ORGAN BLOOD-FLOW AND MICROCIRCULATION DURING INHALATION ANESTHETICS

Halogenated anaesthetics influence smooth muscle tone and thereby the microcirculation by two distinct mechanisms: (1) via reduced responsiveness to adrenergic sympathetic nervous outflow and decreased responsiveness of the cardiocirculatory system to adrenergic stimuli; and (2) via a direct (in the great majority of organ beds) relaxing effect on arteriolar resistance vessels. Besides negative inotropic effects on the heart, the anaesthetics can reduce cardiac output by dilation of venular segments and small veins and hence by a decreased return of blood to the heart. In terms of organ perfusion, the halogenated anaesthetics: (i) induce relative overperfusion, i.e. oxygen supply in excess of oxygen demand in heart and brain; (ii) do not grossly interfere with renal blood flow; but (iii) may profoundly impair hepatic perfusion. Thereby, halothane, enflurane and isoflurane exert different changes in organ blood flow. Halothane is the most potent cerebral vasodilator and isoflurane the least; the contrary applies for the heart and the hepatic arterial circulation. The actions of the new anaesthetic agents sevoflurane and desflurane resemble those of enflurane and isoflurane. © 1993 Baillière Tindall.