PRE-OP WARMING If the patient starts off surgery with a higher core temperature, it might not drop as low during induction.

You apply warm cotton blankets and actively warm patients before, during and after surgery without a second thought to maintaining normothermia. But there's more than you might think that goes into keeping patients' core body temperatures above 36 ?C. Here are a 6 things you might not know about hypothermia prevention.

1. FDA did not endorse forced air
Fearful that hospitals and surgical centers would stop warming patients altogether over concerns about the safety of forced-air warming (FAW), the FDA sent healthcare providers a letter (osmag.net/4ezKYS) in August reiterating the importance of actively warming surgical patients with "thermoregulation devices." Because the letter mentions forced air by name, it was easy to misinterpret the letter as an FDA endorsement of FAW. "The FDA continues to recommend the use of thermoregulating devices (including forced air thermal regulating systems) for surgical procedures when clinically warranted," reads the letter.

In truth, the FDA was responding to a growing number of joint replacement surgeons who have discontinued warming their hip and knee implant patients over concerns about the risks of infection due to airborne contamination from FAW.

2. About those forced-air lawsuits
3M is facing more than 4,000 product liability claims that it knew about the potential increased risk of joint infections linked with the use of Bair Hugger during hip and knee replacement surgeries. The plaintiffs claim that the forced-air system circulated airborne contamination around the surgical field, thus causing their deep-joint infections.

The federal court overseeing the lawsuits has ordered 2 knee replacement infection lawsuits prepared for a bellwether trial that could begin as early as April 30, 2018. (A bellwether trial is a small consolidation of lawsuits, taken from a larger group of similar cases, to be tried first. The bellwether trial is like a practice run to help anticipate the results of the future similar cases.) The 2 cases were filed on behalf of individuals who developed deep-joint infections allegedly related to the use of the Bair Hugger during their total knee replacements.

3M denies that the Bair Hugger is a vector for transporting germs, noting that its warming blanket machine has been used in more than 200 million surgeries since 1987. The plaintiffs could have a hard time linking FAW to SSIs because none of them has definitive physical proof that the blower swept bacteria-laden particles off of the floor and deposited them into their wounds during surgery. Instead, they hope to rely on expert testimony and computer simulations to try to prove that the Bair Hugger disrupts an operating room's normal downward airflow that's meant to keep bacteria on the floor.

The FDA has been "unable to identify a consistently reported association between the use of forced-air thermal regulating systems and surgical site infection."

Paul Austin, CRNA, PhD, a professor at Texas Wesleyan University in Fort Worth, Texas, who has no financial interest in any patient warming technology and has analyzed FAW's impact on post-op infection risk, says there's no direct association. Dr. Austin questions the validity of research that assesses FAW's impact on infection risk that was conducted in simulated settings, which aren't realistic methods for determining how blowing units impacts laminar air flow around the OR table as surgical team members move around the room.

Dr. Austin also says the study that's often cited by FAW opponents compared infection rates in procedures involving forced-air warming and conductive heating mattresses and showed that infection rates decreased when FAW was not used. But Dr. Austin says the study fails to mention what proportion of patients in each group had risk factors — including physical status, incontinence and antibiotic regimens — that made them more susceptible to SSIs. "Those factors are typically noted in Table 1 of studies," points out Dr. Austin.

COVER UP Forced-air warming is the target of thousands of lawsuits claiming that it caused post-op infections in total joint patients.

3. Body temperature drops quickly
Core body temperature drops significantly in the first 20 to 30 minutes of anesthesia time and rebounds in actively warmed patients, so it might be more challenging to maintain normothermia during shorter surgeries. "Surgical teams understand that hypothermia is an issue, but they don't appreciate how fast core temperatures drop in that short period of time," says Dr. Austin. "Even when active rewarming is used, you don't have the time to reestablish normothermia."

Nearly two-thirds of surgical patients become hypothermic during the first hour of anesthesia, says Daniel Sessler, MD, the Michael Cudahy Professor and Chair of the Department of Outcomes Research at the Cleveland (Ohio) Clinic. Although one study reported that 10 minutes of pre-warming is sufficient, Dr. Sessler says to stick with 30 minutes of active warming in pre-op. The likelihood that patients will become hypothermic during the initial phase of surgery points to the importance of pre-op warming and instituting intraoperative warming as soon as possible, says Dr. Austin. "If the patient starts off surgery with a higher body heat content, it might not drop as low during induction," he explains.

4. Raising the OR thermostat
You should keep the ambient temperature in the OR between 68 ?F and 75 ?F, according to AORN recommendations. Dr. Sessler recently conducted a study to find out how much of an impact raising the thermostat has on patient warmth. "It makes surprisingly little difference," he says. "It's such a small effect that it's not worth it. It just makes [surgical team members] miserable."

Dr. Austin agrees that you can't crank up the heat high enough to make a significant difference in patient warming, but still recommends keeping the ambient room temperature within the AORN-recommended range during physically demanding specialties such as orthopedics when surgeons might want the room cooler for their own comfort. "For those cases," says Dr. Austin, "think about investing in cooling vests for overheated surgeons."

5. How to measure temperature
Dr. Sessler says the accuracy required when measuring a patient's core body temperature during surgery is up for debate. However, he says, the inaccuracy between actual core body temperature and the reading obtained should not exceed 0.5 ?C, which is the smallest difference that has been shown to be associated with hypothermia-induced complications.

Temperatures measured on the skin's surface are about 2 ?C lower than core, according to Dr. Sessler, who says more accurate core body temperature readings are obtained at the tympanic membrane, pulmonary artery, distal esophagus or nasopharynx.

Dr. Sessler says that when a patient is intubated, a nasopharyngeal probe to measure temperature is the way to go. Why? The probe is inserted through the nostril and into the back of the throat, allowing for an extremely accurate temperature reading. However, take note of the probe's position. Dr. Sessler says it needs to be inserted 10 to 20 centimeters down the nostril, which is farther than most clinicians think.

Keep in mind that Surgical Care Improvement Project (SCIP) Core Measure 10 requires you to actively warm patients of all ages who undergo procedures under general or neuraxial anesthesia that last an hour or longer. You must also record at least 1 normothermic body temperature reading (36 ?C) within 30 minutes immediately prior to or 15 minutes immediately after anesthesia end time.

6. Heat from above + below
If you combine conductive heat that rises up through a thin mattress with forced air that blows over the body, you'll warm patients more efficiently than if you used either method alone, says Dr. Sessler. Although most outpatient procedures don't require 2 forms of heating, consider using both over- and under-body systems during lengthier procedures, he adds. OSM