Rajek A, Lenhardt R, Sessler D I, Kurz A, Laufer G, Christensen R, Matsukawa T, Hiesmayr M
Department of Cardiothoracic and Vascular Anesthesia, Outcomes Research Laboratory, Vienna, Austria.
Anesthesiology. 1998 Jun;88(6):1511-8. doi: 10.1097/00000542-199806000-00015.
Afterdrop following cardiopulmonary bypass results from redistribution of body heat to inadequately warmed peripheral tissues. However, the distribution of heat between the thermal compartments and the extent to which core-to-peripheral redistribution contributes to post-bypass hypothermia remains unknown.
Patients were cooled during cardiopulmonary bypass to nasopharyngeal temperatures near 31 degrees C (n=8) or 27 degrees C (n=8) and subsequently rewarmed by the bypass heat exchanger to approximately 37.5 degrees C. A nasopharyngeal probe evaluated core (trunk and head) temperature and heat content. Peripheral compartment (arm and leg) temperature and heat content were estimated using fourth-order regressions and integration over volume from 19 intramuscular needle thermocouples, 10 skin temperatures, and "deep" foot temperature.
In the 31 degrees C group, the average peripheral tissue temperature decreased to 31.9+/-1.4 degrees C (means+/-SD) and subsequently increased to 34+/-1.4 degrees C at the end of bypass. The core-to-peripheral tissue temperature gradient was 3.5+/-1.8 degrees C at the end of rewarming, and the afterdrop was 1.5+/-0.4 degrees C. Total body heat content decreased 231+/-93 kcal. During pump rewarming, the peripheral heat content increased to 7+/-27 kcal below precooling values, whereas the core heat content increased to 94+/-33 kcal above precooling values. Body heat content at the end of rewarming was thus 87+/-42 kcal more than at the onset of cooling. In the 27 degrees C group, the average peripheral tissue temperature decreased to a minimum of 29.8 +/-1.7 degrees C and subsequently increased to 32.8+/-2.1 degrees C at the end of bypass. The core-to-peripheral tissue temperature gradient was 4.6+/-1.9 degrees C at the end of rewarming, and the afterdrop was 2.3+/-0.9 degrees C. Total body heat content decreased 419+/-49 kcal. During pump rewarming, core heat content increased to 66+/-23 kcal above precooling values, whereas peripheral heat content remained 70+/-42 kcal below precooling values. Body heat content at the end of rewarming was thus 4+/-52 kcal less than at the onset of cooling.
Peripheral tissues failed to fully rewarm by the end of bypass in the patients in the 27 degrees C group, and the afterdrop was 2.3+/-0.9 degrees C. Peripheral tissues rewarmed better in the patients in the 31 degrees C group, and the afterdrop was only 1.5+/-0.4 degrees C.
体外循环后的体温过低是由于身体热量重新分布到未充分升温的外周组织所致。然而，热腔之间的热量分布以及核心到外周的重新分布对外循环后体温过低的影响程度仍不清楚。
在体外循环期间，将患者冷却至鼻咽温度接近31℃（n = 8）或27℃（n = 8），随后通过体外循环热交换器将其复温至约37.5℃。用鼻咽探头评估核心（躯干和头部）温度及热量含量。外周腔（手臂和腿部）的温度及热量含量通过对19个肌内针式热电偶、10个皮肤温度和“深部”足部温度进行四阶回归及体积积分来估算。
在31℃组中，外周组织平均温度降至31.9±1.4℃（平均值±标准差），随后在体外循环结束时升至34±1.4℃。复温结束时，核心与外周组织温度梯度为3.5±1.8℃，体温过低为1.5±0.4℃。全身热量含量减少231±93千卡。在泵复温期间，外周热量含量增加至比预冷值低7±27千卡，而核心热量含量增加至比预冷值高94±33千卡。因此，复温结束时的身体热量含量比冷却开始时多87±42千卡。在27℃组中，外周组织平均温度降至最低29.8±1.7℃，随后在体外循环结束时升至32.8±2.1℃。复温结束时，核心与外周组织温度梯度为4.6±1.9℃，体温过低为2.3±0.9℃。全身热量含量减少419±49千卡。在泵复温期间，核心热量含量增加至比预冷值高66±23千卡，而外周热量含量仍比预冷值低70±42千卡。因此，复温结束时的身体热量含量比冷却开始时少4±52千卡。
27℃组患者在体外循环结束时外周组织未能完全复温，体温过低为2.3±0.9℃。31℃组患者外周组织复温较好，体温过低仅为1.5±0.4℃。
