Prospective Study of Postoperative Respiratory Depression Metrics After Cesarean Delivery Among Women Receiving Intrathecal Morphine.

Abstract

The Society for Obstetric Anesthesia and Perinatology (SOAP) recommends monitoring for respiratory depression after cesarean delivery according to intrathecal morphine (ITM) dose. The aim of the study was to compare respiratory metrics after ITM administration, to determine evidence for the SOAP recommendations. Prospective observational cohort study design. Following institutional review board approval, women undergoing non-emergency cesarean delivery with spinal anesthesia in a single center were enrolled. Women were offered 50 µg, 150 µg or transversus abdominis plane (TAP) block without ITM, for postoperative analgesia. Respiratory monitoring, continuous acoustic respiratory rate (RR) and pulse oximetry oxygen saturation (SpO2) monitor Masimo Radius-7, was used after surgery up to 12 hours postoperatively. The primary outcome was bradypnea, number of women with RR ≤ 8 breaths per minute according to dose. Among 80 recruits, 33 (41%) chose 50 µg, 46 (57%) chose 150 µg, and one chose TAP block. Bradypnea events were detected 564 times among 27 (81.8%) women receiving 50 µg and 529 times among 40 (87.0%) women receiving 150 µg. Median [interquartile range (IQR)] duration of bradypnea per patient was 1.58 [1.15-2.42] in 50 µg group and 1.09 [0.83-1.70] in 150 µg group, P < .001. The event rate of bradypnea was 1.89 (95% confidence intervals [CIs], 1.73-2.05) events per person-hour among women receiving 50 µg versus 1.23 (95% CI, 1.12-1.34) events per person-hour among women receiving 150 µg, P = .624. Most, 62% of bradypnea occurred by 6 hours, and 86% of events by 12 hours. Apnea and hypoxemia event rates were similar, but hypoxemia duration was significantly prolonged after 150 µg, median 48 [IQR, 36-90] versus 56 sec [IQR, 40-106]; P = .001. Nursing assessments done per institutional protocol did not identify any respiratory events. No woman required oxygen or naloxone administration. We found no statistically significant differences in RR comparing 50 and 150 µg ITM, using continuous monitoring. Although the 150 µg group experienced a higher incidence of hypoxemia events, these were not clinically significant.