function in the ICU. Although diaphragm dysfunction has been associated with weaning failure, this diagnosis should not discourage clinicians from performing spontaneous breathing trials and considering extubation. Recent therapeutic developments aimed at preserving or restoring respiratory muscle function are promising.

Effectiveness of exercise training on the dyspnoea of individuals with long COVID: A randomised controlled multicentre trial

BACKGROUND

COVID-19-related acute respiratory distress syndrome (CARDS) is a severe evolution of the Sars-Cov-2 infection and necessitates intensive care. COVID-19 may subsequently be associated with long COVID, whose symptoms can include persistent respiratory symptoms up to 1 year later. Rehabilitation is currently recommended by most guidelines for people with this condition.

OBJECTIVES

To evaluate the effects of exercise training rehabilitation (ETR) on dyspnoea and health-related quality of life measures in people with continuing respiratory discomfort following CARDS.

METHODS

In this multicentre, two-arm, parallel, open, assessor-blinded, randomised controlled trial, we enroled adults previously admitted with CARDS to 3 French intensive care units who had been discharged at least 3 months earlier and who presented with an mMRC dyspnoea scale score > 1. Participants received either ETR or standard physiotherapy (SP) for 90 days. The primary outcome was dyspnoea, as measured by the Multidimensional Dyspnoea Profile (MDP), at day 0 (inclusion) and after 90 days of physiotherapy. Secondary outcomes were the mMRC and 12-item Short-Form Survey scores.

RESULTS

Between August 7, 2020, and January 26, 2022, 487 participants with CARDS were screened for inclusion, of whom 60 were randomly assigned to receive either ETR (n = 27) or SP (n = 33). Mean MDP following ETR was 42% lower than after SP (26.15 vs. 44.76); a difference of -18.61 (95% CI -27.78 to -9.44; p<10-4).

CONCLUSION

People who were still suffering from breathlessness three months after being discharged from hospital with CARDS had significantly improved dyspnoea scores when treated with ETR therapy for 90 days unlike those who only received SP. Study registered 29/09/2020 on Clinicaltrials.gov (NCT04569266).

The effect of threshold inspiratory muscle training on the duration of weaning in intensive care unit-admitted patients: A randomized clinical trial

Background

The purpose of this study was to evaluate the effect of threshold inspiratory muscle training (IMT) on the duration of weaning in intensive care unit (ICU)-admitted patients.

Materials and Methods

This randomized clinical trial enrolled 79 ICU-admitted, mechanically ventilated patients in 2020-2021 in Imam Reza Hospital, Mashhad. Patients were randomly divided into intervention (n = 40) and control (n = 39) groups. The intervention group received threshold IMT and conventional chest physiotherapy, while the control group only received conventional chest physiotherapy once a day. Before and after the end of the intervention, the strength of inspiratory muscles and the duration of weaning were measured in both the groups.

Results

The duration of weaning was shorter in the intervention group (8.4 ± 1.1 days) versus the control group (11.2 ± 0.6 days) (P < 0.001). The rapid shallow breathing index decreased by 46.5% in the intervention group and by 27.3% in the control group after the intervention (both P < 0.001), and the between-group comparison showed a significantly higher reduction in the intervention group than control group (P < 0.001). The patients' compliance after the intervention compared to the 1^st day increased to 16.2 ± 6.6 in the intervention group and 9.6 ± 6.8 in the control group (both P < 0.001), and the between-group comparison showed a significantly higher increase in the intervention group than control group. The maximum inspiratory pressure increased by 13.7 ± 6.1 in the intervention group and by 9.1 ± 6.0 in the control group (P < 0.001). Furthermore, the weaning success was 54% more probable in the intervention group than control group (P < 0.05).

Conclusion

The results of this study showed the positive effect of IMT with threshold IMT trainer on increased strength of respiratory muscles and reduced weaning duration.

Prevalence and Influencing Factors of Physical Restraints in Intensive Care Units: A Retrospective Cohort Study

Purpose

Physical restraints are used routinely in intensive care units (ICUs) and have negative effects. It is critical to identify the impact factors of physical restraints on critically ill patients. The present study investigated the prevalence of physical restraints and impact factors associated with their use in a large cohort of critically ill patients over one year.

Patients and Methods

A retrospective cohort study was performed in multiple ICUs at a tertiary hospital in China in 2019 using observational data from electronic medical records. The data consisted of demographics and clinical variables. Logistic regression was used to assess the independent impact factors for the use of physical restraint.

Results

The analysis consisted of 3776 critically ill patients with a prevalence of physical restraint use of 48.8%. The logistic regression analysis indicated that physical restraint use was associated with independent risk factors, including surgical ICU admission, pain, tracheal tube placement, and abdominal drainage tube placement. Physical restraint use was associated with independent protective factors, including male sex, light sedation, muscle strength, and ICU length of stay.

Conclusion

The prevalence of physical restraint use in critically ill patients was high. Tracheal tubes, surgical ICU, pain, abdominal drainage tubes, light sedation, and muscle strength were independent variables associated with the use of physical restraint. These results will assist health professionals in identifying high-risk physical restraint patients based on their impact factors. Early removal of the tracheal tube and abdominal drainage tube, pain relief, light sedation, and improvements in muscle strength may help reduce the use of physical restraints.

Diaphragm Neurostimulation Assisted Ventilation in Critically Ill Patients

Diaphragm neurostimulation consists of placing electrodes directly on or in proximity to the phrenic nerve(s) to elicit diaphragmatic contractions. Since its initial description in the 18th century, indications have shifted from cardiopulmonary resuscitation to long-term ventilatory support. Recently, the technical development of devices for temporary diaphragm neurostimulation has opened up the possibility of a new era for the management of mechanically ventilated patients. Combining positive pressure ventilation with diaphragm neurostimulation offers a potentially promising new approach to the delivery of mechanical ventilation which may benefit multiple organ systems. Maintaining diaphragm contractions during ventilation may attenuate diaphragm atrophy and accelerate weaning from mechanical ventilation. Preventing atelectasis and preserving lung volume can reduce lung stress and strain and improve homogeneity of ventilation, potentially mitigating ventilator-induced lung injury. Furthermore, restoring the thoracoabdominal pressure gradient generated by diaphragm contractions may attenuate the drop in cardiac output induced by positive pressure ventilation. Experimental evidence suggests diaphragm neurostimulation may prevent neuroinflammation associated with mechanical ventilation. This review describes the historical development and evolving approaches to diaphragm neurostimulation during mechanical ventilation and surveys the potential mechanisms of benefit. The review proposes a research agenda and offers perspectives for the future of diaphragm neurostimulation assisted mechanical ventilation for critically ill patients.

Effectiveness of diaphragmatic ultrasound as a predictor of successful weaning from mechanical ventilation: a systematic review and meta-analysis

BACKGROUND

Several measurements have been used to predict the success of weaning from mechanical ventilation; however, their efficacy varies in different studies. In recent years, diaphragmatic ultrasound has been used for this purpose. We conducted a systematic review and meta-analysis to evaluate the effectiveness of diaphragmatic ultrasound in predicting the success of weaning from mechanical ventilation.

METHODS

Two investigators independently searched PUBMED, TRIP, EMBASE, COCHRANE, SCIENCE DIRECT, and LILACS for articles published between January 2016 and July 2022. The methodological quality of the studies was assessed using the Quality Assessment of Diagnostic Accuracy Studies-2 tool; additionally, the certainty of the evidence is evaluated using the GRADE (Grading of Recommendations Assessment, Development, and Evaluation) methodology. Sensitivity and specificity analysis was performed for diaphragmatic excursion and diaphragmatic thickening fraction; positive and negative likelihood ratios and diagnostic odds ratios (DOR) with their confidence intervals (95% CI) were calculated by random effects analysis, summary receiver operating characteristic curve was estimated. Sources of heterogeneity were explored by subgroup analysis and bivariate meta-regression.

RESULTS

Twenty-six studies were included, of which 19 were included in the meta-analysis (1204 patients). For diaphragmatic excursion, sensitivity was 0.80 (95% CI 0.77-0.83), specificity 0.80 (95% CI 0.75-0.84), area under the summary receiver operating characteristic curve 0.87 and DOR 17.1 (95% CI 10.2-28.6). For the thickening fraction, sensitivity was 0.85 (95% CI 0.82-0.87), specificity 0.75 (95% CI 0.69-0.80), area under the summary receiver operating characteristic curve 0.87 and DOR 17.2 (95% CI 9.16-32.3). There was heterogeneity among the included studies. When performing a subgroup analysis and excluding studies with atypical cutoff values, sensitivity and specificity increased for diaphragmatic thickening fraction; sensitivity increased and specificity decreased for diaphragmatic excursion; when comparing studies using pressure support (PS) versus T-tube, there was no significant difference in sensitivity and specificity; bivariate meta-regression analysis shows that patient position at the time of testing was a factor of heterogeneity in the included studies.

CONCLUSIONS

Measurement of diaphragmatic excursion and diaphragmatic thickening fraction predict the probability of successful weaning from mechanical ventilation with satisfactory diagnostic accuracy; however, significant heterogeneity was evident in the different included studies. Studies of high methodological quality in specific subgroups of patients in intensive care units are needed to evaluate the role of diaphragmatic ultrasound as a predictor of weaning from mechanical ventilation.

Neuromuscular Ultrasound in Intensive Care Unit-Acquired Weakness: Current State and Future Directions

Intensive care unit-acquired weakness (ICUAW) is one of the most common causes of muscle atrophy and functional disability in critically ill intensive care patients. Clinical examination, manual muscle strength testing and monitoring are frequently hampered by sedation, delirium and cognitive impairment. Many different attempts have been made to evaluate alternative compliance-independent methods, such as muscle biopsies, nerve conduction studies, electromyography and serum biomarkers. However, they are invasive, time-consuming and often require special expertise to perform, making them vastly impractical for daily intensive care medicine. Ultrasound is a broadly accepted, non-invasive, bedside-accessible diagnostic tool and well established in various clinical applications. Hereby, neuromuscular ultrasound (NMUS), in particular, has been proven to be of significant diagnostic value in many different neuromuscular diseases. In ICUAW, NMUS has been shown to detect and monitor alterations of muscles and nerves, and might help to predict patient outcome. This narrative review is focused on the recent scientific literature investigating NMUS in ICUAW and highlights the current state and future opportunities of this promising diagnostic tool.

The ratio of respiratory rate to diaphragm thickening fraction for predicting extubation success

BACKGROUND

Several parameters are used to predict successful extubation but their accuracy varies among studies. We hypothesized that combining conventional and diaphragmatic parameters would be more effective than using just one. Our primary objective was to evaluate the performance of the respiratory rate in relation to the diaphragm thickening fraction (RR/DTF) ratio to predict the success of extubation.

METHODS

We enrolled 130 adult patients who required invasive mechanical ventilation, planned to be extubated, and used a spontaneous breathing trial (SBT) in the intensive care unit from July 2020 to April 2022. We measured the conventional parameters and the diaphragmatic parameters 2 h after SBT. The RR/DTF was calculated by dividing the respiratory rate (RR) by the diaphragm thickening fraction (DTF). The definition of weaning success is successful extubation within 48 h.

RESULTS

Of 130 patients, 8 patients (6.2%) were reintubated within 48 h. The RR/DTF was significantly lower in the successful extubation group than in the extubation failure group (right hemidiaphragm; 0.47 (0.33-0.64) vs 1.1 (0.6-2.32), p < 0.001 and left hemidiaphragm; 0.45 (0.31-0.65) vs 0.78 (0.48-1.75), p < 0.001). The right RR/DTF using a cut-off point at ≤ 0.81 had a sensitivity of 87.7%, a specificity of 75%, and areas under the receiver operating characteristic curve (AUROC) of 0.762 for predicting successful extubation (p = 0.013). The sensitivity, specificity, and AUROC for predicting extubation success of right DTF at a cut-off point of ≥ 26.2% were 84.3%, 62.5%, and 0.775, respectively (p = 0.009).

CONCLUSION

The RR/DTF ratio is a promising tool for predicting extubation outcome. Additionally, using RR/DTF was more reliable than conventional or diaphragmatic parameters alone in predicting extubation success.

Reference values of diaphragmatic dimensions in healthy children aged 0-8 years

Diaphragmatic thickness (Tdi) and diaphragm thickening fraction (dTF) are widely used parameters in ultrasound studies of the diaphragm in mechanically ventilated children, but normal values for healthy children are scarce. We determined reference values of Tdi and dTF using ultrasound in healthy children aged 0-8 years old and assessed their reproducibility. In a prospective, observational cohort, Tdi and dTF were measured on ultrasound images across four age groups comprising at least 30 children per group: group 1 (0-6 months), group 2 (7 months-1 year), group 3 (2-4 years) and group 4 (5-8 years). Ultrasound images of 137 healthy children were included. Mean Tdi at inspiration was 2.07 (SD 0.40), 2.09 (SD 0.40), 1.69 (SD 0.30) and 1.72 (SD 0.30) mm for groups 1, 2, 3 and 4, respectively. Mean Tdi at expiration was 1.64 (SD 0.30), 1.67 (SD 0.30), 1.38 (SD 0.20) and 1.42 (SD 0.20) mm for groups 1, 2, 3 and 4, respectively. Mean Tdi at inspiration and mean Tdi at expiration for groups 1 and 2 were significantly greater than those for groups 3 and 4 (both p < 0.001). Mean dTF was 25.4% (SD 10.4), 25.2% (SD 8.3), 22.8% (SD 10.9) and 21.3% (SD 7.1) for group 1, 2, 3 and 4, respectively. The intraclass correlation coefficients (ICC) representing the level of inter-rater reliability between two examiners performing the ultrasounds was 0.996 (95% CI 0.982-0.999). ICC of the inter-rater reliability between the raters in 11 paired assessments was 0.989 (95% CI 0.973-0.995).   Conclusion: Ultrasound measurements of Tdi and dTF were highly reproducible in healthy children aged 0-8 years.    Trial registration: ClinicalTrials.gov identifier (NCT number): NCT04589910. What is Known: • Diaphragmatic thickness and diaphragm thickening fraction are widely used parameters in ultrasound studies of the diaphragm in mechanically ventilated children, but normal values for healthy children to compare these with are scarce. What is New: • We determined normal values of diaphragmatic thickness and diaphragm thickening fraction using ultrasound in 137 healthy children aged 0-8 years old. The diaphragmatic thickness of infants up to 1 year old was significantly greater than that of children from 2 to 8 years old. Diaphragmatic thickness decreased with an increase in body surface area. These normal values in healthy children can be used to assess changes in respiratory muscle thickness in mechanically ventilated children.

Diaphragm Ultrasound in Critically Ill Patients on Mechanical Ventilation—Evolving Concepts

Mechanical ventilation (MV) is a life-saving respiratory support therapy, but MV can lead to diaphragm muscle injury (myotrauma) and induce diaphragmatic dysfunction (DD). DD is relevant because it is highly prevalent and associated with significant adverse outcomes, including prolonged ventilation, weaning failures, and mortality. The main mechanisms involved in the occurrence of myotrauma are associated with inadequate MV support in adapting to the patient’s respiratory effort (over- and under-assistance) and as a result of patient-ventilator asynchrony (PVA). The recognition of these mechanisms associated with myotrauma forced the development of myotrauma prevention strategies (MV with diaphragm protection), mainly based on titration of appropriate levels of inspiratory effort (to avoid over- and under-assistance) and to avoid PVA. Protecting the diaphragm during MV therefore requires the use of tools to monitor diaphragmatic effort and detect PVA. Diaphragm ultrasound is a non-invasive technique that can be used to monitor diaphragm function, to assess PVA, and potentially help to define diaphragmatic effort with protective ventilation. This review aims to provide clinicians with an overview of the relevance of DD and the main mechanisms underlying myotrauma, as well as the most current strategies aimed at minimizing the occurrence of myotrauma with special emphasis on the role of ultrasound in monitoring diaphragm function.

Respiratory Variations of Central Venous Pressure as Indices of Pleural Pressure Swings: A Narrative Review

The measurement of pleural (or intrathoracic) pressure is a key element for a proper setting of mechanical ventilator assistance as both under- and over-assistance may cause detrimental effects on both the lungs and the diaphragm. Esophageal pressure (Pes) is the gold standard tool for such measurements; however, it is invasive and seldom used in daily practice, and easier, bedside-available tools that allow for rapid and continuous monitoring are greatly needed. The tidal swing of central venous pressure (CVP) has long been proposed as a surrogate for pleural pressure (Ppl); however, despite the wide availability of central venous catheters, this variable is very often overlooked in critically ill patients. In the present narrative review, the physiological basis for the use of CVP waveforms to estimate Ppl is presented; the findings of previous and recent papers that addressed this topic are systematically reviewed, and the studies are divided into those reporting positive findings (i.e., CVP was found to be a reliable estimate of Pes or Ppl) and those reporting negative findings. Both the strength and pitfalls of this approach are highlighted, and the current knowledge gaps and direction for future research are delineated.

Performance of Noninvasive Airway Occlusion Maneuvers to Assess Lung Stress and Diaphragm Effort in Mechanically Ventilated Critically Ill Patients

BACKGROUND

Monitoring and controlling lung stress and diaphragm effort has been hypothesized to limit lung injury and diaphragm injury. The occluded inspiratory airway pressure (Pocc) and the airway occlusion pressure at 100 ms (P0.1) have been used as noninvasive methods to assess lung stress and respiratory muscle effort, but comparative performance of these measures and their correlation to diaphragm effort is unknown. The authors hypothesized that Pocc and P0.1 correlate with diaphragm effort and lung stress and would have strong discriminative performance in identifying extremes of lung stress and diaphragm effort.

METHODS

Change in transdiaphragmatic pressure and transpulmonary pressure was obtained with double-balloon nasogastric catheters in critically ill patients (n = 38). Pocc and P0.1 were measured every 1 to 3 h. Correlations between Pocc and P0.1 with change in transdiaphragmatic pressure and transpulmonary pressure were computed from patients from the first cohort. Accuracy of Pocc and P0.1 to identify patients with extremes of lung stress (change in transpulmonary pressure > 20 cm H2O) and diaphragm effort (change in transdiaphragmatic pressure < 3 cm H2O and >12 cm H2O) in the preceding hour was assessed with area under receiver operating characteristic curves. Cutoffs were validated in patients from the second cohort (n = 13).

RESULTS

Pocc and P0.1 correlate with change in transpulmonary pressure (R2 = 0.62 and 0.51, respectively) and change in transdiaphragmatic pressure (R2 = 0.53 and 0.22, respectively). Area under receiver operating characteristic curves to detect high lung stress is 0.90 (0.86 to 0.94) for Pocc and 0.88 (0.84 to 0.92) for P0.1. Area under receiver operating characteristic curves to detect low diaphragm effort is 0.97 (0.87 to 1.00) for Pocc and 0.93 (0.81 to 0.99) for P0.1. Area under receiver operating characteristic curves to detect high diaphragm effort is 0.86 (0.81 to 0.91) for Pocc and 0.73 (0.66 to 0.79) for P0.1. Performance was similar in the external dataset.

CONCLUSIONS

Pocc and P0.1 correlate with lung stress and diaphragm effort in the preceding hour. Diagnostic performance of Pocc and P0.1 to detect extremes in these parameters is reasonable to excellent. Pocc is more accurate in detecting high diaphragm effort.

EDITOR’S PERSPECTIVE

The relationship between diaphragm thickness and the severity of the disease in pregnant patients with Covid-19

OBJECTIVE

We aimed to investigate whether there is a relationship between diaphragm thickness and disease severity in Covid-19 pregnant subgroups.

MATERIAL AND METHODS

In this prospective study 100 pregnant patients were enrolled. Thickness of the diaphragm muscle at end-expiration was measured using B-Mode US. Hemoglobin,WBC, NLR, procalcitonin and LDH levels were measured.

RESULTS

There was a statistically significant difference between the groups in terms of diaphragm thickness, and the diaphragm thickness was thinner in the severe disease group (p < 0.001). There was no statistically significant difference between the groups with mild to moderate disease severity (p = 0.708).

CONCLUSION

Covid-19 patients who developed serious infection has thinner diaphragms than those who did not. Low diaphragm muscle thickness at the outset of Covid-19 disease, may predispose to poor clinical outcomes. Diaphragmatic ultrasound may be a promising tool to evaluate the risk of Covid-19 disease severity.

Methodological and Clinimetric Evaluation of Inspiratory Respiratory Muscle Ultrasound in the Critical Care Setting: A Systematic Review and Meta-Analysis

OBJECTIVE

Significant variations exist in the use of respiratory muscle ultrasound in intensive care with no society-level consensus on the optimal methodology. This systematic review aims to evaluate, synthesize, and compare the clinimetric properties of different image acquisition and analysis methodologies.

DATA SOURCES

Systematic search of five databases up to November 24, 2021.

STUDY SELECTION

Studies were included if they enrolled at least 50 adult ICU patients, reported respiratory muscle (diaphragm or intercostal) ultrasound measuring either echotexture, muscle thickness, thickening fraction, or excursion, and evaluated at least one clinimetric property. Two independent reviewers assessed titles, abstracts, and full text against eligibility.

DATA EXTRACTION

Study demographics, ultrasound methodologies, and clinimetric data.

DATA SYNTHESIS

Sixty studies, including 5,025 patients, were included with 39 studies contributing to meta-analyses. Most commonly measured was diaphragm thickness (DT) or diaphragm thickening fraction (DTF) using a linear transducer in B-mode, or diaphragm excursion (DE) using a curvilinear transducer in M-mode. There are significant variations in imaging methodology and acquisition across all studies. Inter- and intrarater measurement reliabilities were generally excellent, with the highest reliability reported for DT (ICC, 0.98; 95% CI, 0.94-0.99). Pooled data demonstrated acceptable to excellent accuracy for DT, DTF, and DE to predicting weaning outcome after 48 to 72 hours postextubation (DTF AUC, 0.79; 95% CI, 0.73-0.85). DT imaging was responsive to change over time. Only three eligible studies were available for intercostal muscles. Intercostal thickening fraction was shown to have excellent accuracy of predicting weaning outcome after 48-hour postextubation (AUC, 0.84; 95% CI, 0.78-0.91).

CONCLUSIONS

Diaphragm muscle ultrasound is reliable, valid, and responsive in ICU patients, but significant variation exists in the imaging acquisition and analysis methodologies. Future work should focus on developing standardized protocols for ultrasound imaging and consider further research into the role of intercostal muscle imaging.

Subjective Assessment of Motor Function by the Bedside Nurses in Mechanically Ventilated Surgical Intensive Care Unit Patients Predicts Tracheostomy

OBJECTIVE

In many institutions, intensive care unit (ICU) nurses assess their patients' muscle function as part of their routine bedside examination. We tested the research hypothesis that this subjective examination of muscle function prior to extubation predicts tracheostomy requirement.

METHODS

Adult, mechanically ventilated patients admitted to 7 ICUs at Beth Israel Deaconess Medical Center (BIDMC) between 2008 and 2019 were included in this observational study. Assessment of motor function was performed every four hours by ICU nurses. Multivariable logistic regression analysis controlled for acute disease severity, delirium risk assessment through the confusion assessment method for the ICU (CAM-ICU), and pre-defined predictors of extubation failure was applied to examine the association of motor function and tracheostomy within 30 days after extubation.

RESULTS

Within 30 days after extubation, 891 of 9609 (9.3%) included patients required a tracheostomy. The inability to spontaneously move and hold extremities against gravity within 24 h prior to extubation was associated with significantly higher odds of 30-day tracheostomy (adjusted OR 1.56, 95% CI 1.27-1.91, p < 0.001, adjusted absolute risk difference (aARD) 2.8% (p < 0.001)). The effect was magnified among patients who were mechanically ventilated for >7 days (aARD 21.8%, 95% CI 12.4-31.2%, p-for-interaction = 0.015).

CONCLUSIONS

ICU nurses' subjective assessment of motor function is associated with 30-day tracheostomy risk, independent of known risk factors. Muscle function measurements by nursing staff in the ICU should be discussed during interprofessional rounds.

Effectiveness of physical exercise and neuromuscular electrical stimulation interventions for preventing and treating intensive care unit-acquired weakness: A systematic review of randomized controlled trials

OBJECTIVE

Intensive care unit-acquired weakness is a frequent problem that develops as a secondary disorder while patients are suffering from life-threatening conditions. This study aimed to evaluate the effectiveness of physical exercise or neuromuscular electrical stimulation interventions on (i) preventing loss of muscle mass and weakness in critically ill patients admitted to intensive care units; (ii) recovering patients discharged from the intensive care unit with acquired weakness.

METHODS

A systematic review of randomized controlled trials was carried out, with studies identified in PubMed, Scopus, and Web of Science. The studies included assessed muscle mass and muscle strength, and performed a time × group analysis of effects. The risk of bias assessment was performed using the Revised Cochrane risk-of-bias tool for randomized trials.

RESULTS

Six trials with low risk of bias examined muscle mass, muscle strength, and functionality in 182 adult patients. In critically ill patients admitted to intensive care units, both neuromuscular electrical stimulation and bed/chair cycling for five to ten days prevented significant muscle loss. neuromuscular electrical stimulation in lower and upper limbs resulted in a significant reduction in the length of the hospitalization. In addition, cycle ergometer increased muscle strength and functionality. In patients discharged from the intensive care unit with acquired weakness, both neuromuscular electrical stimulation and physical exercise interventions increased muscle strength, but only physical exercise increased functionality.

CONCLUSIONS

Physical exercise and neuromuscular electrical stimulation interventions prevent excessive muscle mass loss in critically ill patients admitted to the intensive care unit and increase muscle strength in patients discharged from the intensive care unit with acquired weakness. Physical exercise seems more adequate for improving functionality.

Early passive orthostatic training prevents diaphragm atrophy and dysfunction in intensive care unit patients on mechanical ventilation: A retrospective case‒control study

BACKGROUND

Intensive care unit (ICU) patients on mechanical ventilation (MV), who are always bedridden, easily develop diaphragm atrophy and dysfunction. However, few studies have assessed diaphragmatic thickness and functional changes after early passive orthostatic training.

OBJECTIVES

This is the first study to investigate the efficacy of early passive orthostatic training in preventing diaphragm atrophy and dysfunction in ICU patients on MV.

METHODS

In this randomized retrospective case‒control study, 81 ICU patients on MV for 8 days or longer were enrolled. Forty-four patients received early passive orthostatic training initiated within 72 h of MV initiation (training group), and 37 patients did not receive training (no-training group). The protocol was performed for seven days, once a day for 30 min. The primary outcomes were diaphragmatic thickness and diaphragm contractile fraction (TFdi). The ventilatory parameters were secondary outcomes.

RESULTS

This study included 81 (45 male) ICU patients on MV [(mean ± SD) age = (60.63 ± 7.88) years]. The training group had a larger diaphragmatic thickness at end-expiration (Tdi_,ee) and a smaller magnitude of decrease in Tdi_,ee and TFdi (p = 0.001, 0.029, and <0.001, respectively) than the no-training group after 7 days of training. The mean arterial pressure, fraction of inspired oxygen, and white blood cell levels were decreased in the training group compared with the no-training group (p = 0.003, 0.001, and 0.026, respectively), but lactic acid levels decreased slightly in the training group with no significant difference (p = 0.708).

CONCLUSIONS

Early passive orthostatic training is suitable to ameliorate diaphragm atrophy and dysfunction in ICU patients on MV.

Inspiratory muscle strength and function in mechanically ventilated COVID-19 survivors 3 and 6 months after intensive care unit discharge

Background

Knowledge regarding the long-term impact of invasive mechanical ventilation on the inspiratory muscles and functional outcomes in COVID-19 survivors is limited.

Methods

In this single-centre prospective cohort study, we evaluated invasively ventilated patients with COVID-19 pneumonia 3 and 6 months post-intensive care unit (ICU) discharge. Outcomes included: maximal inspiratory pressure (MIP), ultrasound parameters for diaphragm function, 6-min walk distance (6MWD), dyspnoea and quality of life. We evaluated associations between MIP and duration of mechanical ventilation with follow-up outcomes.

Results

50 COVID-19 survivors discharged from ICU between 15 October 2020 and 1 April 2021 were enrolled. Overall, survivors showed a recovery trajectory over time. However, impaired MIP remained in 24 (48%) and 12 (24%) at 3 and 6 months, respectively. Diaphragm dysfunction was not observed. At 3 months, 23 (46%) had impaired functional capacity versus 10 (20%) at 6 months. Dyspnoea persisted in 44 (88%) patients at 3 months and 38 (76%) at 6 months. Quality of life was slightly decreased at 3 months with further improvements at 6 months. MIP was correlated to 6MWD, 6MWD % predicted, dyspnoea across follow-up, and quality of life at 3 months. The duration of invasive ventilation was correlated with 6MWD and 6MWD % predicted.

Conclusion

In invasively ventilated COVID-19 survivors, inspiratory muscle strength impairments persisted 6 months after ICU discharge, while maintaining normal diaphragm function. Decreased functional capacity, dyspnoea and slightly reduced health status were observed. Early screening of survivors is of utmost importance to identify those with impairments and at risk of delayed or incomplete recovery.

No association between thickening fraction of the diaphragm and extubation success in ventilated children

Introduction

In mechanically ventilated adults, thickening fraction of diaphragm (dTF) measured by ultrasound is used to predict extubation success. Whether dTF can also predict extubation success in children is unclear.

Aim

To investigate the association between dTF and extubation success in children. Second, to assess diaphragm thickness during ventilation and the correlation between dTF, diaphragm thickness (Tdi), age and body surface.

Method

Prospective observational cohort study in children aged 0-18 years old with expected invasive ventilation for >48 h. Ultrasound was performed on day 1 after intubation (baseline), day 4, day 7, day 10, at pre-extubation, and within 24 h after extubation. Primary outcome was the association between dTF pre-extubation and extubation success. Secondary outcome measures were Tdi end-inspiratory and Tdi end-expiratory and atrophy defined as <10% decrease of Tdi end-expiratory versus baseline at pre-extubation. Correlations were calculated with Spearman correlation coefficients. Inter-rater reliability was calculated with intraclass correlation (ICC).

Results

Fifty-three patients, with median age 3.0 months (IQR 0.1-66.0) and median duration of invasive ventilation of 114.0 h (IQR 55.5-193.5), were enrolled. Median dTF before extubation with Pressure Support 10 above 5 cmH₂O was 15.2% (IQR 9.7-19.3). Extubation failure occurred in six children, three of whom were re-intubated and three then received non-invasive ventilation. There was no significant association between dTF and extubation success; OR 0.33 (95% CI; 0.06-1.86). Diaphragmatic atrophy was observed in 17/53 cases, in three of extubation failure occurred. Children in the extubation failure group were younger: 2.0 months (IQR 0.81-183.0) vs. 3.0 months (IQR 0.10-48.0); p = 0.045. At baseline, pre-extubation and post-extubation there was no significant correlation between age and BSA on the one hand and dTF, Tdi- insp and Tdi-exp on the other hand. The ICC representing the level of inter-rater reliability between the two examiners performing the ultrasounds was 0.994 (95% CI 0.970-0.999). The ICC of the inter-rater reliability between the raters in 36 paired assessments was 0.983 (95% CI 0.974-0.990).

Conclusion

There was no significant association between thickening fraction of the diaphragm and extubation success in ventilated children.

Rbm20ΔRRM Mice, Expressing a Titin Isoform with Lower Stiffness, Are Protected from Mechanical Ventilation-Induced Diaphragm Weakness

Diaphragm weakness frequently develops in mechanically ventilated critically ill patients and is associated with increased morbidity, including ventilator weaning failure, mortality, and health care costs. The mechanisms underlying diaphragm weakness are incompletely understood but may include the elastic properties of titin, a giant protein whose layout in the muscle's sarcomeres makes it an ideal candidate to sense ventilation-induced diaphragm unloading, resulting in downstream signaling through titin-binding proteins. In the current study, we investigated whether modulating titin stiffness affects the development of diaphragm weakness during mechanical ventilation. To this end, we ventilated genetically engineered mice with reduced titin stiffness (Rbm20^ΔRRM), and robust (Ttn^ΔIAjxn) or severely (Ttn^Δ112-158) increased titin stiffness for 8 h, and assessed diaphragm contractility and protein expression of titin-binding proteins. Mechanical ventilation reduced the maximum active tension of the diaphragm in WT, Ttn^ΔIAjxn and Ttn^Δ112-158 mice. However, in Rbm20^ΔRRM mice maximum active tension was preserved after ventilation. Analyses of titin binding proteins suggest that muscle ankyrin repeat proteins (MARPs) 1 and 2 may play a role in the adaptation of the diaphragm to mechanical ventilation, and the preservation of diaphragm contractility in Rbm20^ΔRRM mice. Thus, Rbm20^ΔRRM mice, expressing titin isoforms with lower stiffness, are protected from mechanical ventilation-induced diaphragm weakness, suggesting that titin elasticity may modulate the diaphragm's response to unloading during mechanical ventilation.

Exploring the Influence of Dysphagia and Tracheostomy on Pneumonia in Patients with Stroke: A Retrospective Cohort Study

Background: Pneumonia is common in patients with tracheostomy and dysphagia. However, the influence of dysphagia and tracheostomy on pneumonia in patients with stroke remains unclear. The aim of this study was to explore the risk factors related to pneumonia, and the association between dysphagia, tracheostomy and pneumonia in patients with stroke was investigated. Methods: Patients with stroke who experienced tracheostomy and dysphagia were included and divided into two groups based on record of pneumonia at discharge. Clinical manifestations and physical examination were used to diagnose pneumonia, whereas clinical swallowing examination, and videofluoroscopy swallowing studies (VFSS) were used to evaluate swallowing function. Results: There were significant differences between the pneumonia group and the no pneumonia group in total tracheostomy time (6.3 ± 5.9 vs. 4.3 ± 1.7 months, p = 0.003), number of instances of ventilator support (0.41 ± 0.49 vs. 0.18 ± 0.38, p = 0.007), PAS score (5.2 ± 1.92 vs. 4.3 ± 1.79, p = 0.039), impaired or absent cough reflex (76.4 vs. 55.6%, p = 0.035), oropharyngeal phase dysfunction (60.6 vs. 40.8%, p = 0.047), length of hospital stay (36.0 ± 7.2 vs. 30.5 ± 11.7 days, p = 0.025) and direct medical costs (15,702.21 ± 14,244.61 vs. 10,923.99 ± 7250.14 United States dollar [USD], p = 0.042). Multivariate logistic regression showed that the total tracheostomy time (95% confidence interval [CI], 1.966−12.922, p = 0.001), impaired or absent cough reflex (95% CI, 0.084−0.695, p = 0.008), and oropharyngeal phase dysfunction (95% CI, 1.087−8.148, p = 0.034) were risk factors for pneumonia. Spearman’s correlation analysis demonstrated that PAS scores were significantly correlated with cough reflex dysfunction (r = 0.277, p = 0.03), oropharyngeal phase dysfunction (r = 0.318, p < 0.01) and total tracheostomy time (r = 0.178, p = 0.045). The oropharyngeal phase dysfunction was significantly correlated with cough reflex (r = 0.549, p < 0.001) and UES opening (r = 0.643, p < 0.01). Conclusions: Tracheostomy and dysphagia increased the risk of pneumonia in patients with stroke. Total tracheostomy time, duration of ventilator support, degree of penetration and aspiration, and oropharyngeal phase dysfunction are risk factors. Given this, we also found that there may be a correlation between tracheostomy and dysphagia.

The PROMIZING trial enrollment algorithm for early identification of patients ready for unassisted breathing

Background

Liberating patients from mechanical ventilation (MV) requires a systematic approach. In the context of a clinical trial, we developed a simple algorithm to identify patients who tolerate assisted ventilation but still require ongoing MV to be randomized. We report on the use of this algorithm to screen potential trial participants for enrollment and subsequent randomization in the Proportional Assist Ventilation for Minimizing the Duration of MV (PROMIZING) study.

Methods

The algorithm included five steps: enrollment criteria, pressure support ventilation (PSV) tolerance trial, weaning criteria, continuous positive airway pressure (CPAP) tolerance trial (0 cmH₂O during 2 min) and spontaneous breathing trial (SBT): on fraction of inspired oxygen (F_iO₂) 40% for 30–120 min. Patients who failed the weaning criteria, CPAP Zero trial, or SBT were randomized. We describe the characteristics of patients who were initially enrolled, but passed all steps in the algorithm and consequently were not randomized.

Results

Among the 374 enrolled patients, 93 (25%) patients passed all five steps. At time of enrollment, most patients were on PSV (87%) with a mean (± standard deviation) F_iO₂ of 34 (± 6) %, PSV of 8.7 (± 2.9) cmH₂O, and positive end-expiratory pressure of 6.1 (± 1.6) cmH₂O. Minute ventilation was 9.0 (± 3.1) L/min with a respiratory rate of 17.4 (± 4.4) breaths/min. Patients were liberated from MV with a median [interquartile range] delay between initial screening and extubation of 5 [1–49] hours. Only 7 (8%) patients required reintubation.

Conclusion

The trial algorithm permitted identification of 93 (25%) patients who were ready to extubate, while their clinicians predicted a duration of ventilation higher than 24 h.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13054-022-04063-4.

YAP1 silencing attenuated lung injury/fibrosis but worsened diaphragmatic function by regulating oxidative stress and inflammation response in mice

Oxidative stress is a crucial mechanism in the pathophysiology of lung injury/fibrosis and diaphragmatic dysfunction. Yes-associated protein 1 (YAP1) is a key oxidative stress response regulator. However, how lung injury/fibrosis and the subsequent YAP1 silencing treatment affect diaphragmatic function remains largely uncharacterized. In this study, mice models of acute lipopolysaccharide (LPS) and paraquat exposure were used to establish acute lung injury and chronic pulmonary fibrosis. AT2 and C2C12 cells were co-cultured under LPS and paraquat challenge. YAP1 was interfered with shRNA given in vivo and verteporfin administration in vitro. Pulmonary histology, contractile properties, and cross-sectional areas (CSAs) of the diaphragm and gastrocnemius were evaluated. Histological and biochemical analyses were performed for targeted biomarker determination. We found that LPS and paraquat caused significant lung injury/fibrosis and significantly reduced the diaphragmatic-specific force and CSAs compared with the control. YAP1 silencing alleviated inflammatory cell infiltration or collagen deposition in the lungs yet worsened the already impaired diaphragmatic function by increasing inflammatory cytokines (IL-6 and TNF-α), mitochondrial reactive oxidative species (ROS) emission, protein degradation (Murf-1, atrogin-1, and calpain), and decreasing antioxidant capabilities (superoxide dismutase 2 and glutathione peroxidase). No significant improvements were observed in diaphragmatic function by transient YAP1 knockdown in the gastrocnemius. In vitro, LPS- or paraquat-caused cytotoxicity in AT2 cells was mostly alleviated by verteporfin in a concentration that was 20-fold higher than that in C2C12 cells (20 and 1 μg/mL, respectively). Finally, 0.5 μg/mL of verteporfin significantly ameliorated hydrogen peroxide-induced proteolytic activity and antioxidant enzyme suppression in C2C12 cells, whereas 2 μg/mL of verteporfin deteriorated the same. Collectively, lung injury/fibrosis adversely affects the diaphragm. YAP1 inhibition alleviates lung injury/fibrosis but worsens diaphragmatic function potentially by enhancing inflammatory cytokines and ROS-mediated protein degradation. This disparity might be attributed to differences in susceptibility to YAP1 inhibition between muscles and the lungs.

Update on the use of ultrasound in the diagnosis and monitoring of the critical patient

Hemodynamic and respiratory complications are the main causes of morbidity and mortality in in critical care units (CCU). Imaging techniques are a key tool in differential diagnosis and treatment. In the last decade, ultrasound has shown great potential for bedside diagnosis of respiratory disease, as well as for the hemodynamic assessment of critically ill patients. Ultrasound has proven to be a useful guide for identifying the type of shock, estimating cardiac output, guiding fluid therapy and vasoactive drugs, providing security in the performance of percutaneous techniques (thoracentesis, pericardiocentesis, evacuation of abscesses/hematomas), detecting dynamically in real time pulmonary atelectasis and its response to alveolar recruitment maneuvers, and predicting weaning failure from mechanical ventilation. Due to its dynamic nature, simple learning curve and absence of ionizing radiation, it has been incorporated as an essential tool in daily clinical practice in CCUs. The objective of this review is to offer a global vision of the role of ultrasound and its applications in the critically ill patient.

Does mechanical threshold inspiratory muscle training promote recovery and improve outcomes in patients who are ventilator-dependent in the intensive care unit? The IMPROVE randomised trial

BACKGROUND

In patients who are ventilator-dependent in the intensive care unit, inspiratory muscle training may improve inspiratory muscle strength and accelerate liberation from the ventilator, but optimal training parameters are yet to be established, and little is known about the impact of inspiratory muscle training on quality of life or dyspnoea. Thus, we sought to ascertain whether inspiratory muscle training, commenced while ventilator-dependent, would improve outcomes for patients invasively ventilated for 7 days or longer.

METHODS

In this randomised trial with assessor blinding and intention-to-treat analysis, 70 participants (mechanically ventilated ≥7 days) were randomised to receive once-daily supervised high-intensity inspiratory muscle training with a mechanical threshold device in addition to usual care or to receive usual care (control). Primary outcomes were inspiratory muscle strength (maximum inspiratory pressure % predicted) and endurance (fatigue resistance index) at ventilator liberation and 1 week later. Secondary outcomes included quality of life (SF-36v2, EQ-5D), dyspnoea, physical function, duration of ventilation, and in-hospital mortality.

RESULTS

Thirty-three participants were randomly allocated to the training group, and 37 to the control group. There were no statistically significant differences in strength (maximum inspiratory pressure) (95% confidence interval [CI]: -7.4 to 14.0) or endurance (fatigue resistance index) (95% CI: -0.003 to 0.436). Quality of life improved significantly more in the training group than in the control group (EQ-5D: 17.2; 95% CI: 1.3-33.0) (SF-36-PCS: 6.97; 95% CI: 1.96-12.00). Only the training group demonstrated significant reductions in dyspnoea (-1.5 at rest, -1.9 during exercise). There were no between-group differences in duration of ventilation or other measures. In-hospital mortality was higher in the control group than in the training group (9 vs 4, 24% vs 12%, p = 0.23).

CONCLUSIONS

In patients who are ventilator-dependent, mechanical threshold loading inspiratory muscle training improves quality of life and dyspnoea, even in the absence of strength improvements or acceleration of ventilator liberation.

Relationships between double cycling and inspiratory effort with diaphragm thickness during the early phase of mechanical ventilation: A prospective observational study

Background

Increased and decreased diaphragm thickness during mechanical ventilation is associated with poor outcomes. Some types of patient-ventilator asynchrony theoretically cause myotrauma of the diaphragm. However, the effects of double cycling on structural changes in the diaphragm have not been previously evaluated. Hence, this study aimed to investigate the relationship between double cycling during the early phase of mechanical ventilation and changes in diaphragm thickness, and the involvement of inspiratory effort in the occurrence of double cycling.

Methods

We evaluated adult patients receiving invasive mechanical ventilation for more than 48 h. The end-expiratory diaphragm thickness (Tdi_ee) was assessed via ultrasonography on days 1, 2, 3, 5 and 7 after the initiation of mechanical ventilation. Then, the maximum rate of change from day 1 (ΔTdi_ee%) was evaluated. Concurrently, we recorded esophageal pressure and airway pressure on days 1, 2 and 3 for 1 h during spontaneous breathing. Then, the waveforms were retrospectively analyzed to calculate the incidence of double cycling (double cycling index) and inspiratory esophageal pressure swing (ΔP_es). Finally, the correlation between double cycling index as well as ΔP_es and ΔTdi_ee% was investigated using linear regression models.

Results

In total, 19 patients with a median age of 69 (interquartile range: 65–78) years were enrolled in this study, and all received pressure assist-control ventilation. The Tdi_ee increased by more than 10% from baseline in nine patients, decreased by more than 10% in nine and remained unchanged in one. The double cycling indexes on days 1, 2 and 3 were 2.2%, 1.3% and 4.5%, respectively. There was a linear correlation between the double cycling index on day 3 and ΔTdi_ee% (R² = 0.446, p = 0.002). The double cycling index was correlated with the ΔP_es on days 2 (R² = 0.319, p = 0.004) and 3 (R² = 0.635, p < 0.001).

Conclusions

Double cycling on the third day of mechanical ventilation was associated with strong inspiratory efforts and, possibly, changes in diaphragm thickness.

Occurrence and Effects on Weaning From Mechanical Ventilation of Intensive Care Unit Acquired and Diaphragm Weakness: A Pilot Study

Purpose

Limb intensive care unit (ICU)-acquired weakness (ICUAW) and ICU acquired diaphragm weakness (DW) occur frequently in mechanically ventilated (MV) patients; their coexistence in cooperative and uncooperative patients is unknown. This study was designed to (1) describe the co-occurrence of the two conditions (2) evaluate the impact of ICUAW and DW on the ventilator-free days (VFDs) at 28 days and weaning success, and (3) assess the correlation between maximal inspiratory pressure (MIP) and thickening fraction (TFdi) in patients with DW.

Methods

This prospective pilot study was conducted in a single-center on 73 critically ill MV patients. Muscle weakness was defined as a Medical Research Council score &lt; 48 in cooperative patients or a bilateral mean simplified peroneal nerve test &lt; 5.26 mV in uncooperative patients. Diaphragm dysfunction was defined as MIP &lt; 30 cm H2O or as a TFdi &lt; 29%. Weaning success was defined according to weaning according to a new definition (WIND).

Results

Fifty-seven patients (78%) had ICUAW and 59 (81%) had DW. The coexistence of the two conditions occurred in 48 patients (65%), without association (χ2 = 1.06, p = 0.304). In the adjusted analysis, ICUAW was independently related to VFDs at 28-days (estimate difference 6 days, p = 0.016), and WIND (OR of 3.62 for having WIND different than short weaning), whereas DW was not. The linear mixed model showed a significant but weak correlation between MIP and TFdi (p &lt; 0.001).

Conclusion

This pilot study is the first to explore the coexistence of ICUAW and DW in both cooperative and uncooperative patients; a lack of association was found between DW and ICUAW when considering both cooperative and uncooperative patients. We found a strong correlation between ICUAW but not DW with the VFDs at 28 days and weaning success. A future larger study is warranted in order to confirm our results, and should also investigate the use of transdiaphragmatic twitch pressure measurement during bilateral anterior magnetic phrenic nerve stimulation for the diagnosis of DW.