Diaphragm weakness in mechanically ventilated critically ill patients

INTRODUCTION Studies indicate that mechanically ventilated patients develop significant diaphragm muscle weakness, but the etiology of weakness and its clinical impact remain incompletely understood. We assessed diaphragm strength in mechanically ventilated medical ICU patients, correlated the development of diaphragm weakness with multiple clinical parameters, and examined the relationship between the level of diaphragm weakness and patient outcomes. METHODS Transdiaphragmatic twitch pressure (PdiTw) in response to bilateral magnetic stimulation of the phrenic nerves was measured. Diaphragm weakness was correlated with the presence of infection, blood urea nitrogen, albumin, and glucose levels. The relationship of diaphragm strength to patient outcomes, including mortality and the duration of mechanical ventilation for successfully weaned patients, was also assessed. RESULTS We found that infection is a major risk factor for diaphragm weakness in mechanically ventilated medical ICU patients. Outcomes for patients with severe diaphragm weakness (PdiTw<10 cmH2O) were poor, with a markedly increased mortality (49%) compared to patients with PdiTw≥10 cmH2O (7% mortality, P=0.022). In addition, survivors with PdiTw<10 cmH2O required a significantly longer duration of mechanical ventilation (12.3±1.7 days) than those with PdiTw≥10 cmH2O (5.5±2.0 days, P=0.016). CONCLUSIONS Infection is a major cause of severe diaphragm weakness in mechanically ventilated patients. Moreover, diaphragm weakness is an important determinant of poor outcomes in this patient population.