Causes of Intradialytic Hypotension
Intradialytic hypotension (IDH) is primarily caused by an imbalance between ultrafiltration rate and plasma refilling capacity, with failure of compensatory mechanisms including cardiac output and vascular tone, affecting approximately 25% of all hemodialysis sessions. 1
Definition and Clinical Impact
IDH is defined as:
- Decrease in systolic blood pressure by ≥20 mm Hg or
- Decrease in mean arterial pressure by ≥10 mm Hg
- Associated with symptoms including abdominal discomfort, yawning, sighing, nausea, vomiting, muscle cramps, restlessness, dizziness, fainting, and anxiety 1
IDH has serious consequences:
- Impaired patient well-being
- 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
Major Pathophysiological Mechanisms
1. Volume-Related Factors
- Excessive ultrafiltration rate: Removal of fluid at a rate exceeding plasma refilling capacity 2
- High interdialytic weight gain: Requiring more aggressive fluid removal during dialysis 1
- Incorrect dry weight assessment: Leading to excessive fluid removal 3
2. Cardiovascular Factors
- Impaired cardiac output: Inability to increase cardiac output in response to reduced blood volume 2
- Diastolic dysfunction: Common in patients with left ventricular hypertrophy 1
- Systolic dysfunction: Reduced contractility in patients with heart failure 1
- Valvular heart disease: Affecting cardiac filling and output 1
- Pericardial disease: Including constrictive pericarditis or pericardial effusion 1
3. Vascular Factors
- Defective vascular reactivity: Poor response of resistance and capacitance vessels 1
- Autonomic dysfunction: Common in diabetic patients, causing exaggerated drops in blood pressure 1
- Impaired vasoconstriction: Failure to maintain vascular tone during volume removal 2
- Core temperature increase: Standard dialysis increases core body temperature, impairing vascular responses 1
4. Patient-Specific Risk Factors
- Diabetes mellitus: Associated with autonomic neuropathy 1
- Advanced age (≥65 years): Reduced cardiovascular reserve 1
- Female sex: Higher susceptibility to hypotension 1
- Poor nutritional status: Associated with hypoalbuminemia 1
- Severe anemia: Reduced oxygen-carrying capacity 1
- Predialysis hypotension: Systolic BP ≤100 mm Hg 1
- Medication timing: Antihypertensive medications taken before dialysis 3
- Food intake: Eating before or during dialysis decreases peripheral vascular resistance 3
5. Dialysis-Related Factors
- Rapid osmolality changes: Quick reduction in plasma osmolality causing fluid shifts 4
- Dialysate composition: Acetate in dialysate can trigger hypotension 5
- Dialysate temperature: Standard temperature dialysate fails to prevent vasodilation 5
- High dialysis dose: Associated with increased risk of IDH due to rapid solute removal 4
- Sodium concentration: Inappropriate dialysate sodium leading to osmotic shifts 6
High-Risk Patient Subgroups
The following patients are at particularly high risk for IDH:
- Patients with diabetic CKD Stage 5
- Patients with cardiovascular disease (LVH, diastolic dysfunction, systolic dysfunction)
- Patients with poor nutritional status and hypoalbuminemia
- Patients with autonomic dysfunction
- Patients with severe anemia
- Patients requiring high-volume ultrafiltration
- Patients with predialysis SBP ≤100 mm Hg
- Elderly patients (≥65 years) 1
Common Pitfalls in IDH Management
- Ignoring medication timing: Taking antihypertensive medications shortly before dialysis 3
- Overlooking sodium intake: High sodium intake drives thirst and fluid consumption between sessions 3
- Excessive ultrafiltration rates: Removing fluid too rapidly (>6 ml/h/kg) 3
- Fixed dry weight targets: Failure to regularly reassess and adjust dry weight 3
- Ignoring food intake: Allowing eating immediately before or during dialysis 3
- Overlooking core temperature: Failing to adjust dialysate temperature 1, 3
Understanding these multifaceted causes of IDH is essential for implementing effective preventive strategies and improving patient outcomes during hemodialysis.