Enteral nutrition was started yesterday for a severely malnourished client. Today, the client reports new muscle weakness, and the serum phosphorus level has decreased from 3.4 mg/dL to 1.1 mg/dL. Which action should the nurse take?

A marked phosphorus decrease with weakness soon after calories are restarted suggests refeeding syndrome. Further calorie advancement should pause while the provider is notified and electrolyte replacement and nutrition management are addressed.

Quick answer
Pause further advancement of the feeding and notify the provider promptly. The abrupt hypophosphatemia and weakness after calorie reintroduction are warning signs of refeeding syndrome.

Why this is correct
A malnourished body has depleted intracellular electrolytes. When calories restart, insulin drives phosphorus into cells, and the serum level can fall enough to impair muscle, respiratory, and cardiac function unless feeding and replacement are adjusted.

Easy analogy or mental picture
Refeeding is like restarting a factory after its supply shelves are empty: sudden full production consumes the remaining materials too quickly. The analogy explains cautious advancement, but laboratory trends and individualized electrolyte treatment guide actual care.

Memory hook
Calories restart, phosphorus shifts into cells, weakness appears: pause advancement and escalate.

NCLEX decision rule
When a severely malnourished client develops a rapid phosphorus, potassium, or magnesium decline within days of restarting calories, suspect refeeding syndrome. Prevent further worsening by pausing advancement and promptly coordinating electrolyte and nutrition management.

Why the other choices are wrong
Increasing calories can worsen the electrolyte shift. Free water does not correct phosphorus depletion, waiting until tomorrow delays treatment, and severe hypophosphatemia with weakness is not an expected harmless response.