SERUM BUPIVACAINE CONCENTRATIONS AND TRANSPLACENTAL TRANSFER FOLLOWING REPEATED EPIDURAL ADMINISTRATIONS IN TERM PARTURIENTS DURING LABOR

Bupivacaine is the most widely used local anaesthetic in obstetrics fo r epidural analgesia. Nineteen women (mean age 26.9 +/- 5.3 years) who underwent epidural analgesia during labour were included in this stud y. All parturients received a first injection of 21.8 +/- 2.5 mg 0.25% plain bupivacaine. The following administrations were given on reques t: 0.25% concentration was used when cervix uteri was supple, and a 0. 375% concentration when it was tonic. Blood samples were collected 5 m in after the first injection and then every 30 min until delivery. At delivery blood samples were collected from the infant umbilical cord v ein and from the arm vein of the mother. Bupivacaine was assayed by hi gh pressure liquid chromatography. Serum data were analyzed for each p atient using a non-compartmental model. Bupivacaine was rapidly detect ed in serum, and maximal concentration was reached between 5 and 35 mi n. Pharmacokinetic parameters were estimated in 17 women after the fir st injection: 87 +/- 35 min for elimination half-life, 60 +/- 19 L for apparent volume of distribution and 0.5 +/- 0.3 L/min for plasmatic c learance. For a mean total duration of labour and total dose administe red of respectively 222 +/- 115 min and 57.1 +/- 28.7 mg, the mean val ue of the foeto-maternal ratio was 0.29 +/- 0.10. The infant maximal s erum concentration was 0.26 mu g/mL. No side effects were spontaneousl y reported by the parturients and all infants had an Apgar score of 10 at 5 min after the delivery. We confirm the fast systemic absorption and rapid elimination of bupivacaine which may be used without risk of acute toxicity both in mother and child, even when it is used in a 0. 375% concentration.