To the Editor:
Forced air warming systems, highly effective in maintaining or restoring normothermia in surgical patients , share with other heating devices the potential for burn injury. Two infants (aged 4 mo and 6 wk) sustained thermal burns associated with the use of a Bair Hugger Registered Trademark Cub blanket (Bair Hugger Registered Trademark No. 530 and No. 536, respectively; Augustine Medical, Inc., Eden Prairie, MN) through a mechanism not previously described.
In both cases, the warm air inlet of the Cub blanket was positioned at the feet, and the blanket was folded around the patient in a U configuration. The Bair Hugger Registered Trademark (Model 500/OR) was initially set at the high setting, and later at the medium setting when the patient's temperature reached 37 degrees C. At the conclusion of the surgery, one patient was found to have an erythematous area on the left shoulder, and erythema with several small blisters on the left buttock and thigh (first- and second-degree burns). The other showed two areas of first degree burn: one on the right shoulder and arm, and one on the right thigh and leg. In both cases, these burns resolved within 24 h without sequelae.
Forced air convective warming devices have enjoyed a remarkable safety record. As of December 1994, the Food and Drug Administration had on file only 15 reports of mishaps associated with their use. A review of these reports showed that five types of operator error were responsible for the majority of burns: 1) warming nonperfused or poorly perfused skin, 2) contact of heated plastic with skin, 3) use of the delivery hose without a warming cover, 4) use of another manufacturer's warming cover, and 5) use of Bair Hugger Registered Trademark model 200/250 an anesthetized patients (This model is intended for use on awake patients, and has a higher heat output and a higher set thermostat).
The similarity of topography and circumstances of the injuries points to a common mechanism. Both patients exhibited two distinct areas of burn, with the most severe on the lower part of the body. A reenactment of their positioning revealed that these areas were just opposite the exit vents provided in the Cub blankets to accommodate the output of the Bair Hugger Registered Trademark (33 L/min). The unit used in both cases was found by the manufacturer to deliver warmed air at a temperature of 45 degrees C, which is within specified factor guidelines (43 +/- 3 degrees C).
We believe that the Cub blankets were placed in such a way that air warmed to a temperature of 45 degrees C was blowing directly through the vents onto the patients' skin. This is a situation similar to the use of the delivery hose without a blanket, which is known to result in burns. The combination of warming cover, plastic drape, and surgical sheets may have created a microenvironment that prevented the dissipation of heat and contributed to the burns.
In the manufacturer's operation manual, the Cub Short blanket is depicted for use on the upper body, and the Cub Long for both the upper and lower parts of the body. We believe that, in either case, the exit vents should be positioned away from the patient, high settings should be used sparingly, and infants' skin should be checked periodically for thermal injury.
Farid J. Azzam, MD
Jeremy L. Krock, DO
Department of Anesthesiology, Cardinal Glennon Children's Hospital and Saint Louis University, St. Louis, MO 63110