Biscoping J, Bachmann-M B, Kirschbaum M, Hempelmann G
Abteilung für Anaesthesiologie und Operative Intensivmedizin, Justus-Liebig-Universität Giessen.
Reg Anaesth. 1989 May;12(3):50-2.
Pudendal block is a well established method of achieving analgesia during the second stage of labor. Whenever a large amount of a local anesthetic has to be injected in well vascularized tissue, local anesthetic drugs with low systemic toxicity should be used, to minimize side effects. This means that prilocaine is the drug of choice. It is well known that the metabolites of prilocaine induce methemoglobinemia, and thus the question arises as to whether the methemoglobinemia affects the fetus. PATIENTS AND METHODS. Pudendal block was achieved with 2 x 10 ml prilocaine 1% in each of 17 mothers. Plasma concentrations of the local anesthetic in the second stage of labor were determined by gas chromatography in blood samples drawn from the mother and the newborn at the moment of childbirth. In addition, the time course of methemoglobinemia was determined by capillary blood samples from the neonate up to 6 h. To evaluate methemoglobinemia in the newborn, 125 microliters heparinized capillary blood was diluted with 200 microliters 0.9% sodium chloride; methemoglobin was detected by absorbance spectrometry. RESULTS. Before the pudendal block maternal methemoglobin concentrations were about 0.2% of the total hemoglobin concentration and within the physiological range. At the moment of delivery it was increased only to a small extent, without statistical significance. In the neonates mean methemoglobin concentrations were about 1% of total hemoglobin immediately after delivery, increasing up to 1.8% in the next 2 h and then decreasing continuously in all. At the moment of childbirth maternal mean prilocaine concentrations were 0.57 micrograms/ml on an average and 0.29 micrograms/ml in the newborn. DISCUSSION. With respect to systemic toxicity, prilocaine is the drug of choice in local anesthetic procedures when a long duration of anesthesia is not required; it guarantees short latency and adequate relief of pain. Methemoglobinemia induced by its metabolites is not a contraindication for its use in humans. Formerly prilocaine was judged to be contraindicated in pregnant women during delivery because of the small redox capacity of fetal erythrocytes. Our study, however, demonstrates that 200 mg prilocaine for pudendal block does not induce methemoglobinemia in newborns to any significant extent. One explanation for this may be the increased renal elimination of local anesthetics in newborns and the low fetomaternal ratio.
阴部阻滞是在分娩第二产程中实现镇痛的一种成熟方法。每当需要在血管丰富的组织中注射大量局部麻醉药时，应使用全身毒性低的局部麻醉药，以尽量减少副作用。这意味着丙胺卡因是首选药物。众所周知，丙胺卡因的代谢产物会诱发高铁血红蛋白血症，因此就产生了高铁血红蛋白血症是否会影响胎儿的问题。患者与方法。17名产妇均采用2×10毫升1%丙胺卡因进行阴部阻滞。通过气相色谱法测定分娩时从母亲和新生儿采集的血样中局部麻醉药在分娩第二产程中的血浆浓度。此外，通过采集新生儿直至6小时的毛细血管血样来测定高铁血红蛋白血症的时间进程。为评估新生儿的高铁血红蛋白血症，将125微升肝素化毛细血管血用200微升0.9%氯化钠稀释；通过吸光光谱法检测高铁血红蛋白。结果。在阴部阻滞前，母体高铁血红蛋白浓度约为总血红蛋白浓度的0.2%，处于生理范围内。分娩时仅略有升高，无统计学意义。新生儿出生后即刻高铁血红蛋白平均浓度约为总血红蛋白的1%，在接下来的2小时内升至1.8%，然后总体持续下降。分娩时母体丙胺卡因平均浓度平均为0.57微克/毫升，新生儿为0.29微克/毫升。讨论。就全身毒性而言，在不需要长时间麻醉的局部麻醉操作中，丙胺卡因是首选药物；它保证潜伏期短且能充分缓解疼痛。其代谢产物诱发的高铁血红蛋白血症并非其在人类中使用的禁忌证。以前，由于胎儿红细胞的氧化还原能力小，丙胺卡因被判定在孕妇分娩时为禁忌药。然而，我们的研究表明，用于阴部阻滞的200毫克丙胺卡因不会在新生儿中显著诱发高铁血红蛋白血症。对此的一种解释可能是新生儿对局部麻醉药的肾清除增加以及母胎比例低。
