Final answer:
The nurse should identify the combination of mental confusion, a strong peripheral pulse, higher urine specific gravity, and decreased sodium as signs of SIADH, due to excessive secretion of ADH leading to water retention and dilutional hyponatremia.
Step-by-step explanation:
The nurse should identify mental confusion along with a strong peripheral pulse, higher urine specific gravity, and decreased sodium as an indication that the child is developing syndrome of inappropriate antidiuretic hormone secretion (SIADH). SIADH is characterized by the excessive release of antidiuretic hormone (ADH), also known as vasopressin, which prompts the kidneys to reabsorb more water than normal, leading to water retention, and dilutional hyponatremia (decreased serum sodium levels).
With SIADH, despite the increase in water retention, which dilutes blood sodium, the urine specific gravity is high because the kidneys are still concentrating the urine due to the high levels of ADH. This is a key diagnosis point differentiating SIADH from other conditions where urine might be dilute when the serum sodium is low.