McGovern, P.D.; Reed, M.R., et al. Forced-air Warming and Ultra-clean Ventilation Do Not Mix. J. Bone and Joint Surgery Br, 93B:11. 1537-44. Nov 2011.
“Patient warming [Bair Hugger ] ventilation disruption was associated with a significant increase in deep joint infections, as demonstrated by an elevated infection odds-ratio (3.8, p=0.028) for the forced air versus conductive fabric patient groups (n=1437 cases, 2.5-year period).” The researchers concluded, “Air-free warming is, therefore, recommended over forced-air warming for orthopedic procedures.” (View The Abstract)
Dasari, K.B.; Albrecht, M; Harper, M. Effect of forced-air warming on the performance of theatre laminar flow ventilation.Anaesthesia. Vol. 67; 2012: 244-249.
“With forced-air warming, mean (SD) temperatures were significantly elevated over the surgical site vs those measured with the conductive blanket (+2.73 (0.7) °C; p < 0.001).” “We conclude that forced-air warming generates convection current activity in the vicinity of the surgical site. The clinical concern is that these currents may disrupt ventilation airflows intended to clear airborne contaminants from the surgical site.” (View The Abstract)
Legg, A.J.; Cannon, T; Hammer, A.J. Do forced air patient-warming devices disrupt unidirectional downward airflow?Journal of Bone and Joint Surgery Br. 2012;94-B:244-256.
“Forced-air warming resulted in a significant mean increase in the temperature (1.1°C vs 0.4°C, p<0.0001) and number of particles (1038.2 vs 224.8, p=0.0087) over the surgical site when compared with [HotDog®] warming, which raises concern as bacteria are known to require particles for transport.” (View The Abstract)
Legg, A.J.; Hammer, A.J. Forced-air patient warming blankets disrupt unidirectional airflow.Bone and Joint Journal, March 2013 vol. 95-B no. 3 407-410
“The waste heat from forced-air warming (FAW) torso blankets radiated through the surgical drape to form tornado-like vortexes of rapidly spinning air near the surgical site. The vortexes sucked contaminated air from the operating room floor and deposited it over the surgical wound. 2,000 times more contaminant particles were found in the air over the wound with FAW than with air-free HotDog conductive warming. With HotDog, only 1,000 particles per cubic meter of air were present. With FAW, the particle count was 2,174,000 per cubic meter, an increase of 217,300%.” (View The Abstract)
Belani, K; et al. Patient Warming Excess Heat: Effects on Orthopedic Operating Room Ventilation Performance.Anesth Analg. 2013 Aug;117(2):406-11
“The direct mass-flow exhaust from forced-air warming generated hot-air convection currents that mobilized ‘bubbles’ over the anesthesia drape and into the surgical site.” Conductive fabric warming had no such effect. (View The Abstract)
Albrecht M, Leaper D, et al. Forced Air Warming Blowers: An Evaluation of Filtration Adequacy and Airborne Contamination Emissions in the Operating Room.American Journal of Infection Control, 2011; 39:321-8.
Micro-organisms were cultured from the internal air-flow paths of 92.3% of forced-air blowers. 58% of the blowers tested were found to be internally generating and emitting significant levels of airborne contaminants >0.3 µm in size (germ size), up to 35,272 particles per ft3 of air (80 million particles per hour). (View The Abstract)
Reed M, et al. Forced Air Warming Design: An Evaluation of Intake Filtration, Internal Microbial Build-Up, and Airborne-Contamination Emissions. 2013;81(4):275-280.
Micro-organisms were cultured from the internal air-flow paths of 100% of forced-air blowers tested. 100% of the blowers were emitting internally generated particles >0.3 µm in size, up to 112,000 particles per ft3 of air (300 million particles per hour). Emitted particle count was 40 times greater than the intake particle count for that blower, and virtually all of the emitted particles were internally generated. (View The Abstract)
Wood A.M., et al., Infection control hazards associated with the use of forced air warming in operating theatres,Journal of Hospital Infection. 2014 Nov;88(3):132-40.
A Review Article of the published experimental and clinical research into the infection control hazards of using forced-air warming (FAW) in operating theatres to prevent inadvertent hypothermia. “We conclude that FAW does contaminate ultra-clean air ventilation…we recommend that surgeons should at least consider alternative patient-warming systems in areas where contamination of the operative field may be critical.”(View The Abstract)
Scherrer M, et al. Hygiene and room climate in the operating room.Minimally Invasive Thermal Allied Technology. 2003 Nov;12(6):293-9.
“Forced air-warming systems, which are used to maintain normal body temperatures for patients during surgery, disturb the ultra-clean field through the air emitted from the blankets used.”
Moretti B, et al. Active warming systems to maintain perioperative normothermia in hip replacement surgery: a therapeutic aid or a vector of infections? J Hosp Infect 2009;73:58-63
Researchers found an increased bacterial load at the surgical site when FAW was used.
Sugai, H; Koizumi, T; Sumita, S; Yamakage, M; Relative clinical heat transfer effectiveness: Forced- air warming vs. Conductive fabric electric warming, a randomized controlled trial. Journal of Anesthesia and Surgery, Vol 5(2). Available online.
Conductive fabric warming (HotDog) showed significantly higher warming rates than forced-air warming (FAW) (0.35 ̊C/hr vs 0.01 ̊C/hr), when all other relevant variables were held constant in a prospective, randomized controlled trial.
Kimberger O, et al. Resistive polymer versus forced-air warming: Comparable heat transfer and core rewarming rates in volunteers. Anesth Analg 2008; 107: 1621-26
The full body Hot Dog blanket was compared with the full body Bair Hugger blanket in re-warming anesthetized hypothermic volunteers in a controlled cross-over study. The warming rates of the two technologies were virtually identical.
Brandt S, Kimberger O, et al. Resistive-Polymer Versus Forced-Air Warming: Comparable Efficacy in Orthopedic Patients. Anesth Analg 2010; 110:834-8.
80 elective orthopedic surgery patients were randomized to upper-body FAW (Bair Hugger) or resistive polymer warming (Hot Dog) upper body blanket during surgery. The warming rates were comparable for the two groups. No differences in mean skin and mean core temperatures. The waste heat from the FAW also caused the environment of the anesthesiologists workspace to be 1.8°C warmer in the FAW group. “Resistive polymer warming performed as efficiently as FAW in patients undergoing orthopedic surgery.”
Ayers P, et al. Reducing perioperative hypothermia in anesthetized patients. Accepted for publication in Veterinary Anesthesia and Analgesia
A veterinary study at Iowa State University. Twenty-eight dogs were treated either with Hot Dog warming above and below or a Bair Hugger blanket above and a water mattress below. 85.7% of the Hot Dog treated dogs were normothermic (normal temperature) at the end of surgery. Only 14.3% of the Bair Hugger treated dogs were normothermic at the end of the surgery.
Nguyen H, Kimberger O, et al. A New Underbody Resistive Warming Device vs. Forced Air Warming To Prevent Perioperative Hypothermia. A087. Accepted for presentation at the American Society of Anesthesiologists Annual Meeting, October 2010.
24 elective orthopedic surgery patients were randomized to upper-body FAW or resistive polymer warming (Hot Dog) with combined upper body blanket and underbody mattress during surgery. The warming results were nearly identical for the two groups. “The efficacy of resistive polymer warming with the Hot Dog resistive warming system was not inferior to an established FAW system in patients undergoing elective orthopedic surgery.”
A number of other studies have been published showing that the effectiveness of conductive fabric warming is equal to FAW:
1. Perl T, et al. Comparison of forced-air warming and resistive heating. Minerva Anestesiol 2008; 74: 687-90
2. Matsuzaki Y, et al. Warming by resistive heating maintains perioperative normothermia as well as forced air heating. Br J Anaesth 2003; 90: 689-91
3. Camus Y, et al. Prevention of hypothermia by cutaneous warming with new electric blankets during abdominal surgery. Br J Anaesth 1997; 79: 796-97
4. Camus Y, et al. Leg warming minimizes core hypothermia during abdominal surgery. Anesth Analg 1993; 77: 995-99
5. Pathi V, et al. The benefits of active rewarming after cardiac operations: A randomized prospective trial. J Thor CV Surg 1996; 111: 637-41
6. Fanelli A, et al. The efficacy of a resistive heating under-patient blanket versus a forced-air warming system: A randomized controlled trial. Anesth Analg 2009; 108: 199-201
7. Wong P, et al. Randomized clinical trial of perioperative systemic warming in major elective abdominal surgery. Br J Surg 2007; 94: 421-426
8. van der Horst M, et al. Preoperative warming reduces the incidence of hypothermia in total hip and knee replacement surgery under spinal anesthesia. Abstract presented Dutch Anesth Soc. 2009
9. Kober A, et al. Effectiveness of resistive heating compared with passive warming in treating hypothermia associated with minor trauma: A randomized trial. Mayo Clin Proc 2001; 76: 369-75
10. Negishi C, et al. Resistive-heating and forced-air warming are comparably effective. Anesth Analg 2003; 96:1683-7
11. Ng V, et al. Comparison of forced-air warming and electric heating pad for maintenance of body temperature during total knee replacement. Anaesthesia 2006; 61: 1100-04
12. Engelen S, et al. Resistive heating during off-pump coronary bypass surgery. Acta Anaesth Belg2007; 58: 27-31
13. Sheck T, et al. Active warming of critically ill trauma patients during intrahospital transfer: A prospective, randomized trial. Wien Klin Wochenschr 2004; 116: 94-97
Cost Savings Research
Macario, A. and T.R. Clancy. “Computer simulation model of the economics of a reusable fabric technology warming blanket compared to a disposable forced-air warming blanket.” International Anesthesia Research Society (IARS). 2010.
A whitepaper presented at International Anesthesia Research Society (IARS) showed how HotDog patient warming can save users up to 70%. That analysis, by doctors at Stanford University and the University of Minnesota, included “soft costs” like time to clean HotDog blankets, disposal costs, and energy costs. (Macario Poster)
Energy Efficiency Research
Bayazit, Yilmaz; Sparrow, Ephraim M. Energy efficiency comparison of forced-air versus resistance heating devices for perioperative hypothermia management.Energy. 2010 vol. 35, no. 3, pp. 1211-15.
Summary: The energy efficiency of a patient warming devices is the amount of heat produced transferred to the patient. Comparing the energy efficiency of different patient warming devices, the authors found that the HotDog patient warming system was the most efficient and was 2.3 times more efficient than Arizant’s Bair Hugger forced-air warming.
1. Lidwell OM et al. Bacteria isolated from deep joint sepsis after operation for total hip or knee replacement and the sources of the infections with Staphylococcus aureus. J Hosp Infect 1983;4:19-29.
2. Legg, A.J.; Hammer, A.J. Forced-air patient warming blankets disrupt unidirectional airflow. Bone and Joint Journal,March 2013 vol. 95-B no. 3 407-410.
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