An update on general anaesthesia in ruminants

Most of the surgical procedures in ruminants are performed under the effect of local or regional anaesthesia only or in combination with sedation or tranquilization. In veterinary anaesthesia, inhalation anaesthetics are more popular because they provide predictable and rapid adjustment of anaesthetic depth. Intravenous anaesthesia always involves the delivery of a bolus dose or a fast loading infusion to achieve an adequate blood concentration of the anaesthetic drug. Maintenance of anaesthesia can be obtained by infusion of intermittent boluses (IBI), by continuous rate infusion (CRI) or by target controlled infusion (TCI). Inhalation anaesthesia is administered by using an anaesthetic machine. In large ruminants food should be withheld for 24–48 hr and water for at least 12 hr. Calves, sheep, goats, and camelids should be fasted for 12–18 hr prior to general anaesthesia and deprived of water for 8–12 hr. The alpha-2 adrenergic agonist drugs are most commonly used to induce sedation in ruminants. Thiopentone sodium is the most widely used intravenous induction agent. Ketamine is also commonly used in veterinary anaesthesia as induction agent. It provides mild cardiovascular stimulation and is safer than thiopental in sick animals. Propofol, a nonbarbiturate, nonsteroidal hypnotic agent, has been used to provide brief periods of anaesthesia. Economic considerations may limit the applicability of propofol in large ruminants. Bloat and regurgitation are two major complications of ruminant anaesthesia that are encountered due to physioanatomic peculiarities of ruminants. Food withdrawal is a main part of anaesthetic preparation in order to prevent regurgitation, bloat and associated respiratory disorders. Duration of food withdrawal is still a matter of research in different ruminant species. Postoperative myopathy-neuropathy can occur in large ruminants but is not a problem in calves, goat, sheep and camelids. Supportive therapy is a very important aspect of ruminant anaesthesia and can strongly influence the recovery and patient morbidity/mortality. Supportive therapy includes patient positioning, fluid administration, mechanical ventilation, cardiovascular support, good monitoring techniques, and oxygen administration to animals under intravenous anaesthesia.