Final answer:
Firstly, sit the patient up or place him on his side to ease his breathing. Then assess his oxygen saturation and be prepared for further emergency interventions.
Step-by-step explanation:
If you encounter a 39-year-old morbidly obese man in marked respiratory distress, unable to speak in full sentences and with a history of hypertension, the first step should be to sit him up or place him on his side. This position will help to improve his airway patency and facilitate better breathing. Once this is done, the next step includes assessing his oxygen saturation level to determine if he requires supplemental oxygen or more aggressive interventions such as assisted ventilations. It is also important to promptly evaluate whether he is in respiratory failure and to prepare for immediate intervention if his condition does not improve.