Mallat Jihad, Lemyze Malcolm, Tronchon Laurent, Vallet Benoît, Thevenin Didier
Jihad Mallat, Malcolm Lemyze, Laurent Tronchon, Benoît Vallet, Didier Thevenin, Department of Anesthesiology and Critical Care Medicine, Centre Hospitalier du Dr. Schaffner de Lens, 62300 Lens, France.
World J Crit Care Med. 2016 Feb 4;5(1):47-56. doi: 10.5492/wjccm.v5.i1.47.
The mixed venous-to-arterial carbon dioxide (CO2) tension difference [P (v-a) CO2] is the difference between carbon dioxide tension (PCO2) in mixed venous blood (sampled from a pulmonary artery catheter) and the PCO2 in arterial blood. P (v-a) CO2 depends on the cardiac output and the global CO2 production, and on the complex relationship between PCO2 and CO2 content. Experimental and clinical studies support the evidence that P (v-a) CO2 cannot serve as an indicator of tissue hypoxia, and should be regarded as an indicator of the adequacy of venous blood to wash out the total CO2 generated by the peripheral tissues. P (v-a) CO2 can be replaced by the central venous-to-arterial CO2 difference (ΔPCO2), which is calculated from simultaneous sampling of central venous blood from a central vein catheter and arterial blood and, therefore, more easy to obtain at the bedside. Determining the ΔPCO2 during the resuscitation of septic shock patients might be useful when deciding when to continue resuscitation despite a central venous oxygen saturation (ScvO2) > 70% associated with elevated blood lactate levels. Because high blood lactate levels is not a discriminatory factor in determining the source of that stress, an increased ΔPCO2 (> 6 mmHg) could be used to identify patients who still remain inadequately resuscitated. Monitoring the ΔPCO2 from the beginning of the reanimation of septic shock patients might be a valuable means to evaluate the adequacy of cardiac output in tissue perfusion and, thus, guiding the therapy. In this respect, it can aid to titrate inotropes to adjust oxygen delivery to CO2 production, or to choose between hemoglobin correction or fluid/inotrope infusion in patients with a too low ScvO2 related to metabolic demand. The combination of P (v-a) CO2 or ΔPCO2 with oxygen-derived parameters through the calculation of the P (v-a) CO2 or ΔPCO2/arteriovenous oxygen content difference ratio can detect the presence of global anaerobic metabolism.
混合静脉血与动脉血二氧化碳分压差值[P(v-a)CO₂]是混合静脉血（通过肺动脉导管采集）中的二氧化碳分压（PCO₂）与动脉血中PCO₂的差值。P(v-a)CO₂取决于心输出量和整体二氧化碳生成量，以及PCO₂与二氧化碳含量之间的复杂关系。实验和临床研究支持这样的证据，即P(v-a)CO₂不能作为组织缺氧的指标，而应被视为静脉血清除外周组织产生的总二氧化碳能力是否充足的指标。P(v-a)CO₂可以被中心静脉血与动脉血二氧化碳差值（ΔPCO₂）所替代，ΔPCO₂是通过同时采集中心静脉导管中的中心静脉血和动脉血来计算的，因此在床边更容易获得。在脓毒性休克患者的复苏过程中，当决定尽管中心静脉血氧饱和度（ScvO₂）>70%且血乳酸水平升高但仍继续复苏时，测定ΔPCO₂可能会有所帮助。由于高血乳酸水平不是确定该应激源的鉴别因素，ΔPCO₂升高（>6 mmHg）可用于识别复苏仍不充分的患者。从脓毒性休克患者复苏开始就监测ΔPCO₂可能是评估组织灌注中心输出量是否充足的有价值手段，从而指导治疗。在这方面，它有助于滴定血管活性药物以调整氧输送与二氧化碳生成之间的关系，或者在ScvO₂因代谢需求过低的患者中选择进行血红蛋白纠正或液体/血管活性药物输注。通过计算P(v-a)CO₂或ΔPCO₂/动静脉血氧含量差值比值，将P(v-a)CO₂或ΔPCO₂与氧衍生参数相结合，可以检测是否存在整体无氧代谢。
