Why do some patients experience hypertension when initiated on dialysis (Dialysis)

Why Some Patients Experience High Blood Pressure During Dialysis

The majority of hypertensive episodes during dialysis occur due to fluid overload and sodium retention, which can be exacerbated by inadequate ultrafiltration and other pathogenic mechanisms including sympathetic nervous system overactivity and renin-angiotensin system activation. 1

Primary Mechanisms of Intradialytic Hypertension

Fluid and Sodium-Related Factors

• Inadequate achievement of dry weight during dialysis sessions is a major contributor to hypertension, as excess fluid remains in the extracellular compartment 1
• Excessive sodium and water ingestion during the interdialysis period can lead to high predialysis blood pressure 1
• For some patients, conventional dialysis time (4 hours, 3 times weekly) is too short for their ultrafiltration requirements, making it difficult to remove adequate fluid 1
• When ultrafiltration is accelerated to compensate for limited time, some patients experience hypotension, requiring saline administration which further expands extracellular volume 1

Paradoxical Blood Pressure Response

• Some patients experience a paradoxical increase in blood pressure during or after dialysis, a phenomenon that occurs in approximately 10-12% of patients 2, 3
• This paradoxical response may be related to:
  • Activation of the renin-angiotensin-aldosterone system during fluid removal 2
  • Imbalances in endothelium-derived mediators (decreased vasodilators, increased vasoconstrictors) 1, 2
  • Clearance of antihypertensive medications during dialysis 2
  • Increased cardiac output in response to volume changes 2

Other Contributing Factors

• Arterial stiffness caused by arteriosclerosis limits vascular compliance 1
• Salt-related reduction in nitric oxide formation impairs vasodilation 1
• Sympathetic nervous system overactivity is common in end-stage renal disease patients 4
• Erythropoietin therapy can worsen hypertension in 35-44% of patients, particularly those with severe anemia, rapid correction, or pre-existing hypertension 1

Clinical Significance and Outcomes

• Patients who experience blood pressure increases during dialysis have increased rates of both short-term and long-term mortality 2, 3
• Every 10 mmHg increase in systolic blood pressure during hemodialysis is associated with a 6% increased hazard of death 3
• This relationship is particularly significant in patients with predialysis systolic blood pressure less than 120 mmHg 3

Management Approaches

Optimizing Fluid and Sodium Management

• Strict volume control with gradual achievement of dry weight should be the primary approach 1, 5
• Dietary sodium restriction (recommended 4.7-5.8g sodium chloride daily) is essential 1
• Consider reducing dialysate sodium concentration based on pre-hemodialysis plasma sodium 4
• For some patients, longer or more frequent dialysis sessions may be necessary to achieve adequate fluid removal without hemodynamic instability 1, 5

Medication Management

• Antihypertensive medications may need adjustment, with ACE inhibitors or ARBs as first-line agents for most patients 1
• Beta-blockers are preferred for patients with previous myocardial infarction or established coronary artery disease 1
• Calcium channel blockers and anti-alpha-adrenergic drugs may be needed for adequate control 1

Alternative Dialysis Strategies

• Long, slow hemodialysis (3 × 8 hours per week) 6
• Short daily hemodialysis (2-3 hours, 7 times per week) 6, 5
• Nocturnal hemodialysis (6-7 times overnight per week) 6
• These intensive dialysis regimens normalize blood pressure in most patients without antihypertensive medications 5

Important Clinical Considerations

• The relationship between extracellular volume and blood pressure may be sigmoidal rather than linear in some patients, with blood pressure only increasing when physiological autoregulation can no longer cope with fluid excess 1
• A "lag phenomenon" exists where extracellular fluid volume normalizes within weeks, but elevated blood pressure may continue to decrease for 8 months or longer 1
• Target predialysis blood pressure should be 140/90 mmHg (measured in sitting position), provided there is no substantial orthostatic hypotension or symptomatic intradialytic hypotension 1
• Patients transitioning from conventional to daily dialysis often experience improved blood pressure control due to better volume management and possibly decreased sympathetic nervous system activity 1, 4