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5 Burning Questions About Patient Warming
Separating fact from fiction on ways to prevent hypothermia and lower infection risks.
Paul Austin
Publish Date: April 25, 2017   |  Tags:   Infection Prevention
preventing hypothermia HOT TOPIC The evidence suggests preventing hypothermia has a positive role to play in preventing surgical site infections.

Warming patients before, during and after surgery will no doubt boost your satisfaction scores and help prevent post-op infections, but debate is heating up about the best and safest way to keep core body temperatures at or above 36 ?C. Some studies even suggest forced-air warming might actually increase SSI risk by acting as a vector or causing unwanted airflow disturbances, but the evidence doesn't conclusively suggest that to be the case. It would take a robust randomized controlled trial or a very large and well-designed observational study comparing the outcomes of warmed and non-warmed patients, while also factoring in other potential causes of infection, to definitively address the risk. That study hasn't yet been done, so let's look at what is known about the warming methods that can lower the risk of post-op infection.

1. Why does warming matter?
Most of the evidence strongly suggests that preventing hypothermia will lead to improved surgical outcomes. Coagulopathy and an inability to fight infection are among the many detrimental effects of hypothermia. Patients might also suffer increased myocardial oxygen demand, which can cause ischemia, especially in shivering patients. But does hypothermia increase risk of surgical site infections? Not all studies show an association, but a vast majority do indicate that a causal link exists, and there is a good theoretical basis for that link. When you combine those two factors, the scale is certainly tilted toward hypothermia causing post-op infections.

2. What's the best way to warm patients?
The most effective way to prevent hypothermia might be to use active and passive methods in combination.

Fluid warming can help maintain normothermia, but is most efficacious when intravenous fluid, especially large amounts, is infused very rapidly.

Warm circulating water mattresses have largely fallen out of favor. The combination of the patient's weight and the mattress's heat can increase the risk of burns. Trials comparing the efficacy of this method with forced-air warming favored forced-air warming.

warmed blankets COMFORT MEASURE Warmed blankets might not be effective in preventing hypothermia, but they sit atop the list of patient satisfiers.

Forced-air warming has been shown to prevent hypothermia across a variety of procedures, from abdominal cases to total joints. Forced-air warming coverlets are disposable, so sterilization doesn't come into play. They're also lightweight, making them easy to open and place over or under patients. Individualized warming gowns provide warming comfort, but could impede access to the surgical site and may have to be replaced with a different coverlet intraoperatively. Patients undergoing pre-op warming appreciate units that let them control temperature settings, but be sure to monitor their use to prevent overheating.

Conductive fiber warming sends heat through blankets and mattresses that are placed over or under patients to effectively maintain normothermia. Care must be taken to prevent burns if a conductive fiber warming mattress is used. These fabrics aren't disposable, so they must be disinfected between uses, which can become a compliance issue in a busy facility.

Warmed blankets sit at the top of patient satisfiers.However, these common comfort measures are essentially ineffective in preventing hypothermia, at least when they're used alone on at-risk patients during extended procedures. Warmed blankets can help decrease cold air currents moving across the patient's skin, but cannot compare to active warming methods in effectively maintaining normothermia.

Given the risks, benefits and costs of each option, conductive fiber warming and forced-air warming are probably the most efficacious choices for limiting risk of post-op infection.


3. Who's most susceptible to hypothermia?
The very young and very old are at increased risk. It's essential to apply active warming methods to the frail, elderly and emaciated patients who have lost insulating tissue mass. Sickle cell patients are also sensitive to cold and could experience a sickle cell crisis if they become hypothermic. Surgeries that expose large areas of the patient's skin to the cold operating room environment or to cold irrigating fluids, as well as procedures lasting longer than 1 hour, demand the use of active warming methods. The ambient temperature in the operating room should be kept between 68 ?F and 75 ?F, according to AORN, but that recommended range is rarely followed by surgical teams who consider their own comfort before the infection risks of patients. Consider actively warming patients during even short procedures if your staff refuses to turn up the heat in the OR.

4. Is pre-op warming necessary?
Most evidence does show that pre-op warming is effective and should be considered for many patients. Patient temperature falls very rapidly during the first few minutes after inducing general anesthesia and this may be a factor leading to the efficacy of pre-op warming. It is also a reason to institute intraoperative warming as soon as possible in the operating room. Logistics might come into play when pre-warming patients; warming units need to be used in the pre-op holding area and, in smaller facilities with limited capital, those units must be moved to the OR to employ intraoperative warming. There's also a downside to getting patients too warm before surgery; increasing the core body temperature above normothermia can increase risk of tachycardia and nausea.

Don't ignore the importance of warming patients in the PACU. Active warming methods are often turned off when the incision is closed, the drapes are removed and the patient is rolled out of the OR. During that critical time patients can experience a rapid decrease in core body temperature, so active warming should continue or resume in recovery until a normothermic temperature is documented.

forced-air warming coverlet\ UNDER COVER Forced-air warming coverlets are disposable, lightweight and easy to apply.

5. Can forced-air warming be blamed for SSIs?
Importantly, this has been proposed as a concern only for patients undergoing total joint replacements. The evidence that I've reviewed shows there is little risk of infection if forced-air warming units are used according to the manufacturers' directions and proper cleaning methods are employed (osmag.net/Qv5NBj). In addition, ECRI Institute, an independent healthcare device research firm in Plymouth Meeting, Pa., conducted a review of existing studies and says there is insufficient evidence to suggest forced-air warming causes SSIs. However, others have called for not using any device in the operating room that blows air.

Three observational studies have addressed the issue: 2 showed forced-air warming did not increase risk of SSIs and 1 study did suggest a link. The study that implicated forced-air warming was conducted over a number of years and showed an increased risk in orthopedic patients. There were, however, a number of problems with how the study was conducted. The researchers did not identify several key factors: patients' physical status; whether patients had been incontinent post-op, which can increase infection risk in total hip patients; and incidence of blood transfusions. The antibiotic regimen employed by the surgical teams also changed over the study period. Should you disregard an efficacious warming method based on the results of a study with questionable methodology? I'm not so sure.

There are other indirect methods that have been used to assess a possible link between SSIs and forced-air warming. One way is to look at bacteria counts on surfaces of forced-air warming units and in a unit's air path. Researchers who have cultured surfaces and air paths have found evidence of bacteria, but a causal link between the bacteria and SSIs has not been made. Another method involves looking at bacteria counts in and around the surgical wound. Five studies have involved placing agar plates around patients in the OR during cases when forced-air warming was used, but none of the results showed a definitive increase in bacteria load on the plates after surgery.

Researchers have also looked at forced-air warming's impact on laminar airflow patterns in the OR during joint replacement procedures. If laminar flow is used, airflow around the surgical table should shoot straight down from the ceiling to the floor without bouncing back toward the wound. Some research has suggested forced-air warming interrupts the ideal laminar airflow, but a definitive link to SSI risk has not yet been shown in rigorous studies. The other issue is that current research assessing forced-air warming's impact on laminar airflow has been conducted in simulated settings without people moving around the OR table and without a door to an outside hallway opening and closing. Those aren't realistic methods for assessing unwanted airflow, so I'm not convinced the studies represent real-life conditions. Effective testing needs to be done in a live operating room setting, but that would be difficult to accomplish.

Some researchers have suggested the use of alternative warming methods during joint replacement procedures until more robust and definitive studies are conducted to assess the safety of forced-air warming, but have stopped short of condemning the latter method. It's not unreasonable to follow that advice, but you must carefully consider the evidence suggesting forced-air warmers cause SSIs.

Ultimately, it's up to you to stay current on the evidence independent researchers publish in peer-reviewed journals and keep an open mind about findings that touch on the safety and efficacy of patient warming. OSM