Heller Axel R, Zimmermann Katrin, Seele Kristin, Rössel Thomas, Koch Thea, Litz Rainer J
Department of Anesthesiology and Intensive Care Medicine, University Hospital Carl Gustav Carus, Dresden, Germany.
Anesthesiology. 2006 Aug;105(2):346-53. doi: 10.1097/00000542-200608000-00018.
Although local anesthetics (LAs) are hyperbaric at room temperature, density drops within minutes after administration into the subarachnoid space. LAs become hypobaric and therefore may cranially ascend during spinal anesthesia in an uncontrolled manner. The authors hypothesized that temperature and density of LA solutions have a nonlinear relation that may be described by a polynomial equation, and that conversion of this equation may provide the temperature at which individual LAs are isobaric.
Density of cerebrospinal fluid was measured using a vibrating tube densitometer. Temperature-dependent density data were obtained from all LAs commonly used for spinal anesthesia, at least in triplicate at 5 degrees, 20 degrees, 30 degrees, and 37 degrees C. The hypothesis was tested by fitting the obtained data into polynomial mathematical models allowing calculations of substance-specific isobaric temperatures.
Cerebrospinal fluid at 37 degrees C had a density of 1.000646 +/- 0.000086 g/ml. Three groups of local anesthetics with similar temperature (T, degrees C)-dependent density (rho) characteristics were identified: articaine and mepivacaine, rho1(T) = 1.008-5.36 E-06 T2 (heavy LAs, isobaric at body temperature); L-bupivacaine, rho2(T) = 1.007-5.46 E-06 T2 (intermediate LA, less hypobaric than saline); bupivacaine, ropivacaine, prilocaine, and lidocaine, rho3(T) = 1.0063-5.0 E-06 T (light LAs, more hypobaric than saline). Isobaric temperatures (degrees C) were as follows: 5 mg/ml bupivacaine, 35.1; 5 mg/ml L-bupivacaine, 37.0; 5 mg/ml ropivacaine, 35.1; 20 mg/ml articaine, 39.4.
Sophisticated measurements and mathematic models now allow calculation of the ideal injection temperature of LAs and, thus, even better control of LA distribution within the cerebrospinal fluid. The given formulae allow the adaptation on subpopulations with varying cerebrospinal fluid density.
尽管局部麻醉药（LAs）在室温下是高比重的，但注入蛛网膜下腔后几分钟内其密度就会下降。局部麻醉药会变成低比重，因此在脊髓麻醉期间可能会以不受控制的方式向头端上升。作者推测局部麻醉药溶液的温度和密度存在非线性关系，这种关系可用多项式方程描述，并且该方程的转换可以提供各局部麻醉药等比重时的温度。
使用振动管密度计测量脑脊液的密度。从所有常用于脊髓麻醉的局部麻醉药中获取温度依赖性密度数据，在5℃、20℃、30℃和37℃下至少重复测量三次。通过将获得的数据拟合到多项式数学模型中进行假设检验，该模型可计算特定物质的等比重温度。
37℃时脑脊液的密度为1.000646±0.000086 g/ml。确定了三组具有相似温度（T，℃）依赖性密度（ρ）特征的局部麻醉药：阿替卡因和甲哌卡因，ρ1（T） = 1.008 - 5.36×10⁻⁶T²（重比重局部麻醉药，在体温下等比重）；左旋布比卡因，ρ2（T） = 1.007 - 5.46×10⁻⁶T²（中等比重局部麻醉药，比重低于生理盐水）；布比卡因、罗哌卡因、丙胺卡因和利多卡因，ρ3（T） = 1.0063 - 5.0×10⁻⁶T（轻比重局部麻醉药，比重低于生理盐水）。等比重温度（℃）如下：5mg/ml布比卡因，35.1；5mg/ml左旋布比卡因，37.0；5mg/ml罗哌卡因，35.1；20mg/ml阿替卡因，39.4。
精密的测量和数学模型现在能够计算局部麻醉药的理想注射温度，从而更好地控制局部麻醉药在脑脊液中的分布。给定的公式可适用于脑脊液密度不同的亚人群。
