INEFFICIENCY OF UPWARD DISPLACEMENT OPERATING-THEATER VENTILATION

A new thermally based ventilation system ('Floormaster') with inlet of cool clean air at floor level, and evacuation at the ceiling of the a ir warmed by activity in the room (upward displacement ventilation, 17 air changes/h) was compared with a standard positive pressure (plenum ) ventilation system with air supply through an inclined perforated sc reen along one wall at the ceiling and evacuation at floor level (conv entional turbulent or mixing system, 16 air changes/h). The study was made during rigidly standardized sham operations (N = 20) performed in the same operating room by a six-member team wearing non-woven dispos able or cotton clothing. In general the upward displacement system rem oved dust particles too small to carry bacteria (0.16- < 0.3 mu m, 0.0 01 < P < 0.01) more efficiently than the conventional system. However, the displacement system also yielded two to threefold higher air and surface bacterial counts in areas important for surgical asepsis (Roun d area, instrument table) especially with regard to bacterial sediment ation (0.001 < P < 0.05). The major shortcoming of the displacement sy stem was insufficient elimination of the larger bacteria-carrying part icles. The type of clothing worn by the members of the team did not in fluence the overall results. We conclude that an upward displacement s ystem will lead to increased counts of airborne and sedimenting bacter ia and thus increase the risk of postoperative infection in comparison with conventional operating room ventilation systems.