Final answer:
To assess the effectiveness of desmopressin, health care professionals should monitor the patient's urine output, as desmopressin influences the kidneys' ability to conserve water.
Step-by-step explanation:
To determine the effectiveness of desmopressin (DDAVP), a health care professional should monitor a patient's urine output. Desmopressin is a synthetic analogue of the naturally occurring antidiuretic hormone (ADH), which helps to regulate the body's retention of water. It's used to treat conditions like diabetes insipidus, where urine output is abnormally high. By monitoring urine output, health care professionals can assess whether desmopressin is aiding the kidneys in conserving water and thus reducing urine volume, indicating its effectiveness.