Hello there NAVE crew! In this lesson from the Anaesthesia Unravelled webseries we'll talk about 'Premedication'. Due to its content, this lesson will be divided in two parts, this one about premedication with benzodiazepines and phenotiazines, the second about anticholinergics and alpha-2 adrenoceptor agonists.
Premedication is used in practically all anaesthetic procedures. It must be chosen in accordance to each patient and procedure, as well as the induction and maintenance agents. Therefore, we must devise an anaesthetic protocol that makes sense in its entirety.
The main purposes of the premedication are: to help contain the patient, reduce stress, potentiate the induction agents, minimize the adverse effects of induction agents, promote a swift induction, reduce the autonomic reflexes and promote analgesia and myorelaxation. The main pharmacological groups used are the benzodiazepines, phenothiazines, alpha-2 adrenoceptor agonists and opioids.
This group is mainly represented by diazepam and midazolam. The main advantage of benzodiazepines is the absence of adverse effects on the patient's physiological parameters. On the other hand, the depressor effect is practically non-existent in domestic animals. The sedative effect is intense on neonates, geriatric patients, primates, birds and reptiles. Another interesting effect of benzodiazepines is myorelaxation. For these reasons, they are more useful on anaesthetic induction than as premedication.
For a long time, this was the most common group used as premedication, being acepromazine its main agent. Phenothiazines promote tranquillizing effects, mainly in dogs, although are not very effective in cats and large animals. These effects are not dose-response, so if the doses are increased, sedative effects won't be observed. Acepromazine promotes cardiovascular depression, leading to hypotension and negative inotropism. Therefore, this group must be avoided in animals with cardiovascular disease or instability. Other interesting effects promoted by acepromazine are: antisialagogue, antiarrhythmic, antiemetic and block of the thermoregulation centre.
To know a bit about anticholinergics and Alpha-2 agonists go the the video and check it out the references below!
Bressan T, Sobreira T, Carregaro AB. Use of rodent sedation tests to evaluate midazolam and flumazenil in green iguanas. JAALAS, 58: 810-816, 2019.
Carregaro AB. Medicação pré-anestésica. In: Massone F. Anestesiologia Veterinária – Farmacologia e Técnicas. Ed Guanabara Koogan. 7a ed. 2019, 15-20.
Carregaro AB, Freitas GC. Sedativos e cuidados perianestésicos em equinos. In: Luna SPL, Carregaro AB. Anestesia e Analgesia em Equídeos, Ruminantes e Suínos. Ed MedVet. 1a ed. 2019, 281-310.
Carregaro AB, Gehrcke MI, Contenção física e medicação pré-anestésica em ruminantes. In: Luna SPL, Carregaro AB. Anestesia e Analgesia em Equídeos, Ruminantes e Suínos. Ed MedVet. 1a ed. 2019, 311-332.
Cortopassi SRG, Fantoni DT. Medicação pré-anestésica. In: Fantoni DT, Cortopassi SRG. Anestesia em Cães e Gatos. 2a ed. Editora Rocca, 2010. 217-227.
Driessen B, Zarucco L, Kalir B, Bertolotti L. Contemporary use of acepromazine in the anaesthetic management of male horses and ponies: A retrospective study and opinion poll. Eq Vet J, 43: 88-98, 2011.
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