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The researchers’ objective was to determine whether dogs with intracranial space occupying lesions (iSOLs) on MRI, or MRI-determined indicators of intracranial hypertension (ICH) had higher sedation scores with a more rapid onset of recumbency after the administration of IV butorphanol than dogs without intracranial disease.
They hypothesised that 0.2 mg kg-1 of butorphanol administered intravenously would result in statistically significantly higher sedation scores and quicker onset of recumbency in dogs with MRI-iSOL and MRI-ICH.
For the observational study: 'The sedative effect of intravenous butorphanol in dogs with intracranial space occupying lesions or indicators of intracranial hypertension', 53 dogs presented for a brain MRI.
Each dog was sedated with 0.2 mg kg-1butorphanol IV, and the quality of sedation and the onset of recumbency were scored before drug administration and every 5 minutes after administration for 15 minutes using a modified sedation scale.
The maximum sedation score was 18, and onset of recumbency was recorded when a dog lay down without the ability to stand.
Dogs with MRI-iSOL had significantly higher median sedation scores than dogs without MRI-iSOL (12 versus 5 respectively) 15 minutes after butorphanol administration (T15, p < 0.01).
A greater number of dogs with MRI-ICH achieved recumbency (n = 9/10; 90%) than those without MRI-ICH (n = 20/43; 46.5%; p = 0.01).
Emma Sansby, Resident in Anaesthesia and Analgesia at Lumbry Park Veterinary Specialists, who led the research, said: “When intracranial disease is suspected, the administration of butorphanol as a premedicant for anaesthesia could be used to predict the presence of MRI-iSOL and MRI-ICH.
"If a dog becomes recumbent or has a sedation score of more than 10 within 15 minutes of butorphanol administration, the animal should be treated with an anaesthesia protocol adapted to the presence of ICH – so as not to increase intracranial pressure.
“These adaptations include but are not limited to; adequate preoxygenation - to prevent hypoxaemia and elevation of the head to no more than 30 degrees; preventing increases in central venous pressure - by avoiding jugular compression and avoiding excessive intraabdominal and intrathoracic pressure; and a smooth anaesthetic induction - ensuring an adequate depth of anaesthesia prior to tracheal intubation to prevent the cough reflex and judicious mechanical ventilation to enable a low-normal end-tidal carbon dioxide.”
Reference
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