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Diagnosis | Anesthesia-induced exophthalmos

Lab Animal volume 37, pages 248–249 (2008)Cite this article

We believe the marked and prolonged exophthalmos was induced by the use of ketamine and medetomidine. This effect has previously been reported to a lesser degree following the use of xylazine1. Both xylazine and medetomidine are alpha2 adrenoceptor agonists that stimulate receptors centrally to produce sedation and analgesia and stimulate receptors centrally and peripherally to cause bradycardia and decrease the cardiac output2. Medetomidine frequently causes hypotension, but sedative doses of medetomidine typically raise the blood pressure due to an effect on peripheral receptors2. Medetomidine is also known to cause decreased intraocular pressure3.

We elected to use a combination of ketamine, a dissociative anesthetic agent, and medetomidine as a stable and largely reversible surgical anesthetic regime4,5. We followed this anesthesia with a lighter, sustained anesthetic protocol using gaseous anesthesia, for terminal experiments lasting longer than 12 h. The combination of ketamine and medetomidine has been used previously6 and is widely accepted for surgical anesthesia. We selected this dose combination (which is a standard dose in the USA but is considered a high dose in the UK) to give a higher dose of the reversible agent medetomidine in combination with a low dose of the non-reversible ketamine. We find this anesthetic protocol provides fast induction and a suitable anesthetic level for surgery. The effects are prolonged, with no righting reflex or pinch withdrawal for several hours. However, a noticeable side effect is the protrusion of the eyeball.

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Figure 2: Data recorded for a single cell in the visual cortex of the rat shown in Figure 1, approximately 10 h after the start of a visual function experimenttion experiment.

References

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Acknowledgements

The work was undertaken under a Home Office approved project license for the study of visual function. S. Smith was in receipt of an Undergraduate Vacation Scholarship from The Physiological Society.

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Diagnosis | Anesthesia-induced exophthalmos. Lab Anim 37, 248–249 (2008). https://doi.org/10.1038/laban0608-248

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