Abstract
We would like to comment on the letter submitted by R Sasaki and collaborators entitled ‘Temporary inhalation anaesthesia in experimental pigs’ and published in Laboratory Animals 2010;44:66–70.
The letter describes a device for providing brief periods of inhalation anaesthesia in pigs and concludes that temporary inhalation anaesthesia devices will contribute to the progress of surgical research in pigs. We agree with the authors' assertion that effective outcomes in surgical research using experimental animals depend on anaesthetic techniques, but are unclear what the authors mean by ‘progress of surgical research’. We would like to believe that by ‘progress’, they mean achieving levels of anaesthesia and analgesia that meet the objectives of optimizing animal welfare while improving the quality of collected data.
However, we are concerned about the technique recommended. The exposure of patients to vapours arising from the uncontrolled evaporation of volatile liquid anaesthetics is arguably the worst technique employed since ‘modern’ anaesthetic practice began in the mid-19th century! Its association with high mortality in healthy human subjects rapidly led to its withdrawal from medical practice, and while mortality statistics are unavailable for animals exposed to the technique, it can nevertheless be authoritatively condemned on the grounds that it contravenes all the essential elements of ‘safe’ anaesthesia. First, the technique fails to enrich inspired gas with oxygen while ensures that expired carbon dioxide is completely rebreathed. When applied to a heavily sedated animal – which by definition implies impaired ventilatory function – hypoxaemia and hypercarbia are almost inevitable. This can only be aggravated by the inability to control the inspired anaesthetic concentration and therefore anaesthetic depth, which increases the likelihood of overdosage and in turn, cardiac arrest. Furthermore, the technique does not allow intermittent positive pressure ventilation to be imposed should apnoea or cardiac arrest occur.
The use of latex gloves to produce a seal around the animal's muzzle may or may not be effective in minimizing loss of anaesthetic vapour to the environment during anaesthesia itself. However, it is inevitable that workplace contamination will occur once the device is removed and stored for later use. The effects of environmental contamination with waste anaesthetics on the health of chronically exposed humans are controversial, although the universal recommendation is that it be minimized by whatever means possible.
The objectives of the described technique can be achieved in a number of different, affordable – and most importantly – safer ways. Precision vaporizers and anaesthetic breathing systems that prevent carbon dioxide rebreathing while allowing manual ventilation are freely available and inexpensive, as is oxygen. Also many ways of appropriate scavenging are readily available. While endotracheal intubation with cuffed tubes is not always straightforward in pigs, it is a technique worth mastering if only for the benefit of personnel working in potentially contaminated laboratories.
Given that appropriate anaesthesia and analgesia is perhaps one of the more easily achieved of the three 3Rs, i.e. refinement, we are dismayed that such an obsolete and unrefined technique finds itself promoted.