Hot Takes on Patient Warming

We know that pre-operative warming can help prevent hypothermia, which will lead to improved surgical outcomes, fewer surgical site infections, and much happier patients who won't miss shivering and chattering teeth. We're less certain about the ideal warming protocols. How long should you warm patients in pre-op? At what temperature should you warm the blankets that will warm your patients? Is forced-air warming really an infection risk? Luckily, there's no shortage of research on patient warming. Let's look at 5 recent studies for some guidance.

1. No patient can live on intraop warming alone. Many believe that warming a patient during surgery is enough to prevent hypothermia, but intraoperative warming alone isn't nearly as effective as actively warming patients both before and during surgery. A June 2018 study in the Canadian Journal of Anesthesia (osmag.net/a7rHME) compared 2 groups of patients, each of which was warmed during the case with a forced-air warmer (FAW). One group received a minimum of 30 minutes of pre-op FAW, while the control group received a warmed blanket upon request.

Prewarmed patients had less hypothermia than those who were only warmed during surgery. The key finding: Combining prewarming with intraop warming is more effective at maintaining normothermia than warming in the OR alone. While warming patients before and during surgery is no guarantee against redistribution hypothermia, researchers conclude that "their combined application results in greater preservation of intraoperative normothermia compared with intraoperative forced-air warming alone."

2. Does FAW increase the risk of infection? While we're on the subject of forced-air warming, let's address the controversy surrounding it: the claim by some that FAW increases SSI risk by blowing airborne particulate bacteria into the surgical field and depositing them deep into patients' joints during total knee and hip replacements.

Research says it's a claim without merit. A December 2017 literature review in Surgical Technology International found no evidence of an increased SSI risk from FAW (osmag.net/Kj2QPw). Researchers, who reviewed 8 studies reporting outcomes from nearly 2,000 patients, were unequivocal in their conclusion: "There is no current evidence in the orthopaedic literature that forced-air warming devices translate to increased SSIs," they wrote. "Accordingly, these devices should continue to be used for the maintenance of intraoperative normothermia."

The Food and Drug Administration likewise encouraged the continued use of forced-air warming blankets in surgery. In an August 2017 letter to healthcare providers (osmag.net/XaCZr8), the FDA sought to reassure surgeons that it was OK to use FAW devices. The FDA was concerned that many doctors and surgical facilities were avoiding their use in reaction to the 2,000-plus lawsuits patients filed against 3M, maker of the hugely popular Bair Hugger warming system. The lawsuits claim 3M concealed evidence that the device actually increases infection risk by spreading contaminants with blown air and waste heat.

Fear not, said the FDA in its letter: "After a thorough review of available data, the FDA has been unable to identify a consistently reported association between the use of forced-air thermal regulating systems and surgical site infection."

The International Consensus Meeting on Periprosthetic Joint Infection recognized a theoretical risk of SSI associated with forced-warming blankets, but its 400 delegates from 52 countries were quick to add that "no studies have shown an increase in SSIs related to the use of these devices."

Based on my reviews, there's little risk of infection if you use FAW devices according to the manufacturers' instructions and properly clean them.

3. Even a little warming is better than none at all. Is it worthwhile to prewarm in a busy facility where patients spend little time in pre-op? Absolutely, per a review published in the Journal of PeriAnesthesia Nursing (osmag.net/PoUt9K). While 30 minutes of prewarming is thought to be optimal, even shorter periods of warming can help stave off hypothermia, researchers found. The review analyzed 14 studies and concluded that prewarming for even just 10 minutes can significantly reduce the rate of hypothermia.

4. At what temperature should you set blanket and solution warming cabinets? There's some debate as to what temperature you should set blanket and solution warming cabinets. Researchers recommend warming cotton blankets in cabinets set at 200 ?F or less to improve thermal comfort without compromising patient safety.

For the study (osmag.net/mTC6zC), published in the December 2013 Journal of PeriAnesthesia Nursing, 20 healthy volunteers each received 2 blankets — 1 rolled and 1 folded from warming cabinets set at 130 ?F or 200 ?F. Rolled blankets were applied to the neck and folded blankets to the back. Researchers obtained skin temperatures and thermal comfort at fixed time intervals. Skin temperatures from blankets in the 200 ?F cabinet were greater than those in the 130 ?F cabinet, but no skin temperatures reached temperature or duration thresholds for dermal injury.

ECRI Institute, a suburban Philadelphia medical device testing lab, recommends that we limit temperature settings on blanket warming cabinets to 130 ?F and on solution warming cabinets to 110 ?F. Temperature above this level, says ECRI, "unnecessarily increases the risks of burns while providing no additional clinical benefit."

AORN likewise recommends a limit of 130 ?F for blankets. For solutions, AORN recommends we follow the solution manufacturer's specifications. In 2014, ECRI recommended a blanket limit of only 110 ?F because solutions were usually warmed in the same cabinets as blankets, and the lower temperature eliminated the serious burn risk of overheated solutions. ECRI increased its blanket recommendation to 130 ?F because many of today's warming cabinets have independent heating chambers, so you can heat solutions separately from blankets.

5. The longer the patient is warmed in pre-op, the warmer she'll be in post-op. Is a self-warming blanket — its warming pads are activated as soon as you remove the blanket from its packaging and expose it to air — applied in pre-op more effective at reducing post-op hypothermia than FAW during surgery? A study published in Orthopaedic Nursing claims it is.

In the study (osmag.net/9BpBGw), researchers broke patients who underwent total joint procedures (hips and knees) into a forced-air (FAW) group and a self-warming (SW) blanket group. The FAW group were only warmed in the OR after the surgical site was prepped. The SW group, on the other hand, was warmed preoperatively for nearly an hour and a half before the induction of anesthesia. Researchers measured patients' temperatures preoperatively upon arrival and again post-operatively.

They observed post-op hypothermia in 31.3% of the FAW group, compared to just 14% of patients in the SW group. This led researchers to conclude that the longer a patient is warmed pre-op, the warmer that patient's temperature will be post-op. But the study also concluded that "early warming with SW blankets was more effective than FAW devices [intraoperatively] in the prevention of post-op hypothermia in elective [hip and knee arthroplasty]." OSM