Anaesthetics are often defined as compounds that induce a loss of consciousness in humans or loss of righting reflex in animals. Clinical definitions are also extended to include an induced coma that causes a lack of awareness of painful stimuli, sufficient to facilitate surgical applications in clinical and veterinary practice. General anaesthetics do not act as analgesics and should also not be confused with sedatives. The primary function of anaesthetics gases is to block the sensation of pain allowing the patient to undergo surgical or other procedures without distress. There are several different types of anaesthetics general, inhaled, injected, and regional. Of particular concern in the healthcare workplace is exposure to anaesthetic vapours from causes involving dosing technique, equipment leaks or failures, and waste anaesthetic gases (WAG).
The most widely used anaesthetic gases are halogenated ethers such as enflurane, halothane, isoflurane, and desflurane coupled with nitrous oxide. During surgery involving general anaesthesia, the patient is anaesthised with the use of intravenous and inhaled anaesthetics. The most commonly used inhaled anaesthetic agents include two different classes of chemicals: nitrous oxide (N2O) and volatile halogenated agents (vapours). N2O is supplied in a gas form. The halogenated agents are supplied as a liquid, which is then vapourised by the anaesthesia machine into a gaseous state prior to its delivery to the patient. N2O inhaled volatile agents are administered to the patient via a mask or breathing tube which is connected to a corrugated circuit to the anaesthesia machine. The three most commonly used inhaled anaesthetics are isoflurane, sevoflurane, and desflurane. These undergo very little in vivo metabolism in clinical use. Less than 5% of these volatile anaesthetics are metabolised by the patient because they undergo very little metabolic change inside the body, upon exhalation by the patient these agents remain in a form that may pollute the environment. Inhaled anaesthetics are exhaled and scavenged by anaesthesia machines with little or no additional degradation, and are typically vented into the outside environment without abatement as WAGs.
There are two major pathways for the undesirable leakage of anaesthesia gases into the operating room environment: anaesthetic techniques and the anaesthesia machine delivery system. Scavenging systems are designed to collect gases and vapours that are vented from the breathing circuit. The gases are then redirected to a safe area or a dedicated WAG disposal system. Currently, gas scavenging is the most practical engineering control for removing WAGs. Levels of WAGs can be further reduced when gas scavenging is combined with other recommended control procedures such as dilution ventilation. An effective room heating, ventilation, and air conditioning system, when used in combination with an anaesthetic gas scavenging system should reduce, although not entirely eliminate, the contaminating anaesthetic gases. If excessive concentrations of anaesthetic gases are present, then airflow should be increased in the room to allow for more air mixing and further dilution of the anaesthetic gases.
It is the responsibility of each institution to organise and document a program of maintenance and checking of all anaesthetic equipment, including the scavenging system. Additionally, eliminating the use of an anaesthesia technique that could elevate contamination levels in the operating room is another effective means to prevent WAGs. Employing the following anaesthetic practices will minimise contamination of the environment: reducing gas flow during mask inductions; turning off excessive gas flows and vapourisers following an anaesthetic , careful filling of vapourisers, judicious checking of all connections along the anaesthesia circuit and at the machine, and using properly fitting face masks, inflated endotracheal tube, and laryngeal mask airway cuffs. Eckelman, a professor at Northeastern University said, “The health-care system is designed to reduce human mortality and morbidity, but it is also important to understand the indirect or unintended effects that health care has on the environment and public health.”