Post‐operative pain relief following intrathecal injection of acetylcholine esterase inhibitor during lumbar disc surgery: a prospective double blind randomized study

Background: As spinal cholinergic receptors participate in the control of somatic pain, this effect could be potentiated by intrathecal injection of a cholinesterase inhibitor, neostigmine. Objective: This study was designed to evaluate the effectiveness of intrathecal administration of neostigmine on pain relief after single level lumbar disectomy. Methods: Sixty‐six patients with unilateral extruded lumbar disc were randomly allocated into two groups, neostigmine (‘N’), and control (‘C’); the former received 100 μg of neostigmine methylsulphate, whereas the latter received placebo intrathecally after termination of the surgery. Visual Analogue Scale was employed to measure post‐operative pain, which was a primary outcome of the study. Opiate dosage consumed was also recorded as a primary outcome during the first 24 h following surgery. Nausea and vomiting although important were considered as secondary outcomes. Results: Mean Visual Analogue Scale scores post‐operatively at 1, 4 and 8 h were 2·24, 1·82 and 1·88 in group ‘N’ and 5·36, 5·61 and 4·88 in group C. Mean morphine used intravenously in the first 24 h was 0·9 mg in group ‘N’ and 4·7 mg in group C. All results were found to be significantly different in the two groups. The frequency of nausea and vomiting was not significantly different in the two groups ‘C’ (24%) and ‘N’ (18%). Conclusion: Injection of 100 μg hyperbaric neostigmine intrathecally was effective for pain relief, and reduced post‐operative opiate demand.