Horn 2012.

Methods	Design: RCT Operative phase: preoperative Withdrawals: none Setting: 1 centre (Germany) Sample size: 200 Funding: no funding or competing interests declared
Participants	Age (mean): 49/55 years Gender (M/F): 61/139 ASA grade: I ‐ II Surgery type: elective (laparoscopic cholecystectomy; inguinal hernia repair; breast surgery; minor orthopaedic surgery; and ENT surgery) Surgery duration: < 2 hrs (60/65 mins) Anaesthesia type: general
Interventions	Intervention (ABSWa): n = 52 Forced‐air warming (Level 1 Snuggle Warm Upper Body Blanket; Smiths Medical, Rockland, MA, USA) for 10 mins preoperative, set at 44ºC during the warming period Intervention (ABSWb): n = 43 Same (forced‐air warming) for 20 mins preoperatively Intervention (ABSWc): n = 50 Same (forced‐air warming) for 30 mins preoperatively Body area covered: whole body Control: n = 55 Passive insulation with a single cotton blanket Co‐interventions: all IV fluids administered were warmed to 39ºC. In all groups, participants were covered with cotton blankets intra‐ and postoperatively Room temperature: 23ºC
Outcomes	Shivering (4‐point scale) Thermal comfort (sensation) (VAS 0 ‐ 100) Blood loss (no data provided) Fluids infused (no data provided) Other outcomes reported not included in the review: % participants who became hypothermic Tolerance with prewarming Arterial blood pressure Heart rate
Notes	Comparison 1 The 3 intervention groups have been merged in the analysis, giving 1 single comparison Comparison 3
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Randomization was performed by rolling a modified dice with 4 faces, each representing 1 of the 4 treatment groups
Allocation concealment (selection bias)	Unclear risk	No
Blinding of participants and personnel (performance bias) All outcomes	Unclear risk	It was not possible to blind participants or personnel due to the nature of the intervention
Blinding of outcome assessment (detection bias) All outcomes	Low risk	After the pre‐warming procedure, participants were transferred to theatre. General anaesthesia was induced by an anaesthetist blinded to the pre‐warming randomization. Shivering was assessed by an independent blinded observer
Baseline comparability of groups	Low risk	To a high extent according to Table 1
Co‐interventions equal between groups	Low risk	Yes
Incomplete outcome data (attrition bias) All outcomes	Low risk	All participants were analysed
Selective reporting (reporting bias)	Unclear risk	We did not have access to the protocol, therefore we cannot exclude risk of selective reporting with the information provided
Other bias	Low risk