What are the best fluids to use for hyperchloremic metabolic acidosis with hypernatremia?

From the Guidelines

For hyperchloremic metabolic acidosis with hypernatremia, the best fluid choice is hypotonic fluid with minimal chloride content, specifically D5W (5% dextrose in water) or quarter-normal saline (0.2% NaCl). These fluids help correct both the hypernatremia by providing free water and the hyperchloremic acidosis by avoiding additional chloride administration. The initial rate should be calculated based on the patient's free water deficit, typically starting at 100-125 mL/hour, with careful monitoring to avoid too rapid correction (no faster than 10 mEq/L sodium decrease per 24 hours to prevent cerebral edema) 1.

Key Considerations

• In severe acidosis (pH < 7.2), sodium bicarbonate may be added (typically 1-2 ampules in 1L of D5W) to help correct the acid-base imbalance.
• Potassium replacement should be included if hypokalemia is present, usually as potassium acetate rather than potassium chloride to avoid worsening the chloride load 1.
• The underlying cause of the acid-base and electrolyte disturbance must be identified and treated simultaneously.
• Regular monitoring of electrolytes, pH, and urine output is essential during correction, with adjustments to the fluid therapy based on serial measurements every 2-4 hours initially.

Rationale

The use of 0.9% saline can cause hyperchloraemic acidosis, renal vasoconstriction, and acute kidney injury (AKI), as evidenced by several studies 1. In contrast, buffered crystalloids have been shown to be associated with a lower risk of major adverse kidney events (MAKE) compared to 0.9% saline 1. Therefore, the use of hypotonic fluids with minimal chloride content is recommended to correct hyperchloremic metabolic acidosis with hypernatremia.

Monitoring and Adjustments

• Electrolyte levels, pH, and urine output should be monitored closely during fluid therapy.
• Adjustments to the fluid therapy should be made based on serial measurements every 2-4 hours initially.
• The patient's free water deficit should be calculated to determine the initial rate of fluid administration.
• The rate of correction should not exceed 10 mEq/L sodium decrease per 24 hours to prevent cerebral edema.

From the Research

Hyperchloremic Metabolic Acidosis with Hypernatremia

• The condition is characterized by an increase in hydrogen ions and a reduction in bicarbonate concentration in the body, often caused by extrarenal processes or kidney origin 2.
• Hypernatremia, or elevated serum sodium levels, can be associated with metabolic alkalosis, rather than acidosis, as seen in a study of critically ill patients 3.

Fluid Management

• Balanced crystalloid solutions, such as lactated Ringer's or Plasma-Lyte, are recommended over saline (0.9% sodium chloride) for intravenous fluid therapy, as they have a composition closer to extracellular fluid and may prevent hyperchloremic metabolic acidosis 4.
• Lactated Ringer's has been shown to be associated with faster resolution of high anion gap metabolic acidosis compared to normal saline in patients with diabetic ketoacidosis 5.
• The use of balanced crystalloids may reduce the need for vasopressors and lower the risk of complications, including acute kidney injury and death, in critically ill adults 4.

Key Considerations

• The anion gap calculation can help differentiate between high anion gap metabolic acidosis and hyperchloremic metabolic acidosis, guiding diagnosis and treatment 6.
• The choice of fluid for resuscitation should take into account the patient's underlying condition, electrolyte balance, and acid-base status, with balanced crystalloids being a preferred option for many cases 4, 5.