Which type of dehydration occurs when fluid is lost but electrolytes are retained?

The correct answer is hypertonic dehydration. This type of dehydration occurs when there is a loss of water from the body, while the loss of electrolytes is either minimal or non-existent. In hypertonic dehydration, the concentration of solutes in the body increases, leading to a higher osmolality of the blood. This situation often arises from excessive water loss due to factors such as excessive sweating, prolonged fever, or inadequate fluid intake. The body retains electrolytes, which means that the balance between fluid and electrolytes is disrupted, creating a hypertonic environment.

In contrast, isotonic dehydration involves equal loss of both fluid and electrolytes, maintaining a relatively stable osmotic balance. Hypotonic dehydration, on the other hand, is characterized by a greater loss of electrolytes than fluid, leading to low osmolality in the body. Chronic dehydration is a more general term that doesn't specify the status of electrolyte retention or loss, making it less precise for this question. Thus, hypertonic dehydration specifically captures the scenario where fluid is lost but electrolytes are retained, making it the appropriate choice.