What would an infant with severe dehydration typically present with?

An infant with severe dehydration typically presents with absent urine output. In cases of significant fluid loss, either through vomiting, diarrhea, or insufficient fluid intake, the body's first response is to conserve water. The kidneys reduce urine production to try to maintain the body's fluid balance, resulting in little to no urine output.

In contrast, the other options do not align with the presentation of severe dehydration. Excess urine output would indicate an over-hydrated state or possible renal issues, while increased thirst is a common symptom of mild dehydration, not necessarily severe. A swollen abdomen can indicate various conditions, such as an obstruction or infection, but is not a typical presentation of dehydration in infants specifically. Thus, the characteristic of absent urine output directly reflects the body's response to severe fluid loss and is a critical marker for assessing dehydration in this population.