When should a patient on Continuous Renal Replacement Therapy (CRRT) be started on a bicarbonate drip?

From the Guidelines

A patient on Continuous Renal Replacement Therapy (CRRT) should be started on a bicarbonate drip when they develop severe metabolic acidosis that is not adequately corrected by the CRRT itself, typically when serum bicarbonate levels fall below 15-18 mEq/L or arterial pH is less than 7.2 despite optimized CRRT settings, as recommended by the KDIGO guidelines 1. This approach is supported by the KDIGO Clinical Practice Guideline for Acute Kidney Injury, which suggests using bicarbonate, rather than lactate, as a buffer in dialysate and replacement fluid for RRT in patients with AKI, particularly in those with circulatory shock or liver failure and/or lactic acidemia 1. The standard bicarbonate drip consists of sodium bicarbonate 150 mEq in 1000 mL of D5W or sterile water, administered at 50-150 mL/hour (or 7.5-22.5 mEq/hour), with the rate titrated based on serial blood gas measurements every 4-6 hours. Some key points to consider when implementing this therapy include:

• Monitoring for complications including fluid overload, hypernatremia, and paradoxical cerebrospinal fluid acidosis
• Gradually increasing serum bicarbonate to 22-26 mEq/L and normalizing pH
• Adjusting the bicarbonate drip rate based on the patient's response to therapy, as guided by the KDIGO recommendation to deliver RRT to achieve the goals of electrolyte, acid-base, solute, and fluid balance that will meet the patient’s needs 1. The bicarbonate drip works by directly supplementing bicarbonate buffer to neutralize excess hydrogen ions, compensating for the body's inability to clear acid accumulation during renal failure and the potential limitations of the CRRT bicarbonate buffer system in severe acidosis cases.

From the Research

Indications for Bicarbonate Drip in CRRT

• The decision to start a patient on Continuous Renal Replacement Therapy (CRRT) with a bicarbonate drip depends on several factors, including the presence of metabolic acidosis, acute kidney injury, and the patient's overall clinical condition 2, 3.
• Bicarbonate therapy may be beneficial for patients with severe metabolic acidosis, particularly those with accompanying acute kidney injury, as it can improve survival 2.
• In patients with severe liver failure or lactic acidosis, bicarbonate-buffered solutions are preferred over lactate-buffered solutions, as lactate can exacerbate metabolic acidosis 3.

Management of Acid-Base and Electrolyte Imbalances

• CRRT is used to manage electrolyte and acid-base imbalances in critically ill patients with acute kidney injury, and a tailored approach may be necessary to address specific disorders 4.
• The use of sodium bicarbonate can improve acid-base status, but its effect on outcomes such as return of spontaneous circulation and good neurologic survival is unclear 5.
• In cases of metformin-associated lactic acidosis, CRRT has been shown to be effective in controlling metabolic acidosis and eliminating metformin 6.

Key Considerations

• The composition of the substitution/dialysate fluid in CRRT is crucial, and the choice of buffer (lactate or bicarbonate) depends on the patient's individual needs 3.
• Close monitoring of the patient's acid-base and electrolyte status is necessary to adjust the CRRT prescription and ensure optimal management of acid-base and electrolyte imbalances 4.