Final answer:
The nurse should report crackles heard on auscultation when a patient on mannitol for increased intercranial pressure as it indicates possible pulmonary edema, a serious adverse effect of the medication.
Step-by-step explanation:
Mannitol is an osmotic diuretic used primarily to reduce high intercranial pressure by promoting water loss through osmosis. As an effective diuretic, you can expect increased urinary output, which is a normal response to the medication. However, if the nurse hears crackles on auscultation, this could indicate fluid overload in the lungs, a serious condition known as pulmonary edema, and should be reported to the provider immediately. Rhinitis is not directly related to the use of mannitol, and while decreased deep tendon reflexes might be concerning for neurological status, they are not a known direct side effect of mannitol.