Lignocaine is an amide group of local anaesthetic commonly employed for surgical procedures in large animals by local infiltration and nerve blocks. Intravenous administration of lignocaine has been used for regional anaesthesia and arrhythmia since the decade of 1960. Lately, its mechanism of action has been studied in more details in humans, emphasizing its multimodal aspect, which is the main objective of this research. Several studies have revealed that lignocaine infusion significantly reduces the minimum alveolar concentration (MAC) of inhalation agents in a variety of species including horses
(Doherty and Frazier 1998), dogs
(Valverde et al., 2005) and goats
(Doherty et al., 2007). However, there are no reports assessing the probable effects of intravenous lidocaine in anaesthetized adult cattle.
The plasma concentrations of lignocaine and its active metabolite, mono ethyl glycine xylidide, have different pharmacokinetic profiles when administered in the animal anesthetized with isoflurane and in the awaken animal. The volume of central compartment, clearance and elimination half-life of lidocaine are smaller in anesthetized animal than awaken animal, resulting in higher plasma concentrations of lidocaine in the anesthetized animal
(Thomasy et al., 2005). Lidocaine toxicity is more likely to manifest when its plasma concentration reaches 5 µg per mL. Doses between 1 and 2 mg per kg administered as bolus followed by continuous infusion of 25 to 50 µg per kg per min reaches the plasma concentrations of 2 µg per mL are considered nontoxic.
The mechanism of intravenous lignocaine induced reduction in MAC of Isoflurane has not been elucidated. Several possibilities exists; The anaesthetic agents suppress central nervous system sodium channels in a voltage-dependent manner
(Rehberg, 1996). Similarly, action of lignocaine on both peripheral and central nervous systems involves blockade of Na+ channels
(Oliveira de, 2010). Hence both inhalant anaesthetics and lidocaine acts on voltage-gated Na+ channels in the central nervous system and thus their effects during general anesthesia could be additive.