What is the cause of hyponatremia (low sodium levels) and metabolic acidosis?

From the Guidelines

Hyponatremia and metabolic acidosis are often caused by underlying conditions such as liver cirrhosis, diabetic ketoacidosis, lactic acidosis, diarrhea, renal tubular acidosis, and certain medications or toxins, and treatment should focus on addressing the underlying cause while correcting fluid and electrolyte abnormalities. When these conditions coexist, careful evaluation and management are required to prevent complications and improve patient outcomes. According to the most recent and highest quality study 1, the first step in treating hyponatremia is to distinguish the type of hyponatremia, with fluid resuscitation needed for hypovolemic hyponatremia and fluid restriction considered for hypervolemic hyponatremia.

Causes of Hyponatremia and Metabolic Acidosis

• Liver cirrhosis with ascites, as seen in patients with hypervolemic hyponatremia 2, 1
• Diabetic ketoacidosis, lactic acidosis, and other metabolic disorders
• Diarrhea and renal tubular acidosis, leading to loss of bicarbonate and electrolytes
• Certain medications or toxins, which can disrupt electrolyte balance and acid-base status

Treatment Approach

• Identify and treat the underlying cause of hyponatremia and metabolic acidosis, while correcting fluid and electrolyte abnormalities 1
• For severe hyponatremia (sodium <120 mEq/L) with neurological symptoms, cautious correction with hypertonic (3%) saline at 1-2 mL/kg/hr is recommended, aiming for a sodium correction rate not exceeding 8-10 mEq/L in 24 hours to prevent osmotic demyelination syndrome
• For metabolic acidosis, if pH is <7.1 or bicarbonate <12 mEq/L with hemodynamic instability, sodium bicarbonate (1-2 mEq/kg IV) may be administered, as seen in the management of chronic renal failure patients 3
• Fluid management must be tailored to volume status, with fluid restriction considered in cases of hypervolemic hyponatremia and isotonic or hypotonic solutions provided in volume-depleted states

Monitoring and Management

• Continuous monitoring of electrolytes, acid-base status, and neurological function is essential during treatment
• Frequent laboratory monitoring is necessary to prevent complications and adjust treatment as needed
• The simultaneous presence of hyponatremia and metabolic acidosis often indicates significant physiological stress, and careful clinical assessment is crucial for safe management 1

From the Research

Causes of Hyponatremia

• Hyponatremia is often the result of water imbalance rather than sodium imbalance, underscoring the role of antidiuretic hormone (ADH) in the pathophysiology 4
• Hyponatremia can be classified according to the measured plasma osmolality as isotonic, hypertonic or hypotonic 4
• Hypovolaemic hyponatraemia is accompanied by extracellular fluid (ECF) volume deficit, while hypervolaemic hyponatraemia manifests with ECF volume expansion 4
• The syndrome of inappropriate ADH (SIADH) should be suspected in any patient with euvolaemic hyponatraemia with a urine osmolality above 100 mOsm/kg and urine sodium concentration above 40 mEq/l 4

Causes of Metabolic Acidosis

• Metabolic acidosis is frequently observed in clinical practice, especially among critically ill patients and/or in the course of renal failure 5
• Complex mechanisms are involved, in most cases identifiable by medical history, pathophysiology-based diagnostic reasoning and measure of some key acid-base parameters 5
• Metabolic acidosis can be classified into two main subtypes: the high anion gap metabolic acidosis and the normal anion gap (or hyperchloremic) metabolic acidosis 5

Relationship between Hyponatremia and Metabolic Acidosis

• There is no direct relationship between hyponatremia and metabolic acidosis, as they are two distinct electrolyte and acid-base disorders 4, 5
• However, both conditions can occur simultaneously in critically ill patients, and their management requires a comprehensive approach to fluid and electrolyte balance, as well as acid-base homeostasis 4, 5, 6, 7

Management of Hyponatremia and Metabolic Acidosis

• The management of hyponatremia involves restricting free water and hypotonic fluid intake, and using hypertonic saline and vasopressin antagonists to correct symptomatic hyponatremia 4, 6, 7
• The management of metabolic acidosis involves early correction of concurrent clinical problems, such as fluids and hemodynamic optimization, and the administration of alkalizing agents in severe cases 5
• A simple strategy for safe correction of severe hyponatremia involves the concurrent administration of desmopressin and hypertonic saline solution 8