Efficacy of three test doses to detect epidural catheter misplacement

To determine among three currently used epidural test doses which is the most reliable for the detection of accidental intrathecal misplacement of an epidural catheter, and which clinical sign is to be used as a marker.

Ninety orthopedic patients were allocated to either the continuous epidural or the continuous spinal group according to age, < or > 70 yr. They received, in a randomized, double-blind fashion, one of the three solutions: 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. Objective variables studied every two minutes over the first ten minutes after injection included: presence of a sensory level > or = T12, presence of a motor block > or = 1, and anesthesia of segments L1, L2, S2 and S5. Subjective variables studied over the same period included paresthesias, sensation of warmth or cold, and muscle weakness.

When using presence of motor block > or = 1 on the Bromage scale, the administration of 60 mg L2% with epinephrine identified all patients having an intrathecal catheter six minutes after injection, whereas none of the patients receiving the same solution through the epidural catheter presented a motor block. This was not the case for the other two solutions studied.

Lidocaine 2% with epinephrine at a dose of 60 mg is the test dose of choice to detect the intrathecal misplacement of an epidural catheter. The presence of motor block > or = 1 is the only reliable clinical sign.