Background: The incidence of inadvertent perioperative hypothermia (IPH) in Ramathibodi Hospital between 2018 and 2019. Studies evaluating the effectiveness of preoperative warming (prewarming) in preventing IPH are controversial. Especially, its effects on pregnant women undergoing cesarean section under spinal anesthesia (SB). This study aimed to assess whether the prewarming with force air warming (FAW) can prevent IPH or shivering in patients undergoing cesarean section under SB.

Methods: This prospective randomized controlled trial was performed on 44 term-pregnant women, which scheduled for elective cesarean section under SB. Subjects were randomly assigned to either control or prewarming group. The prewarming group received at least 10 min of prewarming with FAW set to 38^oC, whereas the control group received standard usual care without prewarming. Using intention-to-treat analysis, the primary outcome was the change in tympanic temperature. The secondary outcome was the incidence of shivering at post-anesthetic care unit (PACU).

Results: There was a continuous decline in the tympanic temperature after SB in both groups. Using ANCOVA adjusted for baseline, the result did not differ significantly at any time point (P=0.939). Although the prewarming group had a higher temperature prior to SB than control group (36.50±0.31 vs 36.64±0.33, P=0.007), there was no difference in the incidence of hypothermia on arrival at the PACU between the groups (P=0.531). Shivering occurred similarly in the two groups (3 (13.64%) vs 1 (4.55%) patient for the control and prewarming group, respectively; P=0.613).

Conclusion: A brief 10-min of prewarming set at a moderate 38^oC temperature did not prevent inadvertent perioperative maternal hypothermia and shivering. For better thermal benefits, longer period and higher temperature setting of prewarming may be considered.