The concentration of bupivacaine in fetal organs during obstetrical epidural analgesia

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Abstract
The concentration of bupivacaine in organs of non-viable human fetuses after obstetrical epidural analgesia in customary doses was investigated. The concentrations were determined with a gas chromatograph. The material consisted of a fetus who died following termination in the 24th week of pregnancy three minutes after birth without spontaneous respiration. The other fetus was born maturely in the 40th pregnancy week with anencephaly who lived 20 minutes following initial spontaneous respiration. Most noteworthy were the increased concentrations in the liver indicating the important metabolic function of the liver for the metabolism of bupivacaine in the fetus. Further a very high pulmonary concentration was found in the mature fetus. Even though blood gases analysis were not performed we conclude that: the lung is the best perfused organ after birth and onset of spontaneous respiration because of the closure of the ductus arteriosus; because of the increasing agonal respiratory acidosis, bupivacaine accumulates in the lung, the organ from which the acidosis originates. Also, the ionized form the bupivacaine is unable to leave the intracellular space. For the clinical use of epidural analgesia during delivery, these results constitute an important indication for avoiding fetal acidosis before and during the action of such analgesia. This mandates strict and continuous fetal monitoring. Our results in agreement with other authors show that during fetal acidosis and simultaneous administration of bupivacaine the fetal distress may be potentiated by an accelerated transfer of the anesthetic agent into the fetal placental space. Under normal conditions one may assume that this technique of analgesia has a positive effect on the fetus because of the improved placental perfusion.(ABSTRACT TRUNCATED AT 250 WORDS)