Midazolam kinetics before, during and after cardiopulmonary bypass surgery

Gas-chromatographically determined serum concentrations of midazolam were recorded before, during and after cardiopulmonary bypass in patients scheduled for a coronary artery bypass grafting operation. Following single 0.075 mg/kg (n = 6) and 0.15 mg/kg (n = 6) intravenous injections of midazolam, a mean distribution phase half-life of 3.4 and 4.4 min respectively was calculated. At the establishment of the bypass, a rapid drop in the concentration of midazolam was observed followed by a significant increase in concentration during the postperfusion period. The apparent mean elimination phase half-life (281 min) of midazolam was longer than that (about 120 min) measured in earlier works in young, healthy subjects. Thus the metabolism of midazolam during the postperfusion period appears to be slower.