Management of Metabolic Acidosis Post-Plasmapheresis
Monitor electrolytes serially during plasmapheresis and treat hyperchloremic metabolic acidosis with intravenous sodium bicarbonate to achieve serum bicarbonate ≥22 mmol/L, particularly in patients with impaired renal function. 1, 2, 3
Mechanism and Risk Factors
Hyperchloremic metabolic acidosis develops after plasmapheresis due to administration of large volumes of albumin replacement fluid containing high chloride concentrations (typically 132 mmol/L). 3
High-Risk Populations
- Patients with impaired renal function are at highest risk for severe metabolic acidosis, as they cannot adequately excrete the chloride load 3
- Patients receiving multiple daily plasmapheresis sessions accumulate greater chloride burden 3
- Those with pre-existing metabolic derangements require closer monitoring 1
Clinical Recognition
Presenting Symptoms
- Gastrointestinal complaints (nausea, vomiting) 3
- Muscle weakness 3
- Symptoms may develop after 4 or more plasmapheresis treatments 3
Laboratory Findings
- Serum bicarbonate <22 mmol/L (severe cases may drop to 11-12 mmol/L) 2, 3
- Elevated chloride (>111 mmol/L) with normal or near-normal sodium 3
- Normal total-to-ionized calcium ratio rules out citrate accumulation as the cause 3
Treatment Algorithm
Immediate Management
Administer intravenous sodium bicarbonate to achieve serum bicarbonate ≥22 mmol/L. 2, 4
Dosing Protocol
- For severe acidosis (pH <7.20): Give 2-5 mEq/kg body weight IV over 4-8 hours 2, 4
- Initial bolus in emergent situations: 44.6-100 mEq (one to two 50 mL vials) 4
- Titrate based on arterial blood gas monitoring and clinical response 4
Preventive Strategies
Modify the plasmapheresis replacement fluid to prevent recurrence: 5
- Use 3% albumin combined with cryoprecipitate instead of high-chloride albumin solutions 5
- Consider fresh frozen plasma as partial replacement in select cases 6
- Provide daily oral bicarbonate supplementation prophylactically in high-risk patients 3
Monitoring Requirements
Serial monitoring is essential throughout plasmapheresis treatment: 1, 2
- Measure arterial blood gases and serum bicarbonate before each session 2, 4
- Check electrolytes (sodium, chloride, potassium, calcium, magnesium, phosphate) daily 1, 2
- Monitor for hemodynamic shifts and coagulation abnormalities 1
Critical Pitfall to Avoid
Do not attempt full correction of acidosis within the first 24 hours, as this may cause rebound alkalosis due to delayed ventilatory readjustment. 4 Target total CO2 content of approximately 20 mEq/L at end of first day, which typically corresponds to normal blood pH 4.
Special Considerations
Citrate vs. Chloride Acidosis
- Citrate accumulation causes metabolic alkalosis, not acidosis, and presents with elevated total-to-ionized calcium ratio 5, 3
- Hyperchloremic acidosis from albumin solutions shows normal calcium ratio 3
- This distinction is critical for appropriate treatment selection 3
Renal Transplant Patients
Patients with transplant rejection receiving plasmapheresis face compounded risk due to both impaired renal function and need for multiple exchange sessions 3. These patients require: