Preventing Intraoperative Hypothermia with Thermal Heating
Intraoperative hypothermia is a common and potentially harmful complication of surgery, especially for patients undergoing general or regional anesthesia. It is defined as a core body temperature below 36°C, and it can have various adverse effects on the patient’s outcome, such as increased blood loss, surgical site infection, cardiac events, delayed drug metabolism, shivering and prolonged recovery . Therefore, preventing intraoperative hypothermia is a standard of care for all surgical patients, and it requires accurate temperature measurement and appropriate warming devices .
Causes of Intraoperative Hypothermia
The main cause of intraoperative hypothermia is the exposure of the patient’s body to a cooler environment than the normal core temperature of 37°C. This leads to heat loss through radiation, convection, conduction and evaporation. Anesthesia also impairs the thermoregulatory mechanisms of the body, such as vasoconstriction, shivering and behavioral responses, making the patient more susceptible to hypothermia . Additionally, some factors can increase the risk of intraoperative hypothermia, such as long duration of surgery, low ambient temperature, large surgical incisions, infusion of cold fluids or blood products, and preexisting conditions such as hypothyroidism or malnutrition .
Effects of Intraoperative Hypothermia
Intraoperative hypothermia can have detrimental effects on various physiological systems and processes. Some of the most significant effects are:
– Increased blood loss and transfusion requirements: Hypothermia causes platelet dysfunction and impairs the coagulation cascade, resulting in increased bleeding and reduced clotting. It also increases the fibrinolytic activity and reduces the efficacy of blood products. Studies have shown that hypothermic patients lose more blood and require more transfusions than normothermic patients .
– Increased risk of surgical site infection: Hypothermia reduces the oxygen delivery to the tissues and impairs the immune response, making the patient more prone to wound infection. It also decreases the activity of some antibiotics and prolongs the duration of surgery, which are additional risk factors for infection. Studies have shown that hypothermic patients have higher rates of surgical site infection than normothermic patients .
– Increased risk of cardiac events: Hypothermia causes vasoconstriction and increases the systemic vascular resistance, leading to increased blood pressure and cardiac workload. It also alters the cardiac electrophysiology and increases the risk of arrhythmias, ischemia and myocardial infarction. Studies have shown that hypothermic patients have higher rates of cardiac events than normothermic patients .
– Delayed drug metabolism: Hypothermia reduces the activity of some enzymes involved in drug metabolism, such as cytochrome P450. This can affect the pharmacokinetics and pharmacodynamics of some drugs used during surgery, such as anesthetics, analgesics and antibiotics. This can result in prolonged anesthesia, increased side effects or reduced efficacy of drugs .
– Shivering and increased metabolic demands: Hypothermia triggers shivering as a thermoregulatory response to generate heat. However, shivering can have negative consequences for the patient, such as increased oxygen consumption, carbon dioxide production, lactic acidosis, muscle pain and discomfort. Shivering can also interfere with monitoring devices and surgical procedures. Studies have shown that hypothermic patients have higher rates of shivering than normothermic patients .
– Prolonged recovery: Hypothermia can delay the recovery of the patient from anesthesia and surgery. It can cause prolonged sedation, confusion, nausea, vomiting, pain and discomfort. It can also increase the length of stay in the post-anesthesia care unit (PACU) and the hospital. Studies have shown that hypothermic patients have longer recovery times than normothermic patients .
Prevention of Intraoperative Hypothermia
The prevention of intraoperative hypothermia involves two main aspects: measuring and monitoring the patient’s temperature and applying warming devices to prevent heat loss or provide heat gain.
Measuring and monitoring temperature: The patient’s temperature should be measured before anesthesia induction using a reliable method, such as an esophageal or tympanic probe. The patient’s temperature should be monitored continuously during surgery using a core temperature probe, such as an esophageal or bladder probe. The patient’s temperature should be recorded at least every 15 minutes and displayed on a monitor. The patient’s temperature should be maintained above 36°C throughout surgery .
Applying warming devices: The patient’s body should be covered with insulating materials, such as blankets or drapes, to reduce heat loss by radiation and convection. The patient’s head should also be covered, as it accounts for a large proportion of heat loss. The patient’s fluids and blood products should be warmed to 37°C using a fluid warmer to prevent heat loss by infusion. The patient’s skin should be warmed using a forced-air warming device, such as a Bair Hugger, to prevent heat loss by conduction and provide heat gain by convection. The forced-air warming device should cover as much of the patient’s body as possible, without interfering with the surgical site or the monitoring devices. The forced-air warming device should be set to a temperature of 38°C to 43°C, depending on the patient’s temperature and comfort. The forced-air warming device should be checked regularly for proper functioning and safety .
Conclusion
Intraoperative hypothermia is a common and potentially harmful complication of surgery that can affect the patient’s outcome. It can be prevented by measuring and monitoring the patient’s temperature and applying warming devices to prevent heat loss or provide heat gain. The prevention of intraoperative hypothermia is a standard of care for all surgical patients and requires the collaboration of the surgical team.
Bibliography
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