Occupational Safety, Infection Control, and Substance Abuse

Provider Health Effects

One of the first examinations of the impact of exposure to subanesthetic concentrations of inhalational anesthetics on cognitive performance was conducted by Bruce and Bach in the 1970s. They noted that healthy volunteers in the laboratory suffered a decrease in psychomotor performance when exposed to concentrations of N ₂ O as low as 50 ppm, alone or in combination with 1 ppm of halothane. The same study showed that 25 ppm of N ₂ O combined with 0.5 ppm of halothane had no effect. Subsequently, three other groups of researchers studying volunteers in laboratories have been unable to confirm the earlier findings. The lack of agreement between investigators has led some to conclude “that there is no convincing evidence that anesthetics in concentrations equal to those found in unscavenged operating theatres have any effect on the psychomotor performance of healthy subjects in the laboratory.” A study conducted on volunteers in an operating room during normal clinical activities in which trace concentrations of N ₂ O and halothane ranged from 0 to 2300 and 0 to 37 ppm, respectively, also failed to detect impairment in psychomotor performance. In contrast, a series of studies in healthy volunteers showed that subanesthetic concentrations of N ₂ O, isoflurane, and sevoflurane were associated with reductions in psychomotor performance, with some studies suggesting a dose-dependent effect for N ₂ O dose as low as 10% and a sevoflurane dose as low as 0.4%. By way of comparison, 10% N ₂ O is equivalent to 100,000 ppm, significantly higher than the recommended safe level of exposure and the level of exposure in the Bruce and Bach studies. Whether the methods in these studies closely mimic patterns of occupational exposure in clinical practice is debatable, but it must be acknowledged, as discussed later, that occupational exposure may greatly exceed accepted safe levels.

Fetal Health Effects

Anesthetics have been implicated in the development of cancer, spontaneous abortions, and genetic and developmental anomalies. The possibility that chronic exposure to anesthetic waste gases could result in adverse health effects was first appreciated in the late 1960s, when a report of potential harm appeared in the Russian literature; Vaisman reported an increased incidence of abortions (18 spontaneous abortions in 31 pregnancies) among female anesthetists. After this initial report, a multitude of retrospective studies followed. Of these, three large studies conducted during the 1970s and 1980s in the United States and the United Kingdom all concluded that the prevalence of spontaneous abortion was substantially higher in female anesthesiologists than in female physicians working outside the operating room. Studies in this era also concluded that the incidence of congenital anomalies in children of male and female anesthesiologists was higher than in the control groups of physicians. In addition to these reproductive effects, meta-analysis of six of these early studies linked the exposure to anesthetic gases to hepatic disease in male anesthesia personnel and cervical cancer, liver disease, and kidney disease in female anesthesia personnel. A number of studies with similar methodologies failed to detect a relationship between exposure and health. Although many of these older studies suffered from significant methodologic limitations, a 1997 meta-analysis of more than 19 studies completed between 1984 and 1992 reported a relative risk of abortion in female subjects exposed to anesthetic gases to be 1.48 (confidence interval [CI] 95%, 1.4-1.58).

The Task Force on Trace Anesthetic Gases was convened by the American Society of Anesthesiologists (ASA) Committee on Occupational Health of Operating Room Personnel to analyze data from all available epidemiologic studies. The methodologic flaws in the studies impaired the task force’s ability to draw conclusions about an association between occupational exposure to waste anesthetic gases and adverse health effects. Their report, published in 2002, cited data from a prospective survey of 11,500 U.K. female physicians documenting occupation, work practices, lifestyle, and medical and obstetric history, as well as hours of exposure and the use of scavenging equipment. This report showed the incidence of infertility, spontaneous abortion, and children with congenital abnormalities in female anesthesiologists to be the same as that in other physicians. The position of the ASA is that “There is no evidence that trace concentrations of waste anesthetic gases cause adverse health effects to personnel working in locations where scavenging of waste anesthetic gases is carried out” and “the general conclusion… is that currently used anesthetics… have no mutagenic potential.” This reassurance may be of little comfort in light of evidence and clinical experience that show levels of exposure in clinical practice routinely exceed those considered safe by health and regulatory agencies. The task force document also summarized contemporaneous recommendations from the Occupational Safety and Health Administration (OSHA) recommending that from the employee’s “Right to Know,” there are “potential adverse effects of exposure to waste anesthetic gases such as spontaneous abortions, and congenital abnormalities in children.”

Subsequently, there have been several more studies that support the possibility of an intrauterine effect. An analysis of Canadian nurses identified significant odds of congenital anomalies in the offspring of nurses working in settings with exposure to waste anesthetic gases compared with those working in settings where the likelihood of exposure was lower. Subsequent research using chromosomal and molecular DNA analysis identified correlations between exposure and genotoxic effects (e.g., sister chromatid exchanges, breaks in DNA, and chromosomal abnormalities) but did not examine clinical outcomes in offspring. However, these more recent epidemiologic and genetic studies did not quantify exposure but rather assumed exposure by selecting health care workers from settings where exposure was assumed to have taken place.

Given the study limitations, the lack of consensus or updated ASA guidelines, and the findings that safe inhalational anesthetic levels may often be exceeded, it must be acknowledged that harm is possible. Manufacturers of anesthesia work stations, health care systems, and clinicians must remain vigilant to reduce risk.

Mitigating Health effects

The potential health effects of occupational exposure to anesthetic gas can be mitigated through waste anesthesia gas scavenging systems, establishing levels of safe exposure, auditing exposure levels, and enforcing recommended frequencies of air exchanges in locations where anesthesia gas may be found (e.g., operating rooms, procedural suites, and recovery areas).

Although the universal use of scavenging systems is critical to safe, modern anesthesia practice, it can lead to a false sense of security among operating room personnel. Kanmura and colleagues found abnormally high ambient concentrations of N ₂ O in 402 delivered anesthetics, of which 42% were the result of mask ventilation, 19.2% a disconnected scavenging system, 12.5% a leak around pediatric endotracheal tubes, and 11.5% equipment leakage. Furthermore, all of the scavenging system disconnects in this study were attributed to human error rather than equipment failure. Because most anesthesia machines were not equipped to recognize disconnected scavenging systems, a fault that has been corrected on most modern anesthesia machines, a failure of the system on older machines may not be readily apparent. Diligent maintenance and a thorough understanding of anesthesia scavenging systems are essential to comply with NIOSH standards and to minimize operating room exposure. Emerging evidence exists for the role of various activated charcoal compounds to absorb molecules of anesthetic vapor, but these have been trialed only in experimental settings and are not yet available commercially.

Regulations and recommendations regarding workplace safety are established by several governmental agencies. The OSHA is the national agency within the U.S. Department of Labor that sets and enforces standards to ensure “safe and healthful working conditions.” The Centers for Disease Control and Prevention (CDC) and NIOSH are both federal agencies conducting research and making recommendations regarding health and workplace safety. Unlike OSHA, neither the CDC nor NIOSH are regulatory agencies. State and local health departments, as well as hospital infection control departments, are also tasked with enacting and enforcing health care workplace safety standards.

The NIOSH sets recommended exposure limits for the operating room setting, stating “no worker should be exposed … [to] concentrations greater than 2 ppm of any halogenated anesthetic or 25 ppm of N ₂ O” in the 1970s. These exposure limits have not been updated nor do they include newer volatile anesthetic drugs. These exposure levels were selected based on the lowest level known at the time to cause side effects (50 ppm N ₂ O or 1 ppm of halothane caused cognitive impairment in dental students) and the level that could be easily and practically achieved. Subsequently, it was realized that the data used to set the standards might not be generalizable because the subjects were Mormon, a subgroup likely more sensitive to depressant drugs ; a more recent study with a small sample size showed cognitive impairment at 50 ppm of N ₂ O, levels that are routinely found in studies and are well above the NIOSH levels. The threshold of perception of halothane ranges from less than 3 to more than 100 ppm. If the anesthetic can be smelled, its concentration is likely to be many times greater than the maximum recommended level.

Occupational exposure is not limited to operating room staff, because patients continue to exhale trace amounts of N ₂ O for 5 to 8 hours postoperatively. Sessler and Badgwell used lapel dosimeters to measure the concentrations of volatile anesthetics of recovery room nurses during the first hour of PACU care in patients who had received inhaled anesthetics. In this study, breathing zone anesthetic concentrations were in excess of NIOSH recommendations in 37% of patients who received isoflurane, 87% of patients who received desflurane, and 53% of patients who received N ₂ O. A more recent but similar study reported a much lower average concentration (3.1 ppm) of N ₂ O in the breathing zone of recovering patients in a Canadian PACU, also above the recommended safe levels of exposure. These studies demonstrate the importance of proper ventilation in PACUs. Both groups reported PACU room air exchanges of 8 volumes per hour, although much of the air in the Sessler and Badgwell study was recirculated. N ₂ O levels can be reduced to undetectable levels with air exchanges of 20 per hour, with 25% of each exchange taken from fresh air. Although OSHA does not currently regulate exposure to N ₂ O and halogenated anesthetics, the agency does provide guidelines designed to minimize workplace exposure. These include the appropriate assembly and monitoring of scavenging systems, the detection and correction of machine leaks, and the installation of effective ventilation systems. In the operating room, the recommended air exchange rate is a minimum of 15 air exchanges per hour, with at least 3 air exchanges of outdoor air per hour. Laminar flow is better than turbulent flow with regard to measured levels of exposure. In the PACU, at least 6 air changes are recommended, with a minimum of 2 exchanges of outdoor air per hour. OSHA recommends air sampling for anesthetic gases be performed on a biannual basis and records of air sampling methods, locations, dates, and concentrations measured, as well as results of anesthesia machine leak tests, be maintained for at least 20 years. Although OSHA is a government agency, these recommendations are not legally mandated.

In summary, the possibility that waste anesthetic gas at levels routinely encountered in clinical practice could cause deficits in performance and human health remains. Caution must be exercised, and clinicians should limit their exposure as much as possible.

Ionizing Radiation: X-rays

In the past, exposure to radiation occurred mostly in the operating room with the use of portable fluoroscopy and x-ray machines. Advancements in endovascular surgery, hybrid cardiac surgery procedures, electrophysiology studies, and other imaging procedures significantly increase exposure of anesthesia personnel to ionizing radiation relative to traditional operating room cases. Radiation is undetectable with our normal senses, so a basic understanding of its features will minimize exposure.

One Sievert (Sv) is equal to 100 rem and is a measure of the biologic damage from radiation adjusted to apply to all tissues. Estimates of radiation exposure from natural sources vary, depending on geographic location. The average in the United States ranges from 0.8 to 2 mSv (80-200 millirem [mrem]) per year. Natural radiation comes primarily from cosmic rays (approximately 0.4 mSv at sea level, with an increase of 0.1 mSv/1000 feet), as well as from radioactive compounds found in soil, brick, and concrete. For most physicians, the additional radiation from occupational exposure is no greater than that from natural sources. OSHA sets limits of occupational exposure (expressed as rem) that vary by body area; allowable limits are higher for the hands than for the whole body, gonads, or blood-forming parts of the body. An easy rule of thumb is 5 rem (50 mSv) per year, with no more than 1.25 rem (12.5 mSv) in any given calendar quarter. In 2007 the International Commission on Radiological Protection, an international nonprofit, proposed more stringent limits than those proposed by OSHA ( Table 88.1 ), and both agree that limits should be lower for personnel who are pregnant.

Occupational exposure to radiation comes primarily from x-rays scattered by the patient and the surrounding equipment, rather than directly from the x-ray generator itself. One chest radiograph results in approximately 25 mrem of exposure to the patient; procedures requiring multiple films occasionally involve more than 1 rem. The amount of radiation generated during fluoroscopy depends on how long the x-ray beam is on; just as light is reflected from surfaces, x-rays are reflected from the surfaces on which they impinge. This scattering accounts for most occupational exposure. Research findings vary about the degree of exposure typical for anesthesia providers, but most studies show low levels of exposure. Recent studies have compared risk profiles of various positions of the anesthetist and the x-ray beam. A simulation-based study using phantom patient and anesthetist models with dosimeters demonstrated that exposure was greater near the head of the bed (vs. along the sides of the bed) or when the x-ray beam was in either of the lateral positions (e.g., shooting cross-table images). A real-time evaluation of exposure in personnel conducting transesophageal echocardiography (TEE) during transcatheter aortic valve replacement showed that the TEE operator receives 5 times as much radiation as other clinicians involved in the procedure. Furthermore, this exposure is heightened by the use of oblique angles for imaging. Notably, by using additional shielding (e.g., a ceiling-mounted lead acrylic shield), this exposure was reduced by more than 80%.

Mitigating Health Effects

Radiation physicists recommend the “As Low As Reasonably Achievable” guiding principle for radiation exposure to both the patient and practitioner. Technologic innovation leading to advances in imaging technology and industrial design may further limit exposure.

Because the intensity of scattered radiation is inversely proportional to the square of the distance from the source, the best protection is physical separation. A distance of at least 3 feet from the patient is recommended. Six feet of air provides protection the equivalent of 9 inches of concrete or 2.5 mm of lead. Using studies of real-time dosimeters and simulation studies using phantom patients, a recent systematic review found that at a 4.9-foot (1.5 m) distance from the x-ray source, exposure was no greater than that due to background radiation. This finding has been replicated in a handful of studies of clinical exposures. The authors go so far as to question the need for anesthesia personnel to wear lead aprons, which conflicts with OSHA recommendations. Although they may be uncomfortable, aprons containing the equivalent of 0.25 to 0.5 mm of lead sheet are effective in blocking most scattered radiation and such devices are recommended to be worn whenever there is an exposure risk. Uncovered areas, such as the lens of the eye, still bear the risk of injury, and radiation dose to the eyes varies with the type of surgery and the position of the anesthesiologist relative to the patient and x-ray field. OSHA recommends opaque goggles for health care workers in the “direct x-ray field.”

Nonionizing Radiation: Lasers

Laser is an acronym for light amplification by stimulated emission of radiation. Lasers produce infrared, visible, or ultraviolet light. A surgical laser produces intense, focused electromagnetic radiation to cut or destroy tissues. Although the radiation from lasers is nonionizing, it is potentially unsafe both because of its intensity and because of the matter released from tissues during treatment.

Of those in common clinical use, carbon dioxide and neodymium:yttrium-aluminum-garnet (Nd:YAG) lasers emit light in the far-infrared and near-infrared wavelengths, respectively; argon and tunable dye lasers produce visible light.

Eye injuries are the greatest risk to personnel working near lasers. Strict standards for protection have been developed based on current understanding but are subject to periodic revision. Either direct exposure or reflected radiation may cause eye damage. Injuries include corneal and retinal burns, destruction of the macula or optic nerve, and cataract formation. Protective eyewear is designed to filter out the radiation produced by a specific type of laser while still permitting vision. For example, clear plastic lenses block the far-infrared (10,600 nm) radiation from carbon dioxide lasers but provide no protection against the near-infrared (1064 nm) radiation emitted by Nd:YAG lasers. The type of protection provided by a given filter is marked on the frame of the goggles and should be checked before use. Filters that are scratched should not be used. Because certain filters block portions of the visible spectrum, it is prudent to confirm preoperatively that patient monitors can be seen and interpreted correctly with goggles in place. Protective eyewear is recommended for all exposed personnel because reflected radiation can be as hazardous as direct radiation and, unlike x-ray radiation, the intensity is not diminished significantly by the distance traveled in the average operating room.

In addition to direct injury from laser light, clinicians should avoid the smoke plume created by lasers. Under experimental conditions, viable bacteria have been recovered from the plume emanating from laser irradiation, as have compounds known to be carcinogens and environmental toxins. Intact DNA from human papillomavirus (HPV) has been detected in the vapor from both laser-treated plantar warts and genital condylomata and on the gloves of treating physicians. Human immunodeficiency virus (HIV) proviral DNA has been found in laser smoke produced by vaporizing cultures of HIV-positive cells. Although these experiments, which used tissue cultures, do not replicate routine clinical circumstances, they stress the importance of strict attention to smoke removal. Simulation studies confirm that concentrations of laser-generated particulate matter are higher near the operating field than elsewhere in the room, sometimes by a factor of four, regardless of the degree of room ventilation.

As an extreme example, a case report documented the appearance of laryngeal papillomas in a laser surgeon who had previously treated several patients infected with anal condylomata without the benefit of a laser smoke evacuator. Tissue from the surgeon’s laryngeal tumors contained HPV DNA types 6 and 11, the same viral types that are commonly harbored by anogenital condylomata. Hence it is prudent to scavenge all vaporized debris.