Intrathecal morphine does not prevent chronic postsurgical pain after elective Caesarean delivery: a randomised controlled trial

Abstract

Background: Morphine is frequently added to spinal anaesthesia for Caesarean delivery. We aimed to determine whether intrathecal morphine for spinal anaesthesia decreases the risk of chronic postsurgical pain (CPSP).

Methods: In this randomised, double-blind, placebo-controlled trial, 290 healthy parturients undergoing elective Caesarean delivery were randomly assigned in a 1:1 ratio to receive either intrathecal morphine 100 μg (n=145) or normal saline (control; n=145) as a part of spinal anaesthesia. Anaesthetic care and postoperative pain management were standardised in all patients. The primary outcome was the incidence of CPSP at 3 months. Secondary outcomes included CPSP at 6 months, pain severity, and pain interference, measured by the Brief Pain Inventory questionnaire using an 11-point numeric rating scale, at 3 and 6 months after the surgery.

Results: Two hundred and seventy-six patients completed the 3-month follow-up, 139 in the morphine group and 137 in the placebo group. The incidences of CPSP at 3 months were 19% (27 of 139) in the morphine group and 18% (25 of 137) in the placebo group (odds ratio, 1.08; 95% confidence interval, 0.59-1.97; P=0.803). At 6 months, CPSP was present in 23 of 139 (16%) morphine group patients compared with 19 of 137 (14%) in the placebo group (odds ratio, 1.23; 95% confidence interval, 0.63-2.38; P=0.536). Brief Pain Inventory questionnaire scores for pain severity and pain interference at 3 and 6 months were similar between groups.

Conclusions: Administration of morphine 100 μg as a component of spinal anaesthesia for elective Caesarean delivery failed to reduce the incidence of chronic pain at 3 and 6 months after surgery.

Clinical trial registration: NCT03451695.

Keywords: Brief Pain Inventory; Caesarean delivery; chronic postsurgical pain; morphine; spinal anaesthesia.