Dyhre H, Wallin R, Renck H
Department of Anaesthesia, University Hospital MAS, Malmo, Sweden.
Acta Anaesthesiol Scand. 1996 Jan;40(1):86-90. doi: 10.1111/j.1399-6576.1996.tb04392.x.
Objectives were to study the effects of variations in the pH and the buffer capacity of solutions of lignocaine or pethidine on their analgesic efficacy in peripheral nerve block.
Infraorbital nerve blocks (IONB) were induced in rats during light pentobarbitone anaesthesia employing 0.2 ml of test solutions containing 10 mg center dot ml-1 of lignocaine or pethidine dissolved in normal saline, 50 mmol and 150 mmol tris-hydroxymethylaminomethane (THAM) hydrochloride (THAM center dot HCl) of pH 4.8 and 4.5, respectively, or 100 mmol THAM + THAM center dot HCl of pH 7.4. The pH of solutions in saline was varied from 3.0 to 9.3 by adding HCl or NaHCO3. The analgesic efficacy is expressed as the interval from injection to elicitation of a minimal response to electric stimulation at various intensities (threshold intensities) within the blocked area (IONB 3 to 10), and in terms of the area under the curve (AUC, threshold intensities vs. time).
When dissolved in saline, pH 7.4, pethidine exerted more pronounced effects than lignocaine [AUC by 3.5 times (P<0.001), IONB 3 to 10 by 2.7 (P<0.05) to 3.6 (P<0.001) times]. Variations of the pH of solutions did not affect their analgesic efficacy. Lignocaine exerted more pronounced local analgesic effects when mixed with 150 mmol THAM center dot HCl than when mixed with saline (pH 7.4), but manifested even more pronounced effects when dissolved in THAM + THAM center dot HCl [AUC by 3.7 times (P<0.001), IONB 3 to 10 by 2.7 (P<0.01) to 3.8 (P<0.001) times]. When dissolved in THAM + THAM center dot HCl, the analgesic efficacy of pethidine increased by 2.0 to 2.8 times (P<0.001), as compared to a solution in saline at the same pH.
It is concluded that variations in the pH of solutions of lignocaine or pethidine in saline does not affect the analgesic efficacy of the drugs, presumably due to the low buffer capacity of the medium, whereas when dissolved in THAM + THAM center dot HCl, their effect is enhanced.
目的是研究利多卡因或哌替啶溶液的pH值和缓冲容量变化对其在周围神经阻滞中的镇痛效果的影响。
在轻度戊巴比妥麻醉下，给大鼠进行眶下神经阻滞（IONB），使用0.2 ml测试溶液，其中含有溶解于生理盐水、pH值分别为4.8和4.5的50 mmol和150 mmol三羟甲基氨基甲烷（THAM）盐酸盐（THAM·HCl）中的10 mg·ml⁻¹利多卡因或哌替啶，或pH值为7.4的100 mmol THAM + THAM·HCl。通过添加HCl或NaHCO₃使盐溶液中的pH值在3.0至9.3之间变化。镇痛效果用从注射到在阻滞区域（IONB 3至10）内对不同强度（阈值强度）的电刺激产生最小反应的时间间隔表示，并以曲线下面积（AUC，阈值强度与时间）表示。
当溶解于pH值为7.4的生理盐水中时，哌替啶的作用比利多卡因更明显[AUC高3.5倍（P<0.001），IONB 3至10高2.7倍（P<0.05）至3.6倍（P<0.001）]。溶液pH值的变化不影响其镇痛效果。利多卡因与150 mmol THAM·HCl混合时比与生理盐水（pH值7.4）混合时具有更明显的局部镇痛作用，但溶解于THAM + THAM·HCl时表现出更明显的作用[AUC高3.7倍（P<0.001），IONB 3至10高2.7倍（P<0.01）至3.8倍（P<0.001）]。当溶解于THAM + THAM·HCl中时，与相同pH值的生理盐水溶液相比，哌替啶的镇痛效果提高了2.0至2.8倍（P<0.001）。
得出结论，利多卡因或哌替啶在盐溶液中的pH值变化不影响药物的镇痛效果，可能是由于介质的缓冲容量低，而当溶解于THAM + THAM·HCl中时，它们的作用增强。
