What is intra-dialytic (intra-dialysis) hypotension?

What is Intradialytic Hypotension?

Intradialytic hypotension is a serious complication of hemodialysis defined as any symptomatic decrease in blood pressure or a nadir systolic blood pressure <90 mm Hg during dialysis treatment, occurring in 15-50% of hemodialysis sessions and associated with increased mortality, vascular access thrombosis, and inadequate dialysis. 1

Core Definition and Clinical Thresholds

The KDIGO 2020 guidelines recommend that any symptomatic blood pressure decrease or a nadir systolic blood pressure <90 mm Hg should prompt immediate reassessment of blood pressure and volume management. 1 Alternative definitions include:

• A systolic blood pressure drop of 20-40 mm Hg from baseline 1
• A decrease in mean arterial pressure by 10 mm Hg 2, 3
• Nadir systolic blood pressure <100 mm Hg in patients with pre-dialysis systolic blood pressure >160 mm Hg (most potently associated with mortality) 1

The definition requiring interventions (saline bolus, ultrafiltration reduction, or blood pump flow reduction) is also commonly used. 1

Prevalence and Clinical Significance

Intradialytic hypotension affects approximately 25% of all hemodialysis sessions, with prevalence ranging from 15-50% depending on the definition used. 1, 2, 3 This complication is directly associated with vascular access thrombosis, inadequate dialysis dose, and increased mortality. 1

Pathophysiology

The mechanism involves three key interacting factors: 4

• Excessive ultrafiltration rate that exceeds the vascular refilling capacity from tissue spaces 2, 4
• Inadequate cardiac output response due to left ventricular hypertrophy, diastolic dysfunction, or systolic dysfunction 2
• Impaired arteriolar vasoconstriction from autonomic dysfunction, particularly in diabetic patients 2, 4

The magnitude of blood pressure reduction during dialysis most closely relates to the magnitude of ultrafiltration. 1

Clinical Presentation

Symptoms include: 2, 3

• Abdominal discomfort and nausea
• Yawning and sighing (characteristic respiratory manifestations)
• Vomiting and muscle cramps
• Restlessness, dizziness, or fainting
• Anxiety

What Requires Immediate Reassessment

When intradialytic hypotension occurs, reassessment must include: 1

• Ultrafiltration rate - the primary modifiable factor
• Dialysis treatment time - extending time reduces hourly ultrafiltration rate
• Interdialytic weight gain - reflects fluid intake compliance
• Dry-weight estimation - hypotension may indicate target weight is set too low
• Antihypertensive medication use - timing and selection require evaluation

Critical Management Principle

Avoidance of intradialytic hypotension should not come at the expense of maintaining euvolemia or ensuring adequate dialysis time. 1 This represents a key clinical tension - the need to prevent hypotension must be balanced against achieving adequate volume removal and dialysis adequacy.

Acute Management Interventions

When intradialytic hypotension occurs during treatment: 2

• Reduce or temporarily stop ultrafiltration immediately
• Administer intravenous normal saline bolus to expand plasma volume rapidly
• Place patient in Trendelenburg position (head down, legs elevated)
• Provide supplemental oxygen to improve tissue oxygenation

Preventive Strategies

Evidence-based preventive measures include: 1, 5, 6

• Cool dialysate (34-35°C instead of 37°C) - increases peripheral vasoconstriction and cardiac output, reducing hypotension incidence from 44% to 34% 1, 5
• Sodium modeling - starting with higher dialysate sodium (152 mEq/L) and gradually decreasing to 140 mEq/L significantly reduces hypotensive episodes 5
• High sodium dialysate (144 mEq/L) - effective but may increase interdialytic weight gain 5
• Bicarbonate-containing dialysate instead of acetate - acetate inappropriately decreases vascular resistance and increases venous pooling 1, 6
• Extending treatment time to ≥4 hours - reduces hourly ultrafiltration rate 1, 6

Isolated ultrafiltration followed by isovolemic dialysis is notably ineffective and results in significantly more hypotensive episodes than other strategies. 5

Pharmacologic Intervention

Midodrine (oral selective α1-adrenergic agonist) administered within 30 minutes of dialysis initiation raises blood pressure by increasing peripheral vascular resistance and enhancing venous return, effectively minimizing hypotensive events. 1

Patient-Related Factors

• Avoid food intake immediately before or during hemodialysis - causes decreased peripheral vascular resistance and may precipitate hypotension 1, 2
• Limit fluid intake between sessions to reduce interdialytic weight gain 2
• Optimize hemoglobin levels - raising hemoglobin to 11 g/dL reduces hypotension incidence 1

Long-Term Outcomes

Repeated episodes of intradialytic hypotension cause end-organ damage through disruption of perfusion to the heart, central nervous system, kidneys, and gastrointestinal system, contributing to increased cardiovascular and all-cause mortality. 4, 7