Delayed respiratory depression associated with 0.15 mg intrathecal morphine for cesarean section: a review of 1915 cases

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Abstract
A low dose of morphine, given intrathecally is an effective postoperative analgesic technique and is widely used in cesarean section. Delayed respiratory depression is the most feared side effect of this technique. However, this side effect has not been thoroughly reported in the obstetric population. The aim of this study was to describe respiratory depression associated with intrathecal morphine in postcesarean women, and to estimate its incidence. We retrospectively reviewed the obstetric anesthesia database at our institution from April 2000 to December 2006. Patients who were given 0.15 mg intrathecal morphine for cesarean section were identified. From this group, we identified patients who developed bradypnea (respiratory rate ≤ 10 breaths·min−1) within 24 h after the intrathecal injection. Of 1915 women given 0.15 mg intrathecal morphine for postcesarean analgesia, 6 patients exhibited bradypnea within 24 h after the injection of morphine. Four of these 6 patients developed mild respiratory depression, which was treated with supplemental oxygen and/or encouragement of breathing. One patient had severe respiratory depression, and repeated episodes of oxygen desaturation below 90% and 30-s apneas were noted. Naloxone was required for this patient. One woman had obstructive sleep apnea which was not associated with the intrathecal morphine. Of 1915 patients, 5 women (0.26%) developed bradypnea associated with 0.15 mg intrathecal morphine. The incidence of severe bradypnea requiring naloxone was 1/1915 (0.052%).