NCT01056991.

SummaryForced-air warming exhaust may disrupt operating theatre airflows via formation of convection currents, which depends upon differences in exhaust and operating room air temperatures. We investigated whether the floor-to-ceiling temperatures around a draped manikin in a laminar-flow theatre differed when using three types of warming devices: a forced-air warming blanket (Bair Hugger TM ); an over-body conductive blanket (Hot Dog TM ); and an under-body resistive mattress (Inditherm TM ). 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) or resistive mattress (+3.63 (0.7)°C ; p < 0.001). Air temperature differences were insignificant between devices at floor (p = 0.339), knee (p = 0.799) and head height levels (p = 0.573). 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. . However, patient warming systems also release excess heat into the operating theatre that may generate convection currents even within a laminar flow system. It is possible that convection currents could disrupt the intended ceilingto-floor theatre airflows and therefore impede the ventilation system's ability to clear contaminants from the surgical site.There are two distinct categories of patient warming technology, forced-air and conductive heating. Forcedair devices deliver a heated airflow to a disposable coverlet that vents the hot air over the patient's body [6]. Conductive heating devices employ an electrically heated pad in contact with the patient's body [7]. Both types of devices appear to be comparably effective for the prevention of accidental peri-operative hypothermia [8][9][10][11][12][13][14], although forced-air devices are less efficient in transferring the applied heat to the patient than conductive devices [15]. Therefore, we might expect forced-air devices to generate a greater excess heat load on the ventilation system.

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