Final answer:
The correct intervention when a client's serum sodium level increases from 120 to 125 mEq/L due to treatment for SIADH is to maintain the prescribed fluid restriction. This aids in the gradual correction of sodium imbalance and prevents complications associated with rapid shifts in sodium levels.
Step-by-step explanation:
As the client responds to treatment for small cell carcinoma of the lung and accompanying syndrome of inappropriate antidiuretic hormone (SIADH), their serum sodium level has increased from 120 to 125 mEq/L or mmol/L (SI). Based on this finding, the appropriate nursing intervention is to maintain the prescribed fluid restriction. This intervention is consistent with the therapeutic goal of gradually correcting the sodium imbalance and avoiding the risks associated with too rapid a correction, which could lead to central pontine myelinolysis. Additionally, the nurse should continue to monitor the serum sodium levels regularly to ensure that they do not rise too quickly, further assessing overall fluid balance and the presence of any symptoms that may indicate a shift in the client's condition.
Antidiuretic hormone (ADH), also known as vasopressin, plays a crucial role in managing the body's water balance by enabling water reabsorption in the kidneys, thus controlling urine production and plasma osmolarity. Conditions like SIADH result in excessive retention of water, with hyponatremia as one of the consequences. As the client's sodium level increases, carefully monitoring water balance and sodium concentration ensures neither fluid overload nor overly rapid correction occurs.