Causes of Increased Blood Pressure During Hemodialysis
Inadequate achievement of dry weight is the primary cause of increased blood pressure during hemodialysis, with excess fluid remaining in the extracellular compartment despite dialysis sessions. 1
Primary Mechanism: Volume Overload
Failure to reach dry weight is the dominant mechanism driving hypertension in hemodialysis patients. 1 This occurs through several pathways:
Insufficient dialysis time: Conventional 3-4 hour sessions may be too short for patients requiring aggressive ultrafiltration, making adequate fluid removal impossible. 1
Paradoxical volume expansion: When ultrafiltration is accelerated to compensate for limited time, it can precipitate hypotension requiring saline administration, which further expands extracellular volume beyond the original target. 1
Excessive interdialytic sodium and water intake: High sodium intake between sessions (often exceeding the recommended 4.7-5.8g sodium chloride daily) drives fluid accumulation that cannot be adequately removed. 1
The relationship between volume and blood pressure may be sigmoidal rather than linear—blood pressure remains controlled until physiological autoregulation fails, then rises sharply once a threshold is exceeded. 1
Secondary Pathophysiological Mechanisms
Beyond volume overload, multiple pathways contribute to hypertension in dialysis patients:
Vascular and Endothelial Dysfunction
- Arterial stiffness from arteriosclerosis limits vascular compliance, making blood pressure more sensitive to volume changes. 1
- Salt-related reduction in nitric oxide formation impairs normal vasodilation. 1
Neurohumoral Activation
- Sympathetic nervous system overactivity contributes to vasoconstriction and may be particularly important in patients who develop hypertension despite adequate ultrafiltration. 1
- Renin-angiotensin system activation can occur, especially when excessive ultrafiltration triggers compensatory vasoconstriction. 1
Erythropoietin Therapy
- Recombinant human erythropoietin (rhEPO) causes blood pressure elevation in 35% of previously hypertensive patients and 44% of normotensive patients. 1
- Risk is highest in patients with severe anemia, rapid correction of anemia, and pre-existing hypertension. 1
- The hypertensive effect typically occurs within 2-16 weeks of initiation but can develop months later. 1
Paradoxical Intradialytic Hypertension
A small subset of patients experience blood pressure elevation during fluid removal, a phenomenon that is poorly understood. 1
Proposed mechanisms include:
- Excessive renin-angiotensin system stimulation precipitated by rapid volume depletion. 1
- Excessive sympathetic nervous system activation with resulting vasoconstriction. 1
- Removal of dialyzable antihypertensive medications (enalapril, ramipril, atenolol, acebutolol, nadolol, minoxidil) during the dialysis session. 1
In seven patients studied with this characteristic and marked cardiac dilation, intense ultrafiltration paradoxically reduced blood pressure, suggesting cardiac dysfunction may play a role. 1
Critical Clinical Pitfalls
The "lag phenomenon": Even after achieving dry weight and normalizing extracellular fluid volume within weeks, elevated blood pressure may continue to decrease for 8 months or longer. 2 Clinicians must avoid prematurely escalating antihypertensive medications during this period.
Inadequate dialysis prescription: When conventional dialysis time proves insufficient, attempting to accelerate ultrafiltration creates a vicious cycle—hypotension requires saline administration, preventing achievement of dry weight and perpetuating hypertension. 1 The solution is extending dialysis time or frequency, not faster ultrafiltration. 2, 3
Dialysate sodium concentration: Using dialysate sodium >140 mmol/L impairs sodium removal and contributes to volume expansion. 2