Acute effects of ventilator hyperinflation with increased inspiratory time on respiratory mechanics: randomized crossover clinical trial

ABSTRACT Objective: To evaluate the effects of ventilator hyperinflation on respiratory mechanics. Methods: A randomized crossover clinical trial was conducted with 38 mechanically ventilated patients with pulmonary infection. The order of the hyperinflation and control (without changes in the parameters) conditions was randomized. Hyperinflation was performed for 5 minutes in pressure-controlled ventilation mode, with progressive increases of 5cmH2O until a maximum pressure of 35cmH2O was reached, maintaining positive end expiratory pressure. After 35cmH2O was reached, the inspiratory time and respiratory rate were adjusted so that the inspiratory and expiratory flows reached baseline levels. Measurements of static compliance, total resistance and airway resistance, and peak expiratory flow were evaluated before the technique, immediately after the technique and after aspiration. Two-way analysis of variance for repeated measures was used with Tukey's post hoc test, and p < 0.05 was considered significant. Results: Ventilator hyperinflation increased static compliance, which remained at the same level after aspiration (46.2 ± 14.8 versus 52.0 ± 14.9 versus 52.3 ± 16.0mL/cmH2O; p < 0.001). There was a transient increase in airway resistance (6.6 ± 3.6 versus 8.0 ± 5.5 versus 6.6 ± 3.5cmH2O/Ls-1; p < 0.001) and a transient reduction in peak expiratory flow (32.0 ± 16.0 versus 29.8 ± 14.8 versus 32.1 ± 15.3Lpm; p <0.05) immediately after the technique; these values returned to pretechnique levels after tracheal aspiration. There were no changes in the control condition, nor were hemodynamic alterations observed. Conclusion: Ventilator hyperinflation promoted increased compliance associated with a transient increase in airway resistance and peak expiratory flow, with reduction after aspiration.

摘要
研究目的：评估呼吸机肺过度充气（ventilator hyperinflation）对呼吸力学的影响。
研究方法：本研究纳入38例肺部感染机械通气患者，采用随机交叉临床试验设计，随机分配肺过度充气组与对照组（参数保持不变）的干预顺序。肺过度充气操作采用压力控制通气（pressure-controlled ventilation）模式，持续5分钟，以5cmH₂O为梯度逐步提升气道压力，直至达到35cmH₂O的最大压力，期间维持呼气末正压（positive end expiratory pressure）。当气道压力达到35cmH₂O后，调整吸气时间与呼吸频率，使吸气流速与呼气流速恢复至基线水平。分别于操作前、操作即刻及气管吸痰（tracheal aspiration）后，检测静态顺应性（static compliance）、总气道阻力（total resistance）、气道阻力（airway resistance）及峰值呼气流速（peak expiratory flow）。采用重复测量方差分析结合Tukey事后检验（Tukey's post hoc test）进行统计分析，以p<0.05为差异具有统计学意义。
研究结果：呼吸机肺过度充气可提升静态顺应性，且该效果在气管吸痰后仍得以维持（46.2±14.8 vs 52.0±14.9 vs 52.3±16.0mL/cmH₂O；p<0.001）。操作即刻可见气道阻力一过性升高（6.6±3.6 vs 8.0±5.5 vs 6.6±3.5cmH₂O/(L·s⁻¹)；p<0.001），峰值呼气流速一过性降低（32.0±16.0 vs 29.8±14.8 vs 32.1±15.3Lpm；p<0.05），上述指标在气管吸痰后均恢复至操作前基线水平。对照组各项指标无明显变化，亦未观察到血流动力学改变。
研究结论：呼吸机肺过度充气可提升静态顺应性，同时伴随气道阻力与峰值呼气流速的一过性改变，且该一过性异常可在气管吸痰后恢复至基线水平。