A comparison between lidocaine alone and lidocaine with meperidine for continuous spinal anesthesia

Experimental investigations have demonstrated a synergistic interaction between opioids and local anesthetics. This study aims to assess the effective benefit-risk ratio of continuous spinal anesthesia (CSA) induced with either 1.6% lidocaine alone or in combination with 1% meperidine.

Thirty-four elderly patients (80.7 +/- 7.3 years) operated on for fracture of the neck of the femur were randomly allocated to two groups. In the first group (n = 15), CSA was induced with lidocaine 1.6% plain, whereas in the second group (n = 19) 1% meperidine was added. Reinjections were performed in both groups using lidocaine 1.6% alone.

In the lidocaine group, 43 +/- 13 mg was used for induction whereas in the other group the addition of 18 +/- 5 mg of meperidine significantly reduced the dose of lidocaine required to 28 +/- 8 mg (p < 0.001). Delay between two reinjections was increased to 51 +/- 7 minutes in the lidocaine plus meperidine group, compared to 35 +/- 6 minutes in the lidocaine group (p < 0.001). Ephedrine was required for 9 out of the 19 patients in the lidocaine plus meperidine group, whereas it was required for only two patients in the other group (p = 0.05). Mean plasma concentrations of meperidine 1 hour and 3 hours after induction was 45.5 +/- 12 ng/ml and 59 +/- 22 ng/ml, respectively, and drowsiness was observed in 95% of the patients in the second group. Delay before requirement for pain medication was 2.2 +/- 2 hours in the lidocaine group and 14.1 +/- 8 hours in the lidocaine plus meperidine group (p < 0.001).

The association of 1% meperidine with 1.6% lidocaine during the induction of CSA decreases the initial induction dose, prolongs analgesia, produces initial drowsiness, and provides long-lasting pain relief. However, such benefits are offset by some impairment of hemodynamic stability that is likely to make this combination of drugs unacceptable as an enhanced analgesic technique.