When is hemodialysis (HD) recommended for severe metabolic acidosis?

Hemodialysis for Severe Metabolic Acidosis

Hemodialysis is indicated for severe metabolic acidosis when pH falls below 7.20 in the absence of other indications, or when severe acidosis persists despite standard medical therapy including bicarbonate supplementation and optimization of dialysate bicarbonate concentration. 1

Primary Indications for Dialysis in Severe Metabolic Acidosis

Absolute indications for emergent hemodialysis include:

• Severe acidemia with pH <7.20 despite maximal medical management, as this threshold represents life-threatening acid-base disturbance 1
• Persistent severe metabolic acidosis unresponsive to bicarbonate therapy in the setting of acute kidney injury or chronic kidney disease 1
• Metabolic acidosis accompanied by life-threatening hyperkalemia (>6.0 mmol/L), as these conditions frequently coexist and both require urgent dialytic correction 2
• Acidosis with volume overload unresponsive to diuretics, particularly when accompanied by pulmonary edema 1
• Uremic symptoms (encephalopathy, pericarditis) occurring with metabolic acidosis, as these represent absolute indications for immediate dialysis 2

Context-Specific Scenarios

Poisoning and Toxic Ingestions

• Salicylate poisoning with pH <7.20 warrants extracorporeal treatment regardless of salicylate concentration, with intermittent hemodialysis being the preferred modality 1
• Ethylene glycol poisoning with severe acidemia (pH <6.60 or bicarbonate <2 mmol/L) requires immediate hemodialysis, as survival has been documented even with extreme acid-base abnormalities when dialysis is initiated promptly 1
• Acidemia correction occurs rapidly with high-efficiency hemodialysis in toxic ingestions, typically within 4 hours 1

Tumor Lysis Syndrome

• Severe metabolic acidosis in tumor lysis syndrome mandates renal replacement therapy, particularly when accompanied by persistent hyperkalemia and hyperphosphatemia 1, 3, 4
• Frequent (daily) dialysis is recommended due to continuous release of metabolites and ongoing acid production from tumor cell lysis 1, 4

Chronic Dialysis Patients

• For maintenance hemodialysis patients, predialysis serum bicarbonate should be maintained at ≥22 mmol/L through optimization of dialysate bicarbonate concentration (typically 38 mmol/L) and oral bicarbonate supplementation (25-50 mEq/day) 1
• Persistent metabolic acidosis (bicarbonate <22 mmol/L) occurs in up to 73% of hemodialysis patients and requires prescription modification 5

Dialysis Modality Selection

Intermittent hemodialysis (IHD) is the preferred initial modality for severe metabolic acidosis requiring rapid correction 2:

• IHD provides superior efficiency for acid removal and electrolyte correction compared to peritoneal dialysis 1
• High-flux dialyzers with bicarbonate dialysate (38 mmol/L) achieve rapid pH normalization 1

Continuous renal replacement therapy (CRRT) should be reserved for:

• Hemodynamically unstable patients who cannot tolerate intermittent hemodialysis 1, 2
• Patients requiring continuous acid-base control with ongoing acid production 1, 2
• CRRT provides better hemodynamic stability but slower acid correction than IHD 1

Peritoneal dialysis has limited utility in severe metabolic acidosis due to lower efficiency for solute and acid removal, and should only be used when other modalities are unavailable 1

Critical Pitfalls and Caveats

Bicarbonate Buffer Selection

• Both lactate and bicarbonate buffers can correct metabolic acidosis in most CRRT patients, but bicarbonate is strongly preferred in patients with lactic acidosis or liver failure, as lactate-based solutions can worsen acidosis in these populations 1
• Citrate anticoagulation during dialysis can cause both metabolic alkalosis and metabolic acidosis depending on citrate metabolism, requiring close monitoring of systemic acid-base balance 1

Monitoring Requirements

• Predialysis serum bicarbonate should be measured monthly in maintenance dialysis patients to detect persistent acidosis 1
• In acute settings with severe acidosis, arterial blood gas monitoring should guide therapy intensity 1
• Post-dialysis bicarbonate levels should be checked, as 41% of patients may remain acidotic even after hemodialysis treatment 5

Dialysate Composition

• Sorbent system hemodialysis with bicarbonate regeneration can paradoxically cause or worsen metabolic acidosis due to variable and often low dialysate bicarbonate concentrations (mean 16.5 mEq/L), and should be avoided 6
• Standard single-pass hemodialysis with fixed bicarbonate dialysate is safer and more predictable 6

Associated Electrolyte Disturbances

• Do not routinely supplement calcium in patients with concurrent hyperphosphatemia and hypocalcemia, as this worsens calcium-phosphate precipitation in tissues 2
• Only symptomatic hypocalcemia (tetany, seizures) requires cautious calcium gluconate administration 2
• Hyperkalemia frequently accompanies severe metabolic acidosis and may be the primary indication for urgent dialysis 2, 7

Protein Metabolism Considerations

• Uncorrected metabolic acidosis increases protein degradation, branched-chain amino acid oxidation, and decreases albumin synthesis 1
• Higher protein nitrogen appearance (protein breakdown) independently predicts metabolic acidosis in dialysis patients 7
• Correction of acidosis improves nutritional parameters including serum albumin, body weight, and mid-arm circumference 1