Ann Thorac Surg 2003;75:1924-1927
© 2003 The Society of Thoracic Surgeons
Original article: cardiovascular
Occupational exposure to inhalational anesthetics during cardiac surgery on cardiopulmonary bypass
Stephan Mierdl, MDa,
Christian Byhahn, MDa,
Ulf Abdel-Rahman, MDb,
Georg Matheis, MDb,
Klaus Westphal, MDc*
a department of Anesthesiology, Intensive Care Medicine, and Pain Control, J.W. Goethe-University Hospital, Frankfurt, Germany,
b department of Thoracic and Cardiovascular Surgery, J. W. Goethe-University Hospital, Frankfurt, Germany
c Department of Anesthesiology and Intensive Care Medicine, Katharina-Kasper-Kliniken, Frankfurt, Germany
Accepted for publication December 31, 2002.
* Address reprint requests to Dr Westphal, Department of Anesthesiology and Intensive Care Medicine, Katharina-Kasper-Kliniken, Richard-Wagner-Str 14, D-60318 Frankfurt, Germany.
e-mail: klaus.westphal{at}em.uni-frankfurt.de
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Abstract
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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.
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Introduction
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The discussion of whether chronic exposure to waste anesthetic gases results in adverse health effects in health-care workers exists since the introduction of inhalational anesthetic agents. Although numerous studies have been conducted on this subject the results remain controversial. Even if chronic exposure to low levels of these agents does not seem to be responsible for reported health problems, eventual hazards cannot yet be definitively excluded [1–11]. Therefore it is widely recommended to keep exposure as low as possible. In some countries strict limits for exposure have been established by various governmental agencies. In the United States the National Institute of Occupational Safety and Health (NIOSH) recommends not to exceed threshold values of 25 parts per million (ppm) for nitrous oxide. The exposure limit for volatile anesthetic agents is 2 ppm without concomitant nitrous oxide exposure whereas with concomitant nitrous oxide exposure it should not exceed 0.5 ppm [12].
Two older studies investigated occupational exposure to enflurane [13] and isoflurane and desflurane [14] during CPB; however studies focusing on "new" sevoflurane and "old" but popular nitrous oxide do not exist. This study was designed to determine the occupational exposure of perfusionists, cardiac surgeons, and anesthesiologists to nitrous oxide and the volatile anesthetic agents sevoflurane and desflurane when used before but not during cardiopulmonary bypass (CPB).
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Material and methods
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After approval by the Institutional Review Board and informed, written consent, 10 adults undergoing elective coronary artery bypass grafting using CPB were involved in this study.
Anesthesia
After intravenous anesthetic induction with etomidate (0.2 mg/kg), sufentanil (25 µg/kg) and succinylcholine (1 mg/kg) anesthesia was maintained with nitrous oxide 60% in oxygen (n = 10) and sevoflurane (n = 5) or desflurane (n = 5) until the beginning of CPB. With the beginning of CPB the supply of the inhalational anesthetic agents was stopped and anesthesia was maintained with propofol (4 mg · kg-1 · h-1). During the entire operation 25 µg sufentanil was administered for analgesia whenever deemed necessary.
Cardiopulmonary bypass
All patients received intravenous (IV) heparin 350 IU/kg after mammary artery dissection. A heparin-coated (Jostra Bioline Coating [Jostra Medizintechnik, Hirlingen, Germany]) extracorporeal circuit (filter, tubing set and a membrane oxygenator; fresh gas flow during CPB 2 L/min) with a standard roller pump was used. Additional heparin was administered when activated clotting time fell below 400 seconds. The circuit was primed with 1,500 mL Ringer’s solution and 500 mL hydroxyethyl starch 6%. Cardiotomy suction blood was retransfused directly, and in order to hemodilute the patient, autologous blood (1,000 to 1,500 mL) was harvested from the venous line upon initiation of CPB and retransfused after CPB. Buckberg’s solution was employed for myocardial protection.
Sampling strategy
Samples of ambient air in the breathing zone of all participating perfusionists, surgeons, and anesthesiologists were collected every 90 seconds throughout the operation through tubes mounted at the subject’s mouth. In addition, simultaneous measurements of the anesthetic gas concentrations were performed at both outlet nozzle of the oxygenator during the first 4.5 minutes directly after the beginning of CPB. A base line measurement was performed in the operating room before administration of any inhalational anesthetic agents. Waste anesthetic gas concentrations were estimated online using a direct reading photo acoustic infrared spectrometer (Brül&Kjaer 1302, Naerum, Denmark) that allowed parallel determination of several gases.
The samples obtained within 90 seconds intervals were averaged and concentration curves were generated for nitrous oxide, desflurane, and sevoflurane during the time of exposure (time-weighted averages [TWA]). The lowest detection limit of multigas detector was 0.05 ppm for nitrous oxide, 0.015 ppm for desflurane, and 0.02 ppm for sevoflurane. In addition other interfering gases such as glutaraldehyde, 2-propanole, steam, and carbon dioxide were estimated.
Environmental setting
The operating room used during the study was 61.7 m2 in area and 234.5 m3 in volume. The hourly fresh air supply for the operating room was 5,000 m3 without recirculation of exhausted air, resulting in 21.3 air exchanges per hour. The air flow entered through the center of the ceiling was evacuated in the corners of the room at floor and ceiling level, creating a laminar air flow. Furthermore, the anesthesia machine (Cicero; Draeger, Lübeck, Germany) was connected to a waste gas scavenging system (30 L · min-1).
The oxygenator of the extracorporeal circuit was not attached to a waste gas scavenging system. Thus any inhalational anesthetic agents administered to the patient and retained in tissues and blood before CPB were released into the operating room ambient air during the CPB period.
Statistics
Data are presented as mean ± SD. Calculation and data analysis were performed with a statistical package (GraphPad InStat 3.0; GraphPad Software, San Diego, CA). Statistical significance was determined with Wilcoxon’s matched pairs test or the Friedman test with Dunn’s multiple comparisons test where appropriate. The significance level was established at p less than 0.05.
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Results
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Base line measurements before administration of any anesthetic gases revealed levels of the respective agents below the lower detection threshold of the measurement device. After termination of the supply of inhalation anesthetic agents and with the beginning of CPB the average end-tidal measured concentrations of desflurane amounted to 4.60 ± 0.78 vol/100 mL. The mean end-tidal concentration of sevoflurane was 2.07 ± 0.12 vol/100 mL while that of nitrous oxide was 59 ± 4 vol/100 mL. Within the first 4.5 minutes of CPB markedly increased concentrations of the respective anesthetic agents were measured from the outlet socket (Table 1).
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Table 1. Concentrations of Nitrous Oxide, Desflurane, and Sevoflurane at Gas Outlet Sockets of Pumps Oxygenator During First 4.5 Minutes of Cardiopulmonary Bypass
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The time of exposure before and during CPB is shown in Table 2. A 20-minute period required for central venous and bladder catheterization adds to the exposure time of the anesthesiologist that is given in Table 2. Because the patient’s preparation was performed in a room separate from the operating room that had different air conditioning features, waste anesthetic gas levels were not determined during this period.
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Table 2. Operating Room Staff Occupational Exposure to Nitrous Oxide, Desflurane, and Sevoflurane Before and During Cardiopulmonary Bypass (CPB)
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The average concentrations of the anesthetic gases used were low in the breathing zone of both anesthesiologist and surgeon before CPB. During CPB nitrous oxide levels dropped significantly in the breathing zone of both anesthesiologist and surgeon while the desflurane load posed to the surgeon increased significantly during CPB and exceeded the recommended NIOSH limit. In spite of the fact that the perfusionist was sitting close to the oxygenator of the extracorporeal circuit, significant differences in the load between perfusionist and surgeon could not be found; however the anesthesiologist who was furthest away from the pump’s oxygenator was exposed significantly less (Table 2).
Although waste anesthetic gas concentrations were measurable, the recommended threshold value given by the NIOSH of 25 ppm for nitrous oxide as a time-weighted average during exposure was not violated at any time. The recommended limit of 0.5 ppm for desflurane during concomitant exposure to nitrous oxide could not be kept, whereas the administration of sevoflurane did not violate the 0.5 ppm limit (Table 2).
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Comment
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The results of the present study show that inhalational anesthetic agents administered before the beginning of CPB led to occupational exposure of cardiac surgeon, perfusionist, and anesthesiologist to trace concentrations of the agents used. Chronic exposure to waste anesthetic gases has been shown to have adverse effects on the health of exposed individuals. During the past decades a number of studies suggested a correlation between chronic exposure and reproductive toxicity among medical personnel [2, 3, 9–11]. Furthermore, significant reduction of perceptual, cognitive, motor, and driving skills has been demonstrated in a number of studies that investigated the effects of trace concentrations of nitrous oxide and volatile anesthetic agents on exposed personnel [15–17]. Despite these implications none of the operating room personnel complained about any subjective or objective discomfort or impairment during our study.
The time-weighted averages of the nitrous oxide and sevoflurane during CPB were below the threshold limits of 25 ppm and 0.5 ppm recommended by the NIOSH, respectively. The perfusionist was exposed to an average concentration of nitrous oxide of 3.70 ± 1.40 ppm. Sevoflurane exposure was 0.18 ± 0.03 ppm. The surgeon was exposed to slightly lower levels of these agents than perfusionists. If desflurane was used to maintain anesthesia before CPB, the NIOSH limit was exceeded by 32.0% for perfusionists and by 12.4% for surgeons, respectively, while the anesthesiologist received only marginal levels of any agent. Maximum concentrations of anesthetic agents were measured at the gas outlet sockets of the oxygenator immediately at the beginning of CPB. However because of dilution effects, actual exposure of both surgeon and perfusionist was much lower in our study but end-tidal enflurane of 1.1 vol/100 mL resulted in a contaminant level of 2 ppm at 95 cm from the oxygenator in another study, thus posing a potential health hazard to the perfusionist [13].
Although the concentrations of inhalational anesthetic agents measured in the present study were low, the trace concentrations of desflurane measured in the breathing zone of surgeon and perfusionist did not fulfill the strict specifications of the NIOSH. Regardless of the fact that during the bypass period inhalation anesthetic agents were not administered, redistribution mechanisms in the organism of the patients may contribute to the release of these anesthetic agents through oxygenator into the operating room air. If sevoflurane and desflurane were being administered further during CPB the theoretical risk of contamination would have been even higher. Connecting the oxygenator to a waste gas scavenger results in substantial reduction of personnel’s occupational exposure. Hoerauf and coworkers [14] could demonstrate that the use of scavenging devices at the pump’s oxygenator contributed to a significantly reduced exposure of the perfusionist to 0.26 ppm of desflurane. Significantly higher loads up to 6.10 ppm occurred with a renouncement of the suction mechanism. Our data as well as those from older studies [13, 14] underscore the need for routine use of adequate waste gas scavenging systems on CPB equipment if the end-tidal concentration of the volatile agent cannot be significantly decreased before CPB.
A further possibility to diminish the risk of occupational exposure of medical personnel to inhalational anesthetic agents is renouncement of the agents along with the use of nitrous oxide thereby increasing the limit for the respective volatile agent to 2 ppm. With this precaution the administration of desflurane before CPB did not violate the current NIOSH limit.
Even if the trace concentrations of anesthetic agents were low in the present investigation the NIOSH limit for desflurane could not be ensured. Because chronic exposure to waste anesthetic gases can cause significant impairment of cognitive skills and personal performance, not only anesthesiologists must be aware of this potential hazard but also anybody working in areas where inhalational anesthetic agents are being administered should. To keep occupational exposure to waste anesthetic agents as low as possible, all measures must be taken including sufficient air conditioning, waste gas scavengers, recurrent analyses of room air in the vicinity of the pump, and even the consideration to avoid inhalational anesthesia and use intravenous agents instead.
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References
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Abstract
Introduction
