Intraoperative hypothermia is a common and significant issue during surgical procedures. It refers to an unintended drop in a patient’s core body temperature below normal levels. Maintaining a stable body temperature is important for optimal physiological function during and after surgery.
What is Intraoperative Hypothermia?
Intraoperative hypothermia is defined as a core body temperature falling below 36°C (96.8°F) from the start of anesthesia until the completion of surgery. Normal core body temperature is maintained between 36.6°C and 37.4°C. The body’s thermoregulation system, controlled by the hypothalamus, works to keep this temperature stable through mechanisms like vasoconstriction, shivering, and sweating.
During surgery, this natural thermoregulation is impaired, leading to heat loss. Core body temperature is monitored using specialized probes placed in sites such as the esophagus, bladder, or nasopharynx, providing accurate and continuous readings. This allows medical teams to make real-time adjustments.
Causes During Surgery
Anesthesia significantly impairs the body’s natural temperature regulation. Anesthetic agents, including volatile agents and opioids, reduce the thresholds for vasoconstriction and shivering. This impairment leads to vasodilation, causing warm blood from the core to redistribute to cooler peripheral tissues, resulting in a rapid initial temperature drop of about 1-1.5°C in the first hour of general anesthesia.
Environmental factors in the operating room also contribute to heat loss. Operating rooms are often kept cool, typically between 20°C and 24°C, which can lead to heat loss through radiation and convection from the patient’s exposed skin. Exposed body surfaces and cavities during surgery, especially large incisions or open body cavities like the abdomen or chest, further increase heat loss through evaporation. Cold surgical instruments and the operating table can also contribute to heat loss via conduction.
The administration of cold intravenous fluids or blood products also plays a role in temperature reduction. Each liter of intravenous fluid or unit of refrigerated blood administered at ambient temperatures can reduce an adult’s mean body temperature by approximately 0.25°C. Patient-specific factors, such as age (with babies and elderly patients being more susceptible), and a higher surface-to-volume ratio, can increase a patient’s risk of developing hypothermia.
Consequences for Patients
Intraoperative hypothermia has several negative impacts on patient health and recovery. It increases the risk of surgical site infections (SSI) by impairing the immune system, making patients more vulnerable. Studies show even mild hypothermia increases wound complications, with a core temperature below 35.5°C increasing the chance of SSI.
The condition also affects blood clotting, leading to increased blood loss and a greater need for blood transfusions. Hypothermia reduces platelet function and impairs the enzymes involved in the coagulation cascade. Even a mild temperature drop of less than 1°C increases blood loss by approximately 16% and raises the relative risk for transfusion by about 22%.
Cardiac complications are another serious consequence, including arrhythmias and myocardial ischemia. Hypothermia increases the risk of postoperative cardiac issues by up to 55%. It also slows the metabolism of anesthetic drugs, which prolongs recovery from anesthesia and extends the patient’s stay in the post-anesthesia care unit. Patients often experience post-operative shivering and discomfort, which increases metabolic demands and oxygen consumption.
Prevention and Management
Medical teams employ strategies to prevent and manage intraoperative hypothermia. Pre-warming patients before surgery is an effective approach, often using forced-air warming systems for 30 minutes to increase the temperature of peripheral tissues. This helps stabilize the patient’s thermal reserves and minimizes the rapid temperature drop that occurs early in anesthesia due to heat redistribution.
During the procedure, active warming devices are routinely used. These include forced-air warmers, which circulate warmed air over the patient, and circulating water blankets or electric heating mattresses that provide conductive heat. Passive insulation, such as specialized drapes or cotton blankets, can also be applied to cover exposed body surfaces and reduce heat loss, though active warming is generally more effective.
Warming intravenous fluids and blood products to body temperature before administration is another important measure, particularly when large volumes are anticipated. Each liter of unwarmed fluid contributes to heat loss. Maintaining an appropriate operating room temperature, between 22°C and 24°C, helps minimize radiant and convective heat loss from the patient’s skin.