Critical Care最新文献

Background: Prone positioning improves survival in patients with acute respiratory distress syndrome (ARDS) by reducing ventilator-induced lung injury and enhancing ventilation-perfusion matching. Whether these physiological benefits translate to patients supported with veno-venous extracorporeal membrane oxygenation (VV-ECMO) remains uncertain.

Methods: This study compared the effects of prone versus supine positioning on the wet-to-dry lung weight ratio, gas exchange, respiratory mechanics, electrical impedance tomography, histopathology, microbiology, hemodynamics, and extracorporeal circuit function in pigs with severe ARDS undergoing VV-ECMO. Pigs with severe ARDS were placed on VV-ECMO according to EOLIA criteria and then randomized to either prone or supine positioning for 48 h, while receiving an ultraprotective ventilation strategy. Futility analyses were performed at half of the planned sample size using conditional power calculations, with early termination criteria set at < 10% probability of achieving statistical significance.

Results: Eight pigs with severe ARDS were randomized after VV-ECMO initiation. Prone positioning, compared with the supine position, resulted in a similar wet-to-dry lung weight ratio (6.77 [6.13-8.17] vs. 6.70 [6.22-8.48]; p = 0.89), meeting the futility threshold. Compared with the supine position, prone positioning significantly reduced the proportion of ventilation in non-dependent lung regions (51 [47-61.25]% vs. 86 [68.50-90]%; p = 0.02), thereby indicating a redistribution of ventilation toward dependent areas. Consistent with this shift in ventilation distribution, prone positioning redistributed histopathological lung injury, with relative preservation of non-dependent regions and greater damage in dependent zones, but without a net global decrease. Shunt fraction approached 100% in both groups, with no significant differences. Pulmonary CO₂ elimination was 8.45 (1.45-26.13) mL/min in the prone group and 0 (0-0.70) mL/min in the supine group (p = 0.23). Lung compliance showed no intergroup differences (14.67 [12.75-19.91] vs. 16.68 [15.51-19.47] mL/cmH₂O; p = 0.88), with similarly elevated end-inspiratory transpulmonary pressures. No significant differences were observed in systemic or pulmonary hemodynamics, nor in VV-ECMO circuit function.

Conclusions: Prone positioning did not decrease the overall severity of lung injury. Rather, it shifted the distribution of damage, with greater involvement of dependent regions and relative preservation of non-dependent areas.

Background: During bronchoscopy in mechanically ventilated patients, bronchoscope insertion markedly increases airway resistance, elevating peak airway pressure and reducing delivered tidal volume. We sought to determine whether specific ventilator settings (assist volume-controlled with reduced inspiratory flow and tidal volume) lower serious adverse events during flexible fiberoptic bronchoscopy compared with conventional ventilator settings.

Methods: Single-center randomized adjudicator-blinded controlled trial in intubated adult patients undergoing fiberoptic bronchoscopy. Patients were assigned (1:1) to bronchoscopy-optimized settings (inspiratory flow ≤ 25L/min, tidal volume = 5mL/Kg, 1s ≤ inspiratory time ≤ 1.3s, respiratory frequency = 16 breaths/min, positive end-expiratory pressure = 5cmH₂O) or to conventional ventilator settings. The primary endpoint was a composite of serious adverse events requiring premature termination (inability to deliver ventilatory support, significant arterial desaturation, or hemodynamic instability), adjudicated by blinded experts. All analyses were performed on an intention-to-treat basis.

Results: The primary composite endpoint occurred in 1/23 (4%) with optimized settings compared with 22/23 (96%) with conventional settings (risk difference -91.3%; risk ratio 0.05; p < 0.001). Events were driven by ventilatory failure due to pressure-alarm limitation, with lower delivered tidal volume (median 160 vs 400 mL; p < 0.001) and minute ventilation (3.2 vs 7.2 L/min; p < 0.001) under conventional settings. Respiratory and circulatory events were rare and similar between groups (each 1/23 [4%]). Among 19 crossover patients, switching to optimized settings reduced peak airway pressure and restored adequate ventilation.

Conclusions: A bronchoscopy-optimized ventilation strategy substantially reduces pressure-alarm-limited ventilation events and enables the delivery of adequate ventilatory support during fiberoptic bronchoscopy.