Final answer:
Nitroglycerin is the medication that will be administered first to improve gas exchange for a patient experiencing acute decompensated heart failure.
Step-by-step explanation:
The medication that will be administered first to improve gas exchange for a patient experiencing acute decompensated heart failure is Nitroglycerin. Nitroglycerin is a vasodilator that helps relax the smooth muscle in the coronary vessels, allowing for better blood flow and oxygenation to the heart muscle.
Other medications listed such as Morphine sulfate, Nesiritide (Natrecor), Dobutamine (Dobutrex), and Milrinone (Primacor) are also used in the treatment of heart failure, but their primary actions are not specifically targeted at improving gas exchange.