Simulation of nitrous oxide concentrations in operating and recovery rooms

A model was developed to predict nitrous oxide (N2O) concentrations in operating (OR) and recovery rooms. The model incorporates general ventilation characteristics, percentage recirculation and the rate at which N2O is emitted into the OR (emission) for the calculation of environmental exposure. A workplace study was carried out during which N2O concentrations were measured continuously and coupled to anaesthetic activities (type and duration), air-change rate and percentage of recirculated air. The data from this study were used to calculate N2O emission. Subsequently, the model was used to predict the effect of technical measures to reduce emissions on mean environmental exposure. After implementation of the control measures an intervention study was made to check whether the reduction in exposure was predicted by our simulation model. Subsequently the 'validated' simulation model was used: (i) to calculate the exposure for different percentages of recirculation and different air-change rates, and (ii) to estimate N2O levels in another situation, i.e. an operating room in an outpatients clinic. In short, our study shows how modelling can help both occupational hygiene and hospital management to control exposure to anaesthetic gases and to design or adapt ventilation systems of operating rooms and recovery rooms.