Cohen I L, Sheikh F M, Perkins R J, Feustel P J, Foster E D
Department of Surgery, State University of New York at Buffalo.
Crit Care Med. 1995 Mar;23(3):545-52. doi: 10.1097/00003246-199503000-00021.
Respiratory quotient, the ratio of CO2 production to oxygen consumption (VO2), is principally affected by the fuel source used for aerobic metabolism. Since the respiratory quotient, VO2, and CO2 production cannot be directly measured easily, indirect calorimetry is commonly used to determine the value of these variables at the airway level (i.e., airway respiratory quotient, airway VO2, and airway CO2 production). However, under nonsteady-state conditions, a variety of phenomena can alter the relationship between true metabolic activity and measurements determined by indirect calorimetry. During exercise, for example, airway respiratory quotient increases as anaerobic threshold is reached because of the disproportionate increase in airway CO2 production that results from the CO2 liberated through the buffering of excess hydrogen ions by bicarbonate. We hypothesized that hemorrhage and reinfusion might change airway respiratory quotient in a consistent manner as shock is produced and reversed.
Prospective laboratory study.
University animal laboratory.
Eight pigs (25 +/- 2 [SD] kg), anesthetized with fentanyl and relaxed with pancuronium bromide, and mechanically ventilated on room air.
The animals were sequentially hemorrhaged and then autotransfused while metabolic and hemodynamic measurements were obtained, using continuous indirect calorimetry and continuous applications of the Fick principle. Hemoglobin, arterial lactate concentration, and blood gases for calibration were measured serially. Analysis of variance was used to compare various periods in time.
Between baseline and peak hemorrhage, and between peak hemorrhage and postreinfusion, all of the following variables changed significantly (p < .05): airway VO2 (baseline 6.4 +/- 0.9 mL/min/kg, peak hemorrhage 3.9 +/- 0.6 mL/min/kg, postreinfusion 7.0 +/- 1.4 mL/min/kg); airway CO2 production (baseline 5.5 +/- 0.9 mL/min/kg, peak hemorrhage 4.5 +/- 0.9 mL/min/kg, postreinfusion 6.0 +/- 1.4 mL/min/kg); airway respiratory quotient (baseline 0.87 +/- 0.07, peak hemorrhage 1.16 +/- 0.07, postreinfusion 0.87 +/- 0.05); lactate concentration (baseline 2.4 +/- 1.2 mmol/L, peak hemorrhage 6.7 +/- 1.9 mmol/L, postreinfusion 5.1 +/- 2.0 mmol/L); and delta PCO2 (venous PCO2-PaCO2) (baseline 4.5 +/- 3.6 torr [0.6 +/- 0.5 kPa], peak hemorrhage 12.1 +/- 5.3 torr [1.6 +/- 0.7 kPa], postreinfusion 2.7 +/- 2.7 torr [0.4 +/- 0.4 kPa]).
Airway respiratory quotient increases in hemorrhagic shock and decreases again as shock is reversed during reinfusion. This phenomenon appears related to the buffering of excess of hydrogen ion during hemorrhagic shock.
呼吸商是二氧化碳产生量与氧气消耗量（VO₂）的比值，主要受有氧代谢所用燃料来源的影响。由于呼吸商、VO₂和二氧化碳产生量不易直接测量，间接测热法通常用于确定气道水平这些变量的值（即气道呼吸商、气道VO₂和气道二氧化碳产生量）。然而，在非稳态条件下，多种现象会改变真实代谢活动与间接测热法测定值之间的关系。例如，运动期间，当达到无氧阈值时，气道呼吸商会增加，这是因为通过碳酸氢盐缓冲过量氢离子所释放的二氧化碳导致气道二氧化碳产生量不成比例增加。我们假设，出血和再灌注可能会随着休克的产生和逆转而以一致的方式改变气道呼吸商。
前瞻性实验室研究。
大学动物实验室。
8头猪（25±2[标准差]kg），用芬太尼麻醉，泮库溴铵使其肌肉松弛，并在室内空气中进行机械通气。
动物依次进行出血，然后自体输血，同时使用连续间接测热法和连续应用菲克原理获取代谢和血流动力学测量值。连续测量血红蛋白、动脉血乳酸浓度和用于校准的血气。采用方差分析比较不同时间段。
在基线与出血高峰之间，以及出血高峰与再灌注后之间，以下所有变量均发生了显著变化（p<0.05）：气道VO₂（基线6.4±0.9 mL/min/kg，出血高峰3.9±0.6 mL/min/kg，再灌注后7.0±1.4 mL/min/kg）；气道二氧化碳产生量（基线5.5±0.9 mL/min/kg，出血高峰4.5±0.9 mL/min/kg，再灌注后6.0±1.4 mL/min/kg）；气道呼吸商（基线0.87±0.07，出血高峰1.16±0.07，再灌注后0.87±0.05）；乳酸浓度（基线2.4±1.2 mmol/L，出血高峰6.7±1.9 mmol/L，再灌注后5.1±2.0 mmol/L）；以及△PCO₂（静脉血PCO₂ - 动脉血PCO₂）（基线4.5±3.6托[0.6±0.5千帕]，出血高峰12.1±5.3托[1.6±0.7千帕]，再灌注后2.7±2.7托[0.4±0.4千帕]）。
出血性休克时气道呼吸商增加，再灌注期间休克逆转时气道呼吸商再次降低。这种现象似乎与出血性休克期间过量氢离子的缓冲有关。
