Final answer:
Decreased serum osmolality in a patient with a head injury can indicate the development of SIADH, where excessive ADH leads to water retention and hyponatremia. This impacts cellular function and blood pressure regulation, necessitating close monitoring of serum osmolality for management and treatment.
Step-by-step explanation:
A nurse caring for a 15-year-old client with a head injury should recognize that decreased serum osmolality is a potential indication of the development of Syndrome of Inappropriate Antidiuretic Hormone secretion (SIADH). In SIADH, due to excessive release or action of antidiuretic hormone (ADH), there is increased water reabsorption in the kidneys, leading to water retention, dilution of the blood serum, and hyponatremia. This dilution manifests as reduced serum osmolality. Furthermore, due to osmosis, water follows sodium, thus when serum sodium is diluted, water tends to enter cells, potentially causing complications like cellular swelling.
The balance between water and sodium is crucial for blood pressure regulation and overall fluid balance. An interruption in this balance, such as that seen in SIADH, can lead to various cardiovascular issues due to either hypovolemia or hypervolemia. Thus, monitoring of serum osmolality is essential in the management of patients with head injuries, as it provides a clue towards the development of SIADH and the accompanying electrolyte and fluid imbalances.