Final answer:
In infants with HF on diuretic therapy, urine osmolality testing is the best method for a nurse to monitor urine output accurately, as it assesses the kidneys' concentrating ability amidst the diuretic-induced increased urine volume.
Step-by-step explanation:
The most accurate method for a nurse to monitor urine output in an infant with heart failure (HF) receiving diuretic therapy is by measuring urine osmolality. This test evaluates the kidneys' ability to concentrate or dilute urine by measuring the concentration of dissolved particles. Infants are known to produce very dilute urine due to immature kidneys, and given that diuretics such as hydrochlorothiazide increase urine volume by inhibiting the Na+/Cl- symporter in the nephron, it is crucial to ensure proper fluid balance.
In addition to urine osmolality, the nurse should monitor for signs of dehydration and electrolyte imbalances. Since diuretics can cause increased urination, they may lead to a decline in blood volume and pressure. The nurse should keep accurate measurements of intake and output to assess fluid status and prevent potential kidney dysfunction due to overdiuresis. Regular monitoring of urine specific gravity can also help evaluate renal concentrating ability alongside urine osmolality.