Anaesthesia for the patient with cardiac disease.

I have tried to summarize experimental work in human and animal models. This work is complex and difficult to interpret. Clinicians should not take isolated experimental studies and jump to conclusions about clinical use of anaesthetics. Experimenters should not arrive at sweeping conclusions based on a particular experimental study performed under some or other carefully or not so carefully controlled conditions. Editorialists, such as Becker in a recent issue of Anesthesiology, should not conclude that an anaesthetic is "dangerous," based on these kinds of studies. It is especially invalid to use the term "dangerous" unless the author is willing to present us with a viable, experimentally proven, safer alternative. To tell us that isoflurane is "dangerous" implies that we should switch to some unspecified other agent. What conclusions can be arrived at based on these studies? (1) It is possible to produce coronary steal, in dogs, at constant coronary flow, with isoflurane at 41 mmHg perfusion pressure. The comparison between halothane and isoflurane is suspect because is was performed at two markedly different coronary perfusion pressures. (2) Myocardial ischaemia can be induced in humans with coronary artery disease when hypotension and tachycardia is permitted during isoflurane anaesthesia. During these conditions, relative preservation of coronary blood flow greater than that which would be expected because of measured or calculated demand has been interpreted as meaning that the mechanism was that of coronary steal. I am not convinced that this mechanism needs to be invoked here, but we can conclude from these studies that if hypotension and tachycardia are allowed to occur in patients with coronary artery disease, ischaemia is possible.(ABSTRACT TRUNCATED AT 250 WORDS)