Effect of Equilibrated Concentration on the Blood/gas Partition Coefficients of Volatile Anesthetics<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

周建新  医学博士 Jianxin Zhou*
刘　进  教授 Jin Liu#

*首都医科大学附属北京天坛医院ICU，北京，100050
#四川大学华西医院麻醉科，成都，610041

*Intensive Care Unit, Beijing TianTan Hospital, Capital University of Medical Sciences, Beijing, 100050
#Department of Anesthesiology, West China Hospital, West China Medical Center, Sichuan University, Sichuan, Chengdu, 610041

ABSTRACT

Objective：To determine the effect of equilibrated concentration on the blood/gas partition coefficients of volatile anesthetics.
Methods：Gaseous mixtures weree prepared as follows, each contained different concentration of anesthetics: 1) 6.15% desflurane and 2.1% enflurane; 2) 6.15% desflurane and 0.105% enflurane; 3) 2.2% isoflurane and 1.4% halothane; and 4) 2.2% isoflurane and 0.07% halothane.  These mixtures were used as equilibrated gases.  Blood/gas and normal saline/gas partition coefficients were measured by gas chromatography at 1 atm and 37℃.
Results：For partition coefficients of desflurane or isoflurane, there were no significant differences between measured simultaneously with high and low equilibrated concentration of enflurane or halothane (P>0.05). And also no significant differences were found with partition coefficients of enflurane or halothane between measured at high and low equilibrated concentration (P>0.05).
Conclusion：Over the range of equilibrated concentrations studied in this research (at approximately 0.5-2 MAC), we found no evidence of competitive binding between volatile anesthetics and blood constituents. Equilibrated concentration does not affect the measurement of blood/gas partition coefficients, and volatile anesthetics obey Henry's law.
Key words：Anesthetics, Volatile；Blood/gas partition coefficient

　　吸入麻醉药的血/气分配系数(λB/G)是决定吸入麻醉药药代动力学特点的重要理化性质。我们先前的研究建立了同时测定数种吸入麻醉药λB/G的方法^[1]。这一方法的理论基础为吸入麻醉药与血液成分间无可饱和性结合，且麻醉药间无相互竞争作用。虽然我们已证实吸入麻醉药λB/G在单独测定和数种麻醉药混合测定时所得结果间无显著性差异^[1]，但近期有研究提示平衡浓度影响异氟醚λB/G的测定结果^[2]。因此，我们设计了本实验，判断麻醉药间是否存在竞争作用，进一步验证同时测定数种吸入麻醉药λB/G方法的可行性。<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

材料和方法

　　称重法^[3]配制四种吸入麻醉药标准气：①12.3%地氟醚、②4.2%安氟醚、③4.4%异氟醚、和④2.8%氟烷，分别装入8.1L钢瓶待用。每次测定前用4只100ml玻璃注射器分别吸取上述4种标准气50ml。将地氟醚和安氟醚合并(第1组A)，异氟醚和氟烷合并(第2组A)，构成两对混合气。再吸取4种标准气各50ml，先分别将安氟醚和氟烷标准气稀释20倍，合并地氟醚和安氟醚(第1组B)，异氟醚和氟烷(第2组B)，构成另两对混合气。每次实验前均测定混合气中麻醉药的实际浓度。研究药物分组和实际浓度测定见表1和表2。
　　经病人同意后，选择12例拟行心脏二尖瓣置换术的病人(40±10岁)。于诱导前每人经桡动脉采血14ml，肝素抗凝后分为2等份，每份7ml。其中6例病人的血液用于第1组A和B两对麻醉药λB/G的测定，另6例用于第2组A和B两对麻醉药λB/G的测定。我们还测定了这4对麻醉药的生理盐水/气分配系数(λS/G)，每对重复6次。测定分配系数的方法为注射器两次平衡法^[1]，测定条件为1个大气压、37℃。
　　应用配对t检验比较：①地氟醚或安氟醚在第1组A和B两种平衡浓度条件下测定所得λB/G结果间得差异；②异氟醚或氟烷在第2组A和B两种平衡浓度条件下测定所得λB/G结果间的差异。用t检验比较λS/G间的差异。显著性检验水平定为0.05。

结　果

　　4种吸入麻醉药的λB/G结果见表1，λS/G结果见表2。
　　与高浓度安氟醚同时平衡时所测定的地氟醚λB/G(或λS/G)和与低浓度安氟醚同时平衡时所测定的地氟醚λB/G(或λS/G)之间无显著性差异(P>0.05)；用高浓度和低浓度安氟醚平衡时所测定的安氟醚λB/G(或λS/G)无显著性差异(P>0.05)。
　　与高浓度氟烷同时平衡时所测定的异氟醚λB/G(或λS/G)和与低浓度氟烷同时平衡时所测定的异氟醚λB/G(或λS/G)之间无显著性差异(P>0.05)；用高浓度和低浓度氟烷平衡时所测定的氟烷λB/G(或λS/G)无显著性差异(P>0.05)。

参 考 文 献
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3. 叶其泉，刘进，刘明政。二步法配制吸入麻醉药高压标准气。中华麻醉学杂志，1999;19:640－1。
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