Figure 21-9 Dose-dependent redistribution of cerebral blood flow (CBF) in humans. Positron emission tomography (PET) scans demonstrate a dose-dependent reduction in CBF in both sevoflurane-anesthetized (left) and propofol-anesthetized subjects (right). During sevoflurane anesthesia, an increase in concentration from 1.5 to 2.0 minimum alveolar concentration (MAC) leads to an increase in CBF within the subcortex, particularly in the cerebellum. A gradual reduction in mean arterial pressure (MAP) was observed with increasing concentrations of sevoflurane, and MAP was not supported. The CBF values would be expected to be considerably greater had blood pressure been maintained within the normal range. Therefore, the CBF values represented in the figure probably underestimate true CBF during sevoflurane anesthesia. In propofol-anesthetized subjects, CBF was uniformly decreased and redistribution of CBF was not observed. (Data from Kaisti K, Metsahonkala L, Teras M, et al: Effects of surgical levels of propofol and sevoflurane anesthesia on cerebral blood flow in healthy subjects studied with positron emission tomography. Anesthesiology 96:1358–1370, 2002.)