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October 16, 2007
9:00 AM - 11:00 AM
Room Hall D, Area G,
Forced-Air Warmer Did Not Increase the Risk of Contamination Caused by Interference of Clean Airflow
Hiroshi Miyazaki, M.D., Minako Sato, M.D., Kaoru Okazaki, M.D.
Department of Anesthesiology, Yokohama Medical Center, Yokohama, Kanagawa, Japan

Maintaining body temperature of patients is considered to be an important aspect of perioperative safety. A lot of equipment is used for this purpose, and the forced-air warmer is one of the most useful devices. However, though these warmers blow filtered air, still some physicians are concerned about the risk of contamination caused by turbulence of the airflow. This study was conducted to examine whether the forced-air warmer increases the risk of contamination.


Turbulence visualized study

The forced-air warmer(Warm-Touch®, Mallinckrodt inc.,MO) and the genuine blanket(for the upper body) was set up in the usual style of daily practice with a dummy. Dummy's upper limbs were abducted to 90 degrees, and the blanket was put on the patients upper trunk and their limbs. The operating table was located just below the air outlet on the ceiling of the OR. It was located in the down draft of the OR's air cleaning system. Water mist created by an ultrasound nebulizer was used as a tracer of the airflow. The airflow was recorded by video camera and analyzed.

Contamination study

We counted the number of bacteria which were sampled from the surface of the surgical drapes.

Control(dummy) study

The dummy was covered by drape in the same style of the visualized study. The OR ran normal(cleaning air system was turned on) for 3 hours with/without forced-air warmer. After the study period, the bacterial culture plates were put on the surface of the drape. The bacteria samples were obtained from 3 sites(the right arm, the middle of upper trunk and the left arm). The culture plates were incubated for 2days. The number of colonies were counted.

Real site(actual surgeries) study

The surgical cases were divided two groups. The warmer group used warmer for the period of surgery, and non-warmer group did not. This study was designed as non-randomized study. Because, we were not allowed to let patients be in the cool temperature, warmers were used routinely. However, some surgeries needed to avoid it, we had to choose those cases as non-warmer group. At the end of surgery, the bacteria samples were obtained from 3 sites of surgical drape, same as the control study. The samples were incubated for 2 days.


The total number of colonies and the length of surgical times are analyzed by the Welch's t-test.


Visualized airflow around operating table and warmer blankets was not interfered with the forced-air warmer. No turbulence was found in any situations of warmer and blanket(with or without surgical drape, middle of blanket or margin of blanket, above blanket or below blanket)

In the control study(N=4 each), no bacteria was found in any sample. In the real site study, there was no difference of the number of bacteria and length of surgeries between the groups(table).

There were no infected patients during the study period.


Scant literature revealed the risk of contamination by a force-air warmer. Also no investigation has been done to visualize the airflow of warmer in the OR. We could not find any interfere of the down draft of OR's cleaning air system, also there is no increasing of bacteria contamination with using of a warmer. This study confirm the safety of using a forced-air warmer during surgery.[table1]

Anesthesiology 2007; 107: A1594
Length of surgery(min)Number of bacteria
Warmer group208±712.7±2.6
Non-warmer grop183±663.3±6.1