Self-warming blanket versus forced-air warming blanket during total knee arthroplasty under spinal anaesthesia : A randomised non-inferiority trial

Background: Arthroplasty patients are at high risk of hypothermia. Pre-warming with forced air has been shown to reduce the incidence of intraoperative hypothermia. There is, however, a lack of evidence that pre-warming with a self-warming (SW) blanket can reduce the incidence of perioperative hypothermia. This study aims to evaluate the effectiveness of an SW blanket and a forced-air warming (FAW) blanket peri-operatively. We hypothesised that the SW blanket is inferior to the FAW blanket.Methods: In total, 150 patients scheduled for primary unilateral total knee arthroplasty under spinal anaesthesia were randomised to this prospective study. Patients were pre-warmed with SW blanket (SW group) or upper-body FAW blanket (FAW group) set to 38 degrees C for 30 min before spinal anaesthesia induction. Active warming was continued with the allocated blanket in the operating room. If core temperature fell below 36 degrees C, all patients were warmed using the FAW blanket set to 43 degrees C. Core and skin temperatures were measured continuously. The primary outcome was core temperature on admission to the recovery room.Results: Both methods increased mean body temperature during pre-warming. However, intraoperative hypothermia occurred in 61% of patients in the SW group and in 49% in the FAW group. The FAW method set to 43 degrees C could rewarm hypothermic patients. Core temperature did not differ between groups on admission to the recovery room, p =.366 (CI: -0.18-0.06).Conclusions: Statistically, the SW blanket was non-inferior to the FAW method. Yet, hypothermia was more frequent in the SW group, requiring rescue warming as we strictly held to the NICE guideline. ; Peer reviewed