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Diaphragm dysfunction: weaning perspective

ABSTRACT: Weaning is the process of successfully liberating the patient from mechanical ventilation. The majority of patients will separate from the ventilator after a successful spontaneous breathing trial (SBT).1 In a minority of patients, weaning can be challenging and prolonged. Finding the cause of weaning difficulty is crucial to minimize the rates of extubation failure and prolonged ventilation. Diaphragm dysfunction (DD) has been described as a separate entity responsible for weaning failure with an incidence of 23–80%. It has also been associated with difficult weaning, prolonged intensive care unit (ICU) stay and mechanical ventilation, and increased ICU and hospital mortality.2 Sepsis, shock, and ventilator induced diaphragm dysfunction are important risk factors of DD. Diaphragm dysfunction has several mechanisms. Disuse atrophy and microstructural changes of the diaphragm have been described as the two cardinal pathophysiologic features. Establishing the diagnosis of DD can be complex in critically ill patients. Bilateral anterior magnetic phrenic stimulation is widely considered as the gold standard but is only available in large research centers with limited availability. Ultrasonography of the diaphragm is a promising tool given its wide availability, affordability, and non-invasive nature. Ultrasound is operator dependent, however and it does not provide continuous monitoring capabilities. The diaphragm thickening fraction (DTF) can be calculated from measuring the end-expiratory and end-inspiratory diaphragm thickness at the bedside. It correlates well with transdiaphragmatic pressure.3 Electromyography of the diaphragm may overcome the limitation of ultrasound by offering a continuous assessment of the diaphragmatic electrical activity, but it requires the placement of a specialized nasogastric tube. Management of DD is better approached by implementing a preventive and a curative strategy. From animal studies, allowing for spontaneous breathing on mechanical ventilation may prevent the problem. The degree of the recommended patient effort and ventilator assistance to achieve optimal balance between diaphragmatic loading and unloading are yet to be defined. Monitoring DTF while finding the optimal ventilator support level can be useful in this context. Another modality to prevent DD is diaphragm pacing applied through a transvenous phrenic nerve pacing system. Animal studies in pigs showed that this modality resulted in less diaphragm atrophy when pacing was synchronized with ventilation.4 There is an ongoing study to assess the role of diaphragm pacing to recondition and strengthen the diaphragm in difficult to wean mechanically ventilated patients (Clinicaltrials.gov NCT03107949). Once diaphragm dysfunction is established, no specific treatments exist at this time. Other causes of weaning failure like cardiac dysfunction have to be excluded and treated. Improving respiratory load and respiratory muscle weakness imbalance is also crucial. While it appears to improve inspiratory muscle strength parameters, inspiratory muscle training has not consistently shown improvements in weaning success.5 Levosemindan showed some benefit in improving diaphragm contractility and efficiency in healthy volunteers but was later found to increase likelihood of weaning failure in septic patients. Anabolic steroids were not found to be effective in treating diaphragm dysfunction in several studies. More evidence is needed before recommending non-invasive ventilation post-extubation in all DD patients.

SUBMITTER: Kharma N

PROVIDER: S-EPMC6851905 | biostudies-literature | 2019 Jan

REPOSITORIES: biostudies-literature

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Project description:During a T-tube trial following disconnection of mechanical ventilation, patients failing the trial do not develop contractile diaphragmatic fatigue despite increases in inspiratory pressure output. Studies in volunteers, patients, and animals raise the possibility of spinal and supraspinal reflex mechanisms that inhibit central-neural output under loaded conditions. We hypothesized that diaphragmatic recruitment is submaximal at the end of a failed weaning trial despite concurrent respiratory distress. Tidal transdiaphragmatic pressure (?Pdi) and electrical activity (?EAdi) were recorded with esophago-gastric catheters during a T-tube trial in 20 critically ill patients. During the T-tube trial, ?EAdi was greater in weaning failure patients than in weaning success patients (P = 0.049). Despite increases in ?Pdi, from 18.1?±?2.5 to 25.9?±?3.7 cm H2O (P < 0.001), rate of transdiaphragmatic pressure development (from 22.6?±?3.1 to 37.8?±?6.7 cm H2O/s; P < 0.0004), and concurrent respiratory distress, ?EAdi at the end of a failed T-tube trial was half of maximum, signifying inhibition of central neural output to the diaphragm. The increase in ?Pdi in the weaning failure group, while ?EAdi remained constant, indicates unexpected improvement in diaphragmatic neuromuscular coupling (from 46.7?±?6.5 to 57.8?±?8.4 cm H2O/%; P = 0.006). Redistribution of neural output to the respiratory muscles characterized by a progressive increase in rib cage and accessory muscle contribution to tidal breathing and expiratory muscle recruitment contributed to enhanced coupling. In conclusion, diaphragmatic recruitment is submaximal at the end of a failed weaning trial despite concurrent respiratory distress. This finding signifies that reflex inhibition of central neural output to the diaphragm contributes to weaning failure.NEW & NOTEWORTHY Research into pathophysiology of failure to wean from mechanical ventilation has excluded several factors, including contractile fatigue, but the precise mechanism remains unknown. We recorded transdiaphragmatic pressure and diaphragmatic electrical activity in patients undergoing a T-tube trial. Diaphragmatic recruitment was submaximal at the end of a failed trial despite concurrent respiratory distress, signifying that inhibition of central neural output to the diaphragm is an important mechanism of weaning failure.

Project description:BackgroundLung and diaphragm ultrasound methods have recently been introduced to predict the outcome of weaning from mechanical ventilation (MV). The aim of this study is to assess the reliability and accuracy of these techniques for predicting successful weaning in critically ill adults.MethodsWe conducted two studies: a cross-sectional interobserver agreement study between two sonographers and a prospective cohort study to assess the accuracy of lung and diaphragm ultrasound for predicting weaning and extubation outcome. For the interobserver agreement study, we included 50 general critical care patients who were consecutively admitted to the ICU. For the predictive accuracy study, we included consecutively 69 patients on MV who were ready for weaning. We assessed interobserver agreement of ultrasound measurements, using the weighted kappa coefficient for LUSm score (modified lung ultrasound score) and the intraclass correlation coefficient (ICC) and Bland-Altman method for TI (diaphragm thickening index). We assessed the predictive value of LUSm and TI in weaning outcome by plotting the corresponding ROC curves.ResultsWe found adequate interobserver agreement for both LUSm (weighted kappa 0.95) and TI (ICC 0.78, difference according to Bland-Altman analysis?±?12.5%). LUSm showed good-moderate discriminative power for successful weaning and extubation (area under the ROC curve (AUC) for successful weaning 0.80, and sensitivity and specificity at optimal cut-off point 0.76 and 0.73, respectively; AUC for successful extubation 0.78, and optimal sensitivity and specificity 0.76 and 0.47, respectively. TI was more sensitive but less specific for predicting successful weaning (AUC 0.71, optimal sensitivity and specificity 0.93 and 0.48) and successful extubation (AUC 0.76, optimal sensitivity and specificity 0.93 and 0.58). The area under the ROC curve for predicting weaning success was 0.83 for both ultrasound measurements together.ConclusionsInterobserver agreement was excellent for LUSm and moderate-good for TI. A low TI value or high LUSm value indicates high risk of weaning failure.

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Diaphragm dysfunction: weaning perspective

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