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Perioperative Nursing Knowledge: Unintended Hypothermia & Forced-Air Warming Systems

By Christopher J. Hudgins


Unplanned patient hypothermia is a preventable complication of surgery that has been identified as one of the top 10 patient safety concerns for perioperative nurses.[1] It is well documented that unless preventative measures are taken, unintended hypothermia can occur in up to 90 percent of surgical patients.[2] Forced-air warming is the most commonly used modality to prevent and treat this complication.[3] Unfortunately, despite the abundance of research on both unplanned perioperative hypothermia and forced-air warming, there is little information regarding nursing knowledge on the topics.


A survey was developed and administered at the 2018 AORN Global Surgical Conference & Expo in New Orleans, Louisiana. The goal of this survey was twofold. The primary objective was to assess nursing knowledge of unplanned hypothermia. The second objective was to identify any knowledge gaps in the use of forced-air warming systems.

Individuals attending an in-booth education session on the exhibit floor during the conference were asked to anonymously complete a questionnaire. Those who agreed were presented with a survey containing 8 questions. The first 3 questions centered on knowledge of unintended hypothermia and were multiple-choice. The remaining 5 questions were about the use of forced-air warming and were true/false. The surveys were collected before the education presentation commenced.

Eighty-six (86) surveys were included in the results. Surveys that contained responses that were illegible and surveys that were not fully completed were excluded. Individuals completing the survey identified their current position as: circulating nurse = 44 (51%), other = 13 (15%), operating room managers or directors = 13 (15%), educators = 7 (8%), registered nurse first assistants = 5 (6%), retired = 3 (3%), and post-anesthesia care unit or pre-op nurse = 1 (1%). Those who marked “other” were instructed to write in an answer. They identified their current position as: charge nurse, clinical supervisor/leader, consultant, data/business analyst and quality manager.


Question: Unintended perioperative hypothermia is most commonly defined as a core body temperature less than_____? Thirty-nine percent (39%) of the respondents answered this question incorrectly. Perioperative hypothermia is defined as any core temperature less than 96.8°F (36.0°C).[2,4]

AORN recommends that “The patient’s temperature should be measured and monitored in all phases of perioperative care.” [5] It’s critical that nurses recognize hypothermia, so they can share this information with the surgical team and initiate appropriate interventions. This is true in all phases of perioperative care. In fact, AORN recommends that “When hypothermia is identified preoperatively, interventions to normalize the patient’s core temperature should be initiated before the transfer to the OR, if possible.”[5]

Question: Negative effects of inadvertent perioperative hypothermia include _____?  Twelve percent (12%) of the respondents answered this question incorrectly. It’s important for all nurses to recognize that patient warming is not just a comfort measure. Studies show that there are numerous negative effects of inadvertent perioperative hypothermia including: increased rate of wound infection, increased mortality rates, coagulopathy, prolonged and altered drug effects, myocardial ischemia, cardiac disturbances, and delayed emergence from anesthesia.[6-14,30]

A meta-analysis of 18 studies that included 1,575 patients showed cost savings associated with maintaining normothermia ranged from $2,495 to $7,073 per patient.[16] By maintaining normothermia, nurses can help prevent devastating outcomes for patients, and help hospitals avoid additional costs.[16]

Question: The most significant contributor to unintended hypothermia in a surgical patient is _____? Seventy-one percent (71%) of the respondents answered incorrectly. Normal core temperature is approximately 98.6°F (37°C).[2] However, core temperature is normally 2-4°C warmer than that of the periphery.[2] Anesthesia induction causes vasodilation which permits the warm blood in the core to mix with the cooler blood in the periphery. That blood circulates and returns to the heart causing the core temperature to drop.[2] Studies show that surgical patients lose approximately 1.6°C during the first hour of surgery and 81% of this temperature drop is due to core-to-periphery heat redistribution.[2,17] Similar events also occur during regional anesthesia.[2]

Thirty-six percent (36%) of respondents thought that operating room temperature was the most significant contributor to unplanned hypothermia. Although room temperature can play a small role, anesthesia is the main culprit of unplanned hypothermia.[2] AORN recommends that “In all phases of perioperative care, the perioperative nurse should develop an individualized plan of care and implement the interventions chosen for prevention of unplanned hypothermia.”[5] Understanding the physiological cause of unplanned hypothermia will help nurses develop appropriate care plans and implement timely interventions.

Question: To help prevent unintended hypothermia, the mattress on the operating room table can be warmed with a forced-air warming unit before the patient enters the room?

Results: False = 48% / True = 52%

Correct Answer = False

AORN recommends that “Forced-air warming devices should only be used with the manufacturer-designated blanket attached to the hose and according to the manufacturer’s instructions for use.” [5] Forced-air warming units and blankets are intended to be used as systems, with the hose properly attached to the disposable warming blanket and in accordance with good practices for operating room sterile technique.

Thermal comfort is a nursing concern when transferring a patient to a cold operating room and surgical table. However, there are solutions that can help address this issue. For example, underbody forced-air warming blankets are specially designed blankets that are placed on the surgical table before the patient enters the room. When the patient transfers to the surgical table, they lay on top of the blanket allowing immediate warming. One study showed that the use of an underbody forced-air blanket during abdominal surgery helped prevent the temperature drop caused by core-to-periphery redistribution.[18] Another solution is a patient warming gown, provided to the patient for preoperative warming, which travels with the patient and allows them to reach the operating room ready to warm with the warming tool built right into the gown. In addition to comfort warming, these blankets/gowns can be used for intraoperative warming.

Questions: A sheet or cotton blanket should be placed between the patient and a forced-air warming blanket to reduce the risk of thermal injury?

Results: False = 71% / True = 29%

Correct Answer = False

AORN recommends “Warming devices should be used…according to the manufacturer’s written instructions for use.”[5] Two commonly used forced-air warming systems do not recommend placing a sheet or blanket between the forced-air warming blanket and the patient.[19,20] In fact, one manufacturer recommends placing the forced-air blanket “directly on top of the patient in contact with the patient’s skin.”[19] The placement of any barrier between a forced-air warming blanket and the patient could possibly reduce the effectiveness of warming therapy. Of course, clinicians should always review the instructions for use for the specific forced-air warming blanket used at their facility.

It’s important to note that forced-air warming systems have been used in the perioperative setting for over 30 years.[21] There have been millions of patients warmed with this modality which is extremely safe when used as designed and in accordance with the operator’s manual and instructions for use.[21]

Question: The safety strap should be placed over a lower body forced-air warming blanket to prevent it from moving during surgery?

Results: False = 79% / True = 21%

Correct Answer = False

AORN does not make a specific recommendation regarding safety straps and forced-air warming blankets. However, there is a recommendation that “Safety restraints…be applied in a manner that safely secures the patient.”[22] The safety restraints should be used for their intended purpose which is to reduce the risk of a patient falling off the surgical table.[22]

It’s important to understand that forced-air warming is a convective warming modality.[23] Patient warming occurs with this modality when warm air flows through perforations in a blanket and transfers heat to the surface of the patient’s skin.[24] The placement of a safety strap or other positioning device over a forced-air warming blanket may reduce or prevent that air flow to a portion of the blanket. This could affect heat transfer to the patient and reduce effectiveness of treatment or cause a patient injury.

One manufacturer recommends “Do not place patient securement devices (i.e. safety strap or tape) over the warming blanket.”[19] Nurses should review the instructions for use for the specific forced-air warming blanket used at their facility.

Question: The forced-air warming unit should not be turned on in the operating room until the patient has been prepped and draped?

Results: False = 42% / True = 58%

Correct Answer = False

The practice of waiting until the patient is prepped and draped before turning on a forced-air warming unit is usually driven by surgeon preference. The time between entering the room and the start of the procedure varies from patient to patient and can be delayed due to difficult intubations, line placement, patient positioning, etc. Thiele states that “Some investigators have expressed concern regarding the potential for forced-air warming systems to increase bacterial contamination of the surgical wound and have advocated not activating the system until after the patient has been completely draped.[25] He goes on to state “There is absolutely no empiric support for this practice. Denying the patient access to active warming – especially during the beginning of the procedure before the application of surgical drapes when heat loss and redistribution are greatest – puts the patient at an increased risk for hypothermia, which can increase the risk of SSI.”[25]

A recent study showed that early initiation of warming in the operating room was important even for patients that were prewarmed in a pre-operative area. The patient’s odds of becoming hypothermic increased 4.9 percent for each minute that passed between the termination of prewarming until initiation of warming in the operating room.[26]

Question: When using a forced-air warming blanket with a head drape, the drape should be tucked tightly around the patient’s head to help prevent heat loss.

Results: False = 63% / True = 37%

Correct Answer = False

AORN recommends “When using a forced-air warming blanket with a head drape, the drape should be vented or placed in a manner that allows the air to flow freely from under the drape and the blower should be turned on whenever the drape is in place.”[5] A head drape that is tucked tightly around an intubated patient’s head could become a fire hazard. If there is a leak around the endotracheal tube or in the anesthesia manifold, an oxygen rich environment could be created under the drape. One study showed that this situation can occur in as little as five to 10 minutes.[27] When this occurs, an ignition and fuel source (commonly present in the operating room during surgical procedures) are all that’s required to start a fire.[28]

AORN also recommends that “Potential hazards associated with fire safety in the practice setting should be identified.”[28] It is widespread practice for the anesthesia provider to deploy the head drape on an upper body forced-air warming blanket following intubation and tube securement. When head drapes are utilized, perioperative nurses should ensure that the warming unit is on and that air can flow freely from under the drape. When a potential fire hazard is identified, such as the head drape not being vented, the perioperative nurse should immediately alert the anesthesia provider and the surgical team.


The sampling size of this survey was small, but the results do indicate knowledge gaps. A surprising number (39%) of respondents could not define unplanned hypothermia and an even higher number (71%) could not identify its cause. This is critical because recognition allows prompt treatment, and knowledge of the cause allows appropriate product selection and possible prevention.

An alarming number (52%) of respondents indicated that the mattress on the operating room table could be warmed with a forced-air warming unit. A smaller, but equally alarming number (37%) indicated that the head drape on a forced-air warming blanket should be tucked tightly around the patient’s head. These are both patient safety issues that could result in severe injury or death.

These gaps in knowledge indicate a need for education on unplanned perioperative hypothermia and product education on forced-air warming systems.


The sampling size was smaller than anticipated. The goal was to have a minimum of 100 completed surveys. Future surveys should include a larger number of respondents from geographically diverse locations to avoid possible bias. The survey was also conducted in a vendor education area on the convention floor. This may not have been a conducive location due to traffic patterns and noise level.


This survey was limited in scope due to time restraints. Additional information that should be included in unit-based surveys and competencies (based on facility policy and specific manufacturer recommendations) include:

  • AORN and manufacturers recommend that forced-air warming blanket not blow warm air directly onto a dispersive return electrode because of the possible risk of patient injury.[19,29]
  • A forced-air warming blanket should not be used over a transdermal medication patch because of the risk for increased drug delivery and patient injury or death.[19,20]
  • It is contraindicated to apply forced-air warming to the lower extremities during aortic cross-clamping because thermal injury could occur to the ischemic limbs.[19,20]


This survey revealed a knowledge gap in unintended perioperative hypothermia. It’s crucial that perioperative nurses recognize unplanned hypothermia and its physiological causes and effects. This knowledge allows appropriate planning and initiation of safe interventions.

AORN recommends that nurses receive education on unplanned hypothermia.[5] Perioperative educators and managers are encouraged to use this survey as a template to conduct a knowledge assessment at their facility. The results can be used to guide the development of educational programs and enhance safe perioperative patient care.

Additionally, AORN offers the Prevention of Perioperative Hypothermia Tool Kit to help educate clinicians and implement evidence-based practices. Many industry partners also offer free professional education courses on unplanned perioperative hypothermia. Finally, nurses are encouraged to contact forced-air warming vendors to request assistance with appropriate blanket selection and ongoing product education.

– Christopher J. Hudgins, BS, ASN, RN, CNOR, is a Perioperative Clinical Specialist Manager in the Medical Solutions Division at 3M Health Care. He is also the President Emeritus and Board Member of AORN Atlanta Chapter 1101. 3M Health Care sells forced-air warming blankets and gowns.


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