Convection warmers--a possible source of contamination in laminar airflow operating theatres?

This work results from concerns that forced-air convection heaters applied to patients in the operating theatre might interfere with ultra-clean ventilation system and thus be a potential source of wound contamination. Air samples were taken in the operative field and the bacterial load calculated by estimating the number of colony forming units per cubic metre of air (cfu/m(3)). Six tests were carried out, two in empty theatres and four during standard orthopaedic operating lists. Differences were seen between empty theatres and those standing empty for short periods during busy operating lists. Increases were seen on entry to theatre of staff and patients with the convection heaters off. A further small rise was seen after the convection heaters were turned on when applied to patients. This study showed that use of warm air convection heaters on patients produced a small increase in the number of colony forming units in ultra-clean air theatres but the levels were unlikely to have clinical significance. By far the greatest effect on numbers was movement and presence of the patient and theatre staff in the theatre.