British Journal of Anaesthesia, Vol 78, Issue 2 160-162, Copyright © 1997 by The Board of Management and Trustees of the British Journal of Anaesthesia
J. M. Peutrell, K. Holder and M. Gregory
The maximum recommended dose for extradural infusions of bupivacaine in
children older than 1 month is 0.5 mg kg-1 h-1 but there are few specific
reports of the associated blood concentrations during infusions in babies.
Toxic symptoms can occur in children at plasma concentrations of
bupivacaine as low as 2 micrograms ml-1. We attempted to measure venous
plasma concentrations of total and free bupivacaine in babies aged 3-12
months during extradural infusions given at a rate commonly used in our
hospital. We studied eight babies (mean age 33 weeks; mean weight 7.8 kg).
After a mean initial dose of 1.2 mg kg-1 (range 1.1-1.3 mg kg-1),
bupivacaine was infused at a mean rate of 0.38 (0.36-0.39) mg kg-1 h-1 for
a mean of 31 (4-44) h. Blood was obtained at 4, 8, 16, 24, 32 and 40 h
after starting the infusion and plasma separated by centrifugation. Total
plasma bupivacaine concentration was measured using high pressure liquid
chromatography (HPLC). Plasma concentrations of total bupivacaine were
mostly less than 2 micrograms ml-1. One baby had a concentration of 2.02
micrograms ml-1 at 32 h and showed clear evidence of accumulation of
bupivacaine. Babies can accumulate bupivacaine and achieve plasma
concentrations above the threshold for toxic side effects, despite infusion
rates below the currently accepted maximum. The samples size in our study
was small but we believe an extradural infusion rate of 0.375 mg kg-1 h-1
is probably an absolute maximum for babies younger than 12 months.
CLINICAL INVESTIGATIONS
Plasma bupivacaine concentrations associated with continuous extradural infusions in babies
Royal Hospital for Sick Children, St Michael's Hill, Bristol BS2 8EG
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