Department of Pulmonary and Critical Care Medicine, University of Minnesota School of Medicine, Minneapolis, MN.
Department of Mathematics, Vanderbilt University, Nashville, TN.
Crit Care Med. 2022 Nov 1;50(11):1599-1606. doi: 10.1097/CCM.0000000000005631. Epub 2022 Jul 21.
Head-elevated body positioning, a default clinical practice, predictably increases end-expiratory transpulmonary pressure and aerated lung volume. In acute respiratory distress syndrome (ARDS), however, the net effect of such vertical inclination on tidal mechanics depends upon whether lung recruitment or overdistension predominates. We hypothesized that in moderate to severe ARDS, bed inclination toward vertical unloads the chest wall but adversely affects overall respiratory system compliance (C rs ).
Prospective physiologic study.
Two medical ICUs in the United States.
Seventeen patients with ARDS, predominantly moderate to severe.
Patients were ventilated passively by volume control. We measured airway pressures at baseline (noninclined) and following bed inclination toward vertical by an additional 15°. At baseline and following inclination, we manually loaded the chest wall to determine if C rs increased or paradoxically declined, suggestive of end-tidal overdistension.
Inclination resulted in a higher plateau pressure (supineΔ: 2.8 ± 3.3 cm H 2 O [ p = 0.01]; proneΔ: 3.3 ± 2.5 cm H 2 O [ p = 0.004]), higher driving pressure (supineΔ: 2.9 ± 3.3 cm H 2 O [ p = 0.01]; proneΔ: 3.3 ± 2.8 cm H 2 O [ p = 0.007]), and lower C rs (supine Δ: 3.4 ± 3.7 mL/cm H 2 O [ p = 0.01]; proneΔ: 3.1 ± 3.2 mL/cm H 2 O [ p = 0.02]). Following inclination, manual loading of the chest wall restored C rs and driving pressure to baseline (preinclination) values.
In advanced ARDS, bed inclination toward vertical adversely affects C rs and therefore affects the numerical values for plateau and driving tidal pressures commonly targeted in lung protective strategies. These changes are fully reversed with manual loading of the chest wall, suggestive of end-tidal overdistension in the upright position. Body inclination should be considered a modifiable determinant of transpulmonary pressure and lung protection, directionally similar to tidal volume and positive end-expiratory pressure.
头高位身体定位是一种常规的临床实践，可预测性地增加呼气末跨肺压和充气肺容积。然而，在急性呼吸窘迫综合征（ARDS）中，这种垂直倾斜对潮气量力学的净效应取决于肺复张还是过度充气占主导地位。我们假设，在中重度 ARDS 中，床面朝向垂直倾斜会减轻胸壁负荷，但会对整体呼吸系统顺应性（Crs）产生不利影响。
前瞻性生理研究。
美国的两个医疗 ICU。
17 例 ARDS 患者，主要为中重度。
患者通过容量控制被动通气。我们在基线（未倾斜）和床面额外倾斜 15°后测量气道压力。在基线和倾斜后，我们手动加载胸壁，以确定 Crs 是否增加或反常下降，提示终末过度充气。
倾斜导致平台压升高（仰卧位Δ：2.8±3.3 cm H2O [p=0.01]；俯卧位Δ：3.3±2.5 cm H2O [p=0.004]），驱动压升高（仰卧位Δ：2.9±3.3 cm H2O [p=0.01]；俯卧位Δ：3.3±2.8 cm H2O [p=0.007]），Crs 降低（仰卧位Δ：3.4±3.7 mL/cm H2O [p=0.01]；俯卧位Δ：3.1±3.2 mL/cm H2O [p=0.02]）。倾斜后，手动加载胸壁可使 Crs 和驱动压恢复到基线（倾斜前）值。
在晚期 ARDS 中，床面朝向垂直倾斜会对 Crs 产生不利影响，因此会影响肺保护性策略中常用的平台压和驱动潮气量的数值。通过手动加载胸壁可完全逆转这些变化，提示直立位时终末过度充气。身体倾斜应被视为跨肺压和肺保护的可调节决定因素，与潮气量和呼气末正压的方向相似。
