Effect of forced‐air warming on the performance of operating theatre laminar flow ventilation*

Abstract

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.

Peri‐operative warming devices: performance and clinical application

“…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 [71] and contaminate the surgical site with floor-level air mobilised by convection currents [72]. 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 [73].…”

Meta‐analysis: effectiveness of forced‐air warming for prevention of perioperative hypothermia in surgical patients

“…However, close attention should be paid to avoid burn injury, surgical wound contamination and the effect of hot airflow on surgical sites (Dasari et al . ).…”

Infection control hazards associated with the use of forced-air warming in operating theatres

“…14 The effect of excess heat produced by different warming systems has been analysed and FAW was found to produce the highest amount of excess heat when compared with other warming systems. 56 In this study, pockets of hot air were found above the operating site, which is against the flow of the UCV flow, and these authors have suggested that this indicates a significant disruption to the unidirectional nature of UCV flow. Again, this study could not make any conclusions about whether these changes would be a direct infection risk but they identified that there may be ways to mitigate this potential risk by channelling the warm air out of the UCV flow.…”

“…Again, this study could not make any conclusions about whether these changes would be a direct infection risk but they identified that there may be ways to mitigate this potential risk by channelling the warm air out of the UCV flow. 56 Other researchers have studied particle counts over operating sites in UCV flow comparing no warming, FAW, and radiant warming. 59 They found a highly statistically significant increase in the number of particles of all sizes tested in the FAW group compared to other groups (Figure 4).…”

“…This in turn can lead to increased contamination at the surgical site. 55,56 Two research groups have used neutrally buoyant air/helium bubbles to track the movement of air when using forced air and alternative warming systems. McGovern et al randomized FAW and RHW and demonstrated that significantly more unclean air moved from outside of the UCV area into the simulated surgical site of knee replacement surgery using FAW, when compared with warming using resistive polymer fabric over-blankets.…”