Enhanced recovery after caesarean section: an intrathecal morphine dosing study

Abstract Objective To compare the analgesic and side effect profiles of three intrathecal morphine doses as part of an enhanced recovery protocol in obstetric patients undergoing caesarean section. Methods A prospective cohort study including ASA 2 females, over 18 years old having repeat elective caesarean sections. Primary outcomes include total oral morphine equivalents (mg) at 24 and 48 h, proportion of opioid free patients (24 and 48 h), and frequency of ITM-related side-effects. Secondary outcome measures include duration of analgesia, pain scores at 24 h, FAS at 24 h and length of stay. Results Five hundred seventy-four patients were divided into 150 mcg (190 patients), 125 mcg (191 patients) and 100 mcg (193 patients) intrathecal morphine groups. Effective analgesia was provided by all doses of ITM with a dose-dependent increase in side-effects. The median opioid consumption at 24 h was 10 mg in the 150 mcg group and 20 mg in the 125 mcg and 100 mcg groups. At 48 h, the median opioid consumption was 30 mg in the 150 mcg group and 45 mg in the 125 mcg and 100 mcg groups. The proportion of opioid-free patients at 24 and 48 h decreased with decreasing dose of ITM; 41% in 150 mcg group, 31% in the 125 mcg group and 28% in the 100 mcg group at 24 h. At 48 h, this reduces to 24% in the 150 mcg group, 15% (37.5% reduction in the 125 mcg group, and 13% (45.8% reduction) in the 100 mcg group. This designates analgesic inferiority of both 125 mcg and 100 mcg ITM doses compared to 150 mcg dosing. There was no significant difference between 125 and 100 mcg dosing. The duration of analgesia was greater in 150 mcg dosing (median duration 21 h) compared to 125 mcg (13 h) and 100 mcg (12 h) groups. No significant difference in pain scores was noted between doses. FAS scores demonstrated a trend towards functional limitation in 125 mcg and 100 mcg dosing compared to 150 mcg. There was no difference between the 125 mcg and 100 mcg groups. Increased pruritus was seen in the 150 mcg and 125 mcg groups (41%) compared to the 100 mcg group (32%). Increased nausea and vomiting was seen in the 150 mcg (49%) and 125 mcg (42%) groups compared to the 100 mcg group (24%). No difference in LOS was noted between doses (median difference 1.1 h). Conclusion All doses of ITM provide effective analgesia with 100 mcg dosing providing the best trade-off between analgesic efficacy and side effect profile.