Oxygenation Decisions and Delivery Devices

Oxygenation Versus Ventilation

Oxygenation means getting oxygen into the blood; ventilation means moving air in and out of the lungs. The two are linked but not identical, and the difference governs every oxygen decision. An oxygen device only helps a patient who is moving air on their own — who has an adequate rate and depth (tidal volume) of breathing. If breathing is too slow, too shallow, or absent, an oxygen mask cannot push that oxygen into the lungs; that patient needs assisted ventilation with a bag-valve-mask, not a cannula.

The tested decision rule is therefore two-step:

1. Is the patient breathing adequately? If NO → assist ventilations (next section). If YES →
2. How hypoxic are they? Choose the device that matches the need and titrate to a target.

This is a common NREMT trap: a patient breathing 5 times per minute is inadequate and needs ventilation, so applying a non-rebreather alone is the wrong answer no matter how high the flow.

Matching the Device to the Patient

For a patient who is breathing adequately, the EMR selects an oxygen delivery device based on how much supplemental oxygen is needed:

The nasal cannula is comfortable and good for low-level needs, but never run it below 1 L/min or it dries the nasal passages, and above ~6 L/min it provides no added benefit and irritates. The non-rebreather has a reservoir bag that must be pre-inflated before placing it on the face, and the flow must be high enough (10–15 L/min) to keep that bag inflated as the patient inhales.

Titrate to Target, Don't Over-Oxygenate

Older teaching gave every serious patient high-flow oxygen automatically. Current evidence-based practice is to titrate oxygen to maintain an SpO2 (pulse-oximetry oxygen saturation) of at least 94%, because both hypoxia and unnecessary hyperoxia can be harmful. A patient who is satisfied with a nasal cannula at 2 L/min and reads 97% does not need a non-rebreather; conversely, a patient in shock, severe respiratory distress, or with carbon monoxide exposure should get high-flow oxygen regardless of the reading.

Always treat the patient, not just the number — pulse oximetry can read falsely in poor perfusion, cold extremities, or CO poisoning.

Worked scenario

A 60-year-old with chest pain is anxious, breathing 18 times per minute with good chest rise, and her SpO2 is 90% on room air. Because she is breathing adequately but mildly hypoxic, a reasonable start is a nasal cannula at 2–4 L/min, then recheck the SpO2 and titrate upward (to a non-rebreather at 10–15 L/min) if she stays below 94%. If, instead, she became drowsy and her breathing slowed to 6 shallow breaths per minute, the correct move would shift to assisted ventilation with a BVM at 15 L/min — oxygen flow alone cannot fix inadequate ventilation. Reassess SpO2 and work of breathing after every change.

Oxygen Safety and Special Situations

Oxygen is a drug and a hazard. It vigorously supports combustion, so no smoking, open flames, or sparks are allowed near oxygen, and cylinders must be secured so a fall does not shear the valve. EMRs should know cylinder basics: oxygen tanks are color-coded (green in the US) and a tank approaching the ~200 psi 'safe residual' should be swapped before it runs dry.

A classic tested nuance involves the patient with chronic obstructive pulmonary disease (COPD). In rare cases, high-flow oxygen can blunt a COPD patient's respiratory drive — but the EMR rule is unambiguous: never withhold oxygen from a hypoxic patient who needs it. Give the oxygen required to reach the target saturation and watch the breathing; do not let theory talk you out of treating obvious hypoxia. For most COPD patients the saturation target is slightly lower (around 88–92%), but a clearly hypoxic or critical patient still receives high-flow oxygen.

Pulse oximetry guides titration but has limits. It can read falsely high in carbon monoxide poisoning (the device cannot tell oxygen from carbon monoxide on the hemoglobin), and falsely low or unreadable in cold, poorly perfused, or shocky patients, or with nail polish. So the EMR treats the whole patient — color, mental status, work of breathing, and the mechanism — not just the number on the screen.

Two more practical points round out EMR oxygen care. First, a simple face mask must run at a minimum of about 6 L/min so the patient's own exhaled carbon dioxide is flushed out of the mask rather than rebreathed; running it too low is unsafe, which is one reason EMRs more often reach for either a nasal cannula at the low end or a non-rebreather at the high end. Second, prolonged high-flow oxygen dries and irritates the airway, so when extended delivery is expected, humidified oxygen improves patient comfort.

Throughout, the cycle is the same as every other airway intervention: choose the device for the need, set the correct flow, confirm the reservoir or cannula is working, then reassess the saturation and the breathing and step the therapy up or down to keep the patient at the target.