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

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?

Treatment.

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.

Weak.

Sheep across all four studies developed hypoxaemia (indicated by arterial oxygen tension; either P_aO₂ < 80 mmHg/10 kPa when breathing room air, or a statistically significant fall in P_aO₂ 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 P_aO₂ values was difficult to assess.

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.