Relationship between Hypotension and Cerebral Ischemia during Hemodialysis.

The relationship between BP and downstream ischemia during hemodialysis has not been characterized. We studied the dynamic relationship between BP, real-time symptoms, and cerebral oxygenation during hemodialysis, using continuous BP and cerebral oxygenation measurements prospectively gathered from 635 real-world hemodialysis sessions in 58 prevalent patients. We examined the relationship between BP and cerebral ischemia (relative drop in cerebral saturation >15%) and explored the lower limit of cerebral autoregulation at patient and population levels. Furthermore, we estimated intradialytic exposure to cerebral ischemia and hypotension for each patient, and entered these values into multivariate models predicting change in cognitive function. In all, 23.5% of hemodialysis sessions featured cerebral ischemia; 31.9% of these events were symptomatic. Episodes of hypotension were common, with mean arterial pressure falling by a median of 22 mmHg (interquartile range, 14.3-31.9 mmHg) and dropping below 60 mmHg in 24% of sessions. Every 10 mmHg drop from baseline in mean arterial pressure associated with a 3% increase in ischemic events (P<0.001), and the incidence of ischemic events rose rapidly below an absolute mean arterial pressure of 60 mmHg. Overall, however, BP poorly predicted downstream ischemia. The lower limit of cerebral autoregulation varied substantially (mean 74.1 mmHg, SD 17.6 mmHg). Intradialytic cerebral ischemia, but not hypotension, correlated with decreased executive cognitive function at 12 months (P=0.03). This pilot study demonstrates that intradialytic cerebral ischemia occurs frequently, is not easily predicted from BP, and may be clinically significant.