Pollution in theatre and scavenging

Since the late 1960s there has been speculation that trace anaesthetic gases/vapours may have a harmful effect on operating theatre personnel. It has been concluded from currently available studies that there is no association between occupational exposure to trace levels of waste anaesthetic vapours in scavenged operating theatres and adverse health effects. However, it is desirable to vent out the exhaled anaesthetic vapours and maintain a vapour-free theatre environment. A prudent plan for minimizing exposure includes maintaining equipment, training personnel and monitoring exposure routinely. Although not universally agreed upon, the recommended maximum accepted concentrations in the United Kingdom (issued in 1996), over an (see Table 3.1 for main causes) 8-hour time-weighted average, are as follows:

• 100 particles per million (ppm) for nitrous oxide

• 50 ppm for enflurane

• 50 ppm for isoflurane

• 10 ppm for halothane

• 20 ppm for sevoflurane (recommended by Abbot Laboratories)

• no limit is set for desflurane, although a 50-ppm target is advisable due to its similarity to enflurane.

These levels were chosen because they are well below the levels at which any significant adverse effects occurred in animals and represent levels at which there is no evidence to suggest human health would be affected.

In the United States, the maximum accepted concentrations of any halogenated agent should be less than 2 ppm. When such agents are used in combination with nitrous oxide, levels of less than 0.5 ppm should be achieved. Nitrous oxide, when used as the sole anaesthetic agent, at 8-hour time-weighted average concentrations should be less than 25 ppm during the administration of an anaesthetic.

The Netherlands has a limit of 25 ppm for nitrous oxide, whereas Italy, Sweden, Norway and Denmark set 100 ppm as their limit for exposure to nitrous oxide. The differences illustrate the difficulty in setting standards without adequate data.

Methods used to decrease theatre pollution are listed as follows.

• 1.

  The facility should have adequate theatre ventilation and air conditioning, with frequent and rapid changing of the circulating air (15–20 times/h). This is one of the most important factors in reducing pollution. Unventilated theatres are four times as contaminated with anaesthetic gases and vapours compared to those with proper ventilation. A non-recirculating ventilation system is usually used. A recirculating ventilation system is not recommended. In labour wards where anaesthetic agents including Entonox are used, rooms should be well ventilated with a minimum of 5 air changes/h.

• 2.

  The circle breathing system recycles the exhaled anaesthetic vapours, absorbing CO ₂ . It requires a very low fresh gas flow, so reducing the amount of inhalational agents used. This decreases the level of theatre environment contamination.

• 3.

  The use of total intravenous anaesthesia.

• 4.

  Regional anaesthesia is another option.

• 5.

  Avoid spillage and use fume cupboards during vaporizer filling. This used to be a significant contributor to the hazard of pollution in the operating theatre. Modern vaporizers use special agent-specific filling devices as a safety feature and to reduce spillage and pollution.

• 6.

  Scavenging.

Sampling procedures for evaluating waste anaesthetic vapour concentrations in air should be conducted for nitrous oxide and halogenated agents on a yearly basis in the United Kingdom and on a quarterly basis in the United States in each location where anaesthesia is administered. Monitoring should include:

• leak testing of equipment and

• sampling air in the theatre personnel breathing zone.

Anaesthetic equipment, gas scavenging, gas supply, flowmeters and ventilation systems must be subject to a planned preventative maintenance (PPM) programme. At least once annually, the general ventilation system and the scavenging equipment should be examined and tested by a responsible person.

It is important to remember that the inhalational anaesthetic agents—chlorofluorocarbons (isoflurane), hydrofluorocarbons (sevoflurane and desflurane) and nitrous oxide—are greenhouse gases and have an effect on the climate.

Exam tip:

It is important to know the causes of pollution in the operating theatre, the methods used to reduce the pollution and the acceptable maximum concentrations (in ppm) of vapours in the operating theatre.