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A long recovery increases the duration of anaesthesia. The risk of perioperative anaesthetic-related complications and death is associated with increasing duration of anaesthesia in dogs (Brainard and others 2006, Brodbelt and others 2008, Robinson and others 2014), horses (Johnston and others 1995, Cohen and others 2004) and humans (Tiret and others 1986). It would seem probable that a similar situation exists in cattle, although there is a lack of information to verify this.
Ketamine and thiopental are suitable as induction agents for general anaesthetic in cattle over 2.5 months of age (Kaur & Singh 2004, Abrahamsen 2013, Clarke and others 2014). Thiopental sodium is a barbiturate acting on GABA receptors in the CNS causing anaesthesia with an onset of action of 20–40 seconds following intravenous injection (Dugdale 2010). It is lipid soluble and redistributes readily to fat and muscle, resulting in a short duration of action unless the animal has low body fat. Thiopental is metabolised by the liver, and there will be prolonged effects in animals with liver disease.
Ketamine is a dissociative anaesthetic, acting as a non-competitive antagonist at N-methyl-d-aspartate (NMDA) receptors. Ketamine prevents binding of glutamate at NMDA receptors, which results in inhibition of activity at the thalamocortical and limbic systems and depression of nuclei in the reticular activating system (Posner and Burns …