Powles A C, Campbell E J
Am J Med. 1979 Jul;67(1):98-104. doi: 10.1016/0002-9343(79)90079-2.
Unless cardiac output is reduced, alveolar ventilation can be monitored without arterial blood gas analysis by estimating arterial carbon dioxide tension (PaO2) from rebreathing measurement of mixed venous carbon dioxide tension (PvCO2) (PaCO2 = 0.8 PvCO2). If cardiac output is reduced, the PvCO2 - PaCO2 difference increases, reflecting the increased venoarterial carbon dioxide (CO2) content difference (Fick principle). A reduction in cardiac output can thus be quantified without catheterization of the central circulation by measuring both PaCO2 and PvCO2. The significance of such a reduction in cardiac output for oxygen (O2) delivery to tissues is determined by calculation of mixed venous O2 saturation (SvO2), using the inter-relationship of CO2 production to O2 consumption. With normal arterial oxygenation (SaO2) and hemoglobin concentration, PaCO2 less than 0.8 PvCO2 - 12 implies a reduction in cardiac output such that SvO2 is less than 33 per cent, which indicates inadequate O2 delivery to tissues. Ear oximetry and rebreathing measurement of PvCO2 are simple, noninvasive, bedside techniques.
除非心输出量降低，否则可通过从混合静脉血二氧化碳分压（PvCO2）的重复呼吸测量中估算动脉血二氧化碳分压（PaCO2）（PaCO2 = 0.8PvCO2）来监测肺泡通气，而无需进行动脉血气分析。如果心输出量降低，PvCO2 - PaCO2差值会增加，反映出静脉血与动脉血二氧化碳（CO2）含量差值增加（菲克原理）。因此，通过测量PaCO2和PvCO2，无需对中心循环进行插管即可量化心输出量的降低。通过利用二氧化碳产生与氧气消耗之间的相互关系计算混合静脉血氧饱和度（SvO2），可确定心输出量降低对组织氧气（O2）输送的意义。在动脉血氧合（SaO2）和血红蛋白浓度正常的情况下，PaCO2小于0.8PvCO2 - 12意味着心输出量降低，使得SvO2小于33%，这表明组织的氧气输送不足。耳部血氧测定和PvCO2的重复呼吸测量是简单的、非侵入性的床边技术。
