5 Oxygen Therapy and Respiratory Support

Oxygen goals and target ranges

Oxygen treats Hypoxemia; it does not by itself correct inadequate ventilation or remove carbon dioxide. Prescribe and titrate oxygen to a target saturation rather than aiming for $100\%$.

For most acutely ill adults receiving oxygen, the AARC guideline recommends an oxygen saturation target of $94\text{–}98\%$. For patients with COPD or a known risk of hypercapnic respiratory failure, a common initial target is $88\text{–}92\%$ while blood-gas results are obtained. Follow the prescribed target and local protocol, since individual circumstances may require a different range.

For example, an adult with a COPD exacerbation and an oxygen saturation of $84\%$ should receive oxygen promptly, titrated toward the prescribed target, often $88\text{–}92\%$, with blood gases obtained when indicated. Do not withhold oxygen from a severely hypoxemic patient because of concern about carbon dioxide retention; control the dose and reassess instead.

Choosing an oxygen or breathing support device

Choose a device suited to the patient’s needs and the required degree of oxygen support, then reassess the response. Devices differ in the amount and consistency of oxygen they deliver.

• Nasal cannula: Comfortable, low-flow oxygen for mild hypoxemia that allows eating and talking. The delivered oxygen concentration varies with breathing pattern and fit.

• Simple face mask: Provides more oxygen than a cannula for short-term use. Use the device’s required minimum Oxygen flow, commonly at least $5\ \mathrm{L/min}$, to reduce rebreathing of exhaled gas.

• Venturi mask: Delivers a specified oxygen concentration and is useful when controlled oxygen is needed. Use the correct adapter and flow setting.

• Reservoir (non-rebreather) mask: Provides rapid, high-concentration oxygen for severe hypoxemia or initial stabilization. Set the flow high enough to keep the reservoir bag inflated during inspiration, and seek urgent help while assessing the cause.

• High-flow nasal cannula (HFNC): Delivers heated, humidified gas at high flows with an adjustable oxygen concentration. It can support selected patients with acute hypoxemic respiratory failure, but requires close monitoring and must not delay intubation if the patient is failing.

• Noninvasive ventilation (NIV): Uses a tight-fitting mask to deliver pressure support, often bilevel, to assist ventilation, or continuous positive airway pressure (CPAP) to support oxygenation. NIV is commonly used for acute hypercapnic respiratory failure, including COPD exacerbation with acidosis, when appropriate and closely supervised.

• Invasive ventilation: A ventilator supports breathing through an endotracheal tube or tracheostomy when noninvasive support is unsuitable or failing, or when the airway cannot be protected.

The $2026$ ATS guideline recommends HFNC over standard oxygen for adults with acute hypoxemic respiratory failure and NIV over standard oxygen for acute hypercapnic respiratory failure. HFNC may be considered for selected patients with hypercapnia and mild acidemia only when close monitoring and prompt escalation to NIV are available.

Safe oxygen use

Check the prescription or emergency plan, device, flow or concentration setting, tubing connections, and oxygen supply. Ensure that the device fits and functions correctly.

Titrate oxygen to the prescribed target and avoid unnecessary prolonged high oxygen concentrations. Reassess the patient after starting oxygen and after any change.

Oxygen supports combustion. Do not allow smoking, vaping, flames, or sparks near oxygen equipment. Keep oxygen away from heat and flammable products, secure cylinders, and follow equipment and fire-safety instructions.

Consider humidification when oxygen flow exceeds $4\ \mathrm{L/min}$ if needed for comfort, according to local practice.

Monitoring and reassessment

Assess the patient, not just the saturation reading. Monitor respiratory rate and effort, work of breathing, mental status, skin color, heart rate, ability to speak, and response to treatment. Confirm that the pulse-oximeter signal is reliable and interpret oxygen saturation alongside the clinical picture.

Pulse oximetry estimates oxygenation; it does not measure ventilation or the partial pressure of carbon dioxide $(\mathrm{PaCO}_2)$. Obtain blood gases when hypercapnia, respiratory acidosis, severe illness, or a poor response is suspected. Rising oxygen requirements, a worsening blood-gas result, or declining alertness call for prompt clinical review.

Document the device, setting, target, saturation, and reassessment.

Escalating respiratory support

Escalate early if conventional oxygen does not maintain the target or the patient develops increasing respiratory distress. Depending on the cause and the patient’s condition, the next step may be HFNC or NIV, with assessment by an appropriately skilled team.

In COPD with acute hypercapnic acidosis, NIV is a key treatment. Worsening acidosis, exhaustion, or other deterioration requires urgent reassessment rather than prolonged trials of support.

Call for emergency or critical-care assistance for severe or rapidly increasing work of breathing, exhaustion, inability to protect the airway, reduced consciousness, apnea, hemodynamic instability, or persistent hypoxemia despite support. Prepare for intubation and invasive ventilation when noninvasive support is contraindicated, not tolerated, or failing. Provide support in a setting able to monitor the patient and rapidly escalate treatment; do not let HFNC or NIV delay necessary intubation.