Intravenous lidocaine infusion in balanced anaesthesia for abdominal surgery: update and clinical experiences

Abstract

Inhalation anaesthesia carries a risk for major perioperative complications, mostly in the severely sick and hemodynamically unstable patient, due to the well known cardiovascular and respiratory depressant effects of volatile anaesthetic agents. In the equine species, this applies particularly to horses with colic symptoms which often suffer from severe cardiopulmonary dysfunctions as well as disturbances in water, acid-base, and electrolyte homeostasis that may rapidly progress to irreversible tissue damage and cell death and thus require immediate abdominal surgery. While the conscious horse may at least initially be able to compensate for some of the cardiovascular effects of the underlying pathological processes, the anaesthetised patient fails to do so largely due to the inhalant anaesthetics suppressing compensatory responses of the animal in a dose-dependent fashion. To overcome these problems the concept of balanced anaesthesia has been developed which entails the combination of a low dosed volatile anaesthetic with potent analgesics (mostly opioids) that have less cardiovascular depressant effects, While successfully established in human and small animal anaesthesia practice for many years, the introduction of balanced anaesthesia in the equine has largely been hampered by the lack of suitable analgesic agents, especially for the horse with systemic disease. First, opioids do not seem to exhibit a MAC-sparing effect in the equine because they elicit central excitation, i.e. they do not consistently reduce the requirement for volatile anaesthetics. Secondly, although a 2-adrenergic agonists are potent analgesics with proven MAC-sparing effects they significantly impair hemodynamic function and are therefore not considered suitable for constant rate infusion in the critically sick patient. A recently described balanced anaesthetic regimen that includes systemic administration of lidocaine appears to provide for the first time an alternative to traditional inhalation anaesthesia for the systemically sick equine patient. Lidocaine, when given intravenously to horses in boluses of 2.5-5 mg/kg followed by constant rate infusion at 50-100 mg/kg/min, has been shown to exhibit analgesia and dose-dependent MAC-sparing effects ranging from 20-70% without causing significant cardiovascular or other appreciable side effects. The rationale for balanced anaesthesia plus currently available information regarding the advantages, mechanism of action, concerns and potential risks associated with intravenous lidocaine infusion during inhalation anaesthesia in the horse are summarised. Preliminary but promising clinical experiences supporting the use of lidocaine infusion in anaesthetised colic horses are presented.