We know that maintaining normothermia is an important component of the perioperative process for all patients, but it's particularly beneficial — some would say essential — to warm your higher-acuity patients. Here, we answer 4 key questions about warming the challenging patients in your facility.

1 Who needs warming?
American Society of Anesthesiology classification 3 and 4 patients have long been considered the higher-acuity patients you have to treat with the most care. "They have multisystem disease, and they have disease that significantly impairs lifestyle, and that significantly increases the potential for complications associated with surgery and anesthesia," says Shari Burns, CRNA, MSN, EdD, the program director and an associate professor of the nurse anesthesia program at Midwestern University in Glendale, Ariz. "Years ago, those patients weren't seen in outpatient facilities. But today, with cost containment, we more regularly see ASA 3 and 4 patients in outpatient settings." But spotting a high-acuity patient is no longer quite that simple.

"There is an enormous mission creep in ambulatory surgery," says Mark Nunnally, MD, associate professor of anesthesia and critical care at University of Chicago Medicine and the chair of the ASA's Committee on Critical Care Medicine. "The procedures are bigger and the patients are sicker. It's important to understand that, although we may consider some aspects of procedures minor, anesthesia may not be."

As such, you can have ASA 2 patients who present as high-acuity patients, even though they were once considered safe for outpatient surgery. Some patient factors that signal the need for concentrated warming efforts that the experts agree you should take into consideration include:

• older age or very young age;
• smoking status (ex-smokers may still desaturate faster than those who have never smoked);
• presence of chronic obstructive pulmonary disease;
• malnourishment;
• comprised immune system for example, hepatitis);
• presence of cardiac disease, poorly contracting heart, congestive heart failure or coronary artery disease;
• risk of ischemia/poor vascular perfusion; and
• presence of diabetes.

"Because patients with these co-morbidities are not always aware of them, it can be helpful to screen by asking, 'Can you climb a flight of stairs? How about 2?' to get a barometer," says Dr. Nunnally. "I would emphasize that diabetes is a red flag for a lot of potential complications."

2 For what procedures?
Procedure factors are also key to determining acuity. Any procedure with a potential for high exposure to bacteria (and, therefore surgical site infection), or for blood or fluid loss poses a higher risk, says Marek Brzezinski, MD, PhD, an associate professor of anesthesia/perioperative care at the University of California, San Francisco, School of Medicine.

"In these types of procedures — it's been shown in orthopedic surgery that hypothermia comes with increased blood loss — and with sicker patients, we have to be aggressive about warming," says Dr. Brzezinski.

Procedure length is also a concern: anything longer than an hour should include warming efforts as part of the perioperative process.

"Years ago, outpatient facilities didn't have surgeries longer than 2 to 3 hours," says Ms. Burns. "Today, there are total knees with 23-hour stays, and I sometimes see 6 to 8 hours for outpatient cosmetic procedures. Length of surgery has been demonstrated to increase the likelihood of hypothermia. Even with a patient considered an ASA 2, the combination of a long surgery time and anesthetic risk means we must be mindful about continuously warming patients and monitoring patient temperatures."

3 Why does warming help?
While studies aren't conclusive about the benefits of warming, there are preliminary studies clearly showing the risks of hypothermia.

"Simply being cold reduces perfusion to and oxygenation of tissue, leads to vasoconstriction, and increases stress-hormone levels and blood glucose levels," says Dr. Brzezinski. "The cascade of events can lead to negative effects on coagulation, blood pressure and immune-cell performance, and lead to bleeding, arrhythmias and surgical site infections."

We know, then, that the normal temperature of 37 ?C is preferable over something cooler. Although different body parts function at different temperatures — fingers and toes are colder than visceral organs — the human body is finely tuned to maintain the core temperature at 37 ?C.

But from the second a patient is put under anesthesia, her body loses the ability to redistribute heat. And that's the key surgical issue: Over the first hour after induction, all parts of the body settle around an average overall temperature a couple degrees lower. Patient warming is therefore about both preventing heat loss and making up for the temperature drop that comes from redistribution (see "Warming Methods at a Glance").

"To have a patient emerge at 37 ?C, you have to add heat so that they come out with, effectively, more heat energy than when they went into the OR, just to maintain the same temperature reading," says Dr. Nunnally.

Further, when a patient is under anesthesia, she loses her normal physiological response to cold: she's unable to shiver and her blood flow is allowed to flow through unconstricted vessels to the skin, taking heat away from the internal organs. So, when emerging from anesthesia, these responses start to "switch on," says Dr. Nunnally.

"The patient starts shivering, increasing vasoconstriction and consumption of oxygen, which increases the burden on the heart," he says. "A post-op temperature between 35 ?C and 36 ?C may not seem like much of a drop, nor is it bad in a normal person. But it is a stress on patients with cardiovascular issues."

4 What's the best way to integrate warming efforts?
Here are 4 tips from our experts to seamlessly integrate warming into the perioperative process.

• Start in pre-op. Your warming efforts start in pre-op holding, where you focus on the limbs. "If you give somebody enough peripheral heat, the difference in temperature won't be that significant after anesthesia induction and subsequent vasodilation," says Dr. Brzezinski. "The nurses should cover patients with warming blankets. Potentially delayed patients should be actively pre-warmed so that they don't risk losing heat before the procedure. Don't wait until after the procedure to re-warm — it's better to not let the patient get to that lower temperature in the first place."
• Use the timeout. "When the patient arrives in the OR, use the timeout as an opportunity to review procedure duration, exposure, fluid loss and the best way to maintain temperature of the patient," says Dr. Brzezinski. For a long procedure, he uses forced-air warming; if significant fluid loss is expected, he starts the IV fluid warmer; if the patient is fragile, he asks for pads to put on the patient's back and legs.
• Maintain the room temperature. Because the patient loses approximately 1 ?C to 1.5 ?C in body temperature in the first hour, that time is crucial. "I try to ensure the ambient room temperature is not too cold — 70 ?F or lower — for that first hour," says Ms. Burns. "Between the OR ambient temperature and other warming efforts, I can minimize the dip or maintain 37 ?C throughout the procedure."
• Combine methods. For a short, simple procedure, all you may need is forced-air warming. However, for a more complicated procedure in, for example, an elderly patient with cardiovascular issues, "not only will I use an active-warming device, but I'll also warm IV fluids, ask the surgery crew to warm the irrigating fluid, and even use a head wrap and booties," says Ms. Burns. "There's really no single method that prevents hypothermia more than another. Combining methods can sometimes be your best option for maintaining normothermia."