Pollution in theatre and scavenging

Published on 07/02/2015 by admin

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Last modified 07/02/2015

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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 maintenance of equipment, training of personnel and routine exposure monitoring. Although not universally agreed upon, the recommended maximum accepted concentrations in the UK (issued in 1996), over an 8-hour, time-weighted average (see Table 3.1 for main causes), are as follows:

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.

Holland 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 below:

1. Adequate theatre ventilation and air conditioning, with frequent and rapid changing of the circulating air (15–20 times per hour). This is one of the most important factors in reducing pollution. Theatres that are unventilated 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 five air changes per hour.

2. Use of the circle breathing system. This system recycles the exhaled anaesthetic vapours, absorbing CO2. 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. Total intravenous anaesthesia.

4. Regional anaesthesia.

5. Avoiding spillage and using 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 UK and on a quarterly basis in the USA in each location where anaesthesia is administered. Monitoring should include:

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.

Pollution in the operating theatre

Scavenging

In any location in which inhalation anaesthetics are administered, there should be an adequate and reliable system for scavenging waste anaesthetic gases. A scavenging system is capable of collecting the waste anaesthetic gases from the breathing system and discarding them safely. Unscavenged operating theatres can show N2O levels of 400–3000 ppm.

The ideal scavenging system

A well-designed scavenging system should consist of a collecting device for gases from the breathing system/ventilator at the site of overflow, a ventilation system to carry waste anaesthetic gases from the operating theatre and a method for limiting both positive and negative pressure variations in the breathing system.

The performance of the scavenging system should be part of the anaesthetic machine check.

Scavenging systems can be divided into passive and active systems.

Passive system

The passive system is simple to construct with zero running cost.

Components

1. The collecting and transfer system which consists of a shroud connected to the adjustable pressure limiting (APL) valve (or expiratory valve of the ventilator). A 30-mm connector attached to transfer tubing leads to a receiving system (Fig. 3.1). The 30-mm wide-bore connector is designed as a safety measure in order to prevent accidental misconnection to other ports of the breathing system (Fig. 3.2).

2. A receiving system (reservoir bag) can be used. Two spring-loaded valves guard against excessive positive pressures (1000 Pa) in case of a distal obstruction or negative pressures (−50 Pa) in case of increased demand in the scavenging system. Without these valves, excessive positive pressure increases the risk of barotrauma should there be an obstruction beyond the receiving system. Excessive negative pressure could lead to the collapse of the reservoir bag of the breathing system and the risk of rebreathing.

3. The disposal system is a wide-bore copper pipe leading to the atmosphere directly or via the theatre ventilation system.

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