Oxygen is classified as a medication and is the most frequently administered drug in EMS. Its primary indication is suspected or confirmed hypoxia or hypoxemia, and it has very few contraindications; oxygen should not be withheld from a patient who needs it. EMTs are trained to recognize signs of hypoxia, including cyanosis, altered mental status, tachypnea, and tachycardia, and to use pulse oximetry to guide therapy. An SpO2 reading below approximately 94% generally indicates the need for supplemental oxygen, although local protocols may set slightly different thresholds.
The choice of delivery device depends on the concentration of oxygen required and the patient's breathing effort. A nasal cannula delivers roughly 24 to 44 percent oxygen at flow rates of 1 to 6 L/min and is appropriate for patients who need only mild supplementation. A non-rebreather mask provides approximately 90 to 100 percent oxygen at 10 to 15 L/min, with flow kept high enough to keep the reservoir bag inflated between breaths. A Venturi mask allows precise, controlled oxygen percentages for patients who need a specific concentration. For patients who are not breathing adequately on their own, a bag-valve mask (BVM) is used with oxygen flowing at 15 L/min or higher, often through a reservoir, to deliver ventilatory support along with high-concentration oxygen.
While oxygen is safe for nearly all EMS patients, EMTs must be aware of special considerations. In some patients with chronic obstructive pulmonary disease (COPD), high-flow oxygen can blunt the hypoxic respiratory drive, but this should never delay oxygen delivery in a patient with acute hypoxia. Humidified oxygen is sometimes preferred during prolonged transports to prevent drying of the mucous membranes and to improve patient comfort. Overall, oxygen remains a mainstay of prehospital care because it is both highly effective and extremely safe when used appropriately.