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Pharmacokinetics of ropivacaine during extradural anesthesia for total hip replacement
1Department of Anaesthesiology and Intensive Care Medicine, Hospital of the Christian-Albrechts-University of Kiel, Germany.
Study Objective:
To determine plasma concentrations of ropivacaine during epidural anesthesia with ropivacaine 10 mg/mL in patients undergoing elective total hip replacement.
Design:
Phase III prospective study.
Setting:
Orthopedic surgical unit of the University Hospital in Kiel, Germany
Patients:
11 ASA physical status I, II, and III patients undergoing elective total hip replacement after premedication with a benzodiazepine.
Interventions:
Peripheral venous plasma samples were collected prior to and 10, 15, 20, 30, 45, 60, 90, and 120 minutes following the epidural dose.
Measurements And Main Results:
After solid phase extraction, plasma concentrations of ropivacaine were measured by high-performance liquid chromatography (HPLC). Free unbound concentrations were determined after ultracentrifugation. In 9 of 11 patients excellent epidural anesthesia was achieved with an initial dose of 144 +/- 13 mg (120 to 150 mg) of ropivacaine corresponding to a dose of 1.9 +/- 0.4 mg/kg body weight. We suspected inadvertent intravascular catheter malposition in one case. Peak plasma concentrations occurred after 20 minutes (10 to 30 min) with a mean of 1.38 +/- 0.42 micrograms/mL (range 0.95 to 2.26 micrograms/mL). Maximum unbound free plasma concentrations of ropivacaine were 0.05 +/- 0.03 microgram/mL (range 0.02 to 0.13 microgram/mL).
Conclusion:
Ropivacaine 10 mg/mL proved to be suitable for epidural anesthesia for total hip replacement. The plasma concentrations after 120 to 200 mg of its epidural application were not associated with signs of local anesthetic toxicity in patients pretreated with benzodiazepines, even in one case of suspected inadvertent intravascular application.