Final answer:
An EMT treating a COPD patient with sudden chest pain and breathing difficulty should consider pulmonary embolus or pulmonary edema, among other possible complications like pneumonia.
Step-by-step explanation:
When treating a COPD patient who had a sudden onset of sharp chest pain and difficulty breathing while doing physical exercise, the EMT should be concerned about the possibility of a pulmonary embolus or pulmonary edema. Pulmonary edema is excess fluid in the air sacs of the lungs, often a symptom of heart or kidney failure. This condition can be life-threatening as it hampers gas exchange in the lungs, causing difficulty breathing and potentially chest pain. The EMT should also consider other conditions such as pneumonia, which involves the filling of alveoli with fluid, or a worsening of the COPD symptoms themselves due to excessive exercise.