Chronic exposure to inhaled anesthetics, especially nitrous oxide, can lead to hematotoxicity. Nitrous oxide irreversibly oxidizes the cobalt atom of vitamin B12, inactivating methionine synthase and so interfering with the recycling of vitamin B12 and folate, which produces a functional deficiency of this important vitamin. Chronic vitamin B12 deficiency can result in megaloblastic anemia and neuropathy. Hematotoxicity is a particular concern in patients who already have low B12 levels or those who are exposed to nitrous oxide for extended periods. Pregnant women exposed to nitrous oxide may also face teratogenic risks, as vitamin B12 disruption can cause developmental problems in the fetus, including cognitive impairment.
Another concern with chronic use of inhaled anesthetics is their potential teratogenic effects. Although clinical trials in humans have not conclusively demonstrated a significant risk, animal studies suggest that inhaled anesthetics, particularly nitrous oxide, may increase the risk of birth defects when administered to pregnant patients. This underscores the importance of careful consideration when using inhaled anesthetics in pregnant women.
Inhaled anesthetics are also greenhouse gases, and the harm here is environmental rather than to the patient. Desflurane has by far the highest 100-year global warming potential (about 2,500 times carbon dioxide, against about 510 for isoflurane and 130 for sevoflurane), and nitrous oxide persists in the atmosphere for over a century and depletes stratospheric ozone. Low fresh gas flows, avoiding desflurane and routine nitrous oxide, and effective scavenging limit both the carbon footprint and the occupational exposure of operating room staff.
| Toxicity | Agent most implicated | Mechanism and clinical point |
|---|---|---|
| Carbon monoxide poisoning | Desflurane | Forms when the agent interacts with dry carbon dioxide absorbers; carbon monoxide accumulates if absorbers are not replaced |
| Nephrotoxicity | Sevoflurane | Fluoride ions and compound A (formed with carbon dioxide absorbent at low fresh gas flows) injure the kidney in animals; no lasting renal injury shown in humans. Label: fresh gas flow at least 1 L/min, 2 MAC-hour limit at 1 to 2 L/min, caution in renal insufficiency |
| Malignant hyperthermia | All volatile agents (not nitrous oxide) | Hypermetabolic crisis in susceptible patients; rising end-tidal carbon dioxide is the first sign; stop the trigger and give dantrolene 2.5 mg/kg IV |
| Hepatotoxicity | Halothane | Repeated exposure can produce halothane-induced hepatitis progressing to acute liver failure |
| Hematotoxicity | Nitrous oxide | Interferes with vitamin B12 recycling; chronic deficiency causes megaloblastic anemia and neuropathy |
| Teratogenicity | Nitrous oxide, volatile agents | Suggested by animal studies and by vitamin B12 disruption; human trials have not conclusively demonstrated significant risk |
| Carcinogenicity | Volatile agents | Raised by some laboratory studies, but no reliable supporting evidence from human studies |
| Neurologic effects | Inhaled agents generally | Cognitive dysfunction and long-term brain injury have been reported inconsistently and are not consistently demonstrated in practice |
