What causes a patient with end-stage renal disease (ESRD) or acute kidney injury (AKI) to worsen after undergoing hemodialysis (HD)?

What Causes Patient Worsening After Hemodialysis

The most common cause of patient worsening after hemodialysis is intradialytic hypotension resulting from excessive ultrafiltration that depletes intravascular volume faster than compensatory mechanisms can respond, leading to end-organ hypoperfusion and associated complications. 1, 2

Primary Mechanisms of Post-Dialysis Deterioration

Intradialytic Hypotension and Hemodynamic Instability

• Excessive ultrafiltration is the leading precipitant, occurring when fluid removal exceeds the rate of vascular refilling from interstitial compartments, causing rapid intravascular volume depletion 1, 2
• Intradialytic hypotension (defined as systolic BP drop ≥20 mmHg or mean arterial pressure drop ≥10 mmHg) occurs in approximately 8% of all HD sessions and requires countermeasures like saline infusion or ultrafiltration reduction 3, 2
• Inadequate peripheral vascular resistance response fails to compensate for acute volume loss—when the normal compensatory increase in PVR does not occur, blood pressure cannot be maintained despite preserved cardiac output 4
• Episodes of intravascular volume depletion during HD contribute to more rapid loss of residual kidney function, creating a vicious cycle of worsening renal capacity 1

Cardiovascular Complications

• Myocardial stunning results from repetitive hypotensive episodes, causing transient left ventricular dysfunction that accumulates over time with repeated dialysis sessions 3
• Cardiac arrhythmias are triggered by rapid electrolyte shifts and volume depletion during aggressive ultrafiltration 3
• Patients with pre-existing left ventricular hypertrophy or cardiac dysfunction are particularly vulnerable to hemodynamic instability during fluid removal 5

Paradoxical Hypertension During or After Dialysis

• Excessive volume depletion can paradoxically trigger hypertension rather than hypotension through overstimulation of the renin-angiotensin system and sympathetic nervous system 1, 6
• Accelerated ultrafiltration may worsen hypertension by causing hypotension that requires saline administration, ultimately worsening volume overload 6, 7
• Removal of certain antihypertensive drugs during dialysis (enalapril, ramipril, atenolol, acebutolol, nadolol, minoxidil, nitroprusside) can precipitate rebound hypertension 1

Secondary Mechanisms

Electrolyte and Acid-Base Disturbances

• Rapid shifts in potassium, calcium, and bicarbonate during dialysis can cause cardiac instability and arrhythmias 1
• Dialysate calcium concentration that is too low (<1.25 mmol/L) can contribute to intradialytic hypotension and hemodynamic instability 1, 5

Residual Kidney Function Loss

• Episodes of hypotension during HD accelerate the loss of residual kidney function through repetitive ischemic injury to remaining nephrons 1
• Loss of residual kidney function increases dependence on ultrafiltration, creating greater hemodynamic stress with each subsequent dialysis session 1

Inadequate Dialysis Delivery

• Hypotensive episodes force premature termination or reduction of dialysis time, resulting in inadequate solute clearance and uremic symptom persistence 1
• Patients may experience prolonged recovery time (>6 hours in 27% of patients), feeling "washed out or drained" after treatment 3

Critical Risk Factors

Patient-Related Factors

• Advanced age and multiple comorbidities reduce cardiovascular reserve and ability to compensate for volume shifts 2
• Pre-existing cardiac dysfunction (congestive heart failure, ischemic heart disease, left ventricular hypertrophy) dramatically increases vulnerability to hemodynamic instability 5
• Malnutrition and low albumin levels worsen prognosis and reduce oncotic pressure for vascular refilling 5

Dialysis Prescription Factors

• Incorrect dry weight assessment is a major contributor—setting target weight too low causes excessive ultrafiltration and hypotension 8, 2
• Large interdialytic weight gains necessitate aggressive ultrafiltration that exceeds compensatory capacity 8, 2
• Inadequate dialysis time (standard 4 hours three times weekly) may be too short for safe fluid removal in volume-overloaded patients 6, 7

Prevention Strategies

Optimizing Ultrafiltration

• Avoid excessive ultrafiltration by accurately assessing dry weight through careful clinical examination for volume overload signs 1, 8
• Extend dialysis time beyond standard 4 hours when necessary to allow slower, better-tolerated fluid removal 6, 7
• Minimize interdialytic weight gain through sodium restriction (<2g/day) and fluid restriction between sessions 8

Dialysis Prescription Modifications

• Reduce dialysate temperature to improve hemodynamic stability during ultrafiltration 1
• Increase dialysate sodium concentration to support blood pressure during fluid removal 1
• Use dialysate calcium concentration of 1.25-1.5 mmol/L to prevent hypotension while avoiding excessive calcium loading 1, 5
• Consider predialysis administration of midodrine (alpha-agonist) for patients with recurrent intradialytic hypotension 1

Preserving Residual Kidney Function

• Maintain target hematocrit to optimize oxygen-carrying capacity and cardiovascular stability 1
• Use loop diuretics in patients with residual kidney function to reduce ultrafiltration requirements 1, 8
• Consider ACE inhibitors or ARBs for blood pressure control and renoprotection, though monitor for excessive GFR reduction 1, 8

Common Pitfalls to Avoid

• Do not aggressively pursue dry weight reduction without considering the patient's cardiovascular reserve and ability to tolerate volume removal 8, 7
• Avoid rapid blood pressure reduction that precipitates intradialytic hypotension requiring saline infusion, which worsens the underlying volume problem 6, 7
• Do not ignore the "lag phenomenon"—blood pressure may continue decreasing for 8 months after achieving euvolemia, requiring ongoing dry weight reassessment 7
• Recognize that conventional 4-hour dialysis three times weekly may be inadequate for safe ultrafiltration in many patients, particularly those with large interdialytic weight gains 6

Special Considerations for Acute Coronary Syndromes

• Timing of dialysis in the first 48 hours after acute coronary syndrome requires individualized assessment of volume status, electrolyte disturbances, and bleeding potential 1
• Dialysis prescriptions should be adjusted to maximize benefits while reducing hypotension risk during this vulnerable period 1
• Collaboration between nephrology and cardiology teams is essential for balancing the need for volume removal against cardiovascular instability 1