Anaesthetic Gas Exposure in Operating Theatres

Anaesthetic gas exposure: what is waste gas, and who is affected?

In general anaesthesia, part of the nitrous oxide and halogenated agents such as sevoflurane, desflurane and isoflurane given to the patient escapes into the room before reaching the patient or with the patient's exhaled air. This gas escaping into the room is called waste anaesthetic gas. Anaesthetic gas exposure is not limited to the anaesthesia team: the surgeon, the theatre nurse, the anaesthesia technician, cleaning staff and the nurses working in the recovery room where the patient wakes up all breathe the same air.

The level of exposure varies not from person to person but from procedure to procedure. The anaesthesia technician standing at the head of a child patient induced by mask and the surgeon at the far end of the operating table may be in the same room, but they do not breathe the same amount of gas. The risk assessment should therefore be carried out by procedure and task, not under the general heading "operating theatre". We explained the steps of chemical risk assessment in our article on the chemical risk assessment method.

Where does waste gas leak from?

Most waste gas comes from a few familiar sources. Knowing the source also shows where the measure should go.

Source	When does it happen?	Measure
Mask edge	Mask induction, especially in child patients	A mask that fits the face, a tight seal, intravenous induction if necessary
Gas flow turned on too early	Before the patient is connected to the circuit	Turning on the flow after the patient is connected
Circuit and connection leaks	Hoses, connectors, absorber canister	Leak test every day and before each case
Around the tube or laryngeal mask	If the cuff is insufficient or the mask does not seat fully	Cuff pressure check, choosing the right size
Vaporiser filling	When transferring from the bottle to the vaporiser	Keyed (closed) filling adaptor, filling at the start of the day rather than between cases where possible
End of procedure	When the mask is removed without turning off the flow; gas exhaled by the patient	Turning off the flow and emptying the circuit into the scavenging system
Recovery room	Gas exhaled by the patient on waking	Room ventilation and bedside arrangement

Many of these sources are related not to equipment but to habits. Turning on the flow before the patient is connected, or removing the mask from the face at the end of the case without turning off the flow, are practices that can be changed quickly through training. Low-flow anaesthesia also reduces the amount of gas that can escape into the room; this clinical decision belongs to the anaesthesia team.

The waste gas scavenging system and operating theatre ventilation

The two systems should not be confused:

The waste gas scavenging system collects excess gas leaving the anaesthesia machine's exhaust valve and the circuit at source and discharges it outside the building. This is the main measure that captures the gas before it spreads into the room.
Operating theatre ventilation dilutes gas that has escaped into the room and carries it outside. Theatre ventilation systems are installed to design standards; however, even good general ventilation may not sufficiently reduce the concentration at the patient's head of gas that is not captured at source.

Practical checklist for the scavenging system:

In every theatre, is the scavenging hose connected to the anaesthesia machine, and is it kinked or crushed?
In active systems, is the suction indicator in the correct range? If there is no indicator, ask the biomedical unit.
Is a leak test carried out and recorded at the machine's morning check and before each case?
Are the maintenance and performance test records of the ventilation and scavenging system up to date?
Does ventilation that runs at low speed at night or at weekends return to normal speed when an emergency operation starts?

These records should not stay in the technical service's file but should be attached to the risk assessment. When the scavenging system fails, the resulting risk is not technical but a risk to employee health.

The recovery room: an often forgotten exposure area

When the operation is over, the patient is taken to the recovery room and continues to exhale the anaesthetic gas in their body for some time. Recovery rooms have no anaesthesia machine or scavenging system; and the nurse works close to the patient's face. Field assessments carried out in recovery units by the US National Institute for Occupational Safety and Health (NIOSH) have shown that halogenated gas levels in these areas can exceed recommended values.

Recommendations for the recovery room:

Verify that room ventilation works as designed and is sufficient for the number of patient beds.
Set up a bed arrangement that lets the nurse working at the bedside keep their face away from the direction of the patient's breath.
Include the operating theatre and the recovery room together in the measurement plan; measuring only in the theatre leaves the picture incomplete.

Operating theatre staff health and health surveillance

Headache, fatigue, nausea, drowsiness and lapses of attention are reported with high levels of waste gas exposure. Nitrous oxide is known to interfere with vitamin B12 metabolism; this effect becomes significant with long-term, high exposure. Effects on reproductive health have been debated, particularly in studies from periods when scavenging systems were not widespread.

For operating theatre staff health, the workplace physician monitors the following:

Asks separately about complaints that may be related to exposure at pre-employment and periodic examinations.
Requests tests if considered necessary; decides which tests are carried out and how often according to exposure. The general rules on examination frequency are in our article on periodic examinations and tests.
Carries out a separate assessment for an employee who reports a pregnancy (see below).

We plan tests with authorised laboratories and healthcare providers.

Working instructions for the anaesthesia team

Because a significant part of waste gas is related to working habits, a written working instruction and short training based on it are the lowest-cost measures. The instruction should contain at least the following steps:

At the start of the day, leak test the anaesthesia machine and confirm that the scavenging hose is connected.
Fill vaporisers, where possible, before the operating list starts, using a keyed filling adaptor; if there is a spill, ventilate the room and record the incident.
Turn on the gas flow after the mask is sealed on the patient's face or the patient is connected to the circuit.
For mask induction, choose a mask that fits the face and keep edge leakage to a minimum.
At the end of the case, turn off the flow, empty the circuit into the scavenging system and only then remove the mask.
An employee who notices a gas smell, an unusual headache or dizziness should report it to the person in charge and to the workplace physician.

Add the instruction to the induction training of nurses and technicians new to the theatre; it should not remain only in the knowledge of anaesthetists.

Measurement: which value is it compared with?

The Annex 1 table of the Regulation on Health and Safety Measures for Work with Chemical Substances contains no occupational exposure limit value for anaesthetic gases. In this case, Art. 19/4 of the Regulation on Industrial Hygiene Measurements, Tests and Analyses applies: where there is no limit value in the legislation, the limit value published by international organisations is used, taking the measurement method into account.

Points to watch in measurement:

Exposure is determined by personal samples taken from the breathing zone of the anaesthesia technician and nurse. A static area measurement is not compared with a personal limit value.
Measurements should also be made on days representing the worst case, such as lists with mask inductions.
Spot surveys with direct-reading instruments are useful for finding leak points but do not replace personal exposure measurement.

We plan measurements with authorised laboratories that report them on ISG-KATİP (the Ministry's online OHS registration system) and enter the results in the risk assessment. When measurement is mandatory at which workplace is explained in our article on workplaces where workplace measurement is mandatory.

Pregnant operating theatre employees

For an operating theatre employee who reports a pregnancy, the assessment is carried out within the framework of the Regulation on the Working Conditions of Pregnant or Breastfeeding Women, Breastfeeding Rooms and Childcare Facilities.

Check the reproductive toxicity classification of every anaesthetic agent used in its safety data sheet; our article on how to read a safety data sheet explains the relevant sections of the form. In practice the safest option is to keep the pregnant employee temporarily away from high-exposure points such as mask induction and the recovery room. For other arrangements, see our article on pregnant and breastfeeding employees.

We address these headings together in our risk assessment and workplace physician services for hospitals, private clinics with operating theatres and healthcare facilities using nitrous oxide for sedation in Bursa and the surrounding provinces. Our approach to the sector is on our healthcare facilities page; measurement and examination dates can be tracked with the OHS calendar tool.

Frequently Asked Questions

Is anaesthetic gas measurement in operating theatres mandatory?

The Chemical Substances Regulation requires regular measurement of chemicals that may pose a risk to employee health and repeat measurement after changes affecting exposure. If the risk assessment finds waste gas exposure significant, measurement should be planned; it is carried out by an authorised laboratory.

Does operating theatre ventilation replace the waste gas scavenging system?

No. Ventilation dilutes gas that has escaped into the room; the scavenging system captures the gas at the point where it leaves the anaesthesia machine. The scavenging system is the main measure, and ventilation complements it.

Is there exposure in the recovery room too?

Yes. The patient continues to exhale anaesthetic gas while waking up, and the nurse works close to the patient's face. The recovery room must be included in the measurement plan and ventilation checks.

Can a pregnant employee continue working in the operating theatre?

When a pregnancy is reported, the employer must assess the exposure and, if there is a risk, change the working conditions or move the employee to other work. The decision is made by the workplace physician and the specialist, together with the classification of the agents used and the measurement results.