Dubin Arnaldo, Pozo Mario Omar, Hurtado Javier
Cátedra de Farmacología Aplicada, Facultad de Ciencias Médicas, Universidad Nacional de La Plata, La Plata, Argentina.
Hospital Británico, Buenos Aires, Argentina.
Rev Bras Ter Intensiva. 2020 Mar;32(1):115-122. doi: 10.5935/0103-507x.20200017. Epub 2020 May 8.
The central venous minus arterial carbon dioxide pressure to arterial minus central venous oxygen content ratio (Pcv-aCO2/Ca-cvO2) has been proposed as a surrogate for respiratory quotient and an indicator of tissue oxygenation. Some small observational studies have found that a Pcv-aCO2/Ca-cvO2 > 1.4 was associated with hyperlactatemia, oxygen supply dependency, and increased mortality. Moreover, Pcv-aCO2/Ca-cvO2 has been incorporated into algorithms for tissue oxygenation evaluation and resuscitation. However, the evidence for these recommendations is quite limited and of low quality. The goal of this narrative review was to analyze the methodological bases, the pathophysiologic foundations, and the experimental and clinical evidence supporting the use of Pcv-aCO2/Ca-cvO2 as a surrogate for respiratory quotient. Physiologically, the increase in respiratory quotient secondary to critical reductions in oxygen transport is a life-threatening and dramatic event. Nevertheless, this event is easily noticeable and probably does not require further monitoring. Since the beginning of anaerobic metabolism is indicated by the sudden increase in respiratory quotient and the normal range of respiratory quotient is wide, the use of a defined cutoff of 1.4 for Pcv-aCO2/Ca-cvO2 is meaningless. Experimental studies have shown that Pcv-aCO2/Ca-cvO2 is more dependent on factors that modify the dissociation of carbon dioxide from hemoglobin than on respiratory quotient and that respiratory quotient and Pcv-aCO2/Ca-cvO2 may have distinct behaviors. Studies performed in critically ill patients have shown controversial results regarding the ability of Pcv-aCO2/Ca-cvO2 to predict outcome, hyperlactatemia, microvascular abnormalities, and oxygen supply dependency. A randomized controlled trial also showed that Pcv-aCO2/Ca-cvO2 is useless as a goal of resuscitation. Pcv-aCO2/Ca-cvO2 should be carefully interpreted in critically ill patients.
中心静脉血与动脉血二氧化碳分压差值与动脉血氧含量减去中心静脉血氧含量的比值（Pcv-aCO2/Ca-cvO2）已被提议作为呼吸商的替代指标和组织氧合的指标。一些小型观察性研究发现，Pcv-aCO2/Ca-cvO2>1.4与高乳酸血症、氧供依赖和死亡率增加有关。此外，Pcv-aCO2/Ca-cvO2已被纳入组织氧合评估和复苏算法中。然而，这些建议的证据相当有限且质量较低。本叙述性综述的目的是分析支持将Pcv-aCO2/Ca-cvO2用作呼吸商替代指标的方法学基础、病理生理学基础以及实验和临床证据。从生理学角度来看，由于氧输送严重降低导致呼吸商增加是一个危及生命的重大事件。然而，这一事件很容易被察觉，可能不需要进一步监测。由于无氧代谢的开始由呼吸商的突然增加指示，且呼吸商的正常范围较宽，因此将Pcv-aCO2/Ca-cvO2的定义临界值设为1.4是没有意义的。实验研究表明，Pcv-aCO2/Ca-cvO2更多地依赖于改变二氧化碳从血红蛋白解离的因素，而非呼吸商，并且呼吸商和Pcv-aCO2/Ca-cvO2可能具有不同的表现。在危重症患者中进行的研究显示，关于Pcv-aCO2/Ca-cvO2预测预后、高乳酸血症、微血管异常和氧供依赖的能力，结果存在争议。一项随机对照试验还表明，Pcv-aCO2/Ca-cvO2作为复苏目标并无用处。在危重症患者中，应谨慎解读Pcv-aCO2/Ca-cvO2。
