Frequently I am asked if a specific sedation protocol should be used for a pet with known, or suspected, intracranial disease. The biggest concern with anesthesia is a shift in the intracranial pressure (ICP), which is directly linked with the mean arterial blood pressure. Therefore, it is commonly recommended that medications are chosen which have minimal effect on blood pressure. Butorphanol is a commonly used premedication for dogs and often part of the recommended protocol for “safe” sedation. A study performed in the UK, and published in Veterinary Anesthesia and Analgesia, evaluated the effect of intravenous butorphanol on dogs with and without intracranial disease.
Study Design
Fifty-three dogs, presenting for brain MRI, were enrolled in the study. Each dog was sedated with 0.2 mg/kg IV butorphanol and the time to recumbency as well as the sedation score were recorded for each dog. The sedation score was adapted from a prior publication (Grint et al 2009) and was scored 0-4 for six separate categories with a maximum score of 19.
Results
Nineteen of the 53 dogs had intracranial disease, the remaining 34 did not. Ten of the 19 dogs also had signs of intracranial hypertension. The overall median sedation score time 0 was 1 (range 0-10) , and 6 (range 0-15) at 15 minutes. Dogs with intracranial disease had a significantly higher sedation score at both 0 and 15 minutes. This was especially notable at 15 minutes when the dogs with intracranial disease had a median sedation score of 12, compared to dogs without intracranial disease who had a median sedation score of 4. A greater number of dogs with intracranial hypertension achieved recumbency than those without intracranial hypertension.
Clinical application
If you sedate a dog with butorphanol for a procedure (dental, radiographs, other) and the dog becomes recumbent at 15 minutes, it would be wise to continue the anesthetic protocol under the assumption that the dog may have intracranial disease. For example, use propofol instead of dexdomitor so that the intracranial blood pressure (and flow) is less likely to be affected. As the authors point out, it is helpful to remember to account for other sedation medications on board and note any recent seizures that could play a role in the level of sedation that an animal achieves. Nothing will replace an MRI diagnosis of the presence of intracranial disease, however keeping the “butorphanol test” in mind might help reduce the risk of undesirable consequences in patients with undiagnosed intracranial disease.
Thought provoking, right? I hope you found this TidBit useful and look forward to working with you soon!