Comparative Study of the Effect of Clonidine and Lisinopril on the Pressor Response to Laryngoscopy and Tracheal Intubation During Induction of General Anaesthesia

Abstract

Since King and colleagues (1951), first described the reflex circulatory responses to direct laryngoscopy and endotracheal intubation, there have been numerous publications concerning both these responses, and the therapeutic maneuvers which can attenuate them. Reflex cardiovascular responses to laryngoscopy and endotracheal intubation in anaesthetized patients include a systemic arterial pressor response, tachycardia, and increases in systemic arterial blood pressure, intraocular pressure and intracranial tension. Although the direct recording of the sympathetic nervous activity is difficult 111 man, measurement of the plasma concentrations of catechulamines consistently shows 1ncreases 111 noradrenaline concentration following laryngoscopy, and thus confirms sympathetic mediation of this response. Complications of these pressor responses following laryngoscopy and endotracheal intubation include: myocardial ischaemia, cardiac failure, intracranial haemorrhage, and increased intracranial and intraocular pressures. These complications are senous enough 111 normotensive individuals, but an exaggerated response to laryngoscopy has been reported 111 patients with hypertension, ischaemia or cerebrovascular disease. Many investigators have made attempts in order to use vanous pharmacologic agents to obtund the possible harms and complications following these pressor responses. High concentrations of inhaled anaesthetics have been tried, but carry the disadvantages of causing delayed recovery and severe cardiovascular depression.