Haemodynamic Effects of Thiopentone, Midazolam, Etomidate and Propofol During Induction of Anaesthesia

Abstract

SummaryThe commonly used anaesthetics have a direct effect on myocardial performance and both arterial and venous peripheral vasculature, with secondary effects on the circulatory system mediated via the sympathetic nerves and catecholamine release. The purpose of this study was to investigate the cardiovascular effects of 4 intravenous anaesthetic agents commonly used for induction of anaesthesia. 100 patients were randomly allocated to 5 groups: (I) thiopentone 4 to 5 mll/kg + fentanyl 0.1 mg; (2) midazolam 0.1 mll/kg + alfentanil 40 /lll/kg; (3) midazolam 0.1 mll/kg + fentanyl 4 /lll/kg; (4) etomidate 0.3 mll/kg + fentanyl O.lmg; (5) propofol 1.5 mll/kg + fentanyl 0.1 mg. Cardiodynamic parameters were assessed by thoracic electrical bioimpedance at baseline, after induction of anaesthesia, during intubation and I and 5 min after intubation.After induction the decrease in mean arterial pressure (as a percentage of baseline) was greatest after midazolam-fentanyl (-25.5%) and in cardiac index after midazolam-fentanyl (-14.3%) and propofol (-14.3%). During intubation mean arterial pressure and total peripheral resistance increased most for thiopentone (+25%, +44%, respectively), etomidate (+21.6%, +43.4%) and propofol (+4.9%, +25.1%). There were slight changes for midazolam + alfentanil (-12.5%, +2.6%) and midazolam + fentanyl (-6.9%, +0.3%). Neither thiopentone nor etomidate sufficiently attenuated stress during laryngoscopy, whereas the combination of midazolam with a high dosage of an opioid suppressed almost all sympathetic stimulation during intubation. The haemodynamic changes after thiopentone, etomidate and propofol are due to negative inotropic effects, including slight vasodilatation with propofol, combined with compensatory sympathetic stimulation. The effects of midazolam with an opioid are based on vasodilation and negative chronotropic effects.The haemodynamic effects of intravenous hypnotics used in endotracheal intubation result in depression of the cardiovascular system and a lack of an anti nociceptive or analgesic effect. Therefore, they can produce either profound deterioration of myocardial and cerebral oxygenation after induction of anaesthesia, or hypertension and tachycardia as a result of insufficient attenuation of the stress response during laryngoscopy and intubation.Supplementation of hypnotics with an analgesic such as fentanyl or alfentanil is generally accepted practice. Therefore, we compared 4 commonly used intravenous induction agents (thiopentone, midazolam, etomidate and propofol) supplemented with fentanyl or alfentanil and examined the cardiovascular responses after induction and during intubation using a new noninvasive bioimpedance technique for the assessment of online cardiac output and contractility parameters.