Liu Ye, Liu Da-wei, Long Yun, Xie Zhi-yi
Department of Critical Care Medicine, China Academy of Medical Science, Beijing, China.
Zhonghua Nei Ke Za Zhi. 2012 Aug;51(8):604-8.
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.
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.
The mean pressure when Vd/Vt% obtained lowest level were (11.2 ± 4.4) cm H2O (1 cm H2O = 0.098 kPa), which had no significant difference when compared to alveolar closing pressure [(11.5 ± 3.2) cm H2O](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 P(min) (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 P(min) (r = 0.770, P = 0.001).
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.
探讨急性呼吸窘迫综合征（ARDS）肺的呼末二氧化碳及其相关指标与通气/灌注的关系，探索临床实践中滴定呼气末正压（PEEP）的可行方法。
对5只油酸肺损伤模型的杂种犬进行机械通气，在每次PEEP水平改变前进行包括肺复张手法（RM）的系列PEEP试验。记录不同PEEP水平下的血流动力学值、呼末二氧化碳分压（PetCO2）和动脉二氧化碳分压。计算动脉-呼末二氧化碳梯度（Pa-etCO2）和死腔分数（Vd/Vt%）。所有犬均接受CT扫描。获得不同压力水平下的肺容积，以及肺泡闭合压、萎陷肺泡、通气充分和不充分肺泡的比例及容积。通过非线性回归方程进行肺泡开闭分析。
Vd/Vt%达到最低水平时的平均压力为（11.2±4.4）cm H2O（1 cm H2O = 0.098 kPa），与肺泡闭合压[（11.5±3.2）cm H2O]相比无显著差异（P>0.05）。当PEEP低于P（min）时，通气不充分和萎陷肺泡的比例与Vd/Vt%呈显著线性相关（r = 0.632，P = 0.004）。当PEEP高于P（min）时，Vd/Vt%与过度膨胀肺泡的比例呈线性相关（r = 0.770，P = 0.001）。
RM后达到最佳通气/循环比时，闭合压与PEEP水平相符。RM后Vd/Vt%的变化可揭示肺萎陷的特征。滴定PEEP使RM后Vd/Vt%最低可能是使PEEP达到最佳通气和循环效果的可行方法。
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