3 Oxygen Delivery and Monitoring

Oxygenation and ventilation

Oxygenation is the movement of oxygen from the lungs into arterial blood and then to tissues. Ventilation is the movement of air into and out of the lungs, removing carbon dioxide. These are related but distinct functions: Supplemental oxygen can improve low blood oxygen, but it does not by itself correct inadequate breathing or remove carbon dioxide.

A patient who is apneic, tiring, confused, or breathing ineffectively may need airway support and assisted ventilation—not simply more oxygen. Oxygen treats hypoxemia; it does not replace airway management or ventilation.

Set an individualized oxygen target

Oxygen is a treatment to adjust to a clinical goal, not a treatment to give routinely to someone who is not hypoxemic. For adults with acute illness, common target ranges are $94\text{–}98\%$ for most patients and $88\text{–}92\%$ for patients at risk of hypercapnic respiratory failure, such as some people with COPD.

Follow the patient's prescribed target and local protocol. Individual conditions may require different targets, so do not treat a saturation number in isolation.

Choose an oxygen-delivery device

Choose a device according to the patient's oxygen need, breathing pattern, comfort, and required precision. Flow and estimated oxygen concentration are approximate for many devices; fit, respiratory rate, and inspiratory demand can affect delivery. Follow device instructions and local protocol.

• Nasal cannula: For spontaneously breathing patients with a modest oxygen need. Common adult flow is $1\text{–}6\ \mathrm{L/min}$, but the delivered oxygen concentration is variable. The device permits talking and eating; higher flows may cause nasal dryness or discomfort.

• Simple face mask: For a patient needing more oxygen than a cannula may provide. Usual flow is $5\text{–}10\ \mathrm{L/min}$. Do not use below $5\ \mathrm{L/min}$, because exhaled carbon dioxide may accumulate in the mask. Delivered oxygen concentration varies with fit and breathing.

• Venturi (air-entrainment) mask: Useful when a more controlled oxygen concentration is needed. Select the specified adapter and set the flow as instructed by its manufacturer; do not obstruct the air-entrainment ports. It is often chosen for patients at risk of hypercapnia while oxygen is titrated to a prescribed target.

• Reservoir mask (non-rebreather): For a spontaneously breathing patient with severe hypoxemia or critical illness while urgent assessment and escalation occur. Use a high flow—commonly $10\text{–}15\ \mathrm{L/min}$, according to the mask instructions—and inflate the reservoir before applying the mask. Check that the reservoir does not collapse substantially during inspiration and that the valves are in place. This mask is not a substitute for assisted ventilation when breathing is inadequate.

• High-flow nasal cannula (HFNC): Delivers heated, humidified gas at high flow with adjustable oxygen concentration in an appropriately monitored setting. It may be considered for acute hypoxemic respiratory failure. Reassess the patient's needs and response; worsening distress or failure to improve requires escalation.

Assess and monitor the patient

Begin by assessing the patient, not just the monitor. Check airway patency, respiratory rate and effort, chest movement, color, mental status, circulation, and ability to speak. Look for accessory-muscle use, exhaustion, cyanosis, or worsening alertness.

Measure and trend SpO₂ using a correctly placed sensor and a reliable signal. Confirm an unexpected reading by checking the probe and waveform or signal quality, and compare the reading with the patient's appearance and symptoms. Poor circulation, cold skin, movement, nail products, and skin pigmentation can affect accuracy. Pulse oximetry can overestimate oxygenation in some people with darker skin, and a reassuring number must not override signs of deterioration.

Check that the oxygen source, flow setting, tubing connections, and mask fit are correct. For a reservoir mask, also check inflation and valves. Record the device and flow or oxygen concentration along with the saturation: the same SpO₂ on different levels of support does not indicate the same clinical status.

Titrate, reassess, and escalate

Adjust oxygen to the prescribed target, then reassess saturation, work of breathing, and mental status. Seek urgent help for persistent hypoxemia, rising oxygen needs, poor respiratory effort, or deterioration. Blood gas testing may be needed if carbon-dioxide retention, acidosis, or an unreliable oximeter reading is suspected. SpO₂ alone does not measure ventilation or carbon dioxide.

Use the lowest oxygen support that safely meets the patient's target. Wean oxygen under the applicable clinical plan rather than leaving unnecessary support in place.

Use oxygen safely

Oxygen-enriched environments make fires start more easily and burn more intensely. Keep oxygen away from smoking, vaping, flames, sparks, and heat, and display and follow facility no-smoking rules.

Secure cylinders and use the correct regulator and equipment. Check connections and prescribed flow, and keep oil or grease away from oxygen fittings.