Relationship between Hypotension and Cerebral Ischemia during Hemodialysis

Abstract

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 (<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 (=0.03). This pilot study demonstrates that intradialytic cerebral ischemia occurs frequently, is not easily predicted from BP, and may be clinically significant.

Cerebral ischemia during hemodialysis—finding the signal in the noise

“…Regional autoregulation may preserve cerebral blood flow in the face of changing driving pressure, but this is not predictable . The lower threshold for cerebral autoregulation in hemodialysis patients is highly variable (95% confidence intervals 38.9 mmHg to 109.3 mmHg), and many lack autoregulation altogether . Most, but not all, transcranial Doppler studies report a decrease in middle cerebral artery blood flow velocity during hemodialysis .…”

“…There are few studies investigating cerebral NIRS during hemodialysis; most have looked at very small numbers of sessions with no evaluation of neurological outcomes . However, our own group has found an association between decline in executive cognitive function over 12 months and typical exposure to intra‐dialytic cerebral ischemia, defined by area under the curve below the cut‐off of a relative 15% drop in NIRS‐measured cerebral saturations . A strength of our study included the large amount of high quality raw physiological data gathered (635 monitored sessions in 58 patients, including continuous volume‐clamp blood pressure, belt respiratory rate, ECG, pulse oximetry, relative blood volume and cerebral NIRS, with robust signal processing and quality control).…”

“…We suggest increased monitoring to detect subclinical hypotension and hypoxia, with consideration of convective treatments, cooling, or supplemental oxygen in high risk patients. There is evidence that blood pressure should generally be maintained above MAP 60 mmHg or systolic blood pressure (SBP) 90 mmHg, but targets should be individualized: where present, the lower limit of cerebral autoregulation can be estimated from baseline MAP in hemodialysis patients as in other populations . In addition, we believe it is important to screen all hemodialysis patients for cognitive impairment as part of routine care, and address non‐dialytic risk factors such as depression, neurotropic medications and lack of physical activity…”

Blood Pressure and Cognitive Decline in Prevalent Hemodialysis Patients

“…The Chronic Renal Insufficiency Cohort examined cross-sectional vascular risk factors for cognitive impairment in 3,591 participants with a mean eGFR of 43 mL/min/1.73 m 2 , finding that hypertension was a significant risk factor for cognitive impairment in unadjusted analyses but not after adjustment for kidney function [9]. A recent study by MacEwen et al [32] in participants on maintenance HD investigated the interplay between BP, cerebral ischemia (measured using cranial near-infrared spectroscopy), and cognitive function. Among the 58 participants, hypotension was associated with cerebral ischemia, but not cognitive impairment; however, the small sample size was a limiting factor in drawing conclusions.…”

Redefining the Burden of Intradialytic Hypotension in the Modern Era of Hemodialysis

“…For example, one recent study demonstrated an incremental decrease in cerebral perfusion as mean arterial pressure decreased during dialysis [8]. While a mean arterial pressure of 60 mm Hg was specific for hypoperfusion, it had poor sensitivity with much higher mean arterial pressures failing to protect against hypoperfusion in individual patients.…”