Ventilation & Oxygen Equipment

Oxygen and ventilation solve different problems, and giving the wrong one is a recognizable exam trap

Supplemental oxygen enriches the air a patient is moving. It assumes the patient is moving air. Ventilation — a bag-valve mask — moves air for a patient who is not moving enough of it themselves. A patient breathing 6 times a minute with shallow chest movement does not have an oxygen-concentration problem; they have a volume problem, and a non-rebreather at 15 L/min enriches a tidal volume that is too small to matter. The reverse error is rarer but real: bagging a patient who is breathing adequately and merely hypoxic adds nothing and risks gastric distention.

So the question is not "how sick does this patient look" but "is air actually moving in adequate volume at an adequate rate?" If yes, and the patient is hypoxic, give oxygen. If no, ventilate — and give oxygen through the bag while you do.

The findings that say ventilation, not a mask

Inadequate breathing has a consistent picture, and any of it should push you toward the bag: a rate that is too slow or too fast to move useful volume, chest rise that is shallow or absent, breath sounds that are diminished or absent, cyanosis, altered mental status, an inability to speak more than a word or two at a time, and in a child, the specific signs that the work of breathing has become unsustainable — nasal flaring, retractions between and below the ribs, grunting, and head bobbing.

One pattern deserves naming because it is regularly misread. A patient in severe respiratory distress who suddenly becomes quiet and sleepy is usually not improving. Falling respiratory effort and a falling level of consciousness in a patient who was working hard a minute ago are signs of exhaustion and rising carbon dioxide, and that patient is about to need ventilation rather than reassurance.

When you assist ventilations in a patient who still has some respiratory drive of their own, time your squeezes to the beginning of their own inspiratory effort. Bagging against a patient who is trying to exhale forces air into the stomach and fights the patient rather than helping them.

Four devices, and the flow rate is part of the device

Each delivery device has a flow range it is designed for, and running it outside that range either fails to work or actively harms. The numbers below are the commonly taught EMT figures; the delivered concentration is always approximate, because it depends on how much room air the patient entrains around the device with each breath.

Table 10.1Four devices, and the flow rate is part of the device

Two floor values are worth holding onto. A nasal cannula below 1 L/min delivers essentially nothing, and above 6 L/min it dries and irritates the nasal mucosa without meaningfully raising the delivered concentration. A non-rebreather below about 10 L/min cannot keep its reservoir bag inflated, and a non-rebreather whose bag collapses on inspiration is not delivering what the label claims — inflate the reservoir before you put the mask on the patient, and turn the flow up if the bag deflates as they breathe.

Titrate to a target, and know the one population with a lower target

The modern practice is to treat hypoxia rather than to reflexively apply high-flow oxygen to everyone who looks unwell. For most patients the target saturation is roughly 94% or above, and reaching it on a nasal cannula is a better outcome than overshooting it on a non-rebreather. For a patient with known COPD, the commonly taught target is lower, around 88–92%, which is closer to their own chronic baseline.

The important qualifier, repeated because it is the thing candidates get wrong in both directions: a lower target is a reason to titrate, never a reason to withhold. A hypoxic COPD patient gets oxygen. Local protocol sets the actual numbers.

Oxygen delivery isn't one-size-fits-all — the device has to match the patient's actual need

A Venturi mask is a specific tool for a specific problem. It delivers a precisely controlled percentage of oxygen, rather than the more variable concentration of a standard mask. That precision is useful in patients with chronic obstructive pulmonary disease (COPD), where the goal is enough oxygen and not more. A small number of COPD patients retain carbon dioxide (CO2) chronically and depend more on low oxygen levels than on rising CO2 as their trigger to breathe, and in those patients a large excess of oxygen can worsen ventilation. That is a reason to titrate, not a reason to withhold. The clinical rule has changed and the exam follows it: a hypoxic COPD patient gets oxygen. Aim for a saturation near the patient's own baseline, commonly the low 90s rather than 100%, and watch mental status and respiratory effort as you go. Leaving a hypoxic patient hypoxic is the larger and more immediate danger, and the old teaching that COPD patients should be denied oxygen out of fear of removing their drive to breathe is no longer taught.

Oxygen equipment has safety features that exist because oxygen systems are genuinely dangerous if mishandled

Oxygen systems are genuinely dangerous if they are mishandled, and the safety features of the equipment exist for that reason. The pin-index safety system on oxygen cylinders exists specifically to prevent the wrong regulator from being connected to the wrong gas cylinder, a real hazard given how many medical gases look similar but behave very differently under pressure. Two pieces of equipment are easily confused. The regulator steps the cylinder's very high internal pressure down to a usable level, while the flowmeter is what actually controls and displays how many liters per minute are being delivered to the patient. One small but real hazard is also worth knowing: adhesive tape or petroleum-based products near oxygen equipment pose a genuine fire risk, because oxygen dramatically accelerates combustion.

Cylinder pressure, safe residual, and not running out on the way in

A full portable oxygen cylinder reads roughly 2,000 psi. The number that matters operationally is the safe residual pressure of about 200 psi: at or below that, the cylinder is treated as empty and changed out, because the last of the pressure does not deliver a reliable flow and because a cylinder emptied completely can draw in contaminants. A gauge reading 300 psi at the start of a long transport is a problem to solve at the scene, not in the back of a moving ambulance.

Handling rules follow from the pressure involved. Secure cylinders so they cannot fall — a cylinder whose valve stem snaps off becomes a projectile driven by 2,000 psi. Open the valve fully, then back it off slightly. Keep the cylinder away from heat, and keep oil, grease, and petroleum products away from every fitting.