How do I correct an anion gap metabolic acidosis?

From the Guidelines

To correct an anion gap metabolic acidosis, first identify and treat the underlying cause while providing supportive care, with the most recent guidelines from 2024 1 emphasizing the importance of individualized treatment based on careful clinical and laboratory assessment. The approach to correcting anion gap metabolic acidosis involves several key steps:

• Identifying and treating the underlying cause, which may include diabetic ketoacidosis, lactic acidosis, toxic ingestions, or renal failure.
• Providing supportive care, such as intravenous fluid resuscitation with normal saline at 10-20 mL/kg/hr initially, and adjusting based on clinical response.
• For severe acidosis (pH < 7.1) with hemodynamic compromise, considering sodium bicarbonate administration at 1-2 mEq/kg IV over 1-2 hours, although its use is generally not recommended due to the risk of worsening intracellular acidosis, as noted in recent studies 1.
• For diabetic ketoacidosis, starting an insulin drip at 0.1 units/kg/hr after fluid resuscitation, with dextrose added when glucose falls below 250 mg/dL, and ensuring a smooth transition from intravenous to subcutaneous insulin to prevent recurrence of ketoacidosis and rebound hyperglycemia.
• Replacing electrolytes, particularly potassium, as levels will fall with treatment, and continuously monitoring cardiac function and serial blood gas and electrolyte measurements to guide therapy. Key considerations include:
• The use of bicarbonate in patients with diabetic ketoacidosis has been shown to make no difference in the resolution of acidosis or time to discharge, and its use is generally not recommended 1.
• Recent studies have reported that the administration of a low dose of basal insulin analog in addition to intravenous insulin infusion may prevent rebound hyperglycemia without increased risk of hypoglycemia 1.
• The importance of individualized treatment based on careful clinical and laboratory assessment, as emphasized in the most recent guidelines from 2024 1.

From the FDA Drug Label

In cardiac arrest, a rapid intravenous dose of one to two 50 mL vials (44.6 to 100 mEq) may be given initially and continued at a rate of 50 mL (44. 6 to 50 mEq) every 5 to 10 minutes if necessary (as indicated by arterial pH and blood gas monitoring) to reverse the acidosis. In less urgent forms of metabolic acidosis, Sodium Bicarbonate Injection, USP may be added to other intravenous fluids The amount of bicarbonate to be given to older children and adults over a four-to-eight-hour period is approximately 2 to 5 mEq/kg of body weight - depending upon the severity of the acidosis as judged by the lowering of total CO2 content, blood pH and clinical condition of the patient Bicarbonate therapy should always be planned in a stepwise fashion since the degree of response from a given dose is not precisely predictable Initially an infusion of 2 to 5 mEq/kg body weight over a period of 4 to 8 hours will produce a measurable improvement in the abnormal acid-base status of the blood.

To correct an anion gap metabolic acidosis, sodium bicarbonate (IV) can be administered. The dosage is as follows:

• In cardiac arrest: 1-2 50 mL vials (44.6-100 mEq) initially, followed by 50 mL (44.6-50 mEq) every 5-10 minutes if necessary.
• In less urgent cases: 2-5 mEq/kg body weight over 4-8 hours. It is essential to monitor the patient's response to therapy and adjust the dose accordingly 2. Bicarbonate therapy should be planned in a stepwise fashion, and it is generally unwise to attempt full correction of a low total CO2 content during the first 24 hours of therapy.

From the Research

Causes of Anion Gap Metabolic Acidosis

• Lactic acidosis caused by decreased oxygen delivery or defective oxygen utilization 3
• Ketoacidosis, usually secondary to diabetes or alcohol 3, 4
• Toxin-induced anion gap acidoses, such as methanol, ethylene glycol, and salicylates 3, 4
• Uremia, associated with a mild acidosis secondary to decreased ammonia secretion and an anion gap caused by the retention of unmeasured anions 3
• Diabetic ketoacidosis (DKA), where D-lactate contributes to the anion gap 5

Treatment of Anion Gap Metabolic Acidosis

• Treatment of lactic acidosis is controversial, and the use of bicarbonate to increase pH is rarely successful 3, 4
• Treatment of ketoacidosis is aimed at turning off ketogenesis and repairing fluid and electrolyte abnormalities 3
• Treatment of toxin-induced anion gap acidoses, such as methanol and ethylene glycol, involves alcohol infusion to decrease formation of toxic metabolites and dialyses to remove toxins 3
• Cessation of acid production via improvement of tissue oxygenation is the only effective treatment for organic acidosis, such as lactic acidosis 4
• Identification of the primary causative etiology is crucial in the treatment of metabolic acidosis, and a stepwise consideration of each of the potential causative etiologies will usually direct the clinician to order the appropriate diagnostic studies 6, 7

Diagnostic Approaches

• Calculation of the anion gap (AG) is a helpful calculation that divides the metabolic acidoses into 2 categories: high AG metabolic acidosis (HAGMA) and hyperchloremic metabolic acidosis 7
• Determining if the metabolic acidosis is of the hyperchloremic or high-anion-gap type (or a combination of both) can help identify the primary causative etiology 6
• Plasma osmolality and osmolal gap calculations can be used together with the AG to guide appropriate clinical decision making 7