Epidural morphine anesthesia for abdominal aortic surgery--pharmacokinetics

Area of Science:

• Pharmacology
• Anesthesiology
• Neurosurgery

Background:

• Epidural analgesia is commonly used for postoperative pain management.
• Understanding the pharmacokinetics of epidural morphine is crucial for optimizing pain control and minimizing side effects.
• Abdominal aortic surgery presents unique physiological conditions that may affect drug distribution and elimination.

Purpose of the Study:

• To characterize the plasma and cerebrospinal fluid (CSF) pharmacokinetics of epidural morphine.
• To investigate the fraction of epidural morphine crossing the dura mater.
• To explore factors influencing interindividual variability in morphine pharmacokinetics during abdominal aortic surgery.

Main Methods:

• Measurement of plasma and CSF morphine concentrations over time following epidural administration.
• Calculation of pharmacokinetic parameters including peak concentration, time to peak, mean residence time (MRT), volume of distribution at steady state (Vdss), and clearance (CL).
• Analysis of the fraction of epidural morphine that crossed the dura.

Main Results:

• Morphine was detected in plasma and CSF within 2 minutes of epidural injection.
• Peak plasma concentrations occurred at 8.0 ± 2.6 minutes, with a plasma MRT of 84 ± 25.7 minutes.
• The fraction of epidural morphine crossing the dura was 3.15% ± 2.4, with peak CSF concentrations at 56 ± 31 minutes and a CSF MRT of 200 ± 28 minutes.
• Variable fractions of morphine remained in the CSF for many hours, indicating prolonged presence.

Conclusions:

• Epidural morphine exhibits distinct pharmacokinetic profiles in plasma and CSF following administration during abdominal aortic surgery.
• A small but significant fraction of epidural morphine crosses the dura, leading to measurable CSF concentrations.
• Interindividual variability in plasma and CSF pharmacokinetics is influenced by factors including the surgical procedure itself.