29/11/2024
Loving this delve into the literature by my amazing colleague and friend! The pitfalls of atipamezole.....knowledge is power! ๐๐ช๐
To follow up on the previous post on medetomidine, how about its antagonist, atipamezole? Specifically, consider its use in bradycardic and hypotensive patients under general anaesthesia.
Remember that medetomidine is a potent alpha-2 receptor agonist that causes dose-dependent sedation and analgesia. The advantages include reliable sedation, analgesia, muscle relaxation, and anxiolysis. Negative cardiovascular side effects include bradycardia, related arrhythmias, hypertension, and (up to) a 50% reduction in cardiac output.
This percentage can be frightening, as can monitoring a patient with bradycardia. But should we rush to treat the number? What is the blood pressure like? Are you rushing to antagnoise the medetomidine under anaesthesia and not considering the effects it will have? Spoiler.. it can make things worse. The heart rate may increase, but the blood pressure may not. Take a look at the literature we have found (for both IV and IM administration):
- The NOAH compendium says โa transient hypotensive effect has been observed during the first 10 minutes post-injection of atipamezole hydrochloride.โ
- Vainio (1990) found โatipamezole significantly increased the medetomidine-depressed heart rate, respiratory frequency and arterial PO2. The drug also transiently decreased the mean arterial blood pressure.โ
- โAttention should be paid to temporary hypotension in cats anesthetized with isofluraneโ when atipamezole was administered after a medetomidine, midazolam and ketamine premedication (Kamohara et al., 2021).
- Zatroch et al. (2019) found that โatipamezole administered IM at half the volume or the same volume as dexmedetomidine was ineffective at increasing pulse rate or cardiac output in anesthetized cats that received dexmedetomidine. However, atipamezole caused short-lasting but severe arterial hypotension.โ
- Martin-Flores et al. (2017) evaluated โthe cardiovascular effects of low-dose atipamezole administered intravenously to isoflurane-anesthetized cats receiving dexmedetomidine,โ and in their cats that were hypertensive, it reduced the blood pressure by ~40%, and โ If this magnitude of decrease in blood pressure occurs when atipamezole is administered to cats with lower blood pressures, as could easily happen if blood pressure is not monitored, clinically important arterial hypotension could ensue.โ
So, instead of always reaching for atipamezole for patients under anaesthesia, consider the following standard steps to treat hypotension: decrease volatile agent > treat any bradycardia (after 20-30 minutes of dex/medetomidine administration) > consider a fluid challenge or colloid therapy if appropriate > administer vasopressors or intropes. This is reflected in the 2024 AAHA Fluid Therapy Guidelines.
Letโs get Lit:
https://pubmed.ncbi.nlm.nih.gov/31034277/
https://pubmed.ncbi.nlm.nih.gov/34704354/
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC385445/
https://journals.sagepub.com/doi/10.1177/1098612X17722265