ICU acquired weakness, a combination of myopathy and neuropathy, is observed in ICU patients with a variable incidence but becomes very common in multi organ failure. It is associated with poorer outcomes and weaning delays from mechanical ventilation. The extent of diaphragmatic dysfunction compared to limb muscle weakness is unclear. Current evidence gives conflicting results when diaphragm function is measured using a maximal inspiratory pressure (1) or electromyography (2).
This study uses a multimodal tool to assess diaphragmatic function using magnetic stimulation of the phrenic nerves, diaphragm ultrasound and pulmonary function tests (3). These are used in patients with ICU acquired weakness (ICUAW) undergoing a spontaneous breathing trial (SBT).
Patients were eligible if they were diagnosed with ICUAW [Medical Research Council (MRC) Score <48], mechanically ventilated for at least 48 h and were undergoing a spontaneous breathing trial.
Diaphragm function was assessed using magnetic stimulation of the phrenic nerves (change in endotracheal tube pressure) (4), maximal inspiratory pressure (MIP) and ultrasonographically (thickening fraction) (5). Diaphragmatic dysfunction was defined by a change in endotracheal tube pressure below 11 cmH2O.
The endpoints were to describe the correlation between diaphragm function and ICUAW and its impact on extubation. Among 185 consecutive patients ventilated for >48 h, 40 (22 %) with a MRC score of 31 were included. Diaphragm dysfunction was observed with ICUAW in 32 patients (80 %). A change in endotracheal tube pressure and MRC score were not correlated. MIP and change in tube pressure after phrenic nerve stimulation were correlated. U/S thickening fraction was correlated with change in tube pressure but not with MRC score.
This study shows an association between diaphragmatic dysfunction and ICUAW. This study did not look at diaphragmatic function in those patients with an MRC> 48. Diaphragm dysfunction is frequent in patients with ICUAW (80 %) but poorly correlated with the ICU-acquired weakness MRC score. Half of the patients with ICU-acquired weakness were successfully extubated but half of the patients who failed the weaning process died during the ICU stay. There is a need for further studies to predict weaning success or failure in the ICU population.
Article review was submitted by James Day on behalf of the ESICM Journal Review Club.
1. American Thoracic Society/European Respiratory Society (2002) ATS/ERS statement on respiratory muscle testing. Am J Respir Crit Care Med 166:518–624. doi: 10.1164/rccm.166.4.518
2. Santos PD, Teixeira C, Savi A et al (2012) The critical illness polyneuropathy in septic patients with prolonged weaning from mechanical ventilation: Is the diaphragm also affected? A pilot study. Respir Care 57:1594–1601. doi: 10.4187/respcare.01396
3. Jung B et al. Diaphragmatic dysfunction in patients with ICU-acquired weakness and its impact on extubation failure. Intensive Care Med. 2016 May;42(5):853-61. doi: 10.1007/s00134-015-4125-2
4. Demoule A, Jung B, Prodanovic H et al (2013) Diaphragm dysfunction on admission to ICU: prevalence, risk factors and prognostic impact—a prospective study. Am J Respir Crit Care Med. doi: 10.1164/rccm.201209-1668OC
5. Matamis D, Soilemezi E, Tsagourias M et al (2013) Sonographic evaluation of the diaphragm in critically ill patients. Technique and clinical applications. Intensive Care Med 39:801–810. doi: 10.1007/s00134-013-2823-1