背景:在压力支持通气(PSV)期间,吸气保持可以测量平台压力(Pplat),驱动压力(ΔP),呼吸系统顺应性(Crs)和压力-肌肉指数(PMI),吸气努力的指数。本研究旨在[1]系统地评估患者的努力程度(用PMI估计),ΔP和潮气量(Vt)响应PSV和[2]的变化而变化,以确认PSV期间Crs测量的鲁棒性。
方法:将18例从急性呼吸衰竭中恢复并通过PSV通气的患者交叉随机分为临床设定PS以上(3和6cmH2O)和以下(-3和-6cmH2O)的四个辅助步骤。进行吸气和呼气保持以测量Pplat,PMI,ΔP,Vt,Crs,P0.1和闭塞吸气气道压力(Pocc)。从体表(sEMG)无创监测呼吸肌的肌电图。
结果:由于PSV下降,Pplat(从20.5±3.3cmH2O到16.7±2.9,P<0.001)和ΔP(从12.5±2.3到8.6±2.3cmH2O,P<0.001)的下降幅度远小于气道峰值压力(从21.7±3.8至9.7±3.8cmH2O,P<0.001),考虑到患者的努力(PMI从-1.2±2.3到6.4±3.2cmH2O)逐渐增加,与隔膜的sEMG一致(r=0.614;P<0.001)。当ΔP随Vt线性增加时,Crs没有逐步变化(P=0.119)。
结论:患者对PSV下降的反应是通过增加吸气努力-通过PMI将Vt和ΔP保持在期望值来估计,因此,限制了临床医生调节它们的能力。当患者在压力控制模式下失去对Vt的控制时,PMI似乎是评估通气过度辅助点的有价值的指标。PSV中Crs的测量是恒定的-可能表明可靠性-独立于辅助水平和患者的努力。
BACKGROUND: During Pressure Support Ventilation (PSV) an inspiratory hold allows to measure plateau pressure (Pplat), driving pressure (∆P), respiratory system compliance (Crs) and pressure-muscle-index (PMI), an index of inspiratory effort. This study aims [1] to assess systematically how patient\'s effort (estimated with PMI), ∆P and tidal volume (Vt) change in response to variations in PSV and [2] to confirm the robustness of Crs measurement during PSV.
METHODS: 18 patients recovering from acute respiratory failure and ventilated by PSV were cross-randomized to four steps of assistance above (+ 3 and + 6 cmH2O) and below (-3 and -6 cmH2O) clinically set PS. Inspiratory and expiratory holds were performed to measure Pplat, PMI, ∆P, Vt, Crs, P0.1 and occluded inspiratory airway pressure (Pocc). Electromyography of respiratory muscles was monitored noninvasively from body surface (sEMG).
RESULTS: As PSV was decreased, Pplat (from 20.5 ± 3.3 cmH2O to 16.7 ± 2.9, P < 0.001) and ∆P (from 12.5 ± 2.3 to 8.6 ± 2.3 cmH2O, P < 0.001) decreased much less than peak airway pressure did (from 21.7 ± 3.8 to 9.7 ± 3.8 cmH2O, P < 0.001), given the progressive increase of patient\'s effort (PMI from -1.2 ± 2.3 to 6.4 ± 3.2 cmH2O) in line with sEMG of the diaphragm (r = 0.614; P < 0.001). As ∆P increased linearly with Vt, Crs did not change through steps (P = 0.119).
CONCLUSIONS: Patients react to a decrease in PSV by increasing inspiratory effort-as estimated by PMI-keeping Vt and ∆P on a desired value, therefore, limiting the clinician\'s ability to modulate them. PMI appears a valuable index to assess the point of ventilatory overassistance when patients lose control over Vt like in a pressure-control mode. The measurement of Crs in PSV is constant-likely suggesting reliability-independently from the level of assistance and patient\'s effort.