Causes of Intradialytic Hypotension
Intradialytic hypotension (IDH) is primarily caused by excessive ultrafiltration rates, cardiac dysfunction, autonomic dysfunction, and inadequate vascular compensation mechanisms that fail to maintain blood pressure during fluid removal during hemodialysis. 1
Definition and Prevalence
- IDH is defined as a decrease in systolic blood pressure by ≥20 mm Hg or a decrease in mean arterial pressure by ≥10 mm Hg, associated with symptoms including abdominal discomfort, yawning, nausea, vomiting, muscle cramps, dizziness, and anxiety
- Affects approximately 25% of all hemodialysis sessions 1
Primary Causes and Pathophysiology
1. Ultrafiltration-Related Factors
- High interdialytic weight gain requiring aggressive fluid removal during dialysis 1
- Excessive ultrafiltration rates (especially rates >6 ml/h per kg) 1
- Rapid plasma osmolality reduction creating osmotic gradients and intracellular fluid shifts 2
- Incorrect assessment of dry weight leading to excessive fluid removal 3
2. Cardiac Factors
- Diastolic dysfunction limiting cardiac filling 1
- Systolic dysfunction reducing cardiac output during volume removal 1
- Valvular heart disease affecting cardiac output 1
- Pericardial disease limiting cardiac compensation 1
3. Vascular Factors
- Defective vascular reactivity preventing adequate vasoconstriction 1
- Autonomic dysfunction impairing compensatory mechanisms 1, 4
- Poor splanchnic flow shifts limiting vascular compensation 4
4. Dialysis Prescription Factors
- High dialysate temperature causing vasodilation 1, 5
- Low dialysate sodium concentration affecting plasma osmolality 1
- Acetate in dialysate triggering vasodilation 5
- Higher Kt/V targets at constrained treatment times causing rapid solute shifts 2
- Higher dialyzer mass transfer-area coefficient for urea 2
5. Patient-Related Risk Factors
- Diabetes mellitus (associated with autonomic neuropathy) 1
- Advanced age (≥65 years) 1
- Female sex 1
- Poor nutritional status 1
- Severe anemia (hemoglobin <11 g/dL) 1
- Predialysis hypotension (SBP ≤100 mm Hg) 1
- Food intake immediately before or during dialysis decreasing peripheral vascular resistance 1
6. Medication-Related Factors
- Antihypertensive medications taken shortly before dialysis 1
- Vasodilating drugs impairing compensatory vasoconstriction 6
Clinical Implications
IDH has serious consequences including:
- Impaired patient well-being and symptoms
- Cardiac arrhythmias
- Predisposition to coronary and cerebral ischemic events
- Vascular access thrombosis
- Inadequate dialysis dose due to compartment effect
- Long-term volume overload from suboptimal ultrafiltration 1
- Increased cardiovascular and all-cause mortality 4
- End-organ damage from repeated hypoperfusion 3
Common Pitfalls in Identifying Causes
- Overlooking sodium intake which drives thirst and fluid consumption between dialysis sessions 1
- Ignoring medication timing such as antihypertensive medications taken shortly before dialysis 1
- Failure to recognize cardiac dysfunction as a major contributor to IDH 1
- Not considering the rapidity of solute removal which can cause osmotic shifts 2
- Inadequate assessment of dry weight leading to inappropriate ultrafiltration targets 3
Understanding these multifactorial causes is essential for developing effective prevention strategies and optimizing dialysis prescriptions for patients at risk of IDH.