Audio Summary Transcript

My name is Rachael Gregson and I am a veterinary anaesthetist working at the University of Edinburgh. In this Knowledge Summary, I was looking at the evidence regarding the development of hypoxaemia, as indicated by arterial partial pressure of oxygen, in healthy adult female sheep undergoing general anaesthesia for research purposes. I chose this question because although it is recognised that alpha-2 adrenoreceptor drugs such as medetomidine cause hypoxaemia, the incidence and clinical significance of the hypoxaemia caused by medetomidine is often hard to predict.

The literature search yielded four papers. All were experimental studies. Three were crossover experimental studies, one of which was run concurrently with another study looking at nutrition, and the fourth was run in parallel with an orthopaedic research study. None of the studies were specifically focused on the potential hypoxaemic effects of medetomidine. Sheep in all four studies developed hypoxaemia, as shown by the arterial partial pressure of oxygen, when administered intravenous medetomidine as part of a general anaesthetic protocol.

However, the strength of evidence was weak. The sheep were receiving various doses of medetomidine at various timepoints during anaesthesia. They received different quantities of supplemental oxygen, if oxygen was given at all, and there was varying ventilatory management. Two studies used mechanical ventilation, and two studies allowed the sheep to breathe spontaneously. Finally, different agents were used to maintain anaesthesia, meaning that overall, the clinical significance of the hypoxaemia that developed was difficult to assess.

In conclusion, in healthy adult female sheep administered intravenous medetomidine as part of an anaesthetic protocol, hypoxaemia can be expected. However, the hypoxaemia is variable, and its effects can be lessened with anaesthetic techniques such as the provision of supplemental oxygen. Finally, it should be noted that medetomidine is not licenced in food-producing animals in the UK, and adherence to the relevant legislation in the country of use is advised.

Thank you.