The history of controlled hypotension.

As the physiology of deliberate hypotension has been unravelled, and as each new pharmacological agent has become available which either depresses or blocks peripheral vascular tone, depresses myocardial performance, or interferes with the conducting tissues within the myocardium, its possible incorporation into the armamentarium of the anaesthetist who offers induced hypotension has been considered. The result has been a sequence of variations in technique of characteristically recognizable vintage. No matter how the condition of induced hypotension is produced, there is usually vasodilatation, and the characteristic disturbance in physiology is of a loss of postural reactivity in the cardiovascular system. Important lessons have been learned concerning the management of shock states. Though it is difficult to evaluate the morbidity of deliberate induced hypotension, and terms such as "physiological trespass" have been used by its antagonists, it would appear that a well-considered and skilfully managed controlled hypotension is no more of a physiological trespass than anaesthesia, nor indeed than the trespass of the surgeon's knife itself.