辅助通气时应用食道测压管的气囊压力-容积曲线校正食道压的可行性研究

Feasibility of using esophageal balloon pressure-volume curve to calibrate esophageal pressure during assisted mechanical ventilation

目的评价在辅助通气时应用食道测压管的气囊压力-容积曲线(P-V曲线)校正食道压(Pes)的可行性。方法采用前瞻性研究方法,选择2017年6月至2019年1月首都医科大学附属北京天坛医院重症医学科收治的术后进行气管插管压力支持通气、呼吸相对平稳且需要进行Pes监测的患者作为研究对象。应用气囊几何容积相对较小(2.8 mL)的食道测压管进行Pes监测。①对食道测压管进行气囊注气试验,即以0.5 mL为间隔向气囊内注气直至2.5 mL,记录呼气末和吸气末测得的Pes,并分别描记呼气末和吸气末的气囊P-V曲线。确定呼气末气囊P-V曲线中呈线性相关的中间段(即中间线性段),该中间线性段的注气容积范围即为气囊合理工作容积(Vwork),其斜率即为食道壁弹性(Ees),呼气末与吸气末Pes出现最大差异时的气囊容积即为气囊最佳工作容积(Vbest),Ees与Vbest的乘积即为向气囊内注气时导致食道壁产生的弹性回缩力。为减少食道壁对Pes监测的影响,校正Pes为在Vbest条件下监测的Pes与食道壁弹性回缩力的差值。分析在Vbest条件下获得的校正Pes与在其他Vwork条件下获得的校正Pes的一致性。②为方便临床应用,进一步提出一种校正Pes的简单方法。基于所有患者的Vwork均为0.5~1.5 mL,通过计算气囊注气容积分别为0.5 mL和1.5 mL时测得的呼吸末Pes差值与气囊注气容积为1.0 mL时的比值来预估Ees,并通过该简单方法计算的Ees来校正气囊注气容积为0.5~1.5 mL时的Pes。分析该简单方法与上述标准方法获得的校正Pes之间的一致性。结果共纳入30例患者,所有吸气末和呼气末的气囊P-V曲线均存在中间线性段,当气囊处于Vwork条件下监测的Pes被校正后不再随气囊注气容积的增加而增加,并与在Vbest条件下获得的校正Pes具有良好的一致性,差异的均值和95%可信区间(95%CI)为-0.02(-1.50~1.50)cmH2O(1 cmH2O=0.098 kPa);同时,应用简单方法计算的Ees和相应的校正Pes与应用标准方法获得的Ees和校正Pes均具有良好的一致性,差异的均值和95%CI分别为-0.2(-1.0~0.6)cmH2O/mL和0.2(-1.1~1.4)cmH2O。结论在辅助通气条件下,应用几何容积相对较小的食道测压管进行Pes监测,并通过气囊P-V曲线校正Pes的方法具有可适用性。为方便临床应用,可采用简单方法,即通过监测食道测压管气囊注气容积分别为0.5、1.0和1.5 mL时的Pes来预估Ees,从而获得校正Pes。

Objective To evaluate the feasibility of esophageal pressure (Pes) calibration by the esophageal balloon pressure-volume (P-V) curve during assisted mechanical ventilation.Methods A prospective study was conducted. The postoperative patients admitted to intensive care unit of Beijing Tiantan Hospital Affiliated to Capital Medical University from June 2017 to January 2019 who needed pressure support ventilation by tracheal intubation and Pes monitoring with stable breath were enrolled. The Pes monitoring was performed by the esophageal balloon with a small geometric volume (2.8 mL). ① Balloon volume tests of esophageal balloon were performed by inflating intermittently 0.5 mL increments up to 2.5 mL, the end-expiratory and end-inspiratory Pes were recorded to obtain end-expiratory and end-inspiratory P-V curves. The intermediate section in end-expiatory P-V curve that showed linear correlation was identified (as intermediate linear section), whose volume range was balloon working volume (Vwork) and slope was esophageal wall elastance (Ees), the balloon volume with the largest difference between end-expiratory and end-inspiratory Pes was the best balloon volume (Vbest), and the product of Ees and Vbest was esophageal wall recoil pressure reacting to balloon filling. To minimize the effect of esophageal wall on Pes, the calibrated Pes was the difference of Pes and esophageal wall recoil pressure. The consistency of calibrated Pes obtained by balloon volume at Vbset and other Vwork were analyzed. ② For the convenience of clinical application, a simplified method was introduced to calibrate Pes. Based on all Vwork of patients located in 0.5-1.5 mL, the difference of end-expiratory Pes between balloon volume at 0.5 mL and 1.5 mL divided by 1.0 mL was used to estimate Ees, and the Pes among 0.5-1.5 mL was calibrated by Ees obtained by the simple method. The consistency of calibrated Pes obtained by the simple method and standard method were observed.Results Totally 30 patients were enrolled, all end-expiratory and end-inspiratory P-V curves existed the intermediate linear section, the calibrated Pes at Vwork did not increase with the balloon being inflated and had a good consistency with the calibrated Pes at Vbest, mean difference and 95% confidence interval (95%CI) was -0.02 (-1.50-1.50) cmH2O (1 cmH2O = 0.098 kPa). The Ees and calibrated Pes estimated by the simple method had a good agreement with the standard method, mean difference and 95%CI was -0.2 (-1.0-0.6) cmH2O/mL and 0.2 (-1.1-1.4) cmH2O, respectively.Conclusions During assisted mechanical ventilation, the use of a small geometric volume esophageal balloon to monitor Pes and balloon P-V curve to calibrate Pes is feasible. The simple method can be used for simplifying clinical application, that's only by monitoring Pes at balloon volume at 0.5, 1.0 and 1.5 mL to evaluate the Ees and calibrate Pes.