Exposure to Waste Anesthetic Gases in the PACU

  • Jain, Uday, MD, PhD
| Aug 12, 2019

Uday-JainPatients who have received inhalational anesthetics in the operating room (OR) continue to exhale them in the post anesthesia care unit (PACU). This leads to the presence of waste anesthetic gases (WAGs) in the PACU. Exposure to WAGs is known to be potentially toxic. This is a significant yet underappreciated problem.

Recommended Exposure Limits

In 1977, the National Institute for Occupational Safety and Health (NIOSH) issued informational advisory regarding recommended exposure limits (RELs) for medical personnel for nitrous oxide and halogenated anesthetics1. These guidelines are not based on strong scientific evidence and are not a standard or regulation.  

When nitrous oxide is the sole anesthetic, REL is 25 parts per million (ppm) time-weighted average over the exposure period. For halogenated anesthetics, rather than a time-weighted average, there is a ceiling of 2 ppm over a sampling period not to exceed one hour.

Limitation of Space

In PACU, several patients may recover in a relatively small area. Patients get exposed to WAGs produced by other patients. Patients who require PACU admission after monitored anesthesia care, regional or total intravenous anesthesia should preferably be placed in a separate area than those who received inhalational anesthetics. Many medical personnel may be exposed in the PACU, which may also be adjacent to other busy areas including preoperative holding area and preoperative clinic. It is advisable to separate phase I recovery area from phase II recovery and other busy areas.


In anesthetizing locations and PACUs, high ventilation is utilized to keep the levels of WAGs lower than RELs. For OR, trauma room, angiography suite, and delivery room, air change rate (room dilution ventilation) of a minimum of 15 air changes per hour with a minimum of 3 changes of outdoor air per hour is recommended2. For PACU, intensive care unit (ICU) and endoscopy suite, a minimum of 6 air changes per hour with a minimum of 2 changes of outdoor air per hour is recommended2. Thus, air change rate in PACU is less than that in the OR.

WAGs May Exceed REL

A number of studies have documented that when the guidelines for ventilation are followed, the measured levels of WAGs in PACU do not exceed the RELs.3, 4, 5 Nitrous oxide is more likely to be detected than the halogenated anesthetics. However, other studies have documented that even when the guidelines are followed, the measured levels of WAGs in PACU exceed the RELs intermittently6 and even usually7.

Extubation in PACU

Higher levels of WAGs are especially likely if patients are extubated in the PACU8. These patients arrive in PACU with greater quantities of residual inhalational anesthetics. Exhaled gases from an airway device are usually scavenged in the OR but not in the PACU. As a result, there is increased amount of WAGs in a patient’s breathing zone and thus potentially in the working zone of medical personnel. This can be mitigated by extubating in the OR and/ or scavenging in the PACU.

Adjustable ventilation

It has been suggested that ventilation may be adjusted to match the WAGs produced. The levels of WAGs can be measured in real time and utilized for regulating the amount of ventilation9. However, this is not common practice as the required equipment is expensive.


Scavenging can reduce the amount of WAGs but is usually not utilized in PACU. Extubated patients may utilize an oxygen mask that also scavenges exhaled gases. Teleflex ISO-Gard® Mask with ClearAir™ Technology is such a mask. It reduced WAG exposure of patients as well as medical personnel10, 11. This mask is not in common use. 

Effect on medical personnel

Exposure to WAGs has been associated with irritability, fatigue, headache, nausea, drowsiness, impaired judgment, and lack of coordination12,13. Halogenated anesthetics have neurotoxic, hepatotoxic, genotoxic, mutagenic and adverse reproductive effects14. They cause respiratory depression. The effect of chronic exposure is cumulative. However, the incidence of clinical disorders is very low.  

Cellular Damage

Halogenated anesthetics are immunosuppressive, genotoxic, and mutagenic. They cause cellular damage, cell proliferation, hyperplasia, and tumor genesis. Genotoxicity and mutagenicity may be due to oxidative metabolism producing reactive oxygen species (ROS). Imbalance between ROS and antioxidants leads to oxidative stress causing damage to the genome. Free radicals which are unstable reactive molecules with unpaired electrons can cause lipoperoxidation, protein damage, and oxidative damage to nucleic acids. Interaction between free radicals from oxygen or nitrogen with DNA bases results in oxidized bases, abase sites and/or DNA strand breaks.

Halogenated anesthetics may cause genotoxicity including sister chromatid exchange, positive comet test of DNA damage and micronucleus formation which diminishes cellular viability. Micronuclei are fragments of chromosomes or whole chromosomes derived from the nucleus of the daughter cell during cell division. They are associated with diminished cellular viability.

Nitrous oxide

It’s presence in PACU is well documented. It oxidizes the cobalt ion in cobalamin (vitamin B12). This inhibits methionine synthetase, reducing production of methionine, tetrahydrofolate, thymidine and nucleic acids including DNA. This reduction can cause megaloblastic anemia, agranulocytosis, spinal cord subacute combined degeneration, and neurobehavioral disorders.

Environmental Damage

The amount of WAGs from PACU is much smaller than the amount generated in OR. WAGs act as greenhouse gases in the troposphere, contributing to global warming15. WAGs cause depletion of the ozone layer in the stratosphere15. This increases the amount of harmful ultraviolet radiation from sun reaching the earth.


WAGs in PACU is a problem that is now receiving increasing attention. It should be confirmed that the ventilation in PACU meets the guidelines. Level I recovery area should be separated from other patient care areas. Extubation in PACU should be avoided as it is likely to increase the level of WAGs beyond the REL. Although WAGs can have many adverse effects, the incidence of clinical disorders is very low. 


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