Learning objectives

• Describe the causes, risk factors, and consequences of perioperative hypothermia
• Prevent and manage perioperative hypothermia

Definition & mechanisms

• Perioperative hypothermia is defined as a core body temperature <36.0°C
• Common consequence of anesthesia
• Inability of the body to respond effectively to the multiple causes of heat loss during surgery and anesthesia

Causes

3 phases:

1. Redistribution: Vasodilatation leads to warm blood reaching the peripheries and cool blood from the peripheries entering the core circulation, causing a rapid decline in temperature
2. Heat loss exceeds heat produced from metabolism as the metabolic rate is reduced by 15-40% during general anesthesia, causing a linear decline in temperature

          Sources of heat loss:

• • Radiation
  • Convection
  • Evaporation
  • Conduction

       3. Plateau phase: Heat loss is balanced by heat produced metabolically, mostly due to maximal vasoconstriction

Risk factors

• ASA grade 2-5 (higher grade, greater risk)
• Preoperative temperature <36.0°C
• Combined general and regional anesthesia
• Major or intermediate surgery
• At risk of cardiovascular complications 
• Low BMI
• Diabetic neuropathy 
• Paraplegia
• Severe hypothyroidism

Consequences

• Increased risk of surgical site infection
• Decrease in drug metabolism
• Increased bleeding and transfusion requirements
• Increased risk of cardiac events
• Shivering
• Delayed discharge from post-anesthesia care unit

Prevention & management

Suggested reading

• Rauch S, Miller C, Bräuer A, Wallner B, Bock M, Paal P. Perioperative Hypothermia-A Narrative Review. Int J Environ Res Public Health. 2021;18(16):8749. Published 2021 Aug 19.
• Riley C, Andrzejowski J. Inadvertent perioperative hypothermia. BJA Educ. 2018;18(8):227-233.

Clinical updates

Ji et al. (BMC Surgery, 2024) provide an updated synthesis of perioperative hypothermia management, confirming forced-air warming (FAW) as the most effective and cost-efficient gold standard for maintaining normothermia, reducing infections, cardiovascular events, bleeding, and length of stay. The review highlights newer alternatives, including carbon-fiber resistive heating systems, self-heating blankets, and circulating-water mattresses, which offer comparable efficacy in selected settings. It emphasizes that warming strategies should be individualized based on surgical type, patient risk, and resource availability, rather than relying on a single modality.