呼气末二氧化碳分压等指标指导急性呼吸窘迫综合征犬肺复张后呼气末正压的选择

Titrating positive end-expiratory pressure after recruitment maneuver according to end-tidal carbon dioxide and its related indicators in acute respiratory distress syndrome dog model

目的探讨呼气末二氧化碳分压（PetCO2）及其相关指标指导急性呼吸窘迫综合征（ARDS）犬肺复张后呼气末正压（PEEP）的选择。方法5只健康犬建立油酸ARDS模型，在进行肺复张后以不同PEEP水平进行机械通气。记录不同PEEP水平下PetCO2、PaCO2等数值，计算动脉．呼气末二氧化碳分压差（Pa—etC02）及死腔量百分比（Vd／Vt％）。所有ARDS犬均进行cT扫描，计算过度通气区、正常通气区、肺泡塌陷区、闭合区占肺总容积的百分比，构建肺开放（闭合）曲线进行静态肺力学分析。结果（1）Vd／Vt％达到最低值的PEEP为（11．2±4．4）cmH，O（1cmH，O=0．098kPa），与肺泡闭合压力[（11．5±3．2）cmH：O]比较，差异无统计学意义（P〉0．05）。（2）PEEP．Vd／Vt％曲线出现最低点前，Vd／Vt％与闭合和塌陷的肺泡比例之和呈线性关系（r=0．632，P=0．004）：高于最低点，Vd／Vt％与过度通气的肺泡比例呈线性关系（r=0．770，P=0．001）。结论肺复张后PEEP水平与肺泡闭合压相符时通气血流比达到最佳。肺复张后Vd／Vt％的变化能反映肺泡闭合的特征。肺复张后使用Vd／Vt％最低点选择PEEP能使通气血流达到最佳。

Objective To investigate the relationship between end-tidal carbon dioxide with its related indicators and ventilation/perfusion of the acute respiratory distress syndrome （ARDS） lung, and to explore a feasible way to titrate positive end-expiratory pressure （PEEP） in clinical practice. Methods Five mixed-breed dogs with oleic acid lung injury model were mechanically ventilated at a serial PEEP trial including a recruitment maneuver （RM） before each PEEP level changed. The value of blood dynamics, end-tidal carbon dioxide partial pressure （ PetCO2 ） and arterial carbon dioxide pressure under different PEEP levels were recorded. Arterial end-tidal carbon dioxide gradient （Pa-etCO2 ） and dead space fraction （ Vd/Vt% ） were calculated. All dogs received CT scan. Lung volume under different pressure levels, and ratio and volume of alveolar closing pressure, collapsed alveoli, sufficiently and insufficiently ventilated alveoli were obtained. Alveolar opening and closing analysis were performed by non-liner regression equation. Results The mean pressure when Vd/Vt% obtained lowest level were （ 11.2±4. 4） cm H20 （1 cm H20 =0. 098 kPa）, which had no significant difference when compared to alveolar closing pressure [ （ 11.5±3.2 ） cm H20 ] （ P 〉 0. 05 ）. The fraction of insufficiently ventilated and collapsed alveoli showed a significant linear correlation with the Vd/Vt% when PEEP was lower than Pmin （ r = 0. 632, P = 0. 004 ）. There was a linear correlation between the Vd/Vt% and the fraction of over-distended alveoli when PEEP was higher than Pmin （ r = 0. 770, P = 0. 001 ）. Conclusions Closing pressure is in accordance with PEEP level after RM having reached the best ventilation/circulation ratio. The characteristics of lung collapse can be revealed by Vd/Vt% changes after RM. To titrate PEEP for the lowest Vd/Vt% after RM may be a feasible way to match the best ventilation and circulation effects of PEEP.