A 3-month-old infant with congenital heart failure is admitted to the pediatric unit with worsening symptoms. The nurse notes increased work of breathing, poor feeding, and weight gain of 1.5 pounds over the past week. Which nursing action should the nurse prioritize first?

Recognize that a weight gain of 1.5 pounds (0.68 kg) in one week in an infant with heart failure is a sensitive indicator of fluid retention, not somatic growth. This volume overload manifests as increased work of breathing, tachypnea, and poor feeding due to pulmonary congestion. Immediately assess vital signs, oxygen saturation, lung sounds for crackles, and signs of respiratory fatigue.

Administer the prescribed dose of intravenous furosemide without delay. The IV route provides the fastest onset of action, typically within 5 minutes, to mobilize fluid from the pulmonary interstitium. This reduces preload and quickly alleviates dyspnea. Ensure the dose is verified according to the infant's weight and institutional protocol.

Closely monitor urine output, expecting a significant increase within 30 minutes of IV administration. Document strict intake and output. Monitor serum potassium levels before and after administration, as loop diuretics cause potassium wasting, increasing the risk of hypokalemia and cardiac dysrhythmias. Observe for signs of dehydration such as dry mucous membranes or sunken fontanelles.

While the diuretic takes effect, position the infant in a semi-upright or high Fowler's position to facilitate lung expansion and reduce the work of breathing. Administer supplemental oxygen as ordered to maintain SpO2 within the target range. Prepare for potential escalation, such as non-invasive ventilation, if respiratory distress does not improve.

After stabilizing the infant's respiratory status, obtain a daily weight using the same scale to establish a new baseline and track fluid loss. A chest X-ray and other diagnostics like echocardiography or BNP levels can be performed to assess cardiac size and function, but these should not delay the diuretic administration.