Final answer:
The most important action to take for a 70-year-old man with crushing chest pain and a blood pressure of 80/50 mm Hg is to apply high-flow oxygen, as it is crucial for addressing potential oxygen deficiency during a cardiac event.
Step-by-step explanation:
During the assessment of a 70-year-old man with crushing chest pain and a blood pressure of 80/50 mm Hg, the most important action to take would be to apply high-flow oxygen. This is because it is vital to address any potential oxygen deficiency that could be compromising his heart and other organs, due to the possibility of a myocardial infarction (heart attack).
Administering nitroglycerin, elevating his legs, or performing an ECG rhythm analysis are also important considerations in the management of a potential cardiac event. However, they are secondary to ensuring the patient is receiving adequate oxygen. Elevating the legs can be beneficial to increase venous return and therefore cardiac output, while nitroglycerin can help to decrease chest pain associated with angina or a heart attack, but only if the blood pressure is not dangerously low as is the case here. That leaves us with an ECG analysis to understand the electrical activity of the heart and diagnose the specific issue, which is also not the immediate priority. Supplemental oxygen is universally regarded as a crucial initial treatment in such scenarios.