Bupivacaine for intercostal nerve blocks in children: blood concentrations and pharmacokinetics

A pharmacokinetic evaluation of bupivacaine was carried out after intercostal nerve blocks performed on 28 occasions in 27 children varying in age from 3 months to 16 yr. Bupivacaine HCl, 0.5%, with epinephrine 1:200,000 was employed. Doses of 2 mg/kg, 3 mg/kg, and 4 mg/kg resulted in peak whole blood arterial bupivacaine (base) concentrations (mean +/- SD) of 0.77 +/- 0.25 microgram/ml, 1.37 +/- 0.23 microgram/ml, and 1.87 +/- 0.53 microgram/ml, respectively. Calculated pharmacokinetic parameters (mean +/- SD) were the following: apparent volume of distribution (VD beta), 2.8 +/- 0.8 L/kg; steady-state volume of distribution (VDss), 2.7 +/- 0.7 L/kg; elimination half-life (t1/2 beta), 147 +/- 80 min; and total body clearance (Cl), 16.0 +/- 7.4 ml X min-1 X kg-1, or 382 +/- 201 ml X min-1 X m-2. Compared with data reported for adult patients, our data indicate that the volume of distribution is greater and clearance is more rapid in children than in adults. The absorption of local anesthetic from the intercostal space appears to be more rapid in children than adults. In an additional group of 11 children, the relationship of the bupivacaine blood:plasma concentration ratio (lambda) to hematocrit was investigated. Hematocrit in this group ranged from 30 to 59, and lambda varied from 0.47 to 0.82. There was a significant relationship between lambda and hematocrit defined by the equation lambda = -0.0079 Hct + 1.028 (r = 0.72, P less than 0.05). Reporting bupivacaine concentration in terms of plasma concentration may introduce an artifact that is dependent on the hematocrit, and we therefore suggest that whole blood concentration values be reported by investigators in the future.