NIOSH concentration limits

Greater than 200,000 health care professionals are exposed to anesthetic gas waste and are at risk of occupational illness. Through improvements in scavenging systems, more effective ventilation systems, an increased attention to equipment maintenance and leak detection, and careful anesthetic practices, there have been significant improvements in minimizing anesthetic gas pollution; however, occupational gas waste exposure still exists.

The National Institute for Occupational Safety and Health (NIOSH) has recommended exposure limits (RELs) for both nitrous oxide and halogenated agents. When nitrous oxide is used as the sole inhaled anesthetic agent, the REL for nitrous oxide (in 1977) is 25 parts per million (ppm) as a time-weighted average (TWA) during the anesthetic administration period. In regards to halogenated anesthetic agents (chloroform, trichloroethylene, halothane, methoxyflurane, fluroxene, and enflurane), NIOSH’s REL (established in 1977) is 2 ppm over a sampling period of an hour. No occupational exposure limits exist for isoflurane, desflurane, and sevoflurane.

Human subject studies evaluating the occupational risk of nitrous oxide suggest that high levels of unscavenged N₂0 can impair fertility, increase the risk of spontaneous abortion, and decrease the ability to perform complex tasks. In animal studies, nitrous oxide has been shown to be teratogenic when rats are chronically exposed to very high concentrations (>1000 ppm).

There are limited studies on the occupational risk of halogenated agents (the majority predated the use of scavenging systems); some have shown an increased risk of spontaneous abortions in exposed female anesthesiologists, nonphysician female OR personnel, and wives of exposed males. An association between halogenated anesthetic exposure and congenital anomalies is inconclusive, but many studies suggest that halothane has teratogenic properties at high concentrations. With limited data available, it is prudent to minimize occupational exposure to all anesthetic agents.