End Goals of Dialysis in Oxalic Acid Poisoning
The primary end goal of dialysis in oxalic acid poisoning is to achieve an anion gap <18 mmol/L, which indicates adequate removal of oxalate and toxic metabolites, combined with resolution of metabolic acidosis (pH >7.35) and normalization of mental status. 1, 2
Biochemical Targets
The most critical biochemical endpoint is anion gap normalization to <18 mmol/L, which serves as the definitive marker that toxic metabolite removal is complete 1, 2, 3. This threshold reflects adequate clearance of both oxalate and its metabolites that drive the metabolic derangement.
Metabolic acidosis must be fully corrected with stable pH >7.35 before considering dialysis cessation 1, 2, 3. This goes beyond simple pH normalization—all acid-base abnormalities must be resolved to ensure metabolic stability 1.
The rationale for these specific targets stems from the pathophysiology: oxalate and its metabolites generate severe metabolic acidosis through multiple mechanisms, and the anion gap directly correlates with toxic metabolite burden 4.
Clinical Endpoints
Normalization of mental status is mandatory before stopping dialysis, including complete resolution of altered consciousness, coma, or seizures that prompted dialysis initiation 1, 2, 3. Neurological manifestations indicate severe toxicity, and their persistence signals ongoing metabolic derangement requiring continued extracorporeal removal 4.
Clinical improvement must include stabilization of neurological function, not just improvement—partial recovery is insufficient 1.
Technical Considerations for Achieving Goals
High-flux hemodialysis is the required modality because it achieves oxalate clearance of 116 mL/min/1.73 m² BSA, vastly superior to peritoneal dialysis (7 mL/min/1.73 m²), allowing rapid removal necessary to reach target endpoints 1, 2, 3.
Technical specifications to optimize metabolite removal include:
- High-flux membrane >1m² capillary surface area per 1m² body surface area 1, 3
- Blood flow rate >250 mL/min (or >150-200 mL/min/m² BSA in children) 2, 3
These parameters are not optional—they are necessary to achieve the clearance rates required to reach biochemical and clinical endpoints within a timeframe that prevents irreversible organ damage 4.
Critical Pitfalls to Avoid
Do not stop dialysis based solely on clinical improvement without confirming anion gap <18 mmol/L and pH >7.35—metabolic derangements can persist despite apparent clinical stabilization 1, 2. The converse is also true: do not continue dialysis indefinitely if all three endpoints (anion gap, pH, mental status) are achieved.
Do not use peritoneal dialysis or standard continuous renal replacement therapy as first-line modalities—their inadequate oxalate clearance will delay achievement of target endpoints and increase risk of irreversible complications 2, 3.
Do not wait for traditional uremic indications to initiate dialysis—the specific thresholds for oxalic acid poisoning (anion gap >27 mmol/L, pH <7.1, altered mental status) are absolute indications that supersede conventional dialysis criteria 2, 3.
Duration Considerations
There is no predetermined duration of dialysis—continue until all three endpoints are met: anion gap <18 mmol/L, pH >7.35, and mental status normalization 1, 2, 3. In practice, this typically requires multiple sessions given the high metabolite burden and ongoing generation from tissue stores 4.
Monitor for rebound increases in metabolite concentrations after dialysis cessation, which occurred in 21% of ethylene glycol poisoning cases (a related toxic alcohol) with median rebound of 30% 4. If clinical deterioration or metabolic acidosis recurs, reinitiate dialysis immediately 4.