Cerebral hyperperfusion syndrome

Cerebral Hyperperfusion Syndrome and Related Conditions

Cerebral vasoconstriction is a normal physiological response under determined conditions to preserve a normal cerebral blood flow. However, there are several syndromes, with impaired cerebral autoregulation and cerebral vasoconstriction, not related with infection or inflammation, which share the same radiological and clinical presentation. We review here the cerebral hyperperfusion syndrome and related conditions such as hypertensive encephalopathy, posterior reversible encephalopathy syndrome, and reversible cerebral vasoconstriction syndrome. These syndromes might share the same pathophysiological mechanism with endothelial damage, cerebral vasoconstriction, blood-brain barrier disturbance, cerebral edema, and, occasionally, intracerebral hemorrhage, with fatal cases described in all. Despite knowledge of these syndromes, they still remain unknown to us. Why these entities present in some patients and not in others goes further than the actual understanding of these diseases. We have to consider that a genetic susceptibility and molecular disturbances may be involved. Thus, more studies are needed in order to better characterize such syndromes.

Optimal blood pressure during cardiopulmonary bypass defined by cerebral autoregulation monitoring

OBJECTIVES

We sought to define the lower and upper limits of cerebral blood flow autoregulation and the optimal blood pressure during cardiopulmonary bypass. We further sought to identify variables predictive of these autoregulation end points.

METHODS

Cerebral autoregulation was monitored continuously with transcranial Doppler in 614 patients during cardiopulmonary bypass enrolled in 3 investigations. A moving Pearson's correlation coefficient was calculated between cerebral blood flow velocity and mean arterial pressure to generate the variable mean velocity index. Optimal mean arterial pressure was defined as the mean arterial pressure with the lowest mean velocity index indicating the best autoregulation. The lower and upper limits of cerebral blood flow autoregulation were defined as the mean arterial pressure at which mean velocity index was increasingly pressure passive (ie, mean velocity index ≥0.4) with declining or increasing blood pressure, respectively.

RESULTS

The mean (± standard deviation) lower and upper limits of cerebral blood flow autoregulation, and optimal mean arterial pressure were 65 ± 12 mm Hg, 84 ± 11 mm Hg, and 78 ± 11 mm Hg, respectively, after adjusting for study enrollment. In 17% of patients, though, the lower limit of cerebral autoregulation was above this optimal mean arterial pressure, whereas in 29% of patients the upper limit of autoregulation was below the population optimal mean arterial pressure. Variables associated with optimal mean arterial pressure based on multivariate regression analysis were nonwhite race (increased 2.7 mm Hg; P = .034), diuretics use (decreased 1.9 mm Hg; P = .049), prior carotid endarterectomy (decreased 5.5 mm Hg; P = .019), and duration of cardiopulmonary bypass (decreased 1.28 per 60 minutes of cardiopulmonary bypass). The product of the duration and magnitude that mean arterial pressure during cardiopulmonary bypass was below the lower limit of cerebral autoregulation was associated with the risk for stroke (P = .02).

CONCLUSIONS

Real-time monitoring of autoregulation may improve individualizing mean arterial pressure during cardiopulmonary bypass and improving patient outcomes.