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 the pathogens causing Surgical site infection (SSI). Different kinds of ventilation systems in operating theatres are used to prevent sterile fields and instruments from contamination by airborne bacteria. Results are inconclusive concerning which ventilation system creates the best conditions.

Objective: The aim of this study was 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: The study was conducted in a newly built operating theatre ward at Södersjukhuset, Stockholm, Sweden. Levels of CFU/m3 were measured in a preparation room using TMV with an intake of air of either 700L/s or 1200L/s and preparation room using UDAF supplied with 700L/s.

Results: Mean values of CFU/m3 air were 0-104.5 in the preparation room with TMV and an air flow of 700L/s. When the air flow was adjusted to 1200L/s the mean values were 0-5.5. In the preparation room with UDAF, the mean values of CFU/m3 air were 0-7. With an air flow of 700L/s the difference between the two rooms was significant (p<.006). When the air flow in the TMV room was increased to 1200L/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 during preparation of surgical instruments in preparation rooms showed that with an air flow of 700L/s UDAF had significantly lower levels of CFU/m3 than TMV.