Final answer:
The nurse should immediately assess the infant's respiratory status using a stethoscope, a pulse oximeter, and notify the attending physician due to signs of respiratory distress in the infant.
Step-by-step explanation:
A mother brings her 3-month-old infant to the clinic for evaluation of a cold with symptoms including "a runny nose for a week." During the physical assessment, the presence of nasal flaring and sternal and intercostal retractions indicate that the infant is experiencing respiratory distress, which is a potential emergency situation. The nurse's immediate next action should be to assess the infant's respiratory status thoroughly by listening to the lungs with a stethoscope, checking the oxygen saturation with a pulse oximeter, and notifying the attending physician for further evaluation to determine the cause of respiratory distress and required interventions. It may also be necessary to prepare for immediate supportive measures like providing supplemental oxygen.
These symptoms should not be ignored as they can be signs of a more serious condition like pneumonia, bronchiolitis, or other lower respiratory tract infections that are more critical than the common cold. Particularly in infants, these signs warrant prompt attention because their respiratory systems are still developing, and they can deteriorate quickly. Lower respiratory tract infections could lead to complications and require interventions beyond home remedies or over-the-counter medications for a cold.