Hypothermia is a frequent perioperative complication. Its appearance can have deleterious effects such as myocardial ischemia or perioperative bleeding. When the negative effects of anesthesia on temperature are aggravated by other factors, such as glycine infusion in transurethral resection, temperature can decrease even more. Once the temperature has decreased, its treatment is difficult. Preoperative warming prevents hypothermia, lowering the temperature gradient between core and peripheral compartments and reducing thermal redistribution. The most recent clinical practice guidelines advocate for active prewarming before induction of general anaesthesia since it is very effective in preventing perioperative hypothermia. However, the ideal warming time prior to the induction of anesthesia has long been investigated. This study aims to evaluate if different time periods of preoperative forced-air warming reduces the incidence of hypothermia at the end of surgery in patients submitted to transurethral resection. This is an observational prospective study comparing routine practice of pre-warming in consecutive surgical patients scheduled to undergo elective transurethral resection between March 2014 and April 2018. Three-hundred patients are included in this study and prewarming will be applied following routine clinical practice. The prewarming time will depend on the time the patient has to wait before entering in the operating theatre. Measurement of temperature will be performed using a tympanic thermometer. Patients will be followed throughout their hospital admission. Data will be recorded using a validated instrument and will be analysed using the statistics program R Core Team.

Maintaining patient's temperature above 36 grades Celsius throughout the perioperative period is challenging. Thus, it is essential to monitor temperature in order to be able to take measures to avoid the appearance of hypothermia. Once the temperature has decreased, its treatment is difficult since the application of heat to the body surface takes a long time to reach the core thermal compartment. Intraoperative warming alone cannot avoid postoperative hypothermia. The application of forced-air warming system during the preoperative period has been shown to be the most effective measure to prevent hypothermia and maintain intraoperative normothermia. However, it would not be efficient to provide a long-time prewarming in short-term surgical procedures. Thus, the ideal warming time prior to the induction of anesthesia has long been investigated.

Due to the searching of optimal prewarming time and the lack of evidence about the efficiency of prewarming in patients submitted to transurethral resection, the conductance of this study is justified.

Inclusion Criteria:

• Patients undergoing elective Transurethral resection under general or spinal anesthesia.

Exclusion Criteria:

• Active infection
• Intake of antipyretics within 24 hours before surgery
• Neuropathy
• Thyroid disorders
• Peripheral vascular disease
• Skin lesions
• History of hypersensitivity to skin contact devices.

This is an observational prospective study comparing routine practice of pre-warming in consecutive surgical patients scheduled to undergo elective transurethral resection between March 2014 and April 2018. Three-hundred patients are included in this study and prewarming will be applied following routine clinical practice. The prewarming time will not be decided by the clinical investigator. Prewarming time will depend on the time the patient has to wait before entering in the operating room.