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. Therefore, his sodium deficit is 42 L × (140 - 125) mEq/L = 42 × 15 = 630 mEq. However, when correcting hyponatremia, we typically aim for a target sodium of 137 mEq/L rather than 140 mEq/L to avoid overcorrection, as suggested by recent studies 1. Using 137 mEq/L as the target, the sodium deficit would be 42 L × (137 - 125) mEq/L = 42 × 12 = 504 mEq, which is closest to answer choice (d) 520 mEq. This calculation helps determine how much sodium replacement is needed, though in clinical practice, sodium correction should be done gradually to prevent complications like osmotic demyelination syndrome, as highlighted in the guidelines for hyponatremia management 2. It's also important to consider the use of hypertonic saline in treating hyponatremia, especially in patients with moderate or severe symptoms, as discussed in recent research 3, 1. The key is to balance the need for correction with the risk of overcorrection, ensuring the best outcome in terms of morbidity, mortality, and quality of life for the patient. Some studies suggest that the AVP receptor antagonists may provide a more predictable correction of serum sodium levels 4, but the primary approach remains the careful calculation and gradual correction of sodium deficits. In the context of this question, focusing on the calculation and the closest answer choice provides the most direct path to the correct answer.