Epidural morphine anesthesia for abdominal aortic surgery--pharmacokinetics

Plasma and CSF pharmacokinetics of morphine given epidurally in combination with general anesthesia for abdominal aortic surgery were recorded. The initial plasma and CSF concentrations of morphine appeared at two minutes. The peak plasma concentrations of morphine were recorded at 8.0 +/- 2.6 minutes after epidural injection. Plasma mean residence time was 84 +/- 25.7 minutes, Vdss 121 +/- 30 L, and C1 1.5 +/- 0.32 L/min. Free morphine was not detected in plasma 360 minutes after epidural administration. The fraction of the epidural morphine that crossed the dura was 3.15% +/- 2.4 The peak CSF morphine concentrations were recorded at 56 +/- 31 minute. MRT (200 +/- 28 minute), Vdss (65 +/- 33.8 ml), and CL (0.32 +/- 0.15 ml/min) showed that variable fractions of morphine remained many hours in the CSF. Factors that could produce the interindividual variability of plasma and CSF concentrations and pharmacokinetics of epidural morphine were discussed. Abdominal aortic surgery appears to influence both plasma and CSF pharmacokinetics.