基于慢吐气方法选择急性呼吸窘迫综合征模型呼气末正压的可行性

The feasibility of positive end-expiratory pressure selection based on prolonged expiration in the model of acute respiratory distress syndrome

目的探讨慢吐气(prolonged expiration)方法联合呼吸机常规监测选择急性呼吸窘迫综合征(acute respiratory distress syndrome,ARDS)动物模型比较合适的呼气末正压(positive end-expiratory pressure,PEEP)的可行性。方法通过盐酸吸入的方法建立ARDS动物模型,通过慢吐气方法进行PEEP滴定,采用呼吸机监测的呼出潮气量计算肺复张容积(recruitment volume,Vrec),Vrec最大的PEEP区间即较合适的PEEP区间,同时用分层电阻抗成像技术(electrical impedance tomography,EIT)计算出肺的过多膨胀和萎陷的比例,从而选择出较合适的PEEP区间进行验证。结果应用慢吐气方法计算的Vrec最大的PEEP区间为5~10 cmH_(2)O(1 cmH_(2)O=0.098 kPa),即较合适的PEEP区间为5~10 cmH_(2)O。EIT通过过度膨胀/萎陷的方法选择的较合适的PEEP水平也在5~10 cm H_(2)O之间,这与慢吐气方法选择的PEEP区间是一致的。且在PEEP为15~20 cmH_(2)O时,应用一定的血管活性药物维持血压,且此时驱动压较大易发生呼吸机相关性肺损伤;在PEEP为小于5 cmH_(2)O时,低于生理性的PEEP,这都不是合适的PEEP水平。结论应用慢吐气方法结合呼吸机常规监测计算肺复张容积选择PEEP的方法具有可行性,选择出较合适的PEEP区间后,结合血流动力学及其他指标,可进一步选择更合适的PEEP水平。

Objective To explore the feasibility of positive end-expiratory pressure(PEEP)selection based on prolonged expiration combined with ventilator monitoring in the model of acute respiratory distress syndrome(ARDS).Methods ARDS model was established by alveolar instillation of hydrochloric acid.Decremental PEEP trial was performed by prolonged expiration maneuver.A prolonged expiration(6-9 seconds)maneuver was performed while abruptly decreasing PEEP from a high to a low level for one breath(from 20 cmH_(2)O to 0 cmH_(2)O in decremental steps of 5 cmH_(2)O).Because inspiratory tidal volume(VT)was unchanged,the difference in expiratory VT values between the expired VT displayed immediately after decreasing PEEP and the breath before changing PEEP was referred to as the total change in lung volume from high to low PEEP.Meanwhile,the predicted change in lung volume was estimated by the product of respiratory system compliance at low PEEP and the change in pressure.The difference of total change of lung volume and predicted value was taken as an estimate of derecruited volume or recruitment volume(Vrec).The PEEP with the largest Vrec may be the appropriate PEEP interval.This PEEP was verified by electrical impedance tomography(EIT)based on the overdistension and collapse.Optimal PEEP level was set based on the appropriate PEEP interval,hemodynamics,and other indicators.Results The PEEP interval with the largest Vrec by prolonged expiration was 5-10 cmH_(2)O.According to EIT,the optimal PEEP level was also in the interval of 5-10 cmH_(2)O with appropriate overdistension and collapse.When PEEP was in 15-20 cmH_(2)O,intravenous norepinephrine was used to maintain mean arterial pressure(MAP)above 65 mmHg,and driving pressure was large to cause the ventilator-associated lung injury.It was unreasonable for physiological PEEP when PEEP was under 5 cmH_(2)O.Conclusion It is feasible to select PEEP using prolonged expiration combined with ventilator monitoring.The PEEP with the largest Vrec assessed by prolonged expiration may be the appropriate PEEP interval.Then,the optimal PEEP level may be further confirmed with hemodynamics and other parameters.