Understanding the Dangers of Perioperative Hypothermia

Perioperative hypothermia is more than just a chilly feeling. Patients whose core body temperatures slip below 36°C are at increased risk of surgical site infections (SSIs), cardiac arrhythmias, blood loss, altered medication metabolism and increased pain. It’s not surprising then that they’re also more likely to experience longer recoveries from surgery and take more time to meet discharge criteria. After noticing that a significant number of our surgical patients suffered post-op complications, we decided to investigate the root cause of the issue and zeroed in on inconsistent temperature measurement practices in use throughout each phase of surgical care as a possible cause for the post-op problems.

These various forms of temperature-taking included oral, rectal, temporal artery, esophageal and pulmonary artery. Each of these techniques displayed varying reliability, which created inconsistency in our ability to identify hypothermia in patients and put a plan in place to prevent it from happening. We decided to modify our core temperature monitoring system, which led to an improvement in patient warming protocols through all phases of surgical care.

Clinical and environmental factors can affect patients’ abilities to regulate their body temperatures. Anesthesia induction causes vasodilation and inhibits the hypothalamus, which is responsible for thermoregulation and decreases the threshold for shivering and cold-induced vasoconstriction. Peripheral body temperature (extremities) is approximately 2°C to 4°C cooler than core body temperature (head and trunk). Vasodilation from anesthesia creates a phenomenon of core and peripheral blood blending, resulting in a shift of thermal energy from the core to the periphery. During this redistribution hypothermia, a patient’s core temperature can rapidly drop by 0.5°C to 1.5°C during the first hour after induction of anesthesia. 

Active prewarming during the preoperative phase of care raises the peripheral body temperature and narrows the temperature gradient between the peripheral and core body compartments, thus minimizing redistribution hypothermia. Prewarming the patient significantly increases the likelihood of maintaining a normal core temperature after anesthesia induction. The literature states that providers should actively prewarm patients between 10 and 30 minutes before induction. Care should be taken to avoid overheating patients, which could lead to sweating and a paradoxical effect on body temperature.

It’s important to identify patients who are susceptible to the chilling effects of anesthesia during the pre-op assessment. Patients are at greater risk of experiencing perioperative hypothermia due to advanced age, systolic blood pressure less than 140mmHg, female gender, low BMI, high-level spinal blocks, longer procedural and anesthesia times, body surface exposure during surgery and history of autonomic dysfunction.

Heat loss due to the surgical environment occurs due to four major contributors: radiation, convection, conduction and evaporation. The most common type of heat loss during surgery is radiation, which occurs as the patient’s own body heat is transferred into the cooler environment. Heat loss through convection is the second most common type and occurs when the layer of air or moisture directly adjacent to the patient’s skin is lower than their body temperature. This can occur when cold prepping solutions are applied or due to the constant movement of cool ambient OR air. Conduction is the transmission of heat onto surfaces that touch the patient and evaporation is the process of losing heat through the dispersal of fluids on the skin such as through perspiration. Consider the combined impact of cold OR temperatures, the application of prepping solutions, administration of anesthesia and exposed skin and you’ll quickly realize why applying active warming measures to combat each of these contributors to hypothermia is essential. 

As you can see, the risk factors of perioperative hypothermia go far beyond simple patient comfort. Yes, a cold patient is a cranky one, but a hypothermic patient is at increased risk of SSIs, cardiac arrhythmias, blood loss, altered medication metabolism and increased pain perception — factors that can delay discharge. 

We understood that failing to maintain normothermia can cause numerous complications and realized the inconsistency of our facility’s temperature measurement practices created the possibility of hypothermia going undetected in a significant number of patients. 

Staff at different points of the perioperative process would use various temperature reading methods: oral, rectal, temporal artery, esophageal and pulmonary artery. In fact, we identified instances of inconsistent temperature taking throughout the surgical encounter for the same patient. Each of these methods had varying reliability, which created inconsistency in our ability to determine which patients were hypothermic and how big of an issue we faced in ensuring staff applied active warming methods appropriately and properly. 

The core temperature is the most accurate temperature source with less variation caused by environmental factors. In the past, the use of invasive devices was the only option for capturing core body temperature readings, a factor that limited their use and availability for relatively minor surgical procedures. Our goal was to implement a consistent, reliable and easy-to-use non-invasive method of recording temperatures in all phases of surgical care. We decided to implement a standardized monitoring system after trialing a non-invasive core temperature measurement device that hospital stakeholders approved for purchase. The device utilizes a single-use sensor that sticks to the patient’s forehead and quickly delivers an accurate temperature reading. It can be used through each phase of care, allowing for clinical efficiency and accuracy. 

Nursing and anesthesia staff members from all perioperative settings received training on using the temperature-taking device. Implementation of the standardized program was successful after providers completed the learning curve, troubleshooting took place and validation of the initial data collection was obtained. Initial findings showed unintended hypothermia was a much more significant issue than we previously thought; informal data gathering suggested 45% of our patients were hypothermic.

Staff were unsure whether to trust the volume of hypothermic patients initially detected with the new device, as it recorded temperatures that were much lower than values recorded with traditional temporal artery probes. The literature reports that temporal artery values are an acceptable reflection of core temperature in the normothermic patient, but unreliable for temperatures outside the normothermic range.

Staff appreciate the ease with which they can transfer data from the non-invasive devices into our hospital’s electronic medical record. The collection of accurate and standardized temperature readings provides an easier way to conduct audits that focus on how compliance with temperature-taking protocols and active warming practices impacts rates of hypothermia among surgical patients.

Our initial investigation into the higher-than-expected rates of surgical complications and the collection of accurate temperatures along the perioperative pathway alerted us that our patient warming protocols needed to be standardized. Every patient in pre-op is now given a forced-air warming gown; they feel more involved in their care by being able to control the temperature of the gown and adjust it to their level of comfort.

The constant flow of warm air circulating through the gown elevates peripheral body temperature, not core body temperature. This active pre-warming technique reduces the temperature gradient from core to peripheral areas. When patients arrive in the OR, a forced-air warming blanket and other modalities are used to maintain their core body temperatures and reduce heat loss. Postoperatively, warming gowns are reapplied and utilized until patients meet criteria for discharge from the recovery unit.