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Two Cases of Intrathecal Morphine-Induced Hypothermia: A Severe, but Treatable Complication
Abstract Number: T3D-6
Abstract Type: Case Report/Case Series
Spinal anesthesia is the most common anesthetic for Cesarean sections (CS) and intrathecal (IT) opioids are often included for intraoperative and postoperative analgesia. Common side effects of IT opioids include pruritis, nausea, vomiting and respiratory depression, though rarely hypothermia can occur[1,4]. Case 1: A 33-year-old G4P2 female with a past medical history of polysubstance abuse presented at 39 weeks for repeat CS. Uncomplicated spinal anesthesia was performed, and included IT morphine 200mcg. Surgery was uneventful and in-line IV fluid warming was done in the OR. Her initial oral temperature in recovery was 36.4 degrees Celsius (C). Three hours after the spinal dose, she became diaphoretic and nauseated. She felt subjectively warm with cold, clammy skin and her temperature was 34.2 C. She remained hypothermic (34.2-34.6 C) despite forced air warming for several hours, continued to sweat despite being hypothermic, and had a 12 beat run of ventricular tachycardia. IV lorazepam 1mg was given 6 hours after the spinal dose and resolution of symptoms and hypothermia was observed 75 minutes later. Hospitalization after this time was unremarkable. Case 2: A 38-year-old healthy G5P1 female at 39w2d gestation presented for scheduled repeat CS. A spinal anesthetic with IT morphine 100mcg, was performed. Surgery proceeded uneventfully and an in-line IV fluid warmer was used. Her axillary temperature was 35.7 C on arrival to recovery. Four hours after the spinal dose, she began to experience nausea, diaphoresis, and felt ‘warm’ despite her skin feeling cool and clammy to touch. During this interval, her oral and rectal temperature consistently measured 34.0-34.4 C. Forced air warming was attempted for 45-60 minutes, though she remained hypothermic and her symptoms unchanged. IV lorazepam 1mg was given 5 hrs after the spinal dose, and 45 mins later her symptoms resolved and her oral temperature was 36.3 C. She was monitored closely and remained normothermic until hospital discharge. Discussion: IT morphine for CS decreases postoperative pain and delays need for rescue analgesia. In a small case series, approximately 7% of patients during a 6-month observation of elective c-section cases had what appeared to be morphine induced hypothermia. Theories on why IT morphine causes hypothermia include GABAergic mechanisms, reducing thermoregulatory set point, and opioid receptor mediated[3,4]. Patient’s treated conservatively took 4-6 hours to improve temperature but had symptoms for several hours. Lorazepam treated patients saw improved symptoms and temperature within 90 mins. Naloxone has been effective in some cases, though concerns exist for antagonism of analgesia. Anesthesia providers should be aware of this potential complication, given its associated patient morbidity and treat ability.
1. Anesthesiology. 1999; 91: 1919-27.
2. Reg Anesth Pain Med. 2003; 28: 140-3.
3. Can J Anesth. 2012; 59:384-8.
4. IJOA. 2005; 14: 279-83.