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Severe hypothermia after intrathecal morphine and reversal with lorazepam
Abstract Number: F5D-10
Abstract Type: Case Report/Case Series
Neuraxial morphine is the analgesic of choice for post-operative pain control for Cesarean section (CS) due to its duration of action and opioid sparing effect. Severe hypothermia after intrathecal (IT) morphine has been observed and reversal with lorazepam has been reported.1 However, the optimal dosage for and time course to resolution of hypothermia is unknown.
A 47 year-old G2P0 presented at 34 weeks gestation for CS due to severe preeclampsia and IV magnesium sulfate was started. Her vital signs were BP 122/74, HR 66, SpO2 100% and T 36.4oC. She underwent an uncomplicated CS under spinal anesthesia and a forced-air blanket and fluid warmer were used. On arrival to the PACU, skin temperature was 35.5oC. After 45 minutes, foley temperature was 34.6oC. She was diaphoretic and reported feeling hot. After another 45 minutes, her temperature was 34.4oC and she remained diaphoretic without shivering despite a forced-air blanket and fluid warmer. She received lorazepam 0.5mg IV and her temperature increased to 34.7oC within two hours. After a second dose of lorazepam, her symptoms resolved and her temperature increased to 36oC within 8 hours.
Hypothermia during CS is a known phenomenon and most women have a 0.5oC decrease in temperature over the first 30 minutes despite active warming. The sympathectomy from spinal anesthesia contributes to hypothermia by causing vasodilation, redistribution of heat to the periphery, and reduction in thermoregulatory mechanisms such as shivering and vasoconstriction.2 Hypothermia related to IT morphine can severely impair the thermoregulatory response related to agonism of mu receptors in the hypothalamus, such that patients paradoxically show diaphoresis without shivering or feeling cold.2,3 Hypothermia can persist for 2-22 hours despite active warming and regression of spinal anesthesia.1
Treatment of hypothermia has included naloxone or lorazepam. Naloxone causes increased temperature and return of normal hypothermic sensations, but there is risk of analgesic reversal. Lorazepam has been proposed since GABA is implicated as a mediator in opioid-induced hypothermia. Further studies are needed to elucidate the appropriate dosage and timing for lorazepam reversal of IT morphine induced hypothermia.
1. Hess PE et al. Int J Obstet Anesth 2005. 14:279-83
2. Sayyid SS et al. Reg Anesth Pain Med 2003. 28:140-3
3. Ryan KF et al. Can J Anesth 2012. 59:384-388