The effects of intrathecal neostigmine on somatic and visceral pain: improvement by association with a peripheral anticholinergic.

This study was designed to qualitatively evaluate the analgesic actions of intrathecal neostigmine alone and with intravenous (IV) N-butyl-scopolamine on somatic and visceral pain. Twenty-seven patients scheduled for both tubal ligation and vaginoplasty were divided into three groups. Patients received a standard anesthetic with thiopental, atracurium, and N2O/O2/enflurane. N-butyl-scopolamine, 20 mg, or saline was administered as a 2-mL IV bolus 20 min before the end of the surgical procedure. The control group (CG) received spinal and IV saline; the neostigmine group (NG), spinal neostigmine and IV saline; and the neostigmine-N-butyl-scopolamine group (NSG), spinal neostigmine and IV N-butyl-scopolamine. Postoperatively, patients assessed their pain on a 10-cm visual analog scale (VAS). The CG had both visceral and somatic pain at the first 30-min assessment, and all patients requested morphine. Patients from the NG had only visceral pain from the first assessment; however, they had lower VAS scores (P = 0.026) and requested less morphine (P = 0.037). Patients from the NSG were pain free during all assessment times (P < 0.0001). Neostigmine was more effective for somatic pain than visceral pain. N-butyl-scopolamine administration acted peripherally as an effective complement for treatment of visceral pain, reflecting an association between central cholinergic effects and peripheral anticholinergic effects in the treatment of visceral postoperative pain.