Comparison of airborne bacteria in rooms with turbulent mixing ventilation vs unidirectional airflow during the preparation of surgical instruments - an experimental study.

Background: Surgical instruments could act as carriers of pathogens causing surgical site infections. Different types of ventilation systems in operating theatres are used to prevent contamination of sterile fields and instruments by airborne bacteria. The results are inconclusive concerning which ventilation system creates the best conditions.

Objective: To investigate levels of airborne bacteria during the preparation of surgical instruments in preparation rooms with turbulent mixing ventilation (TMV) and unidirectional airflow (UDAF).

Methods: This study was conducted in a newly built operating theatre at Södersjukhuset, Stockholm, Sweden. Colony-forming units (CFU)/m3 were measured in a preparation room with TMV with an intake of air of either 700 L/s or 1200 L/s, and a preparation room with UDAF with an intake of air of 700 L/s.

Results: Mean CFU/m3 air ranged from 0 to 104.5 in the preparation room with TMV and airflow of 700 L/s. When airflow was adjusted to 1200 L/s, mean CFU/m3 air ranged from 0 to 5.5. In the preparation room with UDAF, mean CFU/m3 air ranged from 0 to 7. With airflow of 700 L/s, the difference between the two rooms was significant (P<0.006). When the airflow in the preparation room with TMV was increased to 1200 L/s, there was no significant difference between TMV and UDAF (P=0.443).

Conclusions: This experimental study of the differences in levels of airborne bacteria in preparation rooms during preparation of surgical instruments showed that, with airflow of 700 L/s, the preparation room with UDAF had significantly lower CFU/m3 air than the preparation room with TMV.