Background and Objectives. 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.

Methods. 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.

Results. 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).

Conclusions. 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.