January 1, 2014 Volume 78, Number 1
ACE Question

One of your practice partners announces she is pregnant and requests assignment to anesthetic cases that will not put her pregnancy at risk. In a modern operating room setting, exposure to which of the following is MOST likely to be teratogenic to the human fetus?


(A) Magnetic resonance imaging (MRI)

(B) X-rays

(C) Trace amounts of halogenated anesthetic gases

(D) Trace amounts of nitrous oxide


Anesthesia caregivers incur occupational exposure to anesthetic gases, radiation, medications, chemicals, solvents, and infectious agents. Women comprise about 30 percent of anesthesiologists, 36 percent of residents, and 51 percent of clinical anesthetists. In the general population, 10 to 20 percent of women who know they are pregnant will miscarry before 20 weeks gestation. Survey evidence indicates there is a slight increase in the relative risk of spontaneous abortion and congenital abnormalities in offspring of female operating room physicians, however the etiology for this risk remains uncertain.


Although MRI does not involve ionizing radiation, cells are exposed to strong magnetic fields. This technology has been in use for 25 years, and, to date, there is no evidence of adverse fetal outcomes due to in utero exposure to MRI. Occupational exposure has been studied, and according to the 2007 American College of Radiologists Guidance Document for Safe MR Practices pregnant health care providers are permitted to work in and around the MR environment. There is a stipulation that the health care provider should not be within the scanner room during data acquisition. http://www.acr.org/Quality-Safety/Radiology-Safety/MR-Safety


Prenatal radiation exposure represents an undeniable risk to the fetus. This risk is dose-related, dose being expressed in dose equivalents. Dose equivalents are obtained by multiplying the absorbed dose (Gy in the International system) by the damaging ability of the radiation; this is expressed as the Sievert (Sv), and 1 Sv = 100 rem. A single radiograph exposes a patient to less than 1 mSv, computed tomography scans expose the patient to 5 to 10 mSv, and interventional radiology or cardiac catheterization may represent 20 to 70 mSv. The total recommended exposure during pregnancy is 5 mSv, with a monthly limit of 0.5 mSv. At these recommended levels, there have been no observable effects on fetal growth or development. A meta-analysis conducted in 2008 estimated that cardiologists performing a routine catheterization would be exposed to 0.2 to 38 μSv, indicating low exposure rates for health care workers even in high radiation environments. Of utmost importance is to limit time of exposure, remain more than 6 feet from the radiation source, and use shielding. Adherence to these recommendations should result in exposure levels well below the recommended maximum and therefore cause no fetal teratogenicity.


In a 2011 study by McLoughlin et al., no indication of harm was found in a prenatal exposure of <5 mSv, but with increasing exposures came increased morbidity. Prenatal exposure to 5-50 mSv resulted in increased childhood leukemia, other childhood cancers; 5-500 mSv increased miscarriage, central nervous system abnormalities, developmental delay, childhood cancers and with exposures greater than 500 mSV increased neonatal deaths, microcephaly, severe developmental delay, and childhood cancers.


The teratogenicity of halothane and isoflurane has been demonstrated in rats, mice, and hamsters exposed to high levels of agent for prolonged periods. Later animal studies in rats and rabbits in conditions simulating anesthetized human patient exposure revealed no teratogenicity. A recent meta-analysis of occupational exposure, excluding flawed studies, concluded a risk of spontaneous abortion in unscavenged environments to be 1.9. No recent studies show an association of fetal anomalies with exposure of health care workers to potent anesthetic agents.


Numerous studies have examined the potential teratogenic effect of nitrous oxide through inhibition of methionine synthesis. It has been generally agreed that nitrous oxide has been associated with first trimester loss, but not because of teratogenicity. The studies showing spontaneous abortion in humans are both retrospective and epidemiologic. In particular these early studies, conducted in the 1970s and 1980s, were mail surveys of anesthesiologists, operating room nurses, dentists, and dental assistants and suffered from several design flaws. Lack of criteria for poor outcome, poor survey response rates, and lack of validation of the responses are issues. In addition, the operating conditions in various locations did not have scavenging systems, and it has been shown that proper scavenging significantly reduces occupational exposure.


Answer: D


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1. Meyer CL. Occupational hazards for the pregnant anesthesia provider. Adv Anesth. 2011:39-58.

2. Berry AJ, Katz JD. Occupational health. In: Barash PG, Cullen BF, Stoelting RK, Cahalan MK, Stock MC, eds. Clinical Anesthesia. 6th ed. Philadelphia, PA: Wolters Kluwer/Lippincott Williams & Wilkins; 2009:57-63.