What defines isotonic dehydration?

Isotonic dehydration is characterized by the loss of both sodium and water in equal proportions, which leads to a stable sodium concentration in the serum. This means that the overall osmolarity of the body fluids does not change significantly, resulting in a condition where the sodium levels remain within a normal range, typically between 130 and 145 mEq/L.

Selecting the lowest sodium concentration of less than 130 mEq/L indicates that the sodium levels are not adequately maintained. In isotonic dehydration, sodium levels do not drop below normal; rather, they correspond to the loss of water, keeping the concentration basically stable. Therefore, option B aligns with the understanding that isotonic dehydration does not cause hyponatremia (low sodium levels) but is characterized by the relative stability of sodium levels despite the dehydration state.

The other choices do not accurately reflect the characteristics of isotonic dehydration. High sodium levels can indicate hypertonic dehydration, while stating that only water is lost implies a selective loss not applicable to isotonic dehydration, where both water and sodium are lost together. Maintaining adequate water levels would typically signify a normal state of hydration, which does not define isotonic dehydration.