Efficacy of three test doses to detect epidural catheter misplacement

Purpose: To determine among three currently used epidural test doses which is the most reliable for the detection of accidental intrathecal misplaceme nt of an epidural catheter, and which clinical sign is to be used as a mark er. Methods: Ninety orthopedic patients were allocated to either the continuous epidural or the continuous spinal group according to age, < or > 70 yr. Th ey received, in a randomised, double-blind fashion, one of the three soluti ons: 60 mg lidocaine 2% (L2%), 7.5 mg bupivacaine 0.25% (B0.25%), or 15 mg bupivacaine 0.5% (B0.5%); all three solutions contained epinephrine. Object ive variables studied every two minutes over the first ten minutes after in jection included: presence of a sensory level greater than or equal to T-12 , presence of a motor block greater than or equal to 1, and anesthesia of s egments L-1, L-2, S-2 and S-5. Subjective variables studied over the same p eriod included paresthesias, sensation of warmth or cold, and muscle weakne ss, Results: When using presence of motor block greater than or equal to 1 on t he Bromage scale, the administration of 60 mg L2% with epinephrine identifi ed all patients having an intrathecal catheter six minutes after injection, whereas none of the patients receiving the same solution through the epidu ral catheter presented a motor block. This was not the case for the other t wo solutions studied. Conclusion: Lidocaine 2% with epinephrine at a dose of 60 mg is the test do se of choice to detect the intrathecal misplacement of an epidural catheter , The presence of motor block greater than or equal to 1 is the only reliab le clinical sign.