By Kelly M. Pyrek
Maintaining normothermia of the surgical patient is part of the prevention of surgical site infections, and a study by Steelman, et al. (2013) found that perioperative hypothermia was among the top patient safety issues identified by perioperative nurses. In this study, AORN members employed in ambulatory and hospital settings (N = 37,022) received an electronic survey; of the 3,137 returned surveys that contained complete information, 966 respondents (30.8 percent) identified prevention of hypothermia as a high priority. However, debate over the safety of forced-air warming systems continues, and clinicians should first and foremost consider all sides of the argument when making product evaluation and purchasing decisions. Alternatives to forced-air warming include direct-conduction fluid warming systems and systems that use conductive fabric technology. Conductive fabric systems do not require the use of a disposable blanket, which can help reduce waste and keep costs down.
As Wu (2013) explains, " Various types of forced-air warming devices are available from different manufacturers. These warming systems generally consist of a power unit that generates warmed air and a fan that blows the warmed air through a hose into a disposable blanket that has direct contact with the patient. Manufacturers make blankets classified for intraoperative, post-anesthesia care unit, adult, and pediatric use, and the blankets vary in size and shape according to the body part to be covered (e.g., upper body, lower body, full body). Special designs are also available for certain types of surgery (e.g., cardiac surgery blankets)."
Wu (2013) adds, "The first step in warming a patient with forced air is to choose the appropriate device." A study by Brauer, et al. (2009) showed that the design and quality of the blanket may be the key factor that determines the efficacy of a forced-air warming system. Wu (2013) advises, "A well-designed blanket should have an even temperature distribution. The smaller the temperature gradient between the highest and the lowest temperatures provided by the blanket, the better its efficiency."
While blankets pose a risk for fire and burn injuries to patients, the potential risk for contamination of the surgical site is the main risk associated with forced-air warming systems. As Kellam, et al. (2013) state, "The potential that forced-air warming systems may increase the risk of surgical site infections (SSIs) by acting as a vector or causing unwanted airflow disturbances is a concern to health care providers." To investigate this potential, the researchers examined 192 evidence sources in the literature to determine whether forced-air warming devices increase the risk of SSIs in patients undergoing general, vascular, or orthopedic surgical procedures. Of the 15 evidence sources that met the inclusion criteria, the researchers found that most sources indirectly addressed the issue of forced-air warming and only three studies followed patients who were warmed intraoperatively with forced-air warming devices to determine whether there was an increased incidence of SSIs. As Kellam, et al. (2013) note, "All of the sources we examined contained methodological concerns, and the evidence did not conclusively suggest that the use of forced-air warming systems increases the risk of SSIs. Given the efficacy of these devices in preventing inadvertent perioperative hypothermia, practitioners should continue to use and clean forced-air warming systems according to the manufacturer's instructions until well-conducted, large-scale trials can further examine the issue."
Wu (2013) states that it is "unclear whether forced-air warming devices pose a risk for contamination in the OR. A study by Albrecht, et al. (2009) indicated that there is questionable design in the blowers of some forced-air warming systems that may lead to internal contamination of the equipment itself and emission of airborne contamination into the OR. Even though contamination was found inside the forced-air warming devices, these researchers were not able to provide evidence of a link to surgical site infection rates. Another study showed that warm-air convection heaters produced a small increase in the number of colony forming units in ultra-clean air ORs (i.e., laminar flow rooms), but the levels most likely were not clinically significant (Tumia, et al. 2002) A non-randomized controlled study by Huang, et al. (2003) indicated that use of a forced-air warming system did not increase bacterial OR air contamination and was unlikely to adversely affect the surgical field. Further study is needed on this issue; however, manufacturers recommend using single-use blankets so that the risk of potential contamination of surgical sites from inadequately cleaned, reusable blankets is reduced."
John, et al. (2014) observe that "Forced-air warmers operate by distributing heated air generated by a power unit through a specially designed downstream blanket resulting in heat transfer to the covered body surface. This is the most commonly tested body warming modality and is unsurprisingly associated with significantly higher postoperative core temperatures when compared with patient control groups where no warming was used. The dual benefit of transferring heat to the body and reducing heat losses from the skin under the air warmer accounts for this finding. Forced-air warmers have also been evaluated against certain types of passive insulation including the use of cotton blankets, reflective blankets and sleeping bags. These studies have shown superiority of forced-air warming both to prevent postoperative hypothermia and to rewarm already hypothermic individuals."
The researchers address the concern about airborne transmission of microorganisms: " It has been shown that forced-air warming systems can create significant temperature gradients within the operating room that have the potential to disrupt laminar airflow patterns [Dasari, et al. (2012)] and contaminate the surgical site with floor-level air mobilized by convection currents. However, contesting the notion that these devices disrupt operating room ultra-clean airflow patterns, a recent study using smoke as a visual tracer demonstrated effective laminar airflow in the presence of a working forced-air warming system [Sessler, et al. (2011)]. Furthermore, two trials involving colorectal and clean-site surgery have also shown that the use of forced-air warming significantly reduces surgical site infection risk, although neither study stipulated whether or not laminar flow theatres were used. An interesting study sampling air in the operative field of laminar flow theatres showed small increases in colony-forming units when forced-air warmers were turned on, although the authors deemed these unlikely to have clinical significance [Tumia, et al. (2002)]. In fact, the effectiveness of laminar flow at reducing infections has recently been called into question [Brandt, et al. (2008)]. Evidence suggests that forced-air warmers may also harbor microbial pathogens that have the potential to be emitted into the operating theatre environment via the air warmer hose [Avidan, et al. (1997); Albrecht, et al. (2009 and 2011)]. However, the correct use of microbial filters and the recommended perforated blankets has been shown to prevent their transmission [Avidan, et al. (1997). Moreover, analysis of theatre air samples in positive pressure theatres has shown a significant decrease in bacterial counts when forced-air warming was used correctly [Huang, et al. 2003)]."
Clinicians conducting product evaluation in this technology category should also consult the guidelines. AORN’s “Recommended Practices for the Prevention of Unplanned Perioperative Hypothermia” describes forced-air warming as a safe and widely used skin surface warming method for preventing unplanned hypothermia. The American Society of PeriAnesthesia Nurses (ASPAN) Evidence-Based Clinical Practice Guideline for the Promotion of Perioperative Normothermia also recommends the use of forced-air warming systems.
Ramona Conner, MSN, RN, CNOR, editor-in-chief of AORN’s Guidelines for Perioperative Practice, says that "The bottom line is that AORN recommends forced-air warming as one of a number of active and passive warming measures that may be considered." AORN's Guideline for Prevention of Unplanned Patient Hypothermia states that "Methods of warming (i.e., active, passive, a combination of methods) should be chosen and implemented by the perioperative team after a collaborative discussion among the team members." The guideline lists a number of active warming methods (e.g., conductive, convective) such as: increased ambient room temperature, radiant warming, forced-air warming (e.g., blanket, gown), water-filled mattresses, circulating water garments, warmed IV and irrigation fluids, electric warming blankets, carbon-fiber blankets, resistive polymer blankets, electric heating pads, thermal exchange chambers, and negative pressure warming systems.
Wu (2013) synthesized the evidence and recommends the following:
- Choose the forced-air warming device that has the lowest temperature gradient in one blanket (i.e., the temperature difference between various
points on the blanket should differ as little as possible) as well as a blanket that covers the largest area of skin possible without interfering with the surgical site
- Assess the patient for risks before using a forced-air warming system
- Provide forced-air warming systems to patients with higher risks for hypothermia when the number of devices is limited
- Pre-warm patients 30 to 60 minutes before anesthesia induction because forced-air warming increases a patient’s mean-skin temperature by approximately 2 degrees C (3.6 degrees F)
- Monitor the patient’s core body temperature during use of the warming device. If necessary, forced-air warming devices may be used in combination with other warming methods such as warmed irrigation liquid or warmed IV fluids
- Never use a forced-air warming system to warm a patient without using an attached blanket. The substitution of commercial blanket with hospital cotton blankets is not recommended
- Keep the blanket dry
- Assess the condition of patients’ skin and the connection between the hose and blanket during use. Patients undergoing major surgeries can
experience large amounts of blood loss or have other risks that lead to poor perfusion, which places the patient at risk for thermal injury from the blanket. Many units do not have alarms that sound when a disconnection occurs between the hose and blanket, therefore, the nurse should check the connecting points regularly during use
- Use single-use blankets to reduce the risk of cross contamination
- Use caution to interpret bispectral index readings whenever the monitoring sensor is near a forced-air warming blanket
- Use forced-air warming devices in the post-anesthesia care unit
- Educate staff members about hypothermia and warming technology on a regular basis
Bashaw (2016) emphasizes the need for continuing education: "Perioperative team members should receive education about hypothermia, including clinical signs and symptoms of hypothermia and preventive measures. Policies and procedures related to hypothermia should be kept up to date and should address components of perioperative assessment for hypothermia, consistent temperature measurement through all phases of care, use of warming equipment according to manufacturer’s instructions, and competency requirements related to hypothermia prevention. Working as a collaborative team, perioperative nurses and other healthcare providers in the preoperative, intraoperative, and postoperative recovery phases can minimize, if not eliminate, unplanned hypothermia, resulting in optimal outcomes for their patients."
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