Patients lose body heat during surgery because operating rooms are kept cool, the patient is unclothed, anesthetics inhibit the body’s ability to regulate a normal core temperature and the patient is often transfused with ambient temperature fluids. For unwarmed patients undergoing long surgical procedures, data from this study published in Anesthesiology shows that intraoperative unintentional heat loss can lead to hypothermia. A summary of the research by ASA noted, “The study found that 64 percent of surgical patients became hypothermic, with core temperatures below 36°C during the first hour of anesthesia.”
Even with active warming before and during a longer surgery, core body temperature will decrease during the first hour of the procedure. If the patient is actively warmed before and during the surgery, they are less likely to experience a more pronounced core temperature drop. Patients undergoing longer cases are more likely to return to normothermia by the end of the procedure if kept properly warmed.
Why the surgical patient needs to be kept warm during the entire perioperative episode
The previously referenced study analyzed the intraoperative core body temperature patterns of almost 59,000 surgical patients. All the patients were actively warmed with forced air warming (FAW). The threshold for hypothermia is commonly considered to be a core body temperature below 36 degrees Celsius (96.8 degrees Fahrenheit). The study revealed that, even with the use of forced air warming (FAW), 64% of the patients became hypothermic during the first hour under anesthesia, almost half stayed hypothermic for more than one hour, and 20% stayed hypothermic for more than two hours.
Recognizing that common perioperative interventions for keeping patients warm were inadequate, the Association of periOperative Registered Nurses (AORN) updated their Guideline for Prevention of Hypothermia in 2019 to include evidence-based practices for assessing every patient before surgery to determine the best warming method(s), and monitoring of the patient’s body temperature during and after surgery.
Keeping patients warm pre-surgery, intra-surgery, and post-surgery is now the standard-of-care, because perioperative hypothermia (PH) is linked to excessive bleeding, delayed postoperative recovery, increased risk of surgical site infection, cardiac events, and the need for blood transfusions. Even mild PH (1-2 degrees C/2-3 degrees F) can prolong the patient’s hospital stay by up to 20%.
How to keep the patient warm during the perioperative session
According to the previously noted updated AORN guidelines, every surgical patient should be assessed pre-operatively to determine which warming method, or combination of methods, will work best for the patient throughout the perioperative period. Factors to be considered when choosing a warming device should include the patient’s size, location of the IV, type of surgery, expected duration of the surgery, comorbidities, and other risk factors unique to the patient.
This 2021 review study recommends that, “Preoperative hypothermia prevention and identification should be started 1–2 hours before anesthesia administration.” This helps to prevent shivering after clothing removal and helps reduce the patient’s stress level. It also inhibits redistribution temperature drop (RTD) after the induction of anesthesia. Since it is likely that active warming stopped while transferring the patient to the operating room (OR), the AORN guidelines recommend using an active warming device as soon as the patient arrives in the OR, before anesthesia induction begins.
Along with anesthesia, the temperature of the operating theater is also a major factor in the patient’s loss of body heat. Surgeons working under hot lamps wearing surgical scrubs and layers of personal protective equipment may not be aware of how cold the OR is for a patient with nothing but a surgical drape covering them. The ambient temperature in the OR should not be kept at less than 21 degrees Celsius (69.8 degrees Fahrenheit)–and ideally between 23 to 26 degrees Celsius (73.4 to 78.8 degrees Fahrenheit)).
During surgery, the patient’s temperature should be checked at least every 15 minutes so a warming device can be activated as needed to maintain normothermia. The best sites for monitoring a patient’s temperature are the pulmonary artery, distal esophagus, nasopharynx, or tympanic membrane.
Postoperative care should include warming to attain or maintain normothermia. In addition to the potential clinical complications of inadvertent PH, patients who wake up from surgery hypothermic are shivering and uncomfortable. AORN recommends continuing temperature monitoring post-surgery with passive or active warming methods as needed until the patient’s core body temperature is stabilized.
Commonly used warming methods
Nurses and anesthetists have the sometimes difficult task of choosing, installing, and monitoring various methods and devices to maintain normothermia. The standard passive measures for keeping patients warm include eliminating skin exposure by covering the patient in warmed cotton blankets, increasing the room’s ambient temperature, and putting socks on the patient. The most commonly used active warming method is forced air warming (FAW). While more effective than passive methods, active warming devices can cause burns on the skin if used incorrectly.
A forced air warming (FAW) device uses convection to warm the patient. Electric coils in a heat generator pull in and warm the air. Then a blower sends the warm air through a tube to a disposable perforated air blanket that covers the patient. Warm air escapes through the holes in the blanket to warm the patient. The blanket does not have to touch the patient’s skin to be effective. There is controversy and conflicting study results about whether FAW devices increase the risk of surgical site infections or the bacterial load in the surgical environment. They do contribute noise and excess heat to the patient’s environment.
There‘s a better way
Encompass Group, LLC has a better alternative to commonly used passive and active warming methods.
For passive warming, Thermoflect® Heat Reflective Technology® products are simple, safe, and effective. They begin working from the moment they are applied to bank heat and help prevent redistribution temperature drop (RTD) and use science instead of electricity so they are the most efficient and cost-effective pre-warming products available. From the moment you apply them, they begin to bank heat and help prevent redistribution temperature drop, the reduction in core temperature due to the redistribution of blood from the core to peripheral areas to make up for heat loss from the skin.
For conductive warming, The Nova™ system actively warms patients without the complications of forced air and with minimal risk. This thin flexible heater uses a novel carbon veil technology, the proven technology used in car seat heaters, in a disposable medical product. Carbon veil technology banks patient heat even when unpowered.
When powered, Nova™ actively warms the patient without air movement, without noise, and without generating excess heat into the room. Upper, lower, and full body variations allow for full coverage of the patient’s body as needed, without interfering with the surgical site.
The Nova™ is easy to apply and keep on the patient. Caregivers appreciate the easy-to-use single-button controls, adjustable temperature settings, and multi-blanket controller. And it delivers consistent and effective conductive warming with a small-profile power cable connection, not a bulky hose.
The Nova™ system can keep the patient warm through every stage of the perioperative process.
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