Patient warming systems are used routinely to prevent hypothermia under anaesthetic, the benefits of which have been clearly shown in the anaesthetic literature. We were concerned that since these systems take ‘dirty’ air from floor level and distribute it over the patient, bacterial counts could be increased. Also, airflow under the blanket itself could disturb the patients’ own skin cells and thereby influence bacterial counts.

With slit air sampling we analysed air quality at the simulated operative site by passing a known volume of air over an agar plate (tryptone glucose yeast). Using probability curves we were able to calculate the volume of air required to detect 1 colony forming unit (CFU) per m³ with 97% confidence. All tests were performed in an ultra clean air laminar flow theatre.

We assessed the effect of varying degrees of skin shedding under the warming blanket using volunteer patients with Psoriasis. We also simulated activity outside the lamina flow to determine whether counts on the table were influenced.

No colonies were grown in any of the study groups. Plates exposed outside the laminar flow area at floor level showed a relatively high level of contamination. We therefore conclude that the WarmTouch warming system does not influence bacterial counts at the operative site in ultraclean air ventilated theatres.

Patient warming systems are used routinely to prevent hypothermia under anaesthesia. Airflow from warming blankets may potentially influence bacterial counts either by pumping ‘dirty air’ from floor level to the operating area or by blowing the patients’ skin cells into the operating field from airflow under the blanket. Using slit-air sampling we analysed the air quality within a laminar-flow theatre at a simulated operating site. We assessed the effect of ‘high shedding of skin’ under the blanket using volunteer patients with psoriasis. We also simulated general theatre activity outside the laminar-flow area in order to determine whether the bacterial counts in the operating field were affected.

No colonies were grown in any of the groups tested and our results suggest that the patient warming system does not influence bacterial counts at the operating site in an ultraclean air-ventilated theatre, even with patients who have high shedding of skin cells.