Detection of intravascular epidural catheters using 2-chloroprocaine

Background and Objectives. Detecting the intravascular placement of epidural cattheters is essential to avoid local anesthetic toxicity. Small doses of intravenous local anesthetics produce changes in sensorium and are often used to test newly placed epidural catheters. Many parturients receive nalbuphine for analgesia prior to epidurla catheter placement. This study examines how nalbuphine premedication influences symptoms following intravenous 2-chloroprocaine. Methods. Thirty-one volunteers were randomized to receive premedication with placebo or 0.15 mg/kg of nalbuphine intravenously. Starting 10 minutes later, intravenous injections of 0.0, 0.3 0.6, 0.9, 1.2 and 1.5 mg/kg of 2-chloroprociane were given in random order at 10 minute intervals. After each injection volunteers were asked to report changes in hearing, taste, or other symptoms. Results. Symptoms reported (in decreasing order of frequency) were auditory changes, taste changes, dizziness/lightheadedness, tingling in the extremities, and visual changes. The probability that volunteers will report symptoms is proportional to the dose of 2-chloroprocaine administered (auditory symptoms, P<.001; taste symptoms, P=.01; any symptoms, P<.001). Nalbuphine-premedicated volunteers were more likely to report symptoms (auditory symptosms P=.004; taste symptoms, P=.004; any symptoms, P=.02). A dose of at least 1.5 mg/kg appears to be necessary to produce a 90% probability that patients will reprot symptoms when they receive 2-chloroprocaine intravenously. Conclusions. This study suggests that patients who receive nalbuphine for analgesia prior to epidural placement will be more likely to report symptoms after receiving intravenous 2-chloroprocaine during epidural test dosing.