Final answer:
Endotracheal intubation is the best intervention for a patient with a non-maintainable airway, as it establishes a direct open airway to the lungs.
Step-by-step explanation:
For a patient with an airway status of "Not Maintainable," the best intervention is Option 4: Endotracheal intubation. This medical procedure is critical when the patient's respiratory system is compromised, such as during general anesthesia when the muscles necessary for breathing might not adequately move the diaphragm or chest wall. Endotracheal intubation involves placing a tube directly into the trachea to maintain an open airway to the lungs, effectively bypassing any obstruction and ensuring that air can reach the lungs for adequate gas exchange.