Comparison of Active Prewarming Versus Standard Care to Prevent Perioperative Hyporthermia in Short Outpatient Surgery Under General Anesthesia

The prevalence of accidental perioperative hypothermia is high, ranging from 20 to 90% in the literature, and its prevention still remains a major issue despite the many existing prevention techniques. Perioperative hypothermia is defined as a core body temperature below 36.0 ° Celsius.

The deleterious effects of perioperative hypothermia are well known : increased risk of wound infection, adverse cardiac events and blood loss. Moreover, the pharmacology of anesthetic agents can be altered by hypothermia, which in turn could lengthen the emergence of anesthesia. Patient comfort and satisfaction are also related to hypothermia and the feeling of cold generated.

Thus, hypothermia may be associated with prolonged length of stay in the recovery room and in the hospital for outpatient surgeries. Therefore, hypothermia can indirectly increase the costs of an intervention.

Several techniques have been described for the prevention of perioperative hypothermia. Passive warming is a method used to prevent heat loss such as warm cotton blankets, drapes or plastics whereas active warming consist in adding heat to the body surface using a warming system such as forced-air warming to increase mean body temperature. So, the use of a prewarming, an active warming before induction of anesthesia, could reduce the potential for redistribution, the main mechanism of hypothermia under general anesthesia.

Based on a literature review, the combined use of active prewarming with intraoperative active warming appears to be the most effective technique in preventing hypothermia upon arrival in the recovery room for inpatient surgeries lasting longer than 30 minutes. In the literature, the majority of publications on prewarming focus on surgeries lasting at least one hour, despite strong recommendations to use active warming for surgeries of 30 minutes or more. There is not so much data regarding the efficiency of continuous prewarming for short outpatient surgeries, from the preoperative unit to induction of anesthesia.

This prospective randomized controlled study is designed to evaluate if the combination of a continuous active prewarming of at least 30 minutes (Flex Warming Gown, Bair Paws, 3M) with an active intraoperative warming (Bair Hugger, 3M) would be effective in demonstrating a significant difference in temperature at the end of surgery between the two groups (control and intervention) for short (30 to 120 minutes) outpatient surgeries under general anesthesia. This intervention will be compared to the standard care which are a passive warming preoperatively with an active intraoperative warming.

Inclusion criteria

• ASA Physical Status I to III
• Elective Outpatient Surgery under General Anesthesia
• Surgery Length from 30 to 120 minutes (from induction of anesthesia to extubation)

Exclusion criteria

• Patient refusal or inability to consent
• Neuraxial (spinal or epidural) anesthesia
• BMI over 40 (Flex gown limitation)
• Pregnancy
• Active infection
• Systemic disease which impairs thermoregulation (hypothyroidism or hyperthyroidism, adrenal insufficiency, major burns, para / quadriplegia)
• Medications affecting core body temperature (like levothyroxine)
• Facial surgery
• Use of a fluid warmer