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Effect of Intraoperative Phenylephrine infusion on Redistribution Hypothermia during Cesarean Section under Spinal Anesthesia
Abstract Number: F 30
Abstract Type: Original Research
Introduction: General anesthesia and neuraxial techniques alter thermoregulatory responses. This can cause severe hypothermia during spinal anesthesia.1 Forced air warmers and warm IV fluids have not shown to be consistently effective. Phenylephrine infusion has been found to decrease redistribution hypothermia in oral surgery patients under general anesthesia. 2 Our primary goal was to evaluate the effect of phenylephrine infusion on maternal temperature during Cesarean delivery under spinal anesthesia.
Method: Following IRB approval, this observational, on-going study enrolled ASA I-II parturients scheduled for Cesarean delivery with spinal anesthesia (n=15). OR temperature was maintained at 25-26ºC. After co-loading of one liter IV crystalloid (40ºC), spinal anesthesia was performed (hyperbaric bupivacaine 12 mg, fentanyl 15 mcg and morphine 0.2 mg). Additional warm blankets were provided per patient comfort level. All patients received a phenylephrine infusion at 40 mcg/min initiated with spinal placement and titrated to maintain mean arterial pressure within 20% of baseline. Maternal oral temperature was measured at spinal placement and every 10 minutes after for 60 minutes, at newborn delivery and PACU admission.
Results: The overall mean change in maternal temperature for each time point is shown in Table 1. Using univariate analysis, both cumulative dose of phenylephrine received and time at which the temperature was taken were significantly associated with change in maternal temperature (both p < 0.0001). In the univariate model, a 10 minute increase in time was associated with a mean decrease in maternal temperature of 0.044ºC. Each cumulative 1 mg of phenylephrine received was associated with a mean drop in maternal temperature of 0.11ºC.
Conclusion: Past studies have documented the incidence of hypothermia during Cesarean delivery with temperatures below 36ºC to be about 77% with an incidence of 60% for temperatures less than 35.5ºC.3-4 In the current study, though maternal temperature decreased, the concomitant use of phenylephrine infusion prevented the decrease in temperature to be more than 0.22ºC. None of the patients had temperatures less than 36.3ºC. Thus, the use of phenylephrine infusion during Cesarean delivery is beneficial to decrease the magnitude of maternal hypothermia.
1. Anesthesiology 2008;109:318-38
2. Anesth Analg 1999;89:462-5
3. Anesth Analg 2000;91:662-6
4. Anesth Analg 2007;105:1413-9