One of the most common concerns patients express in the immediate post-op period is that of feeling cold. The perception of comfort is a vital part of the patient experience, and it's hard to feel relaxed or healthy when you're shivering. But it's not just perception ' being cold does, in fact, pose a serious health risk from an infection perspective. Specifically, evidence shows that perioperative hypothermia promotes SSI susceptibility.

Unfortunately, the perception of comfort for doctors and nurses typically comes from a slightly cooler environment, especially during longer procedures when they're working under warm surgical lights. But while surgical staffers focus on doing their jobs in cool comfort, patients may be unable to fight off normal physical heat transfer mechanisms, impairing white blood cell reaction and wound-healing strength.

Read on to understand how keeping your patients warm during the procedure can go a long way toward reducing their risk of infection afterward, and how you can ensure OR team comfort without compromising patients.

What makes patients shiver?
Alteration of normal body temperature is an underestimated, often neglected and iatrogenic threat to the anesthetized patient. There are two kinds of hypothemia, broadly defined as the condition that occurs when body temperature falls below 95'F:

• Primary happens when the body's heat-balancing mechanisms are functioning properly, but the body is subjected to extremely cold conditions.
• Secondary happens when the body's heat-balancing mechanisms aren't functioning optimally.

Primary hypothermia develops after a person falls into an icy lake, for example; the OR alone isn't cold enough to cause an otherwise healthy body to become hypothermic. Secondary hypothermia, however, can occur in relatively mild conditions ' for example, when patients experience vasodilation induced by anesthetics and are then exposed to air-conditioned ORs and recovery rooms. Because patients are under anesthesia, they can't signal staff when they're becoming dangerously cooled. It's up to the OR team to ensure this doesn't happen.

To be fair, there are some benefits of hypothermia, including a decreased metabolic rate, increased circulatory arrest tolerance, some protection against ischemia/hypoxia and a reduced release of excitatory amino acids. Unfortunately, none of these enhances infection prevention; in fact, many of the problems related to hypothermia increase the risk of infection. For example, post-anesthetic shivering and patient thermal discomfort are less dangerous than coagulopathy caused by hypothermia, but they are much more common.1

Mechanisms of hypothermia
Hypothermia undermines a patient's immune system by impairing the production of antibodies, and both clinical and animal studies have demonstrated the dysfunction of the immune response caused by hypothermia. One study demonstrated that mild hypothermia significantly impaired specifically interleukin-2 (IL-2) gene expression in phytohemagglutinin (PHA)-stimulated cultures of human peripheral blood mononuclear cells (PBMC), which are immunocompetent cells, and decreased IL-2 release in all variants of primary PBMC cultures.2 The researchers demonstrated that the direct influence of hypothermia on cytokine expression and release from PBMC is not uniform. Reduction of IL-2 production might play a crucial role in the impairment of immune response in hypothermia.

Further, vasoconstriction reduces the flow of nutrients, reducing wound-healing collagen deposits, and subcutaneous oxygen tension to wounds. Neutrophils ' white blood cells that are part of the first line of infection defense ' synthesize free radicals in the presence of oxygen, which destroys bacteria, but neutrophils have a more difficult time doing so when less oxygen is available.

There are four heat transfer mechanisms for the human body: radiation, convection, conduction and evaporation. Of these, radiation and convection most significantly contribute to heat loss in general, and these are the two biggest threats to normothermia in the OR.3 Patients lose heat through the skin because of vasoconstriction (radiation), and gain cold through being exposed to chilly temperatures (convection).

More reasons to warm patients
If not controlled, these factors put patients at an increased risk for wound infections and slowed post-op recoveries. In one prospective study that split 261 surgical patients into groups of hypothermics and normothermics, 20 patients (7.6 percent) developed surgical wound infections; 18 (11.5 percent) of the 156 hypothermics developed SSIs, while just two (2 percent) of 105 normothermics did.4 Hypothermia, therefore, proved to be a significant independent risk of infection with relative risk of 6.3.

Another study suggests that only a 1.9'C change in core body temperature could triple the risk of wound infection after colon resection.5 In a double-blind examination of 200 patients, researchers found surgical-wound infection in 18 of 96 (19 percent) patients assigned to the hypothermia group (34.7 /-0.6'C), but in only six of 104 (6 percent) of patients assigned to the normothermia group (36.6 /-0.5'C). In addition, the hypothermia group remained in the hospital 2.6 days (about 20 percent) longer than the patients in the normothermia cohort.

Based on this data, the researchers concluded that hypothermia itself could delay healing and predispose patients to wound infections. We also can assume that maintaining normothermia intraoperatively likely decreases the incidence of infection complications in patients undergoing colorectal resection and shortens their hospitalizations. Even though patients undergoing colorectal surgery may be particularly sensitive to hypothermia, we can easily extend these findings to other types of surgery.

Another study found that warming patients before short and "clean" procedures could also reduce the rate of infection.6 Researchers looked at 421 patients having breast, varicose vein or hernia surgery who were randomized to three groups: not warmed, given local warming and given systemic warming. The researchers found 19 wound infections in 139 non-warmed patients (14 percent) but in only 13 off the 277 who received warming (5 percent). The study's authors concluded that warming patients before surgery could reduce surgical site infection and may be an alternative to prophylactic antibiotics, since warming has no known side effects or risks of allergic reactions and resistance.

Warming up to warming
A wide array of patient warming devices, ranging from warm blankets to heated table pads, can help keep patients warm. Recently, forced air-warming systems consisting of an electrically powered heater-blower unit and a patient cover have become popular. These devices effectively reduce radiative and convective heat loss simultaneously, but their usage is limited in that they can't warm surgical area itself. In addition, there are concerns that the bulky covers of fluffy airflow devices may increase contamination.

However, forced air doesn't seem to increase the risk of infection from the patient's skin flora; it actually decreases the bacterial count at the surgery site.7 In a study, 16 consecutive patients undergoing aortic surgery with prosthetic graft insertion were put under a forced-air upper-body blanket. Air samples taken around the surgical site showed that the number of bacterial colonies decreased by a mean 36.4 percent at the end of surgery and the body parts near the exhaust air sites also showed decreases, by a mean 9.5 percent. It's also worth noting that none of these patients developed post-op wound or prosthetic infections during a six-month follow-up period.

Regardless of the warming devices and methods you use, the thermostat is one of your best tools for preventing hypothermia. So who is responsible for setting the OR temperature? When trying to engender a team environment, it's easy to say everyone is responsible for maintaining a climate conducive to patient normothermia. That's a nice theory, but in practice it often means that everyone assumes thermostat control is someone else's responsibility and, as a result, it's ignored or forgotten.

It's also easy to assume that the surgeon should control the thermostat, but as the American College of Surgeons points out, that mentality can be dangerous. The organization strongly recommends that surgeons disabuse themselves of outmoded conceptions about their role in the OR because, given the complexity of modern surgery, they can no longer view themselves as "the captains of their ships."8 But surgeons are still influential in making decisions during the procedure, and are therefore in an ideal position to help you initiate a trial aimed at optimizing room temperature.

To start, you needn't set the thermostat at 75'F throughout the entire procedure. Instead, try raising the room's temperature during the induction of anesthesia, especially for pediatric cases, then lowering the temperature to a level more comfortable for the surgical team once the patient is well covered. After the procedure is completed, raise the temperature for anesthesia emergence. If the patient is exposed, put him in a warm blanket immediately during transport. Staffers can stay comfortable by layering clothes, taking them off and adding them as needed during the procedure.

Effective, inexpensive and generous
A review of the literature on the prevention of surgical site infections published in 2001 concluded that the protective effect of patient warming was well established.9 The authors wrote that "there appear to be few arguments against application of this cheap and safe measure" for reducing surgical site infection rates in general or locally at incision sites. Although a definitive answer may still depend on future studies, there's enough data to justify warming your patients to preempt SSIs.

In contrast, patient satisfaction derived from patient warming may be very easy to determine. Those who never shiver won't miss feeling cold and sick after the procedure. If they felt this way after a procedure at another facility but not after being treated at yours, this could enhance your facility's reputation.

No matter what warming devices you use, patients will notice more warmth when you treat them with kindness. I recommend using a compassionate approach best described in the Buddhist concept of "dana," or act of giving even without seeking appreciation. Whether your goal is to reduce infections or better patient satisfaction, the OR may turn out to be a good place to experience the wisdom of the selfless state and to practice compassionate efforts from the Buddhist's perspective.10

References
1. Frank SM, Fleisher LA, Breslow MJ, et al. "Perioperative maintenance of normothermia reduces the incidence of morbid cardiac events." JAMA. 1997:277:1127.
2. Russwurum S, Stonans I, Schwerter K, et al. "Direct Influence of Mild Hypothermia on Cytokine Expression and Release in Cultures of Human Peripheral Blood Mononuclear Cells." J of Interferon & Cytokine Research. 2002: 22 (2) : 215 -21
3. Schwartz, AJ. "Anesthetic issues related to hypothermia." American Society of Anesthesiologists, 53th Annual Meeting Refresher Course Lectures. Orlando, Fla. 12-16 Oct. 2002;222.
4. Flores-Maldonado A, Medina-Escobedo CE, Rios-Rodriguez HM, et al. "Mild perioperative hypothermia and the risk of wound infection." Arch Med Res. 2001:32(3):227-31).
5. Kurz A, Sessler DI, Lenhardt RA, et al. "Perioperative normothermia to reduce the incidence of surgical wound infection and shorten hospitalization." N Engl J Med. 1996: 334:1209.
6. Melling AC, Ali B, Scott EM, et al. "Effects of preoperative warming on the incidence of wound infection after clean surgery: a randomized controlled trial." The Lancet. 2001: 358(9285): 882-6.
7. Huang JKC, Shah EF, Vinodkumar N, et al. "The Bair Hugger Patient Warming System in prolonged vascular surgery: an infection risk?" Crit Care. 2003:7(3):R13-R16.
8. Russell TR. APSF Newsletter. Winter 2006-2007: 73
9. Kluytmans J, Voss A. "Prevention of postsurgical infections: some like it hot." Curr Opin Infect Dis. 2002 Aug;15(4):427-32.
10. Choi JJ. "Meditation and Chronic pain." In: Wu, WH, Smith, LG, ed. Pain Management. New York: Human Sciences Press, 1987. 216-44.