Spinal anaesthesia in newborns: total and free bupivacaine plasma concentration

This study was designed to measure total and free bupivacaine (B) after spinal anaesthesia in newborns and to evaluate a possible influence of adrenaline on B absorption. Twenty-two newborns were randomly allocated to receive either plain B (group 1) or adrenaline added to B (group 2) for spinal anaesthesia. A single blood sample was collected ten min after spinal injection. Total B concentration was found 0.31 +/- 0.17 microgram ml-1 in group 1 and 0.25 +/- 0.09 microgram ml-1 in group 2. Bound B concentration was 0.27 +/- 0.17 microgram ml-1 in group 1 and 0.22 +/- 0.09 microgram ml-1 in group 2. No difference was found between the two groups for these parameters. Albumin but not alpha 1-acid-glyco-protein correlated to age and weight, bound B correlated to alpha 1-acid-glyco-protein but not to albumin. Despite the low plasma concentration of binding proteins in newborns, spinal anaesthesia with B does not result in a high level of free drug. Adrenaline does not have any pharmacological advantage in these patients.