Final answer:
Intubation is necessary when a full-term newborn has a low heart rate despite positive-pressure ventilation. It involves the insertion of a tube into the trachea to support the baby's breathing.
Step-by-step explanation:
When a full-term newborn has a heart rate less than 60 beats per minute despite positive-pressure ventilation, intubation is necessary. Intubation involves the insertion of a tube into the trachea to help maintain and support the baby's breathing. It allows for the delivery of oxygen and medication directly into the lungs, bypassing any potential obstructions in the airway.