Clinical comparison of inhalation anaesthetic agents

Despite the continued revival in the use of local anaesthetic techniques, and the fact that some of the versatility of inhalation agents is being approached by newer short acting i.v. anaesthetic and analgesic agents, volatile anaesthetics will continue to play an important role in the management of patients undergoing surgery. The individual agents have distinct properties and varying benefit-to-risk ratios depending upon the medical status of the patients and the type of surgery to be undertaken. In certain circumstances, such as their role in the anaesthetic management of patients with coronary artery disease, it is possible--even probable--that in some situations the characteristics of one agent will be particularly advantageous, whereas the characteristics of another agent will be more appropriate in another situation. Further investigations directly comparing the three agents in particular clinical situations need to be undertaken before any clear picture will begin to emerge. In other circumstances there is already sufficient evidence to suggest that one of the agents is superior to the other. The stability of cardiac rhythm which accompanies isoflurane anaesthesia is an example of this, and the smoother inhalation induction of anaesthesia obtained with halothane is another. Perhaps the greatest advantage of isoflurane compared with halothane and, to a lesser extent, enflurane is the remarkable molecular stability of the molecule. This stability has implications with regard to the probable lack of toxicity of this agent--both organ toxicity and the effects of long term exposure in operating theatre personnel. Although the agent will need to be in general use for a longer period of time before any definite judgments can be made in this respect, the laws of pharmacology generally dictate that such a prediction will probably be fulfilled. Although this review has been a clinical comparison of halothane, enflurane and isoflurane, the relative cost of these agents must be mentioned. Isoflurane is much more expensive than halothane, and again (as so often seems to be the case when comparing the relative merits or properties of these agents) enflurane is intermediate between the two.