Final answer:
An Arterial Blood Gas (ABG) Analysis should be performed to diagnose the condition accurately, and treatment may require methylene blue for suspected methemoglobinemia.
Step-by-step explanation:
To accurately diagnose a 22-year-old patient who has a slate gray skin color, is unconscious, and exhibits shallow respirations despite resuscitation with 100% oxygen, an Arterial Blood Gas (ABG) Analysis should be performed. This medical test will help assess the gas exchange in the patient's lungs, providing critical information regarding oxygenation and the presence of any acid-base imbalance. The treatment of choice for a patient who is cyanotic and not responding well to oxygen therapy may involve the administration of methylene blue and other supportive measures, as this presentation is suggestive of methemoglobinemia, which can be a side effect of Dapsone.