4 New intravenous induction agents

Abstract

Nonopioid intravenous anaesthetic agents traditionally are used to abbreviate induction times and therefore reduce side effects of inhalat~onal agents during hghter planes of anaesthesia (stage II, excitatory phase, of Guedel's signs for general anaesthesia with ether). Thlopentone, the 'standard induction agent' of the anaesthetist, was synthesized in 1932 by Donalee Tabern and Ernest H. Volwiler of Abbott Company, Chicago, USA. In 1934 Lundy at the Mayo Clinic, and Waters at Madison, Wisconsin, began clinical trials with the compound. Thiopentone, now used for 60 years, has the salient advantage of being a very familiar agent. For newer agents to succeed, they must match or surpass the properties of thlopentone, which has quite a few aspects of an 'ideal induction agent (Fragen and Avram, 1989). It is water soluble, has a shelf-life of more than a year (undissolved), is stable to light, requires a small volume for anaesthetic induction and rarely causes pare on i.v. injection. Thiopentone is absolutely contra-indicated in patients allergic to barbiturates, in patients with acute intermittent porphyria and variegate porphyrm, and in patients where venous access cannot be established. The use of thiopentone is problematic in patients with heart d~sease because of its direct negatlve-inotropic effect on the heart. Results of thiopentone relative overdose include a dose-dependent decrease in stroke volume, cardiac output, and arterial blood pressure. The extent of these reductions is dependent on the resulting reflex tachycardla and peripheral vascular resistance, which may or may not increase. This increase in peripheral vascular resistance is probably caused by an increase in sympathetic activity, since barbiturates directly dilate smooth muscules of blood vessels. Coronary blood flow is increased and coronary vascular resistance significantly decreased after thiopentone. The resultant increase in O2-consumption and uptake of glucose, lactate and free fatty acids by the heart largely stem from the increased haemodynamlc stress on the left ventricle through increases in the heart rate. The multitude of effects of thiopentone on the brain, besides reducing sleep, are often considered as an advantage. Cerebral blood flow (CBF) and