Diaphragm dysfunction in mechanically ventilated patients: Comparing volume and pressure modes.

BACKGROUND: Diaphragm dysfunction (DD) is a common complication of mechanical ventilation and contributes to prolonged ventilation and weaning failure. Data comparing the effects of volume- and pressure-targeted ventilation modes on diaphragm function are limited. This study compared synchronized intermittent mandatory ventilation (SIMV) and bilevel positive airway pressure (BiPAP) using bedside ultrasonography. METHODS: In this prospective study, 40 mechanically ventilated adults admitted to two ICUs were enrolled (20 SIMV, 20 BiPAP) according to routine practice. Diaphragm excursion (DE) and diaphragmatic thickening fraction (DTF) were measured within 24 h of ventilation initiation and daily for up to 7 days during standardized pressure support sessions. DD was defined as DE < 1.5 cm or DTF < 20%. Repeated-measures analysis evaluated changes over time and between groups. RESULTS: Both DE and DTF declined significantly over time in both groups (P < 0.001). No significant differences were observed between SIMV and BiPAP for DE (P = 0.73) or DTF (P = 0.40). DD occurred in 50-70% of patients based on DE and in 25-35% based on DTF, without significant intergroup differences. Duration of mechanical ventilation was similar (median 4 days; P = 0.543). CONCLUSIONS: Both ventilation modes were associated with progressive diaphragm dysfunction, with no significant advantage of either mode.