Final answer:
An EMT-Basic should wait 5 minutes after the first dose of nitroglycerin and, if there's no relief and no contraindications, administer a second dose. After three doses with persistent chest pain, the patient requires emergency hospital transport.
Step-by-step explanation:
If an EMT-Basic is assisting a patient with chest pain who continues to experience no relief after one dose of nitroglycerin, the EMT-Basic should follow their training and protocols which often advise to wait 5 minutes after the first dose. If the chest pain persists and the patient has no contraindications for nitroglycerin, a second dose may be given. It is important to monitor the patient closely for changes in blood pressure, heart rate, and relief of symptoms. If chest pain continues after three doses administered 5 minutes apart, emergency transport to the hospital is critical, as this may be a sign of a myocardial infarction (MI) or another serious condition that requires advanced medical treatment.