In sheep undergoing general anaesthesia does inclusion of medetomidine result in hypoxaemia?

Question In healthy adult female non-pregnant sheep undergoing general anaesthesia for research studies does the inclusion of intravenous medetomidine as part of the anaesthetic protocol cause hypoxaemia?   Clinical bottom line The category of research question was: Treatment. The number and type of study designs that were critically appraised were: Four papers were available for critical appraisal. The quality of the evidence is weak. There were four experimental studies; three of which were cross-over studies and one study which was run in parallel with primary orthopaedic research. None of the studies were specifically focussed on the potential hypoxaemic effects of medetomidine. Critical appraisal of the selected papers meeting the inclusion criteria collectively provide zero/weak/moderate/strong evidence in terms of their experimental design and implementation: Weak. The outcomes reported are summarised as follows… Sheep across all four studies developed hypoxaemia (indicated by arterial oxygen tension; either PaO2 < 80 mmHg/10 kPa when breathing room air, or a statistically significant fall in PaO2 compared with baseline, when breathing oxygen enriched gases), when medetomidine was administered intravenously and in combination with various drugs (i.e. midazolam, propofol, ketamine, halothane, and isoflurane). However, as the sheep were receiving various doses of medetomidine at various timepoints, different quantities of supplemental oxygen (if any), varying ventilatory management (two studies used mechanical ventilation and two studies allowed sheep to breathe spontaneously), and different agents were used to maintain anaesthesia, the clinical significance of the PaO2 values was difficult to assess. In view of the strength of evidence and the outcomes from the studies the following conclusion is made… In clinically healthy (judged by clinical examination) adult female non-pregnant sheep undergoing general anaesthesia (characterised by placement of an endotracheal tube and/or the use of anaesthetic induction agents i.e. barbiturates, ketamine, propofol), the weak evidence presented here suggests that use of intravenous medetomidine can be expected to cause hypoxaemia. However, hypoxaemia is variable and its clinical effects can be lessened with anaesthetic techniques such as the provision of supplemental oxygen.