[Intravenous neostigmine enhances the analgesic effect of epidural anesthesia]

A single-blind trial of the intravenous neostigmine on epidural anesthesia was carried out on 75 patients undergoing lower limb or lower abdominal surgery. They were allocated to three groups of 25: patients of group C received 2 ml of 0.9% saline, patients of group AN 1 ml (0.5 mg) of atropine and 2 ml (1 mg) of neostigmine, and patients of group N 2 ml (1 mg) of neostigmine, intravenously 5 min before epidural injection of 15 ml of 2% mepivacaine solution without epinephrine. We assessed the onset and spread of cold sensory block and analgesia, and the degree of motor block and sedation. The onset time of analgesia at T 11 was significantly shorter in group N [6.2 +/- 2.0 (SD) min] than in groups C (8.5 +/- 2.6 min) and AN (8.7 +/- 2.4 min). The segmental spread of analgesia 10 and 20 min after epidural injection was significantly larger in group N (10.8 +/- 3.9 and 15.4 +/- 2.7 seg, respectively) than in groups C (7.6 +/- 3.4 and 12.8 +/- 3.5 seg, respectively) and AN (7.8 +/- 3.6 and 13 +/- 3.4 seg, respectively). There were no differences in the onset and spread of cold sensory block, and the degree of motor block and sedation among the three groups. The incidence of bradycardia and fecal incontinence was significantly higher in group N than in groups C and AN. These results demonstrate that intravenous neostigmine potentiates the analgesic effect of epidural anesthesia mediated by a cholinergic muscarinic mechanism. However, in clinical practice, it does not seem to be useful, because of the side effects.