Each patient will be randomly assigned to ambient temperature of 19°C, 21°C, or 23°C. Using a factorial approach, patients will also be randomly assigned to passive insulation or forced-air warming, stratified by the three types of surgery listed below. Group allocation will be based on computer generated codes (randomly permuted block sizes) prepared by Department of OUTCOMES RESEARCH statisticians using SAS statistical software. Allocation of consented patients to designated ambient temperature and forced-air vs. passive insulation will be via a web site that will be accessed by investigators in Bejing about 90 minutes before surgery.