What are the causes of intradialytic hypotension in a patient undergoing hemodialysis, particularly in those with a history of cardiovascular disease, diabetes, and multiple comorbidities?

Causes of Intradialytic Hypotension

Intradialytic hypotension results from the interaction between excessive ultrafiltration rate, inadequate cardiac output, and impaired vascular compensatory mechanisms, with the most common underlying cause being volume removal that exceeds the patient's cardiovascular capacity to compensate. 1, 2

Pathophysiologic Mechanisms

The fundamental mechanism involves three interacting factors that determine hemodynamic stability during dialysis 2, 3:

• Excessive ultrafiltration that depletes intravascular volume faster than it can be refilled from the interstitial space 2, 3
• Inadequate cardiac output due to underlying cardiac dysfunction, particularly left ventricular hypertrophy with diastolic dysfunction or systolic heart failure 1
• Impaired vascular compensation from defective reactivity of both resistance and capacitance vessels in CKD patients, preventing appropriate vasoconstriction and blood pressure maintenance 1

Patient-Related Risk Factors

High-Risk Patient Subgroups

Diabetic patients with CKD Stage 5 represent the highest-risk group due to autonomic dysfunction causing exaggerated blood pressure drops and impaired compensatory responses 1:

• Autonomic neuropathy prevents normal sympathetic activation and vascular tone adjustment 1
• Diabetic patients show persistent orthostatic hypotension that worsens during ultrafiltration 1

Cardiovascular Disease

Patients with structural heart disease face substantially elevated risk 1:

• Left ventricular hypertrophy with diastolic dysfunction (with or without heart failure) impairs cardiac filling and output during volume removal 1
• Left ventricular systolic dysfunction and heart failure directly limit cardiac output response 1
• Valvular heart disease restricts hemodynamic compensation 1
• Pericardial disease (constrictive pericarditis or effusion) limits cardiac filling 1
• Coronary artery disease increases vulnerability to ischemia during hypotensive episodes 1

Demographic and Clinical Characteristics

• Age ≥65 years independently increases risk through reduced vascular compliance and comorbidity burden 1, 4
• Female sex associates with higher IDH frequency 4
• Hispanic ethnicity shows increased risk in observational data 4
• Longer dialysis vintage correlates with progressive autonomic dysfunction and cardiovascular disease 4
• Higher body mass index increases ultrafiltration requirements 4

Nutritional and Hematologic Factors

• Poor nutritional status and hypoalbuminemia reduce oncotic pressure and impair vascular refill 1
• Severe anemia limits oxygen delivery and cardiovascular compensation 1

Baseline Hemodynamic Status

• Predialysis systolic blood pressure ≤100 mmHg identifies a particularly vulnerable subgroup (5-10% of patients) including anephric patients and those with long dialysis duration 1

Dialysis Prescription-Related Causes

Ultrafiltration Parameters

Ultrafiltration rate >6-10 mL/h/kg represents the most modifiable risk factor, with observational data showing mortality risk even at rates as low as 6 mL/h/kg 1, 2:

• Excessive interdialytic weight gain necessitates higher ultrafiltration volumes and rates 1, 4
• Second and third weekly treatments show higher IDH frequency due to longer interdialytic intervals and greater fluid accumulation 4
• Rapid intravascular volume depletion outpaces vascular refill from interstitial compartments 2, 3

Dialysate Composition

• Higher dialysate temperature (standard 37°C) increases core body temperature, causing peripheral vasodilation and reducing vascular tone 1
• Dialysate sodium concentration affects osmotic gradients and vascular refill rates 1

Dialysis Dose and Efficiency

Higher dialysis dose (Kt/V) associates with increased IDH risk through rapid osmotic shifts 5:

• Higher membrane efficiency and urea removal rates create transient intradialytic osmotic gradients 5
• Rapid reduction in plasma osmolality promotes intracellular fluid shifts, depleting intravascular volume 5
• Higher mass transfer-area coefficient for urea increases IDH odds (OR 1.15) 5

Medication-Related Causes

• Antihypertensive medications taken before dialysis, particularly nondialyzable agents like carvedilol, exacerbate hypotension during ultrafiltration 1, 6
• Nitrate use before dialysis causes vasodilation that impairs compensatory vascular responses 1

Timing and Variability Factors

• Early morning dialysis sessions (at or before 9:00 AM) show 16% higher risk of IDH compared to afternoon sessions, likely due to circadian blood pressure patterns 7
• Seasonal variations affect IDH frequency in individual patients 1
• Session-to-session variability occurs even in the same patient due to changing hydration status, medication timing, and acute illnesses 1, 3

Incorrect Dry Weight Assessment

Setting target weight below true dry weight represents a critical and common cause of recurrent IDH 3:

• Inadequate assessment of volume status leads to excessive ultrafiltration attempts 3
• Unaccounted changes in patient condition (improved nutrition, muscle mass changes) alter true dry weight 3

Acute Intercurrent Illnesses

• Acute infections, bleeding, or other illnesses alter hemodynamic stability and volume status unpredictably 3
• Food intake during dialysis causes splanchnic vasodilation, diverting blood flow and worsening hypotension 2

Facility-Level Factors

Dialysis facility practices independently predict IDH frequency (range 11.1-25.8% across facilities), suggesting that modifiable practice patterns significantly influence outcomes 4. This variability persists even after adjusting for patient characteristics, indicating that systematic approaches to ultrafiltration management, dry weight assessment, and hemodynamic monitoring differ substantially between centers 4.