Diaphragm thickening in cardiac surgery: a perioperative prospective ultrasound study

Exploring ultrasonographic diaphragmatic function in perioperative anesthesia setting: A comprehensive narrative review

The ultrasound study of diaphragm function represents a valid method that has been extensively studied in recent decades in various fields, especially in intensive care, emergency, and pulmonology settings. Diaphragmatic function is pivotal in these contexts due to its crucial role in respiratory mechanics, ventilation support strategies, and overall patient respiratory outcomes. Dysfunction or weakness of the diaphragm can lead to respiratory failure, ventilatory insufficiency, and prolonged mechanical ventilation, making its assessment essential for patient management and prognosis in critical care and emergency medicine. While several studies have focused on diaphragmatic functionality in the context of intensive care, there has been limited attention within the field of anesthesia. The ultrasound aids in assessing diaphragmatic dysfunction (DD) by measuring muscle mass and contractility and their potential variations over time. Recent advancements in ultrasound imaging allow clinicians to evaluate diaphragm function and monitor it during mechanical ventilation more easily. In the context of anesthesia, early studies have shed light on the patho-physiological mechanisms of diaphragm function during general anesthesia. In contrast, more recent research has centered on evaluating diaphragmatic functionality at various phases of general anesthesia and by comparing diverse types of procedures or anatomical position during surgery. The objectives of this current review are to highlight the use of diaphragm ultrasound for the evaluation of diaphragmatic function during perioperative anesthesia and surgery. Specifically, we aim to examine the effects of anesthetic agents, surgical techniques, and anatomical positioning on diaphragmatic function. We explore how ultrasound aids in assessing DD by measuring muscle mass and contractility, as well as their potential variations over time. Additionally, we will discuss recent advancements in ultrasound imaging that allow clinicians to evaluate diaphragm function and monitor it during mechanical ventilation more easily.

Diaphragmatic dysfunction is associated with postoperative pulmonary complications in the aged patients underwent radical resection of esophageal cancer: a prospective observational study

Background

Diaphragmatic dysfunction escalates the susceptibility to postoperative pulmonary complications (PPCs). Currently, no study reports the occurrence of diaphragmatic dysfunction correlated with PPCs following radical resection of esophageal cancer in aged patients. We aimed to diagnose diaphragmatic dysfunction via ultrasonography and analyze diaphragmatic dysfunction's relation with PPCs after radical resection of esophageal cancer surgery in aged patients.

Methods

This prospective observational study comprised 86 aged patients undergoing radical resection of esophageal cancer. Patient characteristics data and intraoperative details were collected. Ultrasonography was performed before (preoperative) and after (first, third, and fifth day postoperatively) surgery. Outcome measures included PPCs within seven days postoperative, occurrence of diaphragmatic dysfunction, and short-term prognosis.

Results

After excluding 14 patients, we finally analyzed clinical data from 72 patients. The prevalence of PPCs was higher in the patients with diaphragmatic dysfunction than those without (19 of 23, 83% vs. 21 of 49, 43%, P=0.004). Postoperative diaphragmatic dysfunction was positively correlated with PPCs in patients who underwent elective radical esophageal cancer surgery (r=0.37, P=0.001). Persistent diaphragmatic dysfunction, furthermore, was positively correlated with the development of multiple PPCs (r=0.43, P<0.001). The logistic regression analysis revealed that age, total open procedure, and postoperative diaphragmatic dysfunction were identified as significant risk factors for PPCs, while total open procedure was an independent risk factor for diaphragmatic dysfunction.

Conclusions

Postoperative diaphragmatic dysfunction positively correlates with developing PPCs. Continuous monitoring of postoperative diaphragmatic function can screen high-risk patients with PPCs, which has specific clinical significance. Age, total open procedure, and diaphragmatic dysfunction are identified as risk factors for developing PPCs, while total open procedure specifically increases the risk for postoperative diaphragmatic dysfunction.

Ultrasound assessment of diaphragmatic dysfunction in non-critically ill patients: relevant indicators and update

Diaphragm dysfunction (DD) can be classified as mild, resulting in diaphragmatic weakness, or severe, resulting in diaphragmatic paralysis. Various factors such as prolonged mechanical ventilation, surgical trauma, and inflammation can cause diaphragmatic injury, leading to negative outcomes for patients, including extended bed rest and increased risk of pulmonary complications. Therefore, it is crucial to protect and monitor diaphragmatic function. Impaired diaphragmatic function directly impacts ventilation, as the diaphragm is the primary muscle involved in inhalation. Even unilateral DD can cause ventilation abnormalities, which in turn lead to impaired gas exchange, this makes weaning from mechanical ventilation challenging and contributes to a higher incidence of ventilator-induced diaphragm dysfunction and prolonged ICU stays. However, there is insufficient research on DD in non-ICU patients, and DD can occur in all phases of the perioperative period. Furthermore, the current literature lacks standardized ultrasound indicators and diagnostic criteria for assessing diaphragmatic dysfunction. As a result, the full potential of diaphragmatic ultrasound parameters in quickly and accurately assessing diaphragmatic function and guiding diagnostic and therapeutic decisions has not been realized.

Interest of thoracic ultrasound after cardiac surgery or interventional cardiology

Thoracic ultrasound has attracted much interest in detecting pleural effusion or pulmonary consolidation after cardiac surgery. In 2016, Trovato reported, in the World Journal of Cardiology, the interest of using, in addition to echocardiography, thoracic ultrasound. In this editorial, we highlight the value of assessing diaphragm function after cardiac surgery and interventional cardiology procedures. Various factors are able to impair diaphragm function after such interventions. Diaphragm motion may be decreased by chest pain secondary to sternotomy, pleural effusion or impaired muscle function. Hemidiaphragmatic paralysis may be secondary to phrenic nerve damage complicating cardiac surgery or atrial fibrillation ablation. Diagnosis may be delayed. Indeed, respiratory troubles induced by diaphragm dysfunction are frequently attributed to pre-existing heart disease or pulmonary complications secondary to surgery. In addition, elevated hemidiaphragm secondary to diaphragm dysfunction is sometimes not observed on chest X-ray performed in supine position in the intensive care unit. Analysis of diaphragm function by ultrasound during the recovery period appears essential. Both hemidiaphragms can be studied by two complementary ultrasound methods. The mobility of each hemidiaphragms is measured by M-mode ultrasonography. In addition, recording the percentage of inspiratory thickening provides important information about the quality of muscle function. These two approaches make it possible to detect hemidiaphragm paralysis or dysfunction. Such a diagnosis is important because persistent diaphragm dysfunction after cardiac surgery has been shown to be associated with adverse respiratory outcome. Early respiratory physiotherapy is able to improve respiratory function through strengthening of the inspiratory muscles i.e. diaphragm and accessory inspiratory muscles.

Diaphragm thickness modifications and associated factors during VA-ECMO for a cardiogenic shock: a cohort study

BACKGROUND

The incidence, causes and impact of diaphragm thickness evolution in veno-arterial extracorporeal membrane oxygenation (VA-ECMO) for cardiogenic shock are unknown. Our study investigates its evolution during the first week of VA-ECMO and its relationship with sweep gas flow settings.

METHODS

We conducted a prospective monocentric observational study in a 12-bed ICU in France, enrolling patients on the day of the VA-ECMO implantation. The diaphragm thickness and the diaphragm thickening fraction (as index of contractile activity, dTF; dTF < 20% defined a low contractile activity) were daily measured for one week using ultrasound. Factors associated with diaphragm thickness evolution (categorized as increased, stable, or atrophic based on > 10% modification from baseline to the last measurement), early extubation role (< day4), and patients outcome at 60 days were investigated. Changes in diaphragm thickness, the primary endpoint, was analysed using a mixed-effect linear model (MLM).

RESULTS

Of the 29 included patients, seven (23%) presented diaphragm atrophy, 18 remained stable (60%) and 4 exhibited an increase (17%). None of the 13 early-extubated patients experienced diaphragm atrophy, while 7 (46%) presented a decrease when extubated later (p-value = 0.008). Diaphragm thickness changes were not associated with the dTF (p-value = 0.13) but with sweep gas flow (Beta = - 3; Confidence Interval at 95% (CI) [- 4.8; - 1.2]. p-value = 0.001) and pH (Beta = - 2; CI [- 2.9; - 1]. p-value < 0.001) in MLM. The dTF remained low (< 20%) in 20 patients (69%) at the study's end and was associated with sweep gas flow evolution in MLM (Beta = - 2.8; 95% CI [- 5.2; - 0.5], p-value = 0.017). Odds ratio of death at 60 days in case of diaphragm atrophy by day 7 was 8.50 ([1.4-74], p = 0.029).

CONCLUSION

In our study, diaphragm thickness evolution was frequent and not associated with the diaphragm thickening fraction. Diaphragm was preserved from atrophy in case of early extubation with ongoing VA-ECMO assistance. Metabolic disorders resulting from organ failures and sweep gas flow were linked with diaphragm thickness evolution. Preserved diaphragm thickness in VA-ECMO survivors emphasizes the importance of diaphragm-protective strategies, including meticulous sweep gas flow titration.

Effects of transcutaneous electrical diaphragmatic stimulation in critically ill elderly patients: a randomized controlled trial

BACKGROUND

Elderly patients under invasive mechanical ventilation (IMV) are more susceptible to muscle weakness. In the out-of-hospital environment, there are benefits to transcutaneous electrical diaphragmatic stimulation (TEDS), which is an easy-to-apply and low-cost technique.

OBJECTIVE

To evaluate the effect of TEDS on respiratory muscle strength, diaphragm thickness (DT), and IMV time in critically ill elderly patients.

METHODS

This was a randomized controlled trial in which patients were divided into an experimental group (EG) and a control group (CG). TEDS started 24 h after orotracheal intubation and lasted until the end of weaning. Both groups underwent the following assessments during the spontaneous breathing test after weaning from mechanical ventilation (MV): measurement of respiratory muscle strength by pressure gauge, analysis of DT by lung ultrasound, and extubation failure prevention checklist.

RESULTS

There were 23 participants in the EG and 21 in the CG. The median age was 66 (60-79) years. The mean values of the diaphragmatic thickening index in the EG and CG participants were 99.13 ± 26.75 and 66.88 ± 31.77, respectively (p = .001, Cohen's d = 1.094). The mean values of maximum inspiratory pressure in the EG and CG were 22.04 ± 3.41 and 19.34 ± 4.23 cmH2O, respectively (p = .005, Cohen's d = 0.698). The Tobin index and the integrative weaning index were similar between groups (p = .584 and p = .102, respectively). The duration of MV in the EG and CG was 6.28 ± 2.68 and 9.21 ± 2.76 days, respectively (p = .001, Cohen's d = -1.075).

CONCLUSION

Critically ill elderly patients receiving TEDS had shorter MV time, greater inspiratory muscle strength, and greater diaphragmatic contraction capacity according to their thickness fraction.

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.

A randomized controlled trial of the intraoperative use of noninvasive ventilation versus supplemental oxygen by face mask for procedural sedation in an electrophysiology laboratory

PURPOSE

The efficacy of noninvasive ventilation (NIV) during procedures that require sedation and analgesia has not been established. We evaluated whether NIV reduces the incidence of respiratory events.

METHODS

In this randomized controlled trial, we included 195 patients with an American Society of Anesthesiologists Physical Status of III or IV during electrophysiology laboratory procedures. We compared NIV with face mask oxygen therapy for patients under sedation. The primary outcome was the incidence of respiratory events determined by a computer-driven blinded analysis and defined by hypoxemia (peripheral oxygen saturation < 90%) or apnea/hypopnea (absence of breathing for 20 sec on capnography). Secondary outcomes included hemodynamic variables, sedation, patient safety (composite scores of major or minor adverse events), and adverse outcomes at day 7.

RESULTS

A respiratory event occurred in 89/98 (95%) patients in the NIV group and in 69/97 (73%) patients with face masks (risk ratio [RR], 1.29; 95% confidence interval [CI], 1.13 to 1.47; P < 0.001). Hypoxemia occurred in 40 (42%) patients in the NIV group and in 33 (34%) patients with face masks (RR, 1.21; 95% CI, 0.84 to 1.74; P = 0.30). Apnea/hypopnea occurred in 83 patients (92%) in the NIV group vs 65 patients (70%) with face masks (RR, 1.32; 95% CI, 1.14 to 1.53; P < 0.001). Hemodynamic variables, sedation, major or minor safety events, and patient outcomes were not different between the groups.

CONCLUSIONS

Respiratory events were more frequent among patients receiving NIV without any safety or outcome impairment. These results do not support the routine use of NIV intraoperatively.

STUDY REGISTRATION

ClinicalTrials.gov (NCT02779998); registered 4 November 2015.

Ultrasonic prediction of weaning failure in children undergoing cardiac surgery: A prospective observational study

Background and Aim

To assess the utility of ultrasonic markers like B-line score (LUS), diaphragm thickness (DT), thickening fraction (DTF), and excursion (DE) as predictors of weaning outcomes in children on mechanical ventilation (MV) after cardiac surgery.

Methods

This was a prospective observational study done in postcardiac surgical intensive care unit (ICU) of a tertiary care hospital. Children aged 1 month to 18 years, on MV after cardiac surgery from January to November 2017, were included. They were extubated after satisfying institutional weaning criteria. Ultrasound for LUS, DT, DTF, and DE was performed preoperatively, during pressure support ventilation (PSV) before extubation and 4 h after extubation.

Results

Patients were divided into weaning failure and success groups based on reintubation within 48 h of extubation. Of the 50 evaluated patients, 43 (86%) were weaned successfully and 7 (14%) had weaning failure. The left DTF during PSV was lower in patients weaning failure (0.00%, interquartile range (IQR) 0.00-14.28 vs 16.67%, IQR 8.33-22.20, P = 0. 012). The left DTF≤ 14.64% during PSV (area under receiver's operating curve 0.795, P = 0.014), 85% sensitivity, and 57% specificity (positive likelihood ratio 1.97, negative likelihood ratio 0.25) could predict weaning failure.

Conclusion

The left DTF during PSV is a good predictor of weaning failure in children on MV in postoperative ICU after congenital cardiac surgery.

Take home message

In children on mechanical ventilation after cardiac surgery, left DTF during pressure support ventilation is a good predictor of weaning failure.

Diaphragm function in patients with sepsis and septic shock: A longitudinal ultrasound study

BACKGROUND

Previous literature on the determinants of diaphragm dysfunction in septic patients is limited. The goal of this study is to assess diaphragm dysfunction in terms of its prevalence and its potential associated factors in septic intensive care unit (ICU) patients.

METHODS

This prospective and observational study was conducted between June 2015 and July 2019. Ultrasound measures of diaphragm thickness were performed daily on septic patients. The primary outcome was the prevalence of diaphragm dysfunction at baseline and during the ICU stay. The secondary outcome was the diaphragm thickness. Possible associated factors were prospectively recorded.

RESULTS

Fifty patients were enrolled in the study. The prevalence of diaphragm dysfunction was 58%. No diaphragm atrophy was found during the ICU stay. Diaphragm dysfunction was associated with the alteration of consciousness, intra-abdominal sepsis, hypnotics and opioids, and mechanical ventilation. Administration of hypnotics, opioids, and steroids was associated with a decreased diaphragm thickening fraction. Diaphragm dysfunction had no impact on patient outcomes.

CONCLUSIONS

Our data reveal a high prevalence of diaphragm dysfunction in septic patients at the onset of sepsis. Administration of hypnotics, opioids, and steroids was associated with the alteration of diaphragm function as well as intra-abdominal sepsis.

Intraoperative Ventilator Management of the Critically Ill Patient

Strategies for the intraoperative ventilator management of the critically ill patient focus on parameters used for lung protective ventilation with acute respiratory distress syndrome, preventing or limiting the deleterious effects of mechanical ventilation, and optimizing anesthetic and surgical conditions to limit postoperative pulmonary complications for patients at risk. Patient conditions such as obesity, sepsis, the need for laparoscopic surgery, or one-lung ventilation may benefit from intraoperative lung protective ventilation strategies. Anesthesiologists can use risk evaluation and prediction tools, monitor advanced physiologic targets, and incorporate new innovative monitoring techniques to develop an individualized approach for patients.

Persistent diaphragm dysfunction after cardiac surgery is associated with adverse respiratory outcomes: a prospective observational ultrasound study

BACKGROUND

Transient diaphragm dysfunction is common during the first week after cardiac surgery; however, the precise incidence, risk factors, and outcomes of persistent diaphragm dysfunction are not well described.

METHODS

In a single-centre prospective cohort study, we included all consecutive patients over 18 yr who underwent elective cardiac surgery. Diaphragm function was evaluated with ultrasound (M-mode) by recording the excursion of both hemidiaphragms at two different time points: preoperatively and after the seventh postoperative day in patients breathing without assistance. Significant diaphragm dysfunction after the seventh day of the index cardiac surgery was defined as a decrease in diaphragm excursion below the lower limit of normal: at rest, < 9 mm for women and < 10 mm for men; after a sniff test, < 16 mm for women and < 18 mm for men.

RESULTS

Overall, 122 patients were included in the analysis. The median [interquartile range (IQR)] age was 69 [59-74] years and 96/122 (79%) were men. Ten (8%) patients had diaphragm dysfunction after the seventh postoperative day. We did not identify risk factors for persistent diaphragm dysfunction. Persistent diaphragm dysfunction was associated with a longer median [IQR] duration of noninvasive (8 [0-34] vs 0 [0-0] hr; difference in medians, 8 hr; 95% confidence interval [CI], 0 to 22; P < 0.001) and invasive mechanical ventilation (5 [3-257] vs 3[2-4] hr; difference in medians, 2 hr; 95% CI, 0.5 to 41; P = 0.008); a higher reintubation rate (4/10, 40% vs 1/112, 0.9%; relative risk, 45; 95% CI, 7.1 to 278; P < 0.0001), a higher incidence of pneumonia (4/10 [40%] vs 7/112 [6%]; relative risk, 6; 95% CI, 2 to 16; P < 0.001), and longer median [IQR] length of stay in the intensive care unit (8 [5-29] vs 4 [2-6] days; difference in medians, 4 days; 95% CI, 2 to 12; P = 0.002).

CONCLUSION

The incidence of persistent diaphragm dysfunction was 8% in patients undergoing elective cardiac surgery and was associated with adverse respiratory outcomes.

STUDY REGISTRATION

ClinicalTrials.gov (NCT04276844); prospectively registered 19 February 2020.

Ultrasonographic Assessment of Diaphragmatic Function and Its Clinical Application in the Management of Patients with Acute Respiratory Failure

Acute respiratory failure (ARF) is a common life-threatening medical condition, with multiple underlying etiologies. In these cases, many factors related to systemic inflammation, prolonged use of steroids, and lung mechanical abnormalities (such as hyperinflation or increased elastic recoil due to pulmonary oedema or fibrosis) may act as synergic mechanisms leading to diaphragm dysfunction. The assessment of diaphragm function with ultrasound has been increasingly investigated in the emergency department and during hospital stay as a valuable tool for providing additional anatomical and functional information in many acute respiratory diseases. The diaphragmatic ultrasound is a noninvasive and repeatable bedside tool, has no contraindications, and allows the physician to rapidly assess the presence of diaphragmatic dysfunction; this evaluation may help in estimating the need for mechanical ventilation (and the risk of weaning failure), as well as the risk of longer hospital stay and higher mortality rate. This study presents an overview of the recent evidence regarding the evaluation of diaphragmatic function with bedside ultrasound and its clinical applications, including a discussion of real-life clinical cases.

[The perioperative role of high-flow cannula oxygen (HFNO)]

High-flow nasal cannula oxygen (HFNO) is commonly used during the perioperative period. Its numerous physiological benefits, satisfactory tolerance and ease of use have led to its widespread application in intensive care and post-anesthesia care units. HFNO is also used in the operating theater in multiple indications: as oxygen supplementation (associated with pressurization) prior to orotracheal intubation; in digestive and bronchial endoscopies, especially in patients at risk of hypoxemia; and in intraoperative surgery requiring spontaneous ventilation (ENT, thoracic surgery…). During the postoperative period, HFNO can be used in a curative strategy for respiratory failure or in a prophylactic strategy to prevent reintubation. In a curative approach, HFNO seems of interest following cardiac or thoracic surgery but has not been evaluated in respiratory failure subsequent to abdominal surgery, in which case noninvasive ventilation remains the gold standard. The risk of respiratory complications depends on type of surgery and on patient comorbidities. As prophylaxis, HFNO is currently preferred to conventional oxygen therapy after cardiac or thoracic surgery, especially in patients at high risk of respiratory complications. For the clinician, it is important to acknowledge the limits of HFNO and to closely monitor patients receiving HFNO, the objective being to avoid delays in intubation that could lead to increased mortality.

Diaphragm Dysfunction after Cardiac Surgery: Insights from Ultrasound Imaging during Cardiac Rehabilitation

Diaphragm dysfunction is common after cardiac surgery and can be evaluated with ultrasonography (US). We aimed at assessing with US the incidence of diaphragmatic dysfunction and the impact of cardiovascular rehabilitation (CR) on its recovery. A single-center cohort study was performed. Patients were enrolled after cardiac surgery. The 6-min walking test (6MWT) and diaphragm US were performed at CR admission and after 10 rehabilitative sessions. One hundred eighty-five patients were eligible for final analysis. One hundred thirty-one patients (70.8%) were found to have diaphragm dysfunction (excursion <2 cm). After CR, 68 patients regained normal diaphragmatic function; those with persistent dysfunction had a lower level of functional performance on the 6MWT (metabolic equivalents of tasks: 3.3 vs. 3.6, p = 0.013). The patients who underwent combined surgery (adjusted odds ratio [aOR] = 4.09, p = 0.001) and those with post-operative pneumothorax (aOR = 3.02, p = 0.042) were at increased risk of failure to improve diaphragmatic excursion. US parameters were more powerful tools in predicting diaphragmatic evolution compared with the 6MWT indexes: baseline diaphragm excursion and thickening fraction were associated with complete diaphragmatic functional recovery after CR (aOR = 9.101, p < 0.001, and aOR = 1.058, p = 0.020 respectively). US is a valuable tool for the assessment of post-operative diaphragmatic dysfunction and can identify patients at risk of diaphragmatic recovery failure.

Extubation Failure Prediction by Echography of the Diaphragm After Cardiothoracic Surgery: The EXPEDIA Study

BACKGROUND

Successful extubation is difficult to predict. Ultrasound measurement of the diaphragm thickening fraction (DTF) might help predict weaning failure after cardiothoracic surgery.

METHODS

We assessed the predictive performance of diaphragm ultrasound in a derivation cohort of 50 prospectively included cardiothoracic surgery subjects ready for a weaning trial and in a validation cohort of 39 subjects ventilated for ≥ 48 h. DTF was assessed by ultrasound during pressure support ventilation (PSV) then during a T-piece spontaneous breathing trial (SBT). DTF was the percentage change in diaphragm thickness between expiration and inspiration and DTF_max, the higher DTF value of the 2 hemidiaphragms. DTF_max during SBT (static study) and the difference in DTF_max between PSV and SBT (dynamic study) were analyzed.

RESULTS

In the derivation cohort, DTF_max during SBT was 25.6 ± 17.3% in subjects with successful extubation and 65.2 ± 17.3% in those with weaning failure (difference 39.7 [95% CI 27.4-51.9], P < .01). During SBT, DTF_max ≥ 50% was associated with weaning failure (area under the receiver operating characteristic curve [AUC] 0.94 ± 0.05). In the dynamic study, a ≥ 40% DTF_max increase was associated with weaning failure (AUC 0.91 ± 0.06). In the validation cohort, DTF_max during SBT was 20.3 ± 17.1% in subjects with successful extubation and 82.0 ± 51.6% in those with weaning failure (difference 61.8 [95% CI 41.6-82.0], P < .01). During SBT, DTF_max ≥ 50% predicted weaning failure (AUC 0.99 ± 0.02). In the dynamic study, a ≥ 40% increase in DTF_max predicted weaning failure (AUC 0.81 ± 0.09).

CONCLUSIONS

Measuring DTF_max during SBT and the DTF_max change when switching from PSV to SBT may help predict weaning failure after cardiothoracic surgery. The study was registered on ANZCTR.

CLINICAL TRIAL REGISTRATION NUMBER

U1111-1180-1999.

Diaphragm Ultrasound in Cardiac Surgery: State of the Art

In cardiac surgery, patients are at risk of phrenic nerve injury, which leads to diaphragm dysfunction and acute respiratory failure. Diaphragm dysfunction (DD) is relatively frequent in cardiac surgery and particularly affects patients after coronary artery bypass graft. The onset of DD affects patients’ prognosis in term of weaning from mechanical ventilation and hospital length of stay. The authors present a narrative review about diaphragm physiology, techniques used to assess diaphragm function, and the clinical application of diaphragm ultrasound in patients undergoing cardiac surgery.

Functional evaluation of the diaphragm with a noninvasive test

Cardiac surgery with median sternotomy causes iatrogenic damage to the function of the diaphragm muscle that is both temporary and permanent. Myocardial infarction itself causes diaphragmatic genetic alterations, which lead the muscle to nonphysiological adaptation. The respiratory muscle area plays several roles in maintaining both physical and mental health, as well as in maximizing recovery after a cardiac event. The evaluation of the diaphragm is a fundamental step in the therapeutic process, including the use of instruments such as ultrasound, magnetic resonance imaging (MRI), and computed axial tomography (CT). This article reviews the neurophysiological relationships of the diaphragm muscle and the symptoms of diaphragmatic contractile dysfunction. The authors discuss a scientific basis for the use of a new noninstrumental diaphragmatic test in the hope of stimulating research.

Speckle tracking ultrasonography as a new tool to assess diaphragmatic function: a feasibility study

A reliable method of measuring diaphragmatic function at the bedside is still lacking. Widely used two-dimensional (2D) ultrasonographic measurements, such as diaphragm excursion, diaphragm thickness, and fractional thickening (FT) have failed to show clear correlations with diaphragmatic function. A reason for this is that 2D ultrasonographic measurements, like FT, are merely able to measure the deformation of muscular diaphragmatic tissue in the transverse direction, while longitudinal measurements in the direction of contracting muscle fibres are not possible. Speckle tracking ultrasonography, which is widely used in cardiac imaging, overcomes this disadvantage and allows observations of movement in the direction of the contracting muscle fibres, approximating muscle deformation and the deformation velocity. Several studies have evaluated speckle tracking as a promising method to assess diaphragm contractility in healthy subjects. This technical note demonstrates the feasibility of speckle tracking ultrasonography of the diaphragm in a group of 20 patients after an aortocoronary bypass graft procedure. The results presented herein suggest that speckle tracking ultrasonography is able to depict alterations in diaphragmatic function after surgery better than 2D ultrasonographic measurements.

Ultrasound and non-ultrasound imaging techniques in the assessment of diaphragmatic dysfunction

Diaphragm muscle dysfunction is increasingly recognized as an important element of several diseases including neuromuscular disease, chronic obstructive pulmonary disease and diaphragm dysfunction in critically ill patients. Functional evaluation of the diaphragm is challenging. Use of volitional maneuvers to test the diaphragm can be limited by patient effort. Non-volitional tests such as those using neuromuscular stimulation are technically complex, since the muscle itself is relatively inaccessible. As such, there is a growing interest in using imaging techniques to characterize diaphragm muscle dysfunction. Selecting the appropriate imaging technique for a given clinical scenario is a critical step in the evaluation of patients suspected of having diaphragm dysfunction. In this review, we aim to present a detailed analysis of evidence for the use of ultrasound and non-ultrasound imaging techniques in the assessment of diaphragm dysfunction. We highlight the utility of the qualitative information gathered by ultrasound imaging as a means to assess integrity, excursion, thickness, and thickening of the diaphragm. In contrast, quantitative ultrasound analysis of the diaphragm is marred by inherent limitations of this technique, and we provide a detailed examination of these limitations. We evaluate non-ultrasound imaging modalities that apply static techniques (chest radiograph, computerized tomography and magnetic resonance imaging), used to assess muscle position, shape and dimension. We also evaluate non-ultrasound imaging modalities that apply dynamic imaging (fluoroscopy and dynamic magnetic resonance imaging) to assess diaphragm motion. Finally, we critically review the application of each of these techniques in the clinical setting when diaphragm dysfunction is suspected.

Diaphragm Dysfunction After Cardiac Surgery: Reappraisal

OBJECTIVES

The aim of this study was to re-investigate the incidence, risk factors, and outcomes of postoperative diaphragmatic dysfunction (DD) with actual cardiac surgery procedures.

DESIGN

Single-center, retrospective, observational study based on a prospectively collected database.

SETTING

Tertiary care cardiac surgery center.

PARTICIPANTS

Patients who underwent cardiac surgery between January 2016 and September 2019.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

The DD group included patients with clinically perceptible diaphragmatic paralysis, which was confirmed by chest ultrasound (amplitude of the diaphragm movement in time-motion mode at rest, after a sniff test). The primary endpoint was the incidence of DD. Among 3,577 patients included, the authors found 272 cases of DD (7.6%). Individuals with DD had more arterial hypertension (64.3% v 52.6%; p < 0.0001), higher body mass index (BMI) (28 [25-30] kg/m²v 26 [24-29] kg/m²; p < 0.0002), and higher incidence of coronary bypass grafting (CABG) (58.8% v 46.6%; p = 0.0001). DD was associated with more postoperative pneumonia (23.9% v 8.7%; p < 0.0001), reintubation (8.8% v 2.9%; p < 0.0001), tracheotomy (3.3% v 0.3%; p < 0.0001), noninvasive ventilation (45.6% v 5.4%; p < 0.0001), duration of mechanical ventilation (five [four-11] hours v four [three-six] hours; p < 0.0001), and intensive care unit and hospital stays (14 [11-17] days v 13 [11-16] days; p < 0.0001). In multivariate analysis, DD was associated with CABG (odds ratio [OR] 1.9 [1.5-2.6]; p = 0.0001), arterial hypertension (OR 1.4 [1.1-1.9]; p = 0.008), and BMI (OR per point 1.04 [1.01-1.07] kg/m²; p = 0.003).

CONCLUSIONS

The incidence of symptomatic DD after cardiac surgery was 7.6%, leading to respiratory complications and increased ICU stay. CABG was the principal factor associated with DD.

Monitoring diaphragm function in the ICU

PURPOSE OF REVIEW

To review the clinical problem of diaphragm function in critically ill patients and describes recent advances in bedside monitoring of diaphragm function.

RECENT FINDINGS

Diaphragm weakness, a consequence of diaphragm dysfunction and atrophy, is common in the ICU and associated with serious clinical consequences. The use of ultrasound to assess diaphragm structure (thickness, thickening) and mobility (caudal displacement) appears to be feasible and reproducible, but no large-scale 'real-life' study is available. Diaphragm ultrasound can also be used to evaluate diaphragm muscle stiffness by means of shear-wave elastography and strain by means of speckle tracking, both of which are correlated with diaphragm function in healthy. Electrical activity of the diaphragm is correlated with diaphragm function during brief airway occlusion, but the repeatability of these measurements exhibits high within-subject variability.

SUMMARY

Mechanical ventilation is involved in the pathogenesis of diaphragm dysfunction, which is associated with severe adverse events. Although ultrasound and diaphragm electrical activity could facilitate monitoring of diaphragm function to deliver diaphragm-protective ventilation, no guidelines concerning the use of these modalities have yet been published. The weaning process, assessment of patient-ventilator synchrony and evaluation of diaphragm function may be the most clinically relevant indications for these techniques.

Diaphragm Thickening During Venoarterial Extracorporeal Membrane Oxygenation Weaning: An Observational Prospective Study

OBJECTIVES

The respiratory workload, according to the diaphragm thickening fraction (TF) during sweep gas flow (SGF), decrease during weaning from venoarterial extracorporeal membrane oxygenation (VA ECMO) was evaluated for the present study.

DESIGN

Prospective observational study.

SETTING

Monocentric.

PARTICIPANTS

Patients were included if they were suitable for a first VA ECMO weaning trial and were breathing spontaneously.

INTERVENTIONS

SGF was set for 15 minutes when the TF was measured at 4 L/min, 2 L/min, and 1 L/min, with a 10-minute return to baseline between each step. Mechanical ventilation, when required, was set to pressure-support ventilation mode with 7 cmH₂O (pressure support) and a positive end-expiratory pressure of 0 cmH₂O. Diaphragm ultrasound was used to assess the TF at the end of each step. Demographics, left ventricular ejection fraction (LVEF), and outcome were collected.

MEASUREMENTS AND MAIN RESULTS

Fifteen patients were included. Ten patients were extubated, and five were ventilated. TF values were 6.3% [0-10] at 4 L/min, 13.3% [10-26] at 2 L/min, and 26.7% [22-44] at 1 L/min (analysis of variance: p < 0.001 between 4 L/min and 2 L/min and p = 0.03 between 2 L/min and 1 L/min). TF did not differ whether patients were or were not ventilated or whether they were or were not weaned successfully from ECMO. TF was correlated with LVEF at 1 L/min SGF (Pearson R 0.67 [0.21-0.88]; p = 0.009) and at 2 L/min (R 0.7 [0.27-0.89]; p = 0.005) but not at 4 L/min. SGF mitigated the relationship between LVEF and TF (analysis of covariance: p < 0.005).

CONCLUSIONS

Diaphragm TF was related to the SGF of the venoarterial ECMO settings and LVEF at the time of weaning.

Diaphragm ultrasound: A novel approach to assessing pulmonary function in patients with traumatic rib fractures

BACKGROUND

Rib fractures following blunt trauma are a major cause of morbidity. Various factors have been used for risk stratification for complications. Ultrasound (US) measurements of diaphragm thickness (Tdi) and related measures such as thickening fraction (TF) have been verified for use in the evaluation of diaphragm function. In healthy individuals, Tdi by US is known to have a positive and direct relationship with lung volumes including inspiratory capacity (IC). However, TF has not been previously been described in, or used to assess, pulmonary function in rib fracture patients. We examined TF and IC to elucidate the association between acute rib fractures and respiratory function. We hypothesized that TF and IC were related. Secondarily, we examined the relationship of TF in rib fractures patients, in the context of values reported for healthy controls in the literature.

METHODS

We prospectively enrolled adults with acute blunt traumatic rib fractures within 48 hours of admission to a level 1 trauma center. Patients requiring a chest tube or mechanical ventilation at time of consent were excluded. Inspiratory capacity was determined via incentive spirometry. Thickening fraction was determined by bedside US measurements of minimum and maximum Tdi during tidal breathing (TFtidal) or deep breathing (TFDB) was calculated (TF = [TdimaxTdi - TdiminTdi]/TdiminTdi). TFDB values were also compared with previously reported mean ± SD values of 2.04 ± 0.62 in healthy males and 1.70 ± 0.89 in females. Univariate and multivariate analyses were performed.

RESULTS

A total of 41 subjects (58.5% male) with a median age of 64 years (interquartile range [IQR], 53-77 years) were enrolled. Diaphragm US demonstrated a median TFtidal of 0.30 (IQR, 0.24-0.46). Median IC was 1,750 mL (IQR, 1,250-2,000 mL). As compared with previously reported controls, our mean ± SD TFDB in males 0.90 ± 0.51 and 0.88 ± 0.89 in females were significantly lower. Multivariate analysis revealed a significant inverse correlation (-0.439, p = 0.004) between TFtidal and IC, and no relationship between TFDB and IC.

CONCLUSION

To our knowledge, this is the first report of TF in rib fracture patients. The significant inverse association between TFtidal and IC, along with lower than normal TFDB ranges, suggests that, in the setting of rib fractures, there are alterations in the diaphragm-chest cage mechanics, whereby other muscles may play more prominent roles.

LEVEL OF EVIDENCE

Diagnostic tests or criteria, Level III.

ICU-acquired weakness, diaphragm dysfunction and long-term outcomes of critically ill patients

BACKGROUND

Intensive care unit (ICU)-acquired weakness and diaphragm dysfunction are frequent conditions, both associated with poor prognosis in critically ill patients. While it is well established that ICU-acquired weakness severely impairs long-term prognosis, the association of diaphragm dysfunction with this outcome has never been reported. This study investigated whether diaphragm dysfunction is associated with negative long-term outcomes and whether the coexistence of diaphragm dysfunction and ICU-acquired weakness has a particular association with 2-year survival and health-related quality of life (HRQOL).

METHODS

This study is an ancillary study derived from an observational cohort study. Patients under mechanical ventilation were enrolled at the time of their first spontaneous breathing trial. Diaphragm dysfunction was defined by tracheal pressure generated by phrenic nerve stimulation < 11 cmH₂O and ICU-acquired weakness was defined by Medical Research Council (MRC) score < 48. HRQOL was evaluated with the SF-36 questionnaire.

RESULTS

Sixty-nine of the 76 patients enrolled in the original study were included in the survival analysis and 40 were interviewed. Overall 2-year survival was 67% (46/69): 64% (29/45) in patients with diaphragm dysfunction, 71% (17/24) in patients without diaphragm dysfunction, 46% (11/24) in patients with ICU-acquired weakness and 76% (34/45) in patients without ICU-acquired weakness. Patients with concomitant diaphragm dysfunction and ICU-acquired weakness had a poorer outcome with a 2-year survival rate of 36% (5/14) compared to patients without diaphragm function and ICU-acquired weakness [79% (11/14) (p < 0.01)]. Health-related quality of life was not influenced by the presence of ICU-acquired weakness, diaphragm dysfunction or their coexistence.

CONCLUSIONS

ICU-acquired weakness but not diaphragm dysfunction was associated with a poor 2-year survival of critically ill patients.