What are the implications of a bicarbonate level of 20, an anion gap of 13, and hyponatremia?

From the Guidelines

For a patient with a bicarbonate level of 20, an anion gap of 13, and hyponatremia, the primary concern is to address the underlying cause of the metabolic disturbance, with a focus on correcting hyponatremia, as it is a significant risk factor for hepatic encephalopathy 1.

Recommendation:

• Assess volume status: Evaluate the patient for signs of dehydration or fluid overload, as hyponatremia can be caused by hypovolemia or hypervolemia 1.
• Correct hyponatremia: For asymptomatic patients, fluid restriction may be sufficient, but for symptomatic patients, consider administering hypertonic saline (e.g., 3% sodium chloride) at a dose of 1-2 mL/kg over 3-4 hours, with close monitoring of sodium levels, aiming to increase serum sodium by no more than 8 mmol/L per day to avoid central pontine myelinolysis 1.
• Address the anion gap: With an anion gap of 13, which is slightly elevated, consider evaluating for and managing potential causes such as lactic acidosis, ketoacidosis, or ingestion of certain toxins.
• Bicarbonate therapy: For a bicarbonate level of 20, which is slightly low, consider administering sodium bicarbonate if the patient has severe acidosis (pH < 7.1) or if there are specific clinical indications such as certain toxic ingestions, with a dose calculated based on the patient's deficit, typically 0.5-1 mEq/kg.

It is essential to monitor and adjust therapy based on clinical response and laboratory results, and to investigate and treat the underlying cause of the metabolic disturbances, keeping in mind that prevention of hyponatremia is crucial in patients with cirrhosis, with a target blood sodium level >130 mmol/L 1.

From the FDA Drug Label

CLINICAL PHARMACOLOGY Intravenous sodium bicarbonate therapy increases plasma bicarbonate, buffers excess hydrogen ion concentration, raises blood pH and reverses the clinical manifestations of acidosis. Plasma concentration is regulated by the kidney through acidification of the urine when there is a deficit or by alkalinization of the urine when there is an excess. Bicarbonate anion is considered "labile" since at a proper concentration of hydrogen ion (H+) it may be converted to carbonic acid (H2CO3) and thence to its volatile form, carbon dioxide (CO2) excreted by the lung Normally a ratio of 1:20 (carbonic acid: bicarbonate) is present in the extracellular fluid. In a healthy adult with normal kidney function, practically all the glomerular filtered bicarbonate ion is reabsorbed; less than 1% is excreted in the urine.

The implications of a bicarbonate level of 20, an anion gap of 13, and hyponatremia are:

• Metabolic acidosis may be present due to the low bicarbonate level, which is below the normal range of 24 to 31 mEq/liter.
• Electrolyte imbalance is likely, given the combination of low bicarbonate and low sodium levels.
• The anion gap of 13 is within the normal range, which may suggest that the metabolic acidosis is not due to an increase in unmeasured anions. However, the exact implications depend on the clinical context and other laboratory results, which are not provided in the question 2.

From the Research

Implications of Bicarbonate Level, Anion Gap, and Hyponatremia

• A bicarbonate level of 20, an anion gap of 13, and hyponatremia can indicate a metabolic acidosis with a high anion gap 3.
• The anion gap is calculated as [Na+] - ([Cl-] + [HCO3-]) and represents the difference between the measured cations and anions in the blood 4.
• A normal anion gap is typically between 8-12 meq/l, and an elevated anion gap can indicate the presence of unmeasured anions such as lactic acid, keto acids, or other organic acids 5.
• Hyponatremia can be associated with a decreased anion gap, which may be due to hypoalbuminemia or other disorders such as nephrotic syndrome, liver cirrhosis, or intestinal obstruction 6.
• The relationship between the anion gap and serum bicarbonate level can provide clues to the underlying cause of the metabolic acidosis, with a ratio of Δ anion gap/ΔHCO3- of 1 suggesting a simple anion gap acidosis, and ratios <1 or >1 indicating superimposed non-gap acidosis or metabolic alkalosis, respectively 3.
• In patients with chronic kidney disease, metabolic acidosis with a high anion gap is associated with a high risk of disease progression, and consideration of blood pH and serum anion gap is important for diagnosing and treating metabolic acidosis in these patients 7.