Intermittent spontaneous breathing protects the rat diaphragm from mechanical ventilation effects

Rehabilitation Effects of Acupuncture on The Diaphragmatic Dysfunction in Respiratory Insufficiency: A Systematic Review and Meta-analysis

INTRODUCTION

Mechanical ventilation after respiratory insufficiency can induce diaphragm dysfunction through various hypothesized mechanisms. In this study, we evaluated the rehabilitative effect of acupuncture on diaphragm function in patients with respiratory insufficiency using meta-analysis and summarised the rules of acupoints through association rules analysis.

METHODS

Articles (published from January 2000 to February 2024) were retrieved from the following databases: PubMed, Cochrane Library, Embase, Web of Science, CNKI, VIP, SinoMed, and Wanfang. Two researchers conducted literature selection, data extraction, and statistical analysis independently. The risk of bias was assessed utilizing the Physical Therapy Evidence Database (PEDro) scale. The meta-analysis was performed with RevMan 5.4 software, and the quality of each outcome evidence was assessed via the online software GRADEpro GDT. The regularity of acupoint selection was summarized using association rules analysis. This study is registered on PROSPERO, number CRD42024526705.

RESULTS

Eleven articles were eventually included, all of which were of low to moderate quality. Results of the meta-analysis showed a significant increase in diaphragmatic thickening fraction (MD 3.40 [1.52, 5.27]) and diaphragmatic excursion (MD 0.95 [0.58, 1.31]) in patients with respiratory insufficiency after acupuncture treatment. Also, OI (MD 28.52 [15.93, 41.11]) and PaO2 (MD 7.18 [2.22, 12.13]) were significantly elevated and PaCO2 (MD -6.94 [-12.30, -1.59]) was decreased. Mechanical ventilation time (MD-1.86 [-2.28, -1.45]) was also significantly improved. The overall quality of the outcome evidence is deemed moderate. Association rules analysis showed that ST36, RN4, RN6, and others are core acupoints for the treatment of diaphragmatic dysfunction in patients with respiratory insufficiency by acupuncture.

CONCLUSION

Acupuncture shows potential in the rehabilitation of patients with respiratory insufficiency and may serve as a complementary and alternative therapy for related conditions. We suggest the use of ST36 as a core acupoint, in combination with other acupoints. Due to the potential publication bias and high heterogeneity of the current data, further high-quality RCTs are needed to confirm these findings.

Ventilator-induced diaphragm dysfunction: phenomenology and mechanism(s) of pathogenesis

Mechanical ventilation (MV) is used to support ventilation and pulmonary gas exchange in patients during critical illness and surgery. Although MV is a life-saving intervention for patients in respiratory failure, an unintended side-effect of MV is the rapid development of diaphragmatic atrophy and contractile dysfunction. This MV-induced diaphragmatic weakness is labelled as 'ventilator-induced diaphragm dysfunction' (VIDD). VIDD is an important clinical problem because diaphragmatic weakness is a risk factor for the failure to wean patients from MV. Indeed, the inability to remove patients from ventilator support results in prolonged hospitalization and increased morbidity and mortality. The pathogenesis of VIDD has been extensively investigated, revealing that increased mitochondrial production of reactive oxygen species within diaphragm muscle fibres promotes a cascade of redox-regulated signalling events leading to both accelerated proteolysis and depressed protein synthesis. Together, these events promote the rapid development of diaphragmatic atrophy and contractile dysfunction. This review highlights the MV-induced changes in the structure/function of diaphragm muscle and discusses the cell-signalling mechanisms responsible for the pathogenesis of VIDD. This report concludes with a discussion of potential therapeutic opportunities to prevent VIDD and suggestions for future research in this exciting field.

Lung- and Diaphragm-Protective Ventilation by Titrating Inspiratory Support to Diaphragm Effort: A Randomized Clinical Trial

OBJECTIVES

Lung- and diaphragm-protective ventilation is a novel concept that aims to limit the detrimental effects of mechanical ventilation on the diaphragm while remaining within limits of lung-protective ventilation. The premise is that low breathing effort under mechanical ventilation causes diaphragm atrophy, whereas excessive breathing effort induces diaphragm and lung injury. In a proof-of-concept study, we aimed to assess whether titration of inspiratory support based on diaphragm effort increases the time that patients have effort in a predefined "diaphragm-protective" range, without compromising lung-protective ventilation.

DESIGN

Randomized clinical trial.

SETTING

Mixed medical-surgical ICU in a tertiary academic hospital in the Netherlands.

PATIENTS

Patients (n = 40) with respiratory failure ventilated in a partially-supported mode.

INTERVENTIONS

In the intervention group, inspiratory support was titrated hourly to obtain transdiaphragmatic pressure swings in the predefined "diaphragm-protective" range (3-12 cm H2O). The control group received standard-of-care.

MEASUREMENTS AND MAIN RESULTS

Transdiaphragmatic pressure, transpulmonary pressure, and tidal volume were monitored continuously for 24 hours in both groups. In the intervention group, more breaths were within "diaphragm-protective" range compared with the control group (median 81%; interquartile range [64-86%] vs 35% [16-60%], respectively; p < 0.001). Dynamic transpulmonary pressures (20.5 ± 7.1 vs 18.5 ± 7.0 cm H2O; p = 0.321) and tidal volumes (7.56 ± 1.47 vs 7.54 ± 1.22 mL/kg; p = 0.961) were not different in the intervention and control group, respectively.

CONCLUSIONS

Titration of inspiratory support based on patient breathing effort greatly increased the time that patients had diaphragm effort in the predefined "diaphragm-protective" range without compromising tidal volumes and transpulmonary pressures. This study provides a strong rationale for further studies powered on patient-centered outcomes.

Loss of muscular force in isolated rat diaphragms is related to changes in muscle fibre size

OBJECTIVE

Passivity of the diaphragm during prolonged mechanical ventilation can lead to ventilation-induced diaphragmatic dysfunction reasoned by a reduction of diaphragmatic muscle strength. Electrical stimulation may be utilised to modulate diaphragm muscle strength. Therefore we intended to investigate diaphragmatic muscle strength based on stimulation with electric impulses.

APPROACH

Diaphragms of Wistar rats were excised, embedded in various incubation solutions and placed in a diaphragm force measurement device. Pressure amplitudes generated by the diaphragm in dependency of the embedding solution, stimulation frequency and time (360 min) were determined. Furthermore, the diaphragms were histologically evaluated.

MAIN RESULTS

The ex vivo diaphragms evoked no pressure if embedded in incubation solutions with high potassium concentrations and up to >20 cmH₂O if embedded in incubation solutions with extracellular potassium concentrations. Although vitality was well maintained after 360 min (78%) cultivation, the diaphragm's force dropped by 90.8% after 240 min. The decline in the diaphragm's force progressed faster if stimulation was performed every 20 min compared to every 120 min. The size of Type I muscle fibres was largest in diaphragms stimulated every 120 min. The fibre size of Type 2b/x muscle cells was lower in diaphragms after electrical stimulation compared to non-stimulated diaphragms.

SIGNIFICANCE

The force that the diaphragm can develop in ex vivo conditions depends on the incubation solution and the conditions of activation. Activity-related changes in the diaphragm's muscular force are accompanied by specific changes in muscle fibre size.

Oxygen administration for patients with ARDS

Acute respiratory distress syndrome (ARDS) is a fatal condition with insufficiently clarified etiology. Supportive care for severe hypoxemia remains the mainstay of essential interventions for ARDS. In recent years, adequate ventilation to prevent ventilator-induced lung injury (VILI) and patient self-inflicted lung injury (P-SILI) as well as lung-protective mechanical ventilation has an increasing attention in ARDS.

Ventilation-perfusion mismatch may augment severe hypoxemia and inspiratory drive and consequently induce P-SILI. Respiratory drive and effort must also be carefully monitored to prevent P-SILI. Airway occlusion pressure (P_0.1) and airway pressure deflection during an end-expiratory airway occlusion (P_occ) could be easy indicators to evaluate the respiratory drive and effort. Patient-ventilator dyssynchrony is a time mismatching between patient’s effort and ventilator drive. Although it is frequently unrecognized, dyssynchrony can be associated with poor clinical outcomes. Dyssynchrony includes trigger asynchrony, cycling asynchrony, and flow delivery mismatch. Ventilator-induced diaphragm dysfunction (VIDD) is a form of iatrogenic injury from inadequate use of mechanical ventilation. Excessive spontaneous breathing can lead to P-SILI, while excessive rest can lead to VIDD. Optimal balance between these two manifestations is probably associated with the etiology and severity of the underlying pulmonary disease.

High-flow nasal cannula (HFNC) and non-invasive positive pressure ventilation (NPPV) are non-invasive techniques for supporting hypoxemia. While they are beneficial as respiratory supports in mild ARDS, there can be a risk of delaying needed intubation. Mechanical ventilation and ECMO are applied for more severe ARDS. However, as with HFNC/NPPV, inappropriate assessment of breathing workload potentially has a risk of delaying the timing of shifting from ventilator to ECMO. Various methods of oxygen administration in ARDS are important. However, it is also important to evaluate whether they adequately reduce the breathing workload and help to improve ARDS.

Diaphragm protection: what should we target?

PURPOSE OF REVIEW

Diaphragm weakness can impact survival and increases comorbidities in ventilated patients. Mechanical ventilation is linked to diaphragm dysfunction through several mechanisms of injury, referred to as myotrauma. By monitoring diaphragm activity and titrating ventilator settings, the critical care clinician can have a direct impact on diaphragm injury.

RECENT FINDINGS

Both the absence of diaphragm activity and excessive inspiratory effort can result in diaphragm muscle weakness, and recent evidence demonstrates that a moderate level of diaphragm activity during mechanical ventilation improves ICU outcome. This supports the hypothesis that by avoiding ventilator overassistance and underassistance, the clinician can implement a diaphragm-protective ventilation strategy. Furthermore, eccentric diaphragm contractions and end-expiratory shortening could impact diaphragm strength as well. This review describes these potential targets for diaphragm protective ventilation.

SUMMARY

A ventilator strategy that results in appropriate levels of diaphragm activity has the potential to be diaphragm-protective and improve clinical outcome. Monitoring respiratory effort during mechanical ventilation is becoming increasingly important.

Maintenance of spontaneous breathing at an intensity of 60%-80% may effectively prevent mechanical ventilation-induced diaphragmatic dysfunction

Controlled mechanical ventilation (CMV) can cause diaphragmatic motionlessness to induce diaphragmatic dysfunction. Partial maintenance of spontaneous breathing (SB) can reduce ventilation-induced diaphragmatic dysfunction (VIDD). However, to what extent SB is maintained in CMV can attenuate or even prevent VIDD has been rarely reported. The current study aimed to investigate the relationship between SB intensity and VIDD and to identify what intensity of SB maintained in CMV can effectively avoid VIDD. Adult rats were randomly divided according to different SB intensities: SB (0% pressure controlled ventilation (PCV)), high-intensity SB (20% PCV), medium-intensity SB (40% PCV), medium-low intensity SB (60% PCV), low-intensity SB (80% PCV), and PCV (100% PCV). The animals underwent 24-h controlled mechanical ventilation (CMV). The transdiaphragmatic pressure (Pdi), the maximal Pdi (Pdi max) when phrenic nerves were stimulated, Pdi/Pdi max, and the diaphragmatic tonus under different frequencies of electric stimulations were determined. Calpain and caspase-3 were detected using ELISA and the cross-section areas (CSAs) of different types of muscle fibers were measured. The Pdi showed a significant decrease from 20% PCV and the Pdi max showed a significant decrease from 40% PCV (P<0.05). In vivo and vitro diaphragmatic tonus exhibited a significant decrease from 40% PCV and 20% PCV, respectively (P<0.05). From 20% PCV, the CSAs of types I, IIa, and IIb/x muscle fibers showed significant differences, which reached the lowest levels at 100% PCV. SB intensity is negatively associated with the development of VIDD. Maintenance of SB at an intensity of 60%-80% may effectively prevent the occurrence of VIDD.

Oxidants Regulated Diaphragm Proteolysis during Mechanical Ventilation in Rats

WHAT WE ALREADY KNOW ABOUT THIS TOPIC

Diaphragm dysfunction and atrophy develop during controlled mechanical ventilation. Although oxidative stress injures muscle during controlled mechanical ventilation, it is unclear whether it causes autophagy or fiber atrophy.

WHAT THIS ARTICLE TELLS US THAT IS NEW

Pretreatment of rats undergoing 24 h of mechanical ventilation with N-acetylcysteine prevents decreases in diaphragm contractility, inhibits the autophagy and proteasome pathways, but has no influence on the development of diaphragm fiber atrophy.

BACKGROUND

Diaphragm dysfunction and atrophy develop during prolonged controlled mechanical ventilation. Fiber atrophy has been attributed to activation of the proteasome and autophagy proteolytic pathways. Oxidative stress activates the proteasome during controlled mechanical ventilation, but it is unclear whether it also activates autophagy. This study investigated whether pretreatment with the antioxidant N-acetylcysteine affects controlled mechanical ventilation-induced diaphragm contractile dysfunction, fiber atrophy, and proteasomal and autophagic pathway activation. The study also explored whether proteolytic pathway activity during controlled mechanical ventilation is mediated by microRNAs that negatively regulate ubiquitin E3 ligases and autophagy-related genes.

METHODS

Three groups of adult male rats were studied (n = 10 per group). The animals in the first group were anesthetized and allowed to spontaneously breathe. Animals in the second group were pretreated with saline before undergoing controlled mechanical ventilation for 24 h. The animals in the third group were pretreated with N-acetylcysteine (150 mg/kg) before undergoing controlled mechanical ventilation for 24 h. Diaphragm contractility and activation of the proteasome and autophagy pathways were measured. Expressions of microRNAs that negatively regulate ubiquitin E3 ligases and autophagy-related genes were measured with quantitative polymerase chain reaction.

RESULTS

Controlled mechanical ventilation decreased diaphragm twitch force from 428 ± 104 g/cm (mean ± SD) to 313 ± 50 g/cm and tetanic force from 2,491 ± 411 g/cm to 1,618 ± 177 g/cm. Controlled mechanical ventilation also decreased diaphragm fiber size, increased expression of several autophagy genes, and augmented Atrogin-1, MuRF1, and Nedd4 expressions by 36-, 41-, and 8-fold, respectively. Controlled mechanical ventilation decreased the expressions of six microRNAs (miR-20a, miR-106b, miR-376, miR-101a, miR-204, and miR-93) that regulate autophagy genes. Pretreatment with N-acetylcysteine prevented diaphragm contractile dysfunction, attenuated protein ubiquitination, and downregulated E3 ligase and autophagy gene expression. It also reversed controlled mechanical ventilation-induced microRNA expression decreases. N-Acetylcysteine pretreatment had no affect on fiber atrophy.

CONCLUSIONS

Prolonged controlled mechanical ventilation activates the proteasome and autophagy pathways in the diaphragm through oxidative stress. Pathway activation is accomplished, in part, through inhibition of microRNAs that negatively regulate autophagy-related genes.

Effect of controlled ventilation during assist-control ventilation on diaphragm thickness : a post hoc analysis of an observational study

Background : Since diaphragm passivity induces oxidative stress that leads to rapid atrophy of diaphragm, we investigated the effect of controlled ventilation on diaphragm thickness during assist-control ventilation (ACV). Methods : Previously, we measured end-expiratory diaphragm thickness (Tdiee) of patients mechanically ventilated for more than 48 hours on days 1, 3, 5 and 7 after the start of ventilation. We retrospectively investigated the proportion of controlled ventilation during the initial 48-hour ACV (CV48%). Patients were classified according to CV48% : Low group, less than 25% ; High group, higher than 25%. Results : Of 56 patients under pressure-control ACV, Tdiee increased more than 10% in 6 patients (11%), unchanged in 8 patients (14%) and decreased more than 10% in 42 patients (75%). During the first week of ventilation, Tdiee decreased in both groups : Low (difference, -7.4% ; 95% confidence interval [CI], -10.1% to -4.6% ; p < 0.001) and High group (difference, -5.2% ; 95% CI, -8.5% to -2.0% ; p = 0.049). Maximum Tdiee variation from baseline did not differ between Low (-15.8% ; interquartile range [IQR], -22.3 to -1.5) and High group (-16.7% ; IQR, -22.6 to -11.1, p = 0.676). Conclusions : During ACV, maximum variation in Tdiee was not associated with proportion of controlled ventilation higher than 25%. J. Med. Invest. 67 : 332-337, August, 2020.

Dexmedetomidine Impairs Diaphragm Function and Increases Oxidative Stress but Does Not Aggravate Diaphragmatic Atrophy in Mechanically Ventilated Rats

BACKGROUND

Anesthetics in ventilated patients are critical as any cofactor hampering diaphragmatic function may have a negative impact on the weaning progress and therefore on patients' mortality. Dexmedetomidine may display antioxidant and antiproteolytic properties, but it also reduced glucose uptake by the muscle, which may impair diaphragm force production. This study tested the hypothesis that dexmedetomidine could inhibit ventilator-induced diaphragmatic dysfunction.

METHODS

Twenty-four rats were separated into three groups (n = 8/group). Two groups were mechanically ventilated during either dexmedetomidine or pentobarbital exposure for 24 h, referred to as interventional groups. A third group of directly euthanized rats served as control. Force generation, fiber dimensions, proteolysis markers, protein oxidation and lipid peroxidation, calcium homeostasis markers, and glucose transporter-4 (Glut-4) translocation were measured in the diaphragm.

RESULTS

Diaphragm force, corrected for cross-sectional area, was significantly decreased in both interventional groups compared to controls and was significantly lower with dexmedetomidine compared to pentobarbital (e.g., 100 Hz: -18%, P < 0.0001). In contrast to pentobarbital, dexmedetomidine did not lead to diaphragmatic atrophy, but it induced more protein oxidation (200% vs. 73% in pentobarbital, P = 0.0015), induced less upregulation of muscle atrophy F-box (149% vs. 374% in pentobarbital, P < 0.001) and impaired Glut-4 translocation (-73%, P < 0.0005). It activated autophagy, the calcium-dependent proteases, and caused lipid peroxidation similarly to pentobarbital.

CONCLUSIONS

Twenty-four hours of mechanical ventilation during dexmedetomidine sedation led to a worsening of ventilation-induced diaphragm dysfunction, possibly through impaired Glut-4 translocation. Although dexmedetomidine prevented diaphragmatic fiber atrophy, it did not inhibit oxidative stress and activation of the proteolytic pathways.

Ventilator-induced diaphragm dysfunction: translational mechanisms lead to therapeutical alternatives in the critically ill

Mechanical ventilation [MV] is a life-saving technique delivered to critically ill patients incapable of adequately ventilating and/or oxygenating due to respiratory or other disease processes. This necessarily invasive support however could potentially result in important iatrogenic complications. Even brief periods of MV may result in diaphragm weakness [i.e., ventilator-induced diaphragm dysfunction [VIDD]], which may be associated with difficulty weaning from the ventilator as well as mortality. This suggests that VIDD could potentially have a major impact on clinical practice through worse clinical outcomes and healthcare resource use. Recent translational investigations have identified that VIDD is mainly characterized by alterations resulting in a major decline of diaphragmatic contractile force together with atrophy of diaphragm muscle fibers. However, the signaling mechanisms responsible for VIDD have not been fully established. In this paper, we summarize the current understanding of the pathophysiological pathways underlying VIDD and highlight the diagnostic approach, as well as novel and experimental therapeutic options.

The Signaling Network Resulting in Ventilator-induced Diaphragm Dysfunction

Mechanical ventilation (MV) is a life-saving measure for those incapable of adequately ventilating or oxygenating without assistance. Unfortunately, even brief periods of MV result in diaphragm weakness (i.e., ventilator-induced diaphragm dysfunction [VIDD]) that may render it difficult to wean the ventilator. Prolonged MV is associated with cascading complications and is a strong risk factor for death. Thus, prevention of VIDD may have a dramatic impact on mortality rates. Here, we summarize the current understanding of the pathogenic events underlying VIDD. Numerous alterations have been proven important in both human and animal MV diaphragm. These include protein degradation via the ubiquitin proteasome system, autophagy, apoptosis, and calpain activity-all causing diaphragm muscle fiber atrophy, altered energy supply via compromised oxidative phosphorylation and upregulation of glycolysis, and also mitochondrial dysfunction and oxidative stress. Mitochondrial oxidative stress in fact appears to be a central factor in each of these events. Recent studies by our group and others indicate that mitochondrial function is modulated by several signaling molecules, including Smad3, signal transducer and activator of transcription 3, and FoxO. MV rapidly activates Smad3 and signal transducer and activator of transcription 3, which upregulate mitochondrial oxidative stress. Additional roles may be played by angiotensin II and leaky ryanodine receptors causing elevated calcium levels. We present, here, a hypothetical scaffold for understanding the molecular pathogenesis of VIDD, which links together these elements. These pathways harbor several drug targets that could soon move toward testing in clinical trials. We hope that this review will shape a short list of the most promising candidates.

Structural differences in the diaphragm of patients following controlled vs assisted and spontaneous mechanical ventilation

PURPOSE

Ventilator-induced diaphragm dysfunction or damage (VIDD) is highly prevalent in patients under mechanical ventilation (MV), but its analysis is limited by the difficulty of obtaining histological samples. In this study we compared diaphragm histological characteristics in Maastricht III (MSIII) and brain-dead (BD) organ donors and in control subjects undergoing thoracic surgery (CTL) after a period of either controlled or spontaneous MV (CMV or SMV).

METHODS

In this prospective study, biopsies were obtained from diaphragm and quadriceps. Demographic variables, comorbidities, severity on admission, treatment, and ventilatory variables were evaluated. Immunohistochemical analysis (fiber size and type percentages) and quantification of abnormal fibers (a surrogate of muscle damage) were performed.

RESULTS

Muscle samples were obtained from 35 patients. MSIII (n = 16) had more hours on MV (either CMV or SMV) than BD (n = 14) and also spent more hours and a greater percentage of time with diaphragm stimuli (time in assisted and spontaneous modalities). Cross-sectional area (CSA) was significantly reduced in the diaphragm and quadriceps in both groups in comparison with CTL (n = 5). Quadriceps CSA was significantly decreased in MSIII compared to BD but there were no differences in the diaphragm CSA between the two groups. Those MSIII who spent 100 h or more without diaphragm stimuli presented reduced diaphragm CSA without changes in their quadriceps CSA. The proportion of internal nuclei in MSIII diaphragms tended to be higher than in BD diaphragms, and their proportion of lipofuscin deposits tended to be lower, though there were no differences in the quadriceps fiber evaluation.

CONCLUSIONS

This study provides the first evidence in humans regarding the effects of different modes of MV (controlled, assisted, and spontaneous) on diaphragm myofiber damage, and shows that diaphragm inactivity during mechanical ventilation is associated with the development of VIDD.

Effects of theophylline therapy on respiratory muscle strength in patients with prolonged mechanical ventilation: A retrospective cohort study

Mechanical ventilation may cause diaphragm weakness an effect termed ventilator-induced diaphragm dysfunction (VIDD). The prevalence of VIDD among patients receiving mechanical ventilation is very high, with the degree of diaphragmatic atrophy being associated with the length of mechanical ventilation. Theophylline is known to increase diaphragmatic contractility and reduce fatigue, so in this study, we evaluated the effect of theophylline in patients with prolonged mechanical ventilation.Patients who depended on mechanical ventilation were included in the study. We compared the maximum inspiratory pressure (PImax) values, rapid shallow breathing index (RSBI) values, and successful weaning rates of theophylline-treated and non-theophylline-treated patients.Eighty-four patients received theophylline and 76 patients did not. These 2 groups' clinical characteristics, including their PImax and RSBI at initial admission, were similar. The results showed that the theophylline-treated group had significantly better PImax and RSBI, with a higher last PImax (30.1 ± 9.7 cmH2O vs 26.9 ± 9.1 cmH2O; P = .034) and lower last RSBI (107.0 ± 68.4 vs 131.4 ± 77.7; P = .036). The improvements to each respective patient's PImax and RSBI were also significantly higher in the theophylline-treated group (PImax: 20.1 ± 5.7% vs 3.2 ± 1.1%, P = .005; RSBI: 11.2 ± 3.0% vs 2.7 ± 1.6%, P = .015). The weaning success rate of the theophylline-treated group was also higher, but not significantly so.Theophylline might improve respiratory muscle strength in patients with prolonged mechanical ventilation and it needs further prospective studies to confirm.

Endurance exercise protects skeletal muscle against both doxorubicin-induced and inactivity-induced muscle wasting

Repeated bouts of endurance exercise promotes numerous biochemical adaptations in skeletal muscle fibers resulting in a muscle phenotype that is protected against a variety of homeostatic challenges; these exercise-induced changes in muscle phenotype are often referred to as "exercise preconditioning." Importantly, exercise preconditioning provides protection against several threats to skeletal muscle health including cancer chemotherapy (e.g., doxorubicin) and prolonged muscle inactivity. This review summarizes our current understanding of the mechanisms responsible for exercise-induced protection of skeletal muscle fibers against both doxorubicin-induced muscle wasting and a unique form of inactivity-induced muscle atrophy (i.e., ventilator-induced diaphragm atrophy). Specifically, the first section of this article will highlight the potential mechanisms responsible for exercise-induced protection of skeletal muscle fibers against doxorubicin-induced fiber atrophy. The second segment will discuss the biochemical changes that are responsible for endurance exercise-mediated protection of diaphragm muscle against ventilator-induced diaphragm wasting. In each section, we highlight gaps in our knowledge in hopes of stimulating future research in this evolving field of investigation.

The Renin-Angiotensin System and Skeletal Muscle

The renin-angiotensin system (RAS) plays a key role in the control of blood pressure and fluid homeostasis. Emerging evidence also reveals that hyperactivity of the RAS contributes to skeletal muscle wasting. This review discusses the key role that the RAS plays in skeletal muscle wasting due to congestive heart failure, chronic kidney disease, and ventilator-induced diaphragmatic wasting.

Diaphragm Weakness in the Critically Ill: Basic Mechanisms Reveal Therapeutic Opportunities

The diaphragm is the primary muscle of inspiration. Its capacity to respond to the load imposed by pulmonary disease is a major determining factor both in the onset of ventilatory failure and in the ability to successfully separate patients from ventilator support. It has recently been established that a very large proportion of critically ill patients exhibit major weakness of the diaphragm, which is associated with poor clinical outcomes. The two greatest risk factors for the development of diaphragm weakness in critical illness are the use of mechanical ventilation and the presence of sepsis. Loss of force production by the diaphragm under these conditions is caused by a combination of defective contractility and reduced diaphragm muscle mass. Importantly, many of the same molecular mechanisms are implicated in the diaphragm dysfunction associated with both mechanical ventilation and sepsis. This review outlines the primary cellular mechanisms identified thus far at the nexus of diaphragm dysfunction associated with mechanical ventilation and/or sepsis, and explores the potential for treatment or prevention of diaphragm weakness in critically ill patients through therapeutic manipulation of these final common pathway targets.

Can inspiratory muscle training improve weaning outcomes in difficult to wean patients? A protocol for a randomised controlled trial (IMweanT study)

INTRODUCTION

Respiratory muscle dysfunction has been associated with failure to wean from mechanical ventilation. It has therefore been hypothesised that these patients might benefit from inspiratory muscle training (IMT). Evidence, however, is thus far limited to data from small, single-centre studies with heterogeneity in inclusion criteria, training modalities and outcomes. The aim of this study is to evaluate the effects of a novel IMT method on weaning outcomes in selected patients with weaning difficulties.

METHODS

This study is designed as a double-blind, parallel-group, randomised controlled superiority trial with 1:1 allocation ratio. Patients with weaning difficulties will be randomly allocated into either an IMT group (intervention) or a sham-IMT group (control). Ninetypatients (45 in each group) will be needed to detect a 28% difference in the proportion of weaning success between groups (estimated difference in primary outcome based on previous studies) with a risk for type I error (α) of 5% and statistical power (1-β) of 80%. Patients will perform four sets of 6-10 breaths daily against an external load using a tapered flow resistive loading device (POWERbreathe KH2, HaB International, UK). Training intensity in the intervention group will be adjusted to the highest tolerable load. The control group will train against a low resistance that will not be modified during the training period. Training will becontinued until patients are successfully weaned or for a maximum duration of 28 days. Pulmonary and respiratory muscle function, weaning duration, duration of mechanical ventilation, ventilator-free days and length of stay in the intensive care unit will be evaluated as secondary outcomes. Χ2 tests and analysis of covariance with adjustments for baseline values of respective outcomesas covariates will be used to compare results after the intervention period between groups.

ETHICS AND DISSEMINATION

Ethics approval was obtained from the local ethical committee (Ethische Commissie Onderzoek UZ/KU Leuven protocol ID: S60516). Results from this randomised controlled trial will be presented at scientific meetings as abstracts for poster or oral presentations and published in peerreviewed journals.

TRIAL STATUS

Enrolment into the study have started in August 2017. Data collection and data analysis are expected to be completed in September 2021.

TRIAL REGISTRATION NUMBER

NCT03240263.

Diaphragm dysfunction during weaning from mechanical ventilation: an underestimated phenomenon with clinical implications

This article is one of ten reviews selected from the Annual Update in Intensive Care and Emergency Medicine 2018. Other selected articles can be found online at https://www.biomedcentral.com/collections/annualupdate2018. Further information about the Annual Update in Intensive Care and Emergency Medicine is available from http://www.springer.com/series/8901.

Current views of complications associated with neonatal ventilation

Infants born prematurely require external respiratory support device like ventilation for the purpose of life saving. However, these ventilation machines have complications that sometimes unfortunately result in morbidity. New ventilation techniques have been developed to prevent morbidity, but have yet to be fully evaluated. The present review article would discuss current aspects of this life saving gear especially for pediatric patients in clinical setting. Besides basic ventilation apparatus, advancements in the filed like proportional assist ventilation, volume targeted ventilation would be discussed.

Effect of inspiratory synchronization during pressure-controlled ventilation on lung distension and inspiratory effort

Background

In pressure-controlled (PC) ventilation, tidal volume (V_T) and transpulmonary pressure (P_L) result from the addition of ventilator pressure and the patient’s inspiratory effort. PC modes can be classified into fully, partially, and non-synchronized modes, and the degree of synchronization may result in different V_T and P_L despite identical ventilator settings. This study assessed the effects of three PC modes on V_T, P_L, inspiratory effort (esophageal pressure–time product, PTP_es), and airway occlusion pressure, P_0.1. We also assessed whether P_0.1 can be used for evaluating patient effort.

Methods

Prospective, randomized, crossover physiologic study performed in 14 spontaneously breathing mechanically ventilated patients recovering from acute respiratory failure (1 subsequently withdrew). PC modes were fully (PC-CMV), partially (PC-SIMV), and non-synchronized (PC-IMV using airway pressure release ventilation) and were applied randomly; driving pressure, inspiratory time, and set respiratory rate being similar for all modes. Airway, esophageal pressure, P_0.1, airflow, gas exchange, and hemodynamics were recorded.

Results

V_T was significantly lower during PC-IMV as compared with PC-SIMV and PC-CMV (387 ± 105 vs 458 ± 134 vs 482 ± 108 mL, respectively; p < 0.05). Maximal P_L was also significantly lower (13.3 ± 4.9 vs 15.3 ± 5.7 vs 15.5 ± 5.2 cmH₂O, respectively; p < 0.05), but PTP_es was significantly higher in PC-IMV (215.6 ± 154.3 vs 150.0 ± 102.4 vs 130.9 ± 101.8 cmH₂O × s × min⁻¹, respectively; p < 0.05), with no differences in gas exchange and hemodynamic variables. PTP_es increased by more than 15% in 10 patients and by more than 50% in 5 patients. An increased P_0.1 could identify high levels of PTP_es.

Conclusions

Non-synchronized PC mode lowers V_T and P_L in comparison with more synchronized modes in spontaneously breathing patients but can increase patient effort and may need specific adjustments.

Clinical Trial Registration Clinicaltrial.gov # NCT02071277

Electronic supplementary material

The online version of this article (doi:10.1186/s13613-017-0324-z) contains supplementary material, which is available to authorized users.

Diaphragm Dysfunction in Critical Illness

The diaphragm is the major muscle of inspiration, and its function is critical for optimal respiration. Diaphragmatic failure has long been recognized as a major contributor to death in a variety of systemic neuromuscular disorders. More recently, it is increasingly apparent that diaphragm dysfunction is present in a high percentage of critically ill patients and is associated with increased morbidity and mortality. In these patients, diaphragm weakness is thought to develop from disuse secondary to ventilator-induced diaphragm inactivity and as a consequence of the effects of systemic inflammation, including sepsis. This form of critical illness-acquired diaphragm dysfunction impairs the ability of the respiratory pump to compensate for an increased respiratory workload due to lung injury and fluid overload, leading to sustained respiratory failure and death. This review examines the presentation, causes, consequences, diagnosis, and treatment of disorders that result in acquired diaphragm dysfunction during critical illness.

Exercise: Teaching myocytes new tricks

Endurance exercise training promotes numerous cellular adaptations in both cardiac myocytes and skeletal muscle fibers. For example, exercise training fosters changes in mitochondrial function due to increased mitochondrial protein expression and accelerated mitochondrial turnover. Additionally, endurance exercise training alters the abundance of numerous cytosolic and mitochondrial proteins in both cardiac and skeletal muscle myocytes, resulting in a protective phenotype in the active fibers; this exercise-induced protection of cardiac and skeletal muscle fibers is often referred to as "exercise preconditioning." As few as 3-5 consecutive days of endurance exercise training result in a preconditioned cardiac phenotype that is sheltered against ischemia-reperfusion-induced injury. Similarly, endurance exercise training results in preconditioned skeletal muscle fibers that are resistant to a variety of stresses (e.g., heat stress, exercise-induced oxidative stress, and inactivity-induced atrophy). Many studies have probed the mechanisms responsible for exercise-induced preconditioning of cardiac and skeletal muscle fibers; these studies are important, because they provide an improved understanding of the biochemical mechanisms responsible for exercise-induced preconditioning, which has the potential to lead to innovative pharmacological therapies aimed at minimizing stress-induced injury to cardiac and skeletal muscle. This review summarizes the development of exercise-induced protection of cardiac myocytes and skeletal muscle fibers and highlights the putative mechanisms responsible for exercise-induced protection in the heart and skeletal muscles.

Respiratory muscle contractile inactivity induced by mechanical ventilation in piglets leads to leaky ryanodine receptors and diaphragm weakness

Respiratory muscle contractile inactivity during mechanical ventilation (MV) induces diaphragm muscle weakness, a condition referred to as ventilator-induced diaphragmatic dysfunction (VIDD). Although VIDD pathophysiological mechanisms are still not fully understood, it has been recently suggested that remodeling of the sarcoplasmic reticulum (SR) calcium release channel/ryanodine receptors (RyR1) in the diaphragm is a proximal mechanism of VIDD. Here, we used piglets, a large animal model of VIDD that is more relevant to human pathophysiology, to determine whether RyR1 alterations are observed in the presence of diaphragm weakness. In piglets, diaphragm weakness induced by 72 h of respiratory muscle unloading was associated with SR RyR1 remodeling and abnormal resting SR Ca²⁺ leak in the diaphragm. Specifically, following controlled mechanical ventilation, diaphragm contractile function was reduced. Moreover, RyR1 macromolecular complexes were more oxidized, S-nitrosylated and phosphorylated at Ser-2844 and depleted of the stabilizing subunit calstabin1 compared with controls on adaptive support ventilation that maintains diaphragmatic contractile activity. Our study strongly supports the hypothesis that RyR1 is a potential therapeutic target in VIDD and the interest of using small molecule drugs to prevent RyR1-mediated SR Ca²⁺ leak induced by respiratory muscle unloading in patients who require controlled mechanical ventilation.

Diaphragm Dysfunction: Diagnostic Approaches and Management Strategies

The diaphragm is the main inspiratory muscle, and its dysfunction can lead to significant adverse clinical consequences. The aim of this review is to provide clinicians with an overview of the main causes of uni- and bi-lateral diaphragm dysfunction, explore the clinical and physiological consequences of the disease on lung function, exercise physiology and sleep and review the available diagnostic tools used in the evaluation of diaphragm function. A particular emphasis is placed on the clinical significance of diaphragm weakness in the intensive care unit setting and the use of ultrasound to evaluate diaphragmatic action.

Kinetics of ventilation-induced changes in diaphragmatic metabolism by bilateral phrenic pacing in a piglet model

Perioperative necessity of deep sedation is inevitably associated with diaphragmatic inactivation. This study investigated 1) the feasibility of a new phrenic nerve stimulation method allowing early diaphragmatic activation even in deep sedation and, 2) metabolic changes within the diaphragm during mechanical ventilation compared to artificial activity. 12 piglets were separated into 2 groups. One group was mechanically ventilated for 12 hrs (CMV) and in the second group both phrenic nerves were stimulated via pacer wires inserted near the phrenic nerves to mimic spontaneous breathing (STIM). Lactate, pyruvate and glucose levels were measured continuously using microdialysis. Oxygen delivery and blood gases were measured during both conditions. Diaphragmatic stimulation generated sufficient tidal volumes in all STIM animals. Diaphragm lactate release increased in CMV transiently whereas in STIM lactate dropped during this same time point (2.6 vs. 0.9 mmol L^-1 after 5:20 hrs; p < 0.001). CMV increased diaphragmatic pyruvate (40 vs. 146 μmol L^-1 after 5:20 hrs between CMV and STIM; p < 0.0001), but not the lactate/pyruvate ratio. Diaphragmatic stimulation via regular electrodes is feasible to generate sufficient ventilation, even in deep sedation. Mechanical ventilation alters the metabolic state of the diaphragm, which might be one pathophysiologic origin of ventilator-induced diaphragmatic dysfunction. Occurrence of hypoxia was unlikely.

Ventilator-induced diaphragmatic dysfunction: what have we learned?

PURPOSE OF REVIEW

The purpose of the review is to summarize and discuss recent research regarding the role of mechanical ventilation in producing weakness and atrophy of the diaphragm in critically ill patients, an entity termed ventilator-induced diaphragmatic dysfunction (VIDD).

RECENT FINDINGS

Severe weakness of the diaphragm is frequent in mechanically ventilated patients, in whom it contributes to poor outcomes including increased mortality. Significant progress has been made in identifying the molecular mechanisms responsible for VIDD in animal models, and there is accumulating evidence for occurrence of the same cellular processes in the diaphragms of human patients undergoing prolonged mechanical ventilation.

SUMMARY

Recent research is pointing the way to novel pharmacologic therapies as well as nonpharmacologic methods for preventing VIDD. The next major challenge in the field will be to move these findings from the bench to the bedside in critically ill patients.

Dysfunction of respiratory muscles in critically ill patients on the intensive care unit

Muscular weakness and muscle wasting may often be observed in critically ill patients on intensive care units (ICUs) and may present as failure to wean from mechanical ventilation. Importantly, mounting data demonstrate that mechanical ventilation itself may induce progressive dysfunction of the main respiratory muscle, i.e. the diaphragm. The respective condition was termed 'ventilator-induced diaphragmatic dysfunction' (VIDD) and should be distinguished from peripheral muscular weakness as observed in 'ICU-acquired weakness (ICU-AW)'. Interestingly, VIDD and ICU-AW may often be observed in critically ill patients with, e.g. severe sepsis or septic shock, and recent data demonstrate that the pathophysiology of these conditions may overlap. VIDD may mainly be characterized on a histopathological level as disuse muscular atrophy, and data demonstrate increased proteolysis and decreased protein synthesis as important underlying pathomechanisms. However, atrophy alone does not explain the observed loss of muscular force. When, e.g. isolated muscle strips are examined and force is normalized for cross-sectional fibre area, the loss is disproportionally larger than would be expected by atrophy alone. Nevertheless, although the exact molecular pathways for the induction of proteolytic systems remain incompletely understood, data now suggest that VIDD may also be triggered by mechanisms including decreased diaphragmatic blood flow or increased oxidative stress. Here we provide a concise review on the available literature on respiratory muscle weakness and VIDD in the critically ill. Potential underlying pathomechanisms will be discussed before the background of current diagnostic options. Furthermore, we will elucidate and speculate on potential novel future therapeutic avenues.

Influence of weaning methods on the diaphragm after mechanical ventilation in a rat model

BACKGROUND

Mechanical ventilation (MV) is associated with diaphragm weakness, a phenomenon termed ventilator-induced diaphragmatic dysfunction. Weaning should balance diaphragmatic loading as well as prevention of overload after MV. The weaning methods pressure support ventilation (PSV) and spontaneous breathing trials (SBT) lead to gradual or intermittent reloading of a weak diaphragm, respectively. This study investigated which weaning method allows more efficient restoration of diaphragm homeostasis.

METHODS

Rats (n = 8 per group) received 12 h of MV followed by either 12 h of pressure support ventilation (PSV) or intermittent spontaneous breathing trials (SBT) and were compared to rats euthanized after 12 h MV (CMV) and to acutely euthanized rats (CON). Force generation, activity of calpain-1 and caspase-3, oxidative stress, and markers of protein synthesis (phosphorylated AKT to total AKT) were measured in the diaphragm.

RESULTS

Reduction of diaphragmatic force caused by CMV compared to CON was worsened with PSV and SBT (both p < 0.05 vs. CON and CMV). Both PSV and SBT reversed oxidative stress and calpain-1 activation caused by CMV. Reduced pAKT/AKT was observed after CMV and both weaning procedures.

CONCLUSIONS

MV resulted in a loss of diaphragmatic contractility, which was aggravated in SBT and PSV despite reversal of oxidative stress and proteolysis.

Diaphragm Dysfunction in Mechanically Ventilated Patients

Muscle involvement is found in most critical patients admitted to the intensive care unit (ICU). Diaphragmatic muscle alteration, initially included in this category, has been differentiated in recent years, and a specific type of muscular dysfunction has been shown to occur in patients undergoing mechanical ventilation. We found this muscle dysfunction to appear in this subgroup of patients shortly after the start of mechanical ventilation, observing it to be mainly associated with certain control modes, and also with sepsis and/or multi-organ failure. Although the specific etiology of process is unknown, the muscle presents oxidative stress and mitochondrial changes. These cause changes in protein turnover, resulting in atrophy and impaired contractility, and leading to impaired functionality. The term 'ventilator-induced diaphragm dysfunction' was first coined by Vassilakopoulos et al. in 2004, and this phenomenon, along with injury cause by over-distention of the lung and barotrauma, represents a challenge in the daily life of ventilated patients. Diaphragmatic dysfunction affects prognosis by delaying extubation, prolonging hospital stay, and impairing the quality of life of these patients in the years following hospital discharge. Ultrasound, a non-invasive technique that is readily available in most ICUs, could be used to diagnose this condition promptly, thus preventing delays in starting rehabilitation and positively influencing prognosis in these patients.

The course of diaphragm atrophy in ventilated patients assessed with ultrasound: a longitudinal cohort study

Introduction

Mechanical ventilation and the effect of respiratory muscle unloading on the diaphragm cause ventilator-induced diaphragmatic dysfunction (VIDD). Atrophy of the diaphragmatic muscle is a major part of VIDD, and has a rapid onset in most animal models. We wanted to assess the clinical evolution and risk factors for VIDD in an adult intensive care unit (ICU) by measuring diaphragm thickness using ultrasound.

Method

We performed a single-centre observational cohort study, including 54 mechanically ventilated patients. The right hemidiaphragm was measured daily at the zone of apposition on the midaxillary line.

Results

Mean baseline thickness was 1.9 mm (SD ± 0.4 mm), and mean nadir was 1.3 mm (SD ± 0.4 mm), corresponding with a mean change in thickness of 32 % (95 % CI 27–37 %). Length of mechanical ventilation (MV) was associated with the degree of atrophy, whereas other known risk factors for muscle atrophy in an ICU were not. The largest decrease in thickness occurred during the first 72 hours of MV.

Conclusions

Diaphragm atrophy occurs quickly in mechanically ventilated patients and can accurately be monitored using ultrasound. Length of MV, as opposed to other variables, is associated with the degree of atrophy.

Clinical trial registration

Clinicaltrials.gov NCT02299986. Registered 10/11/2014

Electronic supplementary material

The online version of this article (doi:10.1186/s13054-015-1141-0) contains supplementary material, which is available to authorized users.

Effects of controlled mechanical ventilation on sepsis-induced diaphragm dysfunction in rats

OBJECTIVES

Diaphragm dysfunction develops during severe sepsis as a consequence of hemodynamic, metabolic, and intrinsic abnormalities. Similarly, 12 hours of controlled mechanical ventilation also promotes diaphragm dysfunction. Importantly, patients with sepsis are often treated with mechanical ventilation for several days. It is unknown if controlled mechanical ventilation exacerbates sepsis-induced diaphragm dysfunction, and this forms the basis for these experiments. We investigate the effects of 12-hour controlled mechanical ventilation on contractile function, fiber dimension, cytokine production, proteolysis, autophagy, and oxidative stress in the diaphragm of septic rats.

DESIGN

Randomized controlled experiment.

SETTING

Animal research laboratory.

SUBJECTS

Adult male Wistar rats.

INTERVENTIONS

Treatment with a single intraperitoneal injection of either saline or Escherichia coli lipopolysaccharide (5 mg/kg). After 12 hours, the saline-treated animals (controlled mechanical ventilation) and half of the septic animals (lipopolysaccharide + controlled mechanical ventilation) were submitted to 12 hours of controlled mechanical ventilation while the remaining septic animals (lipopolysaccharide) were breathing spontaneously for 12 hours. They were compared to a control group. All animals were studied 24 hours after saline or lipopolysaccharide administration.

MEASUREMENTS AND MAIN RESULTS

Twenty-four hours after saline or lipopolysaccharide administration, diaphragm contractility was measured in vitro. We also measured diaphragm muscle fiber dimensions from stained cross sections, and inflammatory cytokines were determined by proteome array. Activities of calpain, caspase-3, and proteasome, expression of 20S-proteasome α subunits, E2 conjugases, E3 ligases, and autophagy were measured with immunoblotting and quantitative polymerase chain reaction. Lipopolysaccharide and/or controlled mechanical ventilation independently decreased diaphragm contractility and fiber dimensions and increased diaphragm interleukin-6 production, protein ubiquitination, expression of Atrogin-1 and Murf-1, calpain and caspase-3 activities, autophagy, and protein oxidation. Compared with lipopolysaccharide alone, lipopolysaccharide + controlled mechanical ventilation worsened diaphragm contractile dysfunction, augmented diaphragm interleukin-6 levels, autophagy, and protein oxidation, but exerted no exacerbating effects on diaphragm fiber dimensions, calpain, caspase-3, or proteasome activation.

CONCLUSIONS

Twelve hours of controlled mechanical ventilation potentiates sepsis-induced diaphragm dysfunction, possibly due to increased proinflammatory cytokine production and autophagy and worsening of oxidative stress.

[Ventilator-induced diaphragm dysfunction : clinically relevant problem]

Mechanical ventilation is a life-saving intervention for patients with respiratory failure or during deep sedation. During continuous mandatory ventilation the diaphragm remains inactive, which activates pathophysiological cascades leading to a loss of contractile force and muscle mass (collectively referred to as ventilator-induced diaphragm dysfunction, VIDD). In contrast to peripheral skeletal muscles this process is rapid and develops after as little as 12 h and has a profound influence on weaning patients from mechanical ventilation as well as increased incidences of morbidity and mortality. In recent years, animal experiments have revealed pathophysiological mechanisms which have been confirmed in humans. One major mechanism is the mitochondrial generation of reactive oxygen species that have been shown to damage contractile proteins and facilitate protease activation. Besides atrophy due to inactivity, drug interactions can induce further muscle atrophy. Data from animal research concerning the influence of corticosteroids emphasize a dose-dependent influence on diaphragm atrophy and function although the clinical interpretation in intensive care patients (ICU) patients might be difficult. Levosimendan has also been proven to increase diaphragm contractile forces in humans which may prove to be helpful for patients experiencing difficult weaning. Additionally, antioxidant drugs that scavenge reactive oxygen species have been demonstrated to protect the diaphragm from VIDD in several animal studies. The translation of these drugs into the IUC setting might protect patients from VIDD and facilitate the weaning process.

[Intensive care unit acquired weakness. Pathogenesis, treatment, rehabilitation and outcome]

The diagnosis of intensive care unit acquired weakness (ICUAW) in the setting of neurological rehabilitation is steadily increasing. This is due to the fact that the intensive care of patients with sepsis or after cardiac or abdominal surgery is improving. A longer duration of respiratory weaning and comorbidities frequently complicate rehabilitation. Clinically, patients present with a flaccid (tetra) paresis and electrophysiological studies have shown axonal damage. Besides involvement of peripheral nerves, muscle can also be affected (critical illness myopathy) leading to ICUAW with inconstant myopathic damage patterns found by electrophysiological testing. Mixed forms can also be found. A specific therapy for ICUAW is not available. Early mobilization to be initiated on the intensive care unit and commencing neurological rehabilitation improve the outcome of ICUAW. This review highlights the current literature regarding the etiology and diagnosis of ICUAW. Furthermore, studies about rehabilitation and outcome of ICUAW are discussed.

Heat stress protects against mechanical ventilation-induced diaphragmatic atrophy

Mechanical ventilation (MV) is a life-saving intervention in patients who are incapable of maintaining adequate pulmonary gas exchange due to respiratory failure or other disorders. However, prolonged MV is associated with the development of respiratory muscle weakness. We hypothesized that a single exposure to whole body heat stress would increase diaphragm expression of heat shock protein 72 (HSP72) and that this treatment would protect against MV-induced diaphragmatic atrophy. Adult male Wistar rats (n = 38) were randomly assigned to one of four groups: an acutely anesthetized control group (CON) with no MV; 12-h controlled MV group (CMV); 1-h whole body heat stress (HS); or 1-h whole body heat stress 24 h prior to 12-h controlled MV (HSMV). Compared with CON animals, diaphragmatic HSP72 expression increased significantly in the HS and HSMV groups (P < 0.05). Prolonged MV resulted in significant atrophy of type I, type IIa, and type IIx fibers in the costal diaphragm (P < 0.05). Whole body heat stress attenuated this effect. In contrast, heat stress did not protect against MV-induced diaphragm contractile dysfunction. The mechanisms responsible for this heat stress-induced protection remain unclear but may be linked to increased expression of HSP72 in the diaphragm.

Prolonged weaning: from the intensive care unit to home

Weaning is the process of withdrawing mechanical ventilation which starts with the first spontaneous breathing trial (SBT). Based on the degree of difficulty and duration, weaning is classified as simple, difficult and prolonged. Prolonged weaning, which includes patients who fail 3 SBTs or are still on mechanical ventilation 7 days after the first SBT, affects a relatively small fraction of mechanically ventilated ICU patients but these, however, requires disproportionate resources. There are several potential causes which can lead to prolonged weaning. It is nonetheless important to understand the problem from the point of view of each individual patient in order to adopt appropriate treatment and define precise prognosis. An otherwise stable patient who remains on mechanical ventilation will be considered for transfer to a specialized weaning unit (SWU). Though there is not a precise definition, SWU can be considered as highly specialized and protected environments for patients requiring mechanical ventilation despite resolution of the acute disorder. Proper staffing, well defined short-term and long-term goals, attention to psychological and social problems represent key determinants of SWU success. Some patients cannot be weaned, either partly or entirely, and may require long-term home mechanical ventilation. In these cases the logistics relating to caregivers and the equipment must be carefully considered and addressed.

An observational cohort study to determine efficacy, adherence and outcome of the early initiation of pressure support ventilation during mechanical ventilation

Background

Timely initiation of weaning from mechanical ventilation (MV) is important. Non-validated screening criteria may delay weaning if too prescriptive. This study observed physician-led utilisation of pressure support ventilation (PSV), referenced to four reported conventional screening criteria hypothesising that these criteria would have delayed the weaning progress.

Methods

A prospective observational cohort study of adult patients receiving MV in a 30-bed university hospital intensive care unit (ICU). Logistic regression analysis identified factors associated with PSV failure. Outcome is reported according to adherence to the screening criteria.

Results

209 patients were included (age 62.6±15.9 years, male:female 115:94, Acute Physiology and Chronic Health Evaluation (APACHE) II 16.7±6.1). Median (IQR) time to initiate PSV was 11.0 (5.0–22.0) h, and duration of weaning to extubation was 43.0 (13.0–121.5) h. PSV weaning was initiated despite significant hypoxia (partial pressure of arterial oxygen to fraction of inspired oxygen ratio (PaO₂:FiO₂) 35.8±15.9 kPa), moderate positive end-expiratory pressure levels (7.5±2.5 cm H₂O), deep sedation (44% Richmond Agitation and Sedation Scale (RASS) ≤−3) and cardiovascular instability (48.8%). At PSV initiation, 85% of patients violated at least one screening criterion, yet 74.6% of patients remained stable for 24 h and 25.4% of patients were successfully extubated within 12 h. There was no association between individual screening criteria and PSV failure. Failure to sustain a PSV trial was associated with ventilation >7 days (RR=2.12 (1.33 to 3.38), p=0.002) and ICU mortality (RR=2.94 (1.46 to 5.94), p=0.002).

Conclusions

Physician-led transition to PSV and weaning was often initiated early and successfully before patients fulfilled conventional screening criteria. Failure to sustain a PSV trial could be an early indicator of prolonged MV and ICU mortality and warrants further investigation. These data support the view that current screening criteria may delay initiation of weaning.

Sedation using propofol induces similar diaphragm dysfunction and atrophy during spontaneous breathing and mechanical ventilation in rats

BACKGROUND

Mechanical ventilation is crucial for patients with respiratory failure. The mechanical takeover of diaphragm function leads to diaphragm dysfunction and atrophy (ventilator-induced diaphragmatic dysfunction), with an increase in oxidative stress as a major contributor. In most patients, a sedative regimen has to be initiated to allow tube tolerance and ventilator synchrony. Clinical data imply a correlation between cumulative propofol dosage and diaphragm dysfunction, whereas laboratory investigations have revealed that propofol has some antioxidant properties. The authors hypothesized that propofol reduces markers of oxidative stress, atrophy, and contractile dysfunction in the diaphragm.

METHODS

Male Wistar rats (n = 8 per group) were subjected to either 24 h of mechanical ventilation or were undergone breathing spontaneously for 24 h under propofol sedation to test for drug effects. Another acutely sacrificed group served as controls. After sacrifice, diaphragm tissue was removed, and contractile properties, cross-sectional areas, oxidative stress, and proteolysis were examined. The gastrocnemius served as internal control.

RESULTS

Propofol did not protect against diaphragm atrophy, oxidative stress, and protease activation. The decrease in tetanic force compared with controls was similar in the spontaneous breathing group (31%) and in the ventilated group (34%), and both groups showed the same amount of muscle atrophy. The gastrocnemius muscle fibers did not show atrophy.

CONCLUSIONS

Propofol does not protect against ventilator-induced diaphragmatic dysfunction or oxidative injury. Notably, spontaneous breathing under propofol sedation resulted in the same amount of diaphragm atrophy and dysfunction although diaphragm activation per se protects against ventilator-induced diaphragmatic dysfunction. This makes a drug effect of propofol likely.

Effect of intermittent phrenic nerve stimulation during cardiothoracic surgery on mitochondrial respiration in the human diaphragm

OBJECTIVES

Recent studies have shown that brief periods of mechanical ventilation in animals and humans can lead to ventilator-induced diaphragmatic dysfunction, which includes muscle atrophy, reduced force development, and impaired mitochondrial function. Studies in animal models have shown that short periods of increased diaphragm activity during mechanical ventilation support can attenuate ventilator-induced diaphragmatic dysfunction but corresponding human data are lacking. The purpose of this study was to examine the effect of intermittent diaphragm contractions during cardiothoracic surgery, including controlled mechanical ventilation, on mitochondrial respiration in the human diaphragm.

DESIGN

Within subjects repeated measures study.

SETTING

Operating room in an academic health center.

PATIENTS

Five subjects undergoing elective cardiothoracic surgery.

INTERVENTIONS

In patients (age 65.6 ± 6.3 yr) undergoing cardiothoracic surgery, one phrenic nerve was stimulated hourly (30 pulses/min, 1.5 msec duration, 17.0 ± 4.4 mA) during the surgery. Subjects received 3.4 ± 0.6 stimulation bouts during surgery. Thirty minutes following the last stimulation bout, samples of diaphragm muscle were obtained from the anterolateral costal regions of the stimulated and inactive hemidiaphragms.

MEASUREMENTS AND MAIN RESULTS

Mitochondrial respiration was measured in permeabilized muscle fibers with high-resolution respirometry. State III mitochondrial respiration rates (pmol O2/s/mg wet weight) were 15.05 ± 3.92 and 11.42 ± 2.66 for the stimulated and unstimulated samples, respectively (p < 0.05). State IV mitochondrial respiration rates were 3.59 ± 1.25 and 2.11 ± 0.97 in the stimulated samples and controls samples, respectively (p < 0.05).

CONCLUSION

These are the first data examining the effect of intermittent contractions on mitochondrial respiration rates in the human diaphragm following surgery/mechanical ventilation. Our results indicate that very brief periods (duty cycle ~1.7%) of activity can improve mitochondrial function in the human diaphragm following surgery/mechanical ventilation.