4. Discussion
shivering, hypothermia
HEAT, SECONDARY, ADVERSE EFFECTS
In our study, we selected a population of patients scheduled for elective surgery and undergoing general or neuroaxial anesthesia with intraoperative warming. In these patients, a prewarming of at least 10 min with hot air devices did not show differences in the incidence of hypothermia, the duration of hypothermia or in the magnitude of hypothermia as compared to no prewarming. These results are not consistent with those obtained by Horn et al. [In our study, the downward trend in temperature after induction was not prevented in the prewarming group, despite the storage of heat. During the first 60 min of surgery, both groups of patients followed a similar downward temperature curve. These results were different from those reported by Lau et al. [Regarding the prewarming time, Horn et al. [It must be considered that the effect of prewarming subsides after some time after the completion of anesthetic induction if intraoperative warming is not promptly restarted. In patients receiving spinal anesthesia, Jun et al. [Such results were observed despite allowing the patient or the staff in the pre-anesthesia room to regulate the heat unit, thereby possibly reducing the adverse effects related to heating. Indeed, it was previously suggested that allowing the patient to regulate prewarming may also reduce both the patient’s heat discomfort (preoperative) and the interruption of intraoperative warming [Our study has some strengths and several limitations. Overall, although we performed an RCT with rigorous methodology, the blinding of patients and anesthesiologists was not feasible due to the nature of the intervention and represents the first limitation. Second, our study was limited to a single center with the influence of local protocols with profound attention given to perioperative normothermia. Indeed, our protocol includes the rigid control of the rooms’ temperature, early initiation of intraoperative warming, careful monitoring and the assessment of body temperature. All these factors can reduce the need for active prewarming. Third, the incidence of hypothermia in the control group was much lower than hypothesized during the study design and sample size calculation. Hence, our study may have been underpowered to detect significant differences. Fourth, our study did not have the statistical power to analyze subgroups and to explore whether some patients may experience greater benefits from prewarming as compared to others. This may be the case of patients with low body mass index, or those undergoing certain types of surgery. However, our study had a heterogeneous population and cannot answer this question. Finally, our study was also not powered to find differences in SSI, transfusions, hospital stay, shivering and secondary outcomes.