Nussmeier N A, Lambert M L, Moskowitz G J, Cohen N H, Weiskopf R B, Fisher D M, Eger E I
Department of Anesthesia, University of California, San Francisco 94143-0648.
Anesthesiology. 1989 Oct;71(4):519-25. doi: 10.1097/00000542-198910000-00007.
Washin and washout of a volatile anesthetic given through the oxygenator during hypothermic (23.4 +/- 2.1 degrees C) cardiopulmonary bypass were studied in nine patients. The authors administered isoflurane and measured its partial pressure in arterial (Pa) and venous (Pv) blood and the gas exhausted from the oxygenator (PE) at 1, 2, 4, 8, 16, 32, and 48 min during washin. These measurements were repeated during washout, which coincided with rewarming. During washin, PE, Pa, and Pv progressively rose toward inlet gas partial pressure (PI). Equilibration of Pa with PI was 41% after 16 min, 51% after 32 min, and 57% after 48 min of washin. During washout, Pa declined to 24% of its peak after 16 min and to 13% after 32 min. Washin and washout were considerably slower in mixed venous blood. Washin of isoflurane appeared to occur more slowly during cardiopulmonary bypass than during administration via the lungs in normothermic patients, presumably because hypothermia increases tissue capacity, compensating for the effect of hemodilution that otherwise would decrease the blood/gas partition coefficient. During rewarming, washout appeared to occur as rapidly as from the lungs of normothermic patients. This may have resulted from the declining blood/gas partition coefficient (due to rewarming) and relatively limited tissue stores of isoflurane. The relationship between exhaust and arterial partial pressures was reasonably consistent; for clinical purposes, measurement of PE can be used to estimate Pa.
对9例患者在低温（23.4±2.1℃）体外循环期间通过氧合器给予挥发性麻醉剂的洗入和洗出情况进行了研究。作者给予异氟烷，并在洗入期间的1、2、4、8、16、32和48分钟测量其在动脉血（Pa）和静脉血（Pv）中的分压以及从氧合器排出的气体（PE）中的分压。在与复温同时进行的洗出期间重复这些测量。在洗入期间，PE、Pa和Pv逐渐向进气口气体分压（PI）升高。洗入16分钟后，Pa与PI的平衡为41%，32分钟后为51%，48分钟后为57%。在洗出期间，Pa在16分钟后降至其峰值的24%，32分钟后降至13%。混合静脉血中的洗入和洗出明显较慢。与正常体温患者经肺给药相比，体外循环期间异氟烷的洗入似乎发生得更慢，推测是因为低温增加了组织容量，抵消了血液稀释的影响，否则血液稀释会降低血/气分配系数。在复温期间，洗出似乎与正常体温患者经肺洗出的速度一样快。这可能是由于血/气分配系数下降（由于复温）以及异氟烷在组织中的储存相对有限所致。排出气体分压与动脉分压之间的关系相当一致；出于临床目的，测量PE可用于估计Pa。
