Low flow anaesthesia reduces occupational exposure to inhalation anaesthetics Environmental and biological measurements in operating room personnel

In the present study we evaluated the occupational exposure to N₂O and isoflurane during open circuit (OC) (fresh gas flow ≥ minute volume) and low flow (LF) (fresh gas flow=1.5 1/min) anaesthesia. The effects of active scavenging and of a charcoal filter positioned on the exhausting branch of the ventilator on environmental and urinary concentrations of inhalation anaesthetics were also investigated. The study was carried out in the same operating room provided with non-recirculating air changes (10 per hour). It involved anaesthetists and nurses during routine activity. N₂O and isoflurane concentrations (time-weighted average) were measured after 3-hour continuous exposure: 1) in the environment at the level of the personnel's breathing zone (Ci); 2) in the environment at the ventilator zone (C); 3) in urine (Cu). During OC anaesthesia without active scavenging the breathing zone concentration of both N₂O and isoflurane was very high (194.6±15.2 and 5.0±0.4 ppm, respectively). The activation of the scavenging greatly reduced the breathing zone concentration of N₂O (31.6±4.1 ppm) and isoflurane (1.7±0.2 ppm). LF anaesthesia (with active scavenging) significantly reduced the environmental concentration of both anaesthetics (Ci N₂O and isoflurane 22.7±1.8 and 0.6±0.04 ppm, respectively). During LF anaesthesia the breathing zone concentration of N₂O remained low, even without scavenging (22.7 ±1.8 ppm). Similar results were obtained by measuring N₂O and isoflurane concentrations at the ventilator zone and in urine. The application of a charcoal filter to the exhausting branch of the ventilator during LF anaesthesia without active scavenging reduced the environmental concentration of isoflurane to a lower value than that obtained with OC anaesthesia with active scavenging (Ci 0.88±0.1 vs 1.7±0.2 ppm). A linear correlation was found between environmental (Ci) and urinary concentrations of N₂O and isoflurane. Our data show that LF anaesthesia reduces the exposure of the operating room personnel to inhalation anaesthetics. A charcoal filter positioned on the exhausting branch of the ventilator in substitution of the active scavenging is very effective in reducing isoflurane pollution. The evaluation of the urinary concentration of inhalation anaesthetics is a simple and reliable method of monitoring occupationally exposed personnel.