Pollution of the workplace by anesthetic gases. Causes and prevention

Waste anesthetic gas concentrations were measured in areas corresponding to the breathing zones of the anesthetists and operating room nurses for personal exposure (n = 27, time-weighted values) and during special work practices (n = 65). Leaks related to anesthetic machines and high-pressure nitrous oxide components were investigated during (n = 60) and after anesthesia (n = 85). The effect of a local scavenging system on occupational exposure during inhalation induction of anesthesia in children was studied (n = 60). Concentrations of nitrous oxide, halothane, isoflurane, and enflurane were determined by using active dosimeters (SKC 222) and different infrared gas-analyzers. Factors that increase waste anesthetic gas concentrations in operating rooms can be divided into several categories, such as low air conditioning systems, anesthetists' work practices, equipment leakage, including leakage from high-pressure nitrous oxide systems, and inadequate scavenging devices. Equipment leakage is almost invariably present in low-pressure components of the anesthesia machine because so many seals and joints are necessary to permit disassembly for cleaning and replacement. Waste anesthetic gases are also distributed in the exhaled air of patients recovering from anesthesia. To restrict the levels, exposure must be as low as can be achieved with reasonable efforts. Thus, the anesthetic equipment should be designed to avoid leakage, leakage tests should be performed before the use of anesthetic machines, and waste anesthetic gases should be scavenged by central as well as by local systems. Regular and periodic use of a trace gas analyzer permits direct observation of gas leakage and enables anesthetists to modify their work technique in order to reduce avoidable leakage.     

Causes of nitrous oxide contamination in operating rooms

BACKGROUND: To reduce the ambient concentration of waste anesthetic agents, exhaust gas scavenging systems are standard in almost all operating rooms. The incidence of contamination and the factors that may increase the concentrations of ambient anesthetic gases have not been evaluated fully during routine circumstances, however. METHODS: Concentrations of nitrous oxide (N2O) in ambient air were monitored automatically in 10 operating rooms in Kagoshima University Hospital from January to March 1997. Ambient air was sampled automatically from each operating room, and the concentrations of N2O were analyzed every 22 min by an infrared spectrophotometer. The output of the N2O analyzer was integrated electronically regarding time, and data were displayed on a monitor in the administrative office for anesthesia supervisors. A concentration of N2O > 50 parts per million was regarded as abnormally high and was displayed with an alarm signal. The cause of the high concentration of N2O was then sought. RESULTS: During the 3-month investigation, N2O was used in 402 cases. Abnormally high concentrations of N2O were detected at some time during 104 (25.9%) of those cases. The causes were mask ventilation (42 cases, 40.4% of detected cases), unconnected scavenging systems (20 cases, 19.2%), leak around uncuffed pediatric endotracheal tube (13 cases, 12.5%), equipment leakage (12 cases, 11.5%), and others (17 cases, 16.4%). CONCLUSIONS: N2O contamination was common during routine circumstances in our operating rooms. An unconnected scavenging system led to the highest concentrations of N2O recorded. Proper use of scavenging systems is necessary if contamination by anesthetic gas is to be limited.     

Scavenging anesthetic gas from a membrane oxygenator during cardiopulmonary bypass

Concerns remain about the acute and chronic effects on personnel of waste anesthetic gases in the operating room environment. This study demonstrates a simple and effective means of scavenging waste anesthetic gases when halogenated anesthetics are administered through the pump oxygenator during cardiopulmonary bypass. This technique safeguards workers' health by reducing ambient anesthetic levels below the National Institute for Occupational Safety and Health (NIOSH) recommended exposure limits.     

Causes of Nitrous Oxide Contamination in Operating Rooms

Background: To reduce the ambient concentration of waste anesthetic agents, exhaust gas scavenging systems are standard in almost all operating rooms. The incidence of contamination and the factors that may increase the concentrations of ambient anesthetic gases have not been evaluated fully during routine circumstances, however.

Methods: Concentrations of nitrous oxide (N2 O) in ambient air were monitored automatically in 10 operating rooms in Kagoshima University Hospital from January to March 1997. Ambient air was sampled automatically from each operating room, and the concentrations of N2 O were analyzed every 22 min by an infrared spectrophotometer. The output of the N2 O analyzer was integrated electronically regarding time, and data were displayed on a monitor in the administrative office for anesthesia supervisors. A concentration of N2 O > 50 parts per million was regarded as abnormally high and was displayed with an alarm signal. The cause of the high concentration of N2 O was then sought.

Results: During the 3-month investigation, N2 O was used in 402 cases. Abnormally high concentrations of N2 O were detected at some time during 104 (25.9%) of those cases. The causes were mask ventilation (42 cases, 40.4% of detected cases), unconnected scavenging systems (20 cases, 19.2%), leak around uncuffed pediatric endotracheal tube (13 cases, 12.5%), equipment leakage (12 cases, 11.5%), and others (17 cases, 16.4%).     

Cuffed endotracheal tubes in children reduce sevoflurane and medical gas consumption and related costs

Background: This study aims to evaluate sevoflurane and anaesthetic gas consumption using uncuffed vs. cuffed endotracheal tubes (ETT) in paediatric surgical patients. Methods: Uncuffed or cuffed ETT were used in paediatric patients (newborn to 5 years) undergoing elective surgery in a randomized order. Duration of assessment, lowest possible fresh gas flow (minimal allowed FGF: 0.5 l/min) and sevoflurane concentrations used were recorded. Consumption and costs for sevoflurane and medical gases were calculated. Results: Seventy children (35 uncuffed ETT/35 cuffed ETT), aged 1.73 (0.01–4.80) years, were enrolled. No significant differences in patient characteristics, study period and sevoflurane concentrations used were found between the two groups. Lowest possible FGF was significantly lower in the cuffed ETT group [1.0 (0.5–1.0) l/min] than in the uncuffed ETT group [2.0 (0.5–4.3) l/min], P<0.001. Sevoflurane consumption per patient was 16.1 (6.4–82.8) ml in the uncuffed ETT group and 6.2 (1.1–14.9) ml in the cuffed ETT group, P=0.003. Medical gas consumption was 129 (53–552) l in the uncuffed ETT group vs. 46 (9–149) l in the cuffed ETT group, P<0.001. The total costs for sevoflurane and medical gases were 13.4 (6.0–67.3)€/patient in the uncuffed ETT group and 5.2 (1.0–12.5)€/patient in the cuffed ETT group, P<0.001. Conclusions: The use of cuffed ETT in children significantly reduced the costs of sevoflurane and medical gas consumption during anaesthesia. Increased costs for cuffed compared with uncuffed ETT were completely compensated by a reduction in sevoflurane and medical gas consumption.     

Delivery and scavenging system for small animal inhalational anesthesia

BACKGROUND: Inhalational agents have been widely used for anesthesia in laboratory animals. However, the safe use of inhalational agents in small laboratory animals has been limited by the lack of a suitable and effective scavenging system for the removal of waste anesthetic gases. The aim of the present study is to develop an anesthetic system that can be manufactured using common household and laboratory items. MATERIALS AND METHODS: An anesthetic system was designed for rats weighing from 300 to 350 g. A face mask for the rat was made by cutting off the distal part of a 50-ml centrifuge tube. A scavenging hood was made from a transparent plastic food storage box. Exhaust of anesthetic gases from the scavenger hood was facilitated by fitting an outlet connected to a pump. Four experienced researchers or technicians tested the scavenger hood. RESULTS: In 79.2% of the trials the participants could smell halothane when the pump from the scavenger system was not operational. However, when the pump was switched on, halothane was detected only 16.7% of the time (P < 0.001). CONCLUSION: We have developed a simple and effective method of delivering inhalational anesthesia to small laboratory animals and of removing waste anesthetic gases.     

Technical communication: An initial evaluation of a novel anesthetic scavenging interface

Waste anesthetic gas scavenging technology has not changed appreciably in the past 30 years. Open reservoir systems entrain high volumes of room air and dilute waste gases before emission into the atmosphere. This process requires a large vacuum pump, which is both costly to install and, although efficient, operates continuously and at near-full capacity. In an era of increasing energy costs and environmental awareness, carbon footprint reduction is a priority and a more efficient system of safely scavenging waste anesthetic gases is desirable. We tested a low-flow scavenger interface to evaluate the potential for cost and energy savings. The use of this interface in a suite of 4 operating rooms reduced scavenging flow from a constant 37 L/min to a value equal to the fresh gas flow (usually 2 L/min) for each anesthesia machine. Using the ventilator increased this flow by approximately 6 L/min because of the exhaust of ventilator drive gas into the scavenging circuit. Daytime workload of the central vacuum pump decreased from 92% to 12% (expressed as duty cycle). The new system produces energy savings and may increase vacuum pump lifespan.     

The future of the cuffed endotracheal tube

It has been traditionally taught that only uncuffed endotracheal tubes (ETTs) should be used for intubation in children younger than 8, or even 10, years old. However, recent literature suggests that the advantages of using uncuffed ETTs in children may be just another myth of paediatric anaesthesia. Using an uncuffed ETT does allow a tube of larger internal diameter to be used, minimizing resistance to airflow and the work of breathing in the patient who is breathing spontaneously. However, this advantage does not hold for ventilated patients, for whom ventilator settings can be adjusted to provide optimal airflow. Longer duration of intubation and a poorly fitted ETT are risk factors for mucosal damage, whether the ETT is cuffed or uncuffed. Furthermore, a properly sized, positioned, and inflated modern (low-pressure, high-volume) cuffed ETT can offer many advantages over an uncuffed ETT, including greater ease of intubation, better control of air leakage, lower rate and better control of flow of anaesthetic gases, and decreased risk of aspiration and infection.     

Occupational exposure of operating room staff to anesthetic gases during inhaled induction--a comparison with intravenous anesthesia induction

BACKGROUND: The risk of occupational exposure to waste anesthetic gases still remains during inhaled induction. In this study we investigated how much we were occupationally exposed to anesthetic gases during induction period. METHODS: Twenty-six adult patients were induced with sevoflurane 5% using a face mask for three minutes and maintained with sevoflurane 1% after end-tracheal intubations (IH-Group). Twenty-two adult patients were induced with intravenous anesthetics and maintained with sevoflurane 1% after end-tracheal intubations(IV-Group). The concentration of sevoflurane was measured by Multi-gas Monitor 1302 (Bruel & Kjaer: Denmark) every 70 seconds. Sample gas was suctioned from breathing zone of anesthesiologists. All of our operating rooms are equipped with waste gas scavenging system. RESULTS: The peak concentration of sevoflurane is significantly higher in IH-Group (15.91 +/- 22.64 ppm) compared with IV-group (0.36 +/- 0.25 ppm). The period when sevoflurane concentration exceeded 0.5 ppm is significantly longer IH-Group (18.55 +/- 10.51 min.) compared to IV-Group (1.92 +/- 4.56 min.). CONCLUSION: The induction with intravenous anesthetics is a better method in order to reduce occupational exposure of anesthesiologists to anesthetic gases.     

A study of waste gas scavenging in operating theatres.

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.     

Occupational exposure to nitrous oxide and sevoflurane during pediatric anesthesia: evaluation of an anesthetic gas extractor

OBJETIVES: To determine the level of occupational exposure to anesthetic gases in the absence of an extractor during pediatric anesthesia and to assess the efficacy of a purpose-built extraction system. METHODS: The patients were 24 children undergoing tonsillectomy and adenoidectomy. Gases were extracted from the room for 1 group and were not extracted for the other group (n=12 in each group). Induction was with 8% sevoflurane, 60% nitrous oxide (N2O), 40% oxygen at a flow rate of 8 L x min(-1) through a Mapleson C circuit. Maintenance was with 2% sevoflurane at the same flow rate and gas mixture under spontaneous ventilation with an endotracheal tube and a Mapleson D circuit. The circuits were equipped with an airway pressure-limiting valve to allow connection to an anesthetic gas extractor. Ambient levels of sevoflurane and N2O were measured in the breathing area around the anesthesiologist. The surgeon and the nurse were asked about symptoms related to occupational exposure. RESULTS: The mean (SD) exposure to N2O and sevoflurane in the group without an extractor was 423 (290) and 12 (10.9) parts per million (ppm), respectively. In the group working with the extractor, exposure was 94% and 91% lower: 24.7 (26) and 1.1 (1) ppm (P<.001). A higher incidence of noticing a "smell of gas" was registered for the group without an extractor (87% vs 11% in the extractor group, P=.003). Higher rates were also found for general discomfort (62% vs 11%, P=.05), nausea (62% vs 0%, P=.009), and headache (62% vs 0%, P=.009) in the absence of the extractor. CONCLUSIONS: Gas extraction decreased the level of exposure by up to 94%, achieving levels that were below the recommended limits and greatly reducing occupational risk.     

Exposure to sevoflurane and nitrous oxide during four different methods of anesthetic induction

The National Institute for Occupational Safety and Health-recommended exposure levels for nitrous oxide exposure are 25 ppm as a time-weighted average over the time of exposure. The exposure limit for halogenated anesthetics (without concomitant nitrous oxide exposure) is 2 ppm. Inhaled sevoflurane provides an alternative to i.v. induction of anesthesia. However, the inadvertent release of anesthetic gases into the room is likely to be greater than that with induction involving i.v. anesthetics. We therefore evaluated anesthesiologist exposure during four different induction techniques. Eighty patients were assigned to one of the induction groups to receive: 1) sevoflurane and nitrous oxide from a rebreathing bag, 2) sevoflurane and nitrous oxide from a circle circuit, 3) propofol 3 mg/kg, and 4) thiopental sodium 5 mg/kg. Anesthesia was maintained with sevoflurane and nitrous oxide via a laryngeal mask. Trace concentrations were measured directly from the breathing zone of the anesthesiologist. During induction, peak concentrations of sevoflurane and nitrous oxide with the two i.v. methods rarely exceeded 2 ppm sevoflurane and 50 ppm nitrous oxide. Concentrations during the two inhalation methods were generally <20 ppm sevoflurane and 100 ppm nitrous oxide. During maintenance, median values were near 2 ppm sevoflurane and 50 ppm nitrous oxide in all groups. Sevoflurane concentrations during inhaled induction frequently exceeded the National Institute for Occupational Safety and Health-recommended exposure ceiling of 2 ppm but mostly remained <20 ppm. Exposure during the maintenance phase of anesthesia also frequently exceeded the 2-ppm ceiling. We conclude that operating room anesthetic vapor concentrations are increased during inhaled inductions and remain increased with laryngeal mask ventilation. Implications: We compared waste gas concentrations to sevoflurane and nitrous oxide during four different induction methods. During inhaled induction with a rebreathing bag or a circle circuit system, waste gas concentrations frequently exceed National Institute for Occupational Safety and Health limits of 2 ppm sevoflurane and 50 ppm nitrous oxide. Therefore, we recommend that people at risk (e.g., women of child-bearing age) should pay great attention when using this technique.     

The mechanical aspects of anesthetic pollution control

Reduction of anesthetic contamination in the operating room requires removal of excess circuit gases (scavenging), elimination of anesthetic equipment leakage, and avoidance of anesthetic technics which allow unopposed spill of gas into the operating room. Scavenging and disposal of excess anesthetic gases can present hazards to the patient; means to protect the breathing circuit from elevated positive and negative pressures should be of prime consideration in selecting a scavenging system. Leakage from anesthic equipment occurs in the high-pressure (central and tank N2O sources to the machine flowmeters) and the low-pressure portions (from the machine flow-meters to the patient) of the system and can be of sufficient magnitude to virtually negate effective scavenging. These leakage points can be readily detected and corrected using periodic simple test procedures.     

Determination of subanesthetic concentrations of halothane in the environment of operating and recovery rooms

Concentrations of halothane in parts per million (ppm) in the air were determined during 4 days in the operating rooms and the recovery room of pediatric surgery during the course of surgical anesthesia by inhalation. The operating rooms did not have an anesthetic gas scavenging system. Eighteen samples of air were taken by passive diffusion in sampling tubes of activated charcoal (mode Dr?ger Orsa 5). The samples were analysed by gas chromatography). We found concentrations between 4.7 ppm and 34.2 ppm that exceed those considered as admissible that range from 2 to 5 ppm. Our present recommendations to reduce the atmospheric contaminating anesthetic gases are the use of scavenging equipment, air-conditioned rooms and routine inspection and leak detection of apparatus and anesthetic circuits.     

Riscos ocupacionais,danos no material genético e estresse oxidativo frente à exposição aos resíduos de gases anestésicos

Background and objectives

The waste anesthetic gases (WAGs) present in the ambient air of operating rooms (OR), are associated with various occupational hazards. This paper intends to discuss occupational exposure to WAGs and its impact on exposed professionals, with emphasis on genetic damage and oxidative stress.

Special article: general anesthetic gases and the global environment

General anesthetics are administered to approximately 50 million patients each year in the United States. Anesthetic vapors and gases are also widely used in dentists' offices, veterinary clinics, and laboratories for animal research. All the volatile anesthetics that are currently used are halogenated compounds destructive to the ozone layer. These halogenated anesthetics could have potential significant impact on global warming. The widely used anesthetic gas nitrous oxide is a known greenhouse gas as well as an important ozone-depleting gas. These anesthetic gases and vapors are primarily eliminated through exhalation without being metabolized in the body, and most anesthesia systems transfer these gases as waste directly and unchanged into the atmosphere. Little consideration has been given to the ecotoxicological properties of gaseous general anesthetics. Our estimation using the most recent consumption data indicates that the anesthetic use of nitrous oxide contributes 3.0% of the total emissions in the United States. Studies suggest that the influence of halogenated anesthetics on global warming will be of increasing relative importance given the decreasing level of chlorofluorocarbons globally. Despite these nonnegligible pollutant effects of the anesthetics, no data on the production or emission of these gases and vapors are publicly available. The primary goal of this article is to critically review the current data on the potential effects of general anesthetics on the global environment and to describe possible alternatives and new technologies that may prevent these gases from being discharged into the atmosphere.     

Perioperative use of cuffed endotracheal tubes is advantageous in young pediatric burn patients

Uncuffed endotracheal tubes traditionally have been preferred over cuffed endotracheal tubes in young pediatric patients. However, recent evidence in elective pediatric surgical populations suggests otherwise. Because young pediatric burn patients can pose unique airway and ventilation challenges, we reviewed adverse events associated with the perioperative use of cuffed and uncuffed endotracheal tubes. We retrospectively reviewed 327 cases of operating room endotracheal intubation for general anesthesia in burned children 0–10 years of age over a 10-year period. Clinical airway outcomes were compared using multivariable logistic regression, controlling for relevant patient and injury characteristics. Compared to those receiving cuffed tubes, children receiving uncuffed tubes were significantly more likely to demonstrate clinically significant loss of tidal volume (odds ratio 10.62, 95% confidence interval 2.2–50.5) and require immediate reintubation to change tube size/type (odds ratio 5.54, 95% confidence interval 2.1–13.6). No significant differences were noted for rates of post-extubation stridor. Our data suggest that operating room use of uncuffed endotracheal tubes in such patients is associated with increased rates of tidal volume loss and reintubation. Due to the frequent challenge of airway management in this population, strategies should emphasize cuffed endotracheal tube use that is associated with lower rates of airway manipulation.     

Chromatographic analysis of multiple tracer inert gases in the presence of anesthetic gases.

A gas chromatographic method for simultaneous analysis of multiple tracer inert gases in blood and expired gas samples is described. The method enables determination of the distribution of ventilation-perfusion ratios in the lungs during anesthesia with nitrous oxide and halothane. In addition, simultaneous analysis of anesthetic gas concentration in blood permits calculation of the amount of uptake or elimination of anesthetic gases from the Fick principle.     

Occupational exposure to inhalational anesthetics during cardiac surgery on cardiopulmonary bypass

BACKGROUND: Eventual hazards from occupational exposure of operating room personnel to inhalational anesthetic agents cannot yet be definitively excluded. We determined if occupational exposure of operating room personnel to waste anesthetic gases during cardiopulmonary bypass (CPB) complies with the established governmental limits. METHODS: Ten adults underwent inhalational anesthesia for coronary artery bypass grafting with nitrous oxide and either sevoflurane (n = 5) or desflurane (n = 5). The administration of inhalational anesthetic agents was stopped before initiation of CPB. Gas samples were obtained before and during CPB every 90 seconds from the breathing zones of anesthesiologist (A), surgeon (S), and perfusionist (P). Time-weighted averages (TWA) over the time of exposure were calculated. RESULTS: The surgeon's exposure to nitrous oxide was 9.3 +/- 1.9 parts per million (ppm) before and 3.0 +/- 1.4 ppm during CPB (A: 6.7 +/- 1.1 ppm and 0.5 +/- 0.1 ppm; P: 3.7 +/- 1.4 ppm during CPB). Occupational exposure to desflurane was 0.21 +/- 0.10 ppm before and 0.62 +/- 0.28 ppm during CPB for the surgeon (A: 0.02 +/- 0.01 ppm and 0.02 +/- 0.003 ppm; P: 0.82 +/- 0.26 ppm during CPB), thereby exceeding the given limit of 0.5 ppm. Exposure levels of sevoflurane were below the 0.5 ppm limit at all times, as were nitrous oxide levels (threshold limit: 25 ppm). CONCLUSIONS: Although occupational exposure to inhalational anesthetic agents was low at most times during the study and none of the operating room staff complained about subjective or objective impairment or discomfort, all measures must be taken to further minimize occupational exposure, including sufficient air conditioning and routine use of waste gas scavenging systems on CPB equipment.     

The climatisation of anesthetic gases under conditions of high flow to low flow

The aim of climatisation of anesthetic gases in prolonged anesthesia is to maintain tracheobronchial climate comparable to that of spontaneous nasal breathing. The humidity and temperature of inspired gases attained in the circle system at a fresh gas flow of 6.0, 3.0 and 1.5 l/min are inadequate for prolonged anesthesia. According to the results of our study with the scanning electron microscope, the minimal flow technique (0.5 l/min) leads to major improvement of heat (28 to 32 degrees C) and moisture (20 to 27 mg H2O/l) conditions of anesthetic gases in anesthesia systems.