触发灵敏度对压力支持通气患者肺通气均一性的影响

Effect of trigger sensitivity on ventilation homogeneity in patients under pressure support ventilation

目的观察呼吸机触发灵敏度对压力支持通气患者肺通气均一性的影响。方法前瞻性纳入20例使用压力支持模式通气时存在肺不均一性通气的患者,即应用肺电阻抗断层成像监测时重力依赖区通气分布比低于45%。随机使用低和高两种流速触发灵敏度水平通气20 min(采用Servo-i呼吸机流速触发灵敏度的最低和最高限值2 L/min和0.2 L/min)。通过肺电阻抗断层成像评估重力依赖区通气分布和呼气末肺体积,采用食道压监测评估吸气努力和做功。结果与高触发灵敏度相比,低触发灵敏度增加了患者吸气时重力依赖区通气分布百分比[(33±9)%vs.(36±9)%,t=3.735,P=0.001]、食道压变化值[0.8(0.4,1.8)cmH_(2)O vs.1.6(1.0,2.1)cmH_(2)O,Z=2.722,P=0.021]、压力时间乘积[29(15,54)cmH_(2)O·s^(-1)·min^(-1)vs.48(23,74)cmH_(2)O·s^(-1)·min^(-1),Z=3.298,P=0.044],但跨肺压变化值没有明显变化[(12.6±4.3)cmH_(2)O vs.(12.8±4.2)cmH_(2)O,t=0.906,P=0.376]。此外,低触发灵敏度的整体呼气末肺容积变化值为78(29,170)mL,且其变化值主要分布于重力依赖区[75(-6,131)mL]。结论压力支持通气时,降低触发灵敏度可通过增加吸气努力使更多的气体进入肺重力依赖区并改善通气均一性,同时吸气努力和跨肺压仍在可接受范围内。

Objective To investigate the effect of trigger sensitivity on ventilation homogeneity in patients under pressure support ventilation.Methods We prospectively enrolled 20 patients with heterogeneous lung ventilation under pressure support ventilation that was defined by electrical impedance tomography as the distribution of tidal volume in dependent region lower than 45%.The low and high flow trigger sensitivity(the lowest and highest limits of Servo-i were 2 L/min and 0.2 L/min,respectively)were randomly applied for 20 mins.The distribution of tidal volume in dependent region and end-expiratory lung volume(EELV)were evaluated by electrical impedance tomography.The esophageal manometry was used to measure the inspiratory effort and work of breathing.Results Comparing to the high trigger sensitivity,the low trigger sensitivity increased the relative distribution of tidal volume in dependent region[(33±9)%vs.(36±9)%,t=3.735,P=0.001],the esophageal pressure swings during inspiration[0.8(0.4,1.8)cmH_(2)O vs.1.6(1.0,2.1)cmH_(2)O,Z=2.722,P=0.021],and pressure time product[29(15,54)cmH_(2)O·s^(-1)·min^(-1)vs.48(23,74)cmH_(2)O·s^(-1)·min^(-1),Z=3.298,P=0.044];whereas,the change of transpulmonary pressure did not significantly increase[(12.6±4.3)cmH_(2)O vs.(12.8±4.2)cmH_(2)O,t=0.906,P=0.376].The global EELV of a low trigger sensitivity during pressure support ventilation was 78(29,170)mL,which mainly acted on the dependent region[75(-6,131)mL].Conclusion Decreasing trigger sensitivity could allow more air to flow into the dependent lung region and improve homogeneity during pressure support ventilation by increasing inspiratory effort,while the working of breathing and transpulmonary pressure remain within acceptable ranges.