Kvarstein G, Tønnessen T I
Anestesiavdelingen, Rikshospitalet, Oslo.
Tidsskr Nor Laegeforen. 1997 Nov 30;117(29):4251-5.
Under ischemic conditions O2 delivery is insufficient, and the cells convert to anaerobic metabolism with production of lactic acid. The protons formed in this process are to a large extent rapidly buffered inside the cell by proteins and HCO3-. Protons buffered by HCO3- form CO2 in the tissue. Since the blood supply during ischemia is minimal, CO2 is not transported away from the tissue and will reach tensions far above pCO2 found under aerobic conditions. Thus, measuring pCO2 can be used to detect ischemia in an organ. Gastrointestinal tonometry is based on the concept of CO2 accumulation during anaerobiosis. It has been customary to calculate so-called interstitial pH (pHi) by incorporating the measured pCO2 in the tonometer and the HCO3- in an arterial blood gas in the Henderson-Hasselbalch equation. However, this method has several weaknesses, and we recommend using the measured pCO2, or rather the difference between gastrointestinal and arterial pCO2. Experimental studies have shown that pCO2 electrodes sensitively detect the onset of ischemia also in solid organs. The accumulation of pCO2 coincides with the shift from supply-independent to supply-dependent oxygen consumption and correlates with other markers of ischemia. pCO2 measurement at organ level is a promising tool in the monitoring of organ ischemia.
在缺血状态下，氧气供应不足，细胞转变为无氧代谢并产生乳酸。在此过程中形成的质子在很大程度上迅速被细胞内的蛋白质和HCO₃⁻缓冲。由HCO₃⁻缓冲的质子在组织中形成CO₂。由于缺血期间的血液供应极少，CO₂无法从组织中运走，其张力将远高于有氧条件下的pCO₂。因此，测量pCO₂可用于检测器官缺血。胃肠张力测定法基于无氧状态下CO₂蓄积的概念。习惯上是通过将眼压计中测得的pCO₂和动脉血气中的HCO₃⁻代入亨德森-哈塞尔巴尔赫方程来计算所谓的组织间液pH值（pHi）。然而，这种方法有几个缺点，我们建议使用测得的pCO₂，或者更确切地说是胃肠pCO₂与动脉pCO₂之间的差值。实验研究表明，pCO₂电极也能灵敏地检测实体器官缺血的开始。pCO₂的蓄积与从供应非依赖型向供应依赖型氧消耗的转变同时发生，并与其他缺血标志物相关。器官水平的pCO₂测量是监测器官缺血的一种有前景的工具。
