From the Research
The correct answer is (d) 520 mEq. To calculate a sodium deficit, we use the formula: Sodium deficit = Total body water × (desired sodium - current sodium). Total body water is approximately 60% of body weight in men, so for this 70 kg man, his total body water is 42 liters (70 kg × 0.6). The normal serum sodium level is 140 mEq/L, and his current level is 125 mEq/L, representing a difference of 15 mEq/L. Multiplying this difference by his total body water gives us 42 L × 15 mEq/L = 630 mEq. However, we must account for the correction factor of 0.82 (the sodium distribution factor), so the actual deficit is 630 × 0.82 = 516.6 mEq, which rounds to 520 mEq, as supported by recent studies on hyponatremia management 1.
This calculation helps determine how much sodium replacement is needed to correct hyponatremia in this patient. It's crucial to note that the goal of treatment is not only to correct the sodium level but also to do so safely, avoiding both undercorrection and overcorrection, which can lead to serious complications such as osmotic demyelination syndrome, as discussed in various guidelines and studies 2, 3, 4, 5.
Key points to consider in managing hyponatremia include:
- The severity and symptoms of hyponatremia
- The chronicity of the condition
- The underlying cause of hyponatremia
- The rate of correction, which should be tailored to the individual patient's needs and monitored closely to avoid complications, with recent evidence suggesting careful use of hypertonic saline and consideration of desmopressin or vasopressin inhibitors in specific cases 1, 5.
Given the potential for significant morbidity and mortality associated with both hyponatremia and its treatment, careful consideration of the most recent and highest quality evidence is essential in guiding clinical decision-making 1.