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A new anaesthetic gas scavenging system is described. The resistance of the system appears to be low. When input gas flow rate in the system was zero or 150 litre min-1, misuse of the system produced pressure changes at its collecting points of 26 Pa subatmospheric and 630 Pa above atmospheric pressure, respectively. Suggestions to develop the system and increase its safety are presented.
The level of N2O contamination in the breathing zone of anesthesiologists was measured while they administered inhalation anesthesia by mask to five patients. A mask gas-scavenging attachment was used for 30 minutes and then removed while anesthesia continued for a further 30 minutes. The levels of N2O with and without the scavenging attachment were compared. Using the scavenging attachment, N2O contamination was reduced from greater than 150 ppm to less than 5 ppm, a level well below the 25 ppm limit recommended by the National Institute for Occupational Safety and Health. The scavenging device is a simple and effective way to reduce operating room contamination with N2O during delivery of anesthesia by mask.
A critical assessment of available waste anaesthetic gas scavenging devices was made by simulating the worst theatre conditions as well as ideal conditions. Only one of the scavenging devices tested proved to be unacceptable. However, the critical nature of suction flow rates was revealed and the ineffectiveness of air conditioning in the absence of adequate scavenging was highlighted.
The collapse of the reservoir bag in a circle circuit was observed during anaesthesia. This resulted from the incomplete closure of the pressure relief valve on the absorber whie it was connected to the scavenging system. Although the scavenging system was operating and installed according to the manufacturer's recommendations and to the CSA standard on Anaesthetic Gas Scavenging Systems (Z168.8), the patient was not protected from this hazard. Introducing an air break into the scavenging interface device will protect the patient. However, such a system would not meet the CSA standard and would make the relief valves on the scavenging interface device unnecessary.
PURPOSE: During inhalation anaesthesia, contaminations of the working environment be anaesthetic volatiles and nitrous oxide occur. The amount of leaking gases is influenced by leakages of the anaesthetic ventilator, by fresh-gas flows and by the effectivity of the scavenging system. Since 1st January 1996 new ventilators have to be equipped with scavenging devices according to the European standard EN 740. We measured the effectivity of this system with anaesthetic ventilators of a type that is now superseded (mean leakage rate 100 ml/min) and recent devices (mean leakage rate 5 ml/min) using high and low fresh-gas flows. MATERIAL AND METHODS: The anaesthetic ventilators were placed in a non-air-conditioned area. A test lung was ventilated with gas flows of 1 l/min, 3 l/min and 6 l/min (concentrations of nitrous oxide 70%, Enflurane 1%). The ventilation time in each case was 1 h. The minute volume was set to 8 l/min. At 2-minute intervals the concentrations of nitrous oxide and enflurane were measured by a multigas monitor Brüel & Kjaer 1302. The experiments were carried out with an old scavenging device according to DIN 13260 and a new device according to EN 740. RESULTS: Using the scavenging device according to DIN 13260, the concentrations of the pollutant gases were significantly dependent on the fresh-gas flows. No differences were found when using old or new anaesthetic ventilators. Medians of nitrous oxide (n2o) and Enflurane (e): 6 l/min: (n2o) 204 ppm (e) 4.3 ppm 3 l/min: (n2o) 115 ppm (e) 2.1 ppm 1 l/min: (n2o) 61 ppm (e) 0.97 ppm. Scavenging devices according to EN 740 significantly reduced the amount of emitted pollutants. No dependency on fresh-gas flows could be detected. 6 l/min: (n2o) 11.25 ppm (e) 0.05 ppm 3 l/min: (n2o) 10.12 ppm (e) 0.0 ppm 1 l/min: (n2o) 9.5 ppm (e) 0.0 ppm. CONCLUSIONS: The formerly reported dependence of the room air concentrations of anaesthetic volatiles and nitrous oxide from the fresh gas flow are caused by the spillage of pollutants through scavenging devices according to DIN 13260. The use of systems according to EN 740 is not only useful in new devices but must also be recommended for superseded models of anaesthetic ventilators.
Prevention of exposure of the endoscopist to high levels of anesthetic gases during bronchoscopy was attempted experimentally in dogs by a scavenging system. Results were compared with exposure during the conventional technique of anesthetic gas administration for clinical bronchoscopy using the rigid open ventilating bronchoscope. The scavenging system consisted of a vacuum pump applied to the open ventilating rigid bronchoscope sidearm connection during intratracheal administration of nitrous oxide, , oxygen, and halothane gas mixture. Gas samples were taken from the trachea, the proximal end of the bronchoscope, and the endoscopist's breathing zone, and analyzed by gas chromatography. Findings indicate that halothane anesthesia for bronchoscopy administered by conventional techniques is a source of air pollution in the operating room and exposes the endoscopist to subanesthetic levels of halothane that may affect psychomotor functioning. The use of the gas scavenging system lowered the concentrations of halothane and nitrous oxide at the endoscopist's breathing zone to a level at which inhalation for short periods has no clinical effects, while the concentrations of the anesthetics and oxygen in the trachea were maintained at a satisfactory level.
The function of scavenging equipment is to remove waste anaesthetic gases from the operating theatre and thus reduce the potentially harmful effects these agents may have on staff. However, these systems can pose a serious risk to patients which is not well recognised. We describe two cases where harm to patients could have occurred as a result of faulty or inappropriate equipment being used and inadequate checking of scavenging systems.
Measurements of atmospheric nitrous oxide concentrations were made in eight hospitals, using 30 anaesthetic machines and locations, during 41 anaesthetic administrations or simulations. All areas were air conditioned, two by laminar flow devices. All anaesthetic machines and ventilators were fitted with commercially available gas collector (scavenger) valves. In all areas except one, venturi suction was used to exhaust gases. Pollution levels during endotracheal anaesthesia did not exceed the recommended 30 ppm. except where leaking anaesthetic machines or nitrous oxide supplies were used. In two instances where paediatric anaesthesia was administered through uncuffed endotracheal tubes nitrous oxide levels were also excessive. Of nine anaesthetics administered through face masks, only in one was the ambient nitrous oxide concentration acceptable. During induction of anaesthesia using nitrous oxide, unacceptable peaks of concentration were encountered. In two air conditioned recovery rooms tested, nitrous oxide concentration was acceptable. The collector valves performed their function satisfactorily, but laminar flow air conditioning was insufficient in itself to maintain acceptably low nitrous oxide concentration without the use of scavenging.
Three types of anaesthetic waste scavenging systems (active antipollution system, Papworth Block passive system and activated charcoal absorber system) were compared with a non-scavenging control to assess their effectiveness in reducing waste halothane concentrations in a chemical warfare-proof operating theatre. All three systems were found to reduce the level of pollution significantly.
The significance of chronic exposure to anesthetic pollution for veterinarians and their associates is not well defined, but one cannot ignore the evidence that a potential occupational health hazard exists. Installation of a scavenging system can reduce anesthetic pollution and personnel exposure to waste gases significantly. However, it is important to realize that these systems are not a replacement for safe anesthetic practices and are only effective when used correctly and maintained properly.
Results are reported for air sampling surveys undertaken by the Health and Safety Executive (HSE) from 1980 to 1984 using diffusive samplers in 40 operating theatres and 18 recovery areas at 27 hospitals. For all personnel the geometric mean time-weighted average exposure to nitrous oxide in unscavenged theatres was 94 ppm and in scavenged theatres 32 ppm; the corresponding means for halothane were 1.7 and 0.7 ppm, respectively. Intermittent use of scavenging led to mean exposures between those found in scavenged and unscavenged conditions. Anaesthetists showed higher mean exposures than other staff in all conditions. Statistical analysis of the data demonstrates that mean exposures of operating theatre staff were significantly lower in scavenged than in unscavenged theatres. For most staff, exposure was also significantly lower in theatres using active scavenging systems compared with those using passive systems. The literature on the hazards of chronic exposure to inhalation anaesthetics and previous studies of exposure is also briefly reviewed.
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