When do I prescribe oxygen therapy to a patient?

When to Prescribe Oxygen Therapy

Oxygen should be prescribed to achieve a target saturation of 94-98% for most patients, or 88-92% for those at risk of hypercapnic respiratory failure, based on clinical assessment of hypoxemia. 1

Target Oxygen Saturation Ranges

For Most Patients:

• Target saturation range: 94-98% 1
• This applies to most acutely ill patients without risk of hypercapnic respiratory failure

For Patients at Risk of Hypercapnic Respiratory Failure:

• Target saturation range: 88-92% 1, 2
• This includes patients with:
  • COPD
  • Chest wall deformities
  • Neuromuscular disorders
  • Morbid obesity

Specific Clinical Indications for Oxygen Therapy

Continuous Long-Term Oxygen Therapy

• Strong indication: Severe resting hypoxemia with PaO₂ ≤55 mm Hg or SpO₂ ≤88% 1
  • Must be measured when patient is stable (not during/after exacerbation)
  • Should be used ≥15 hours daily to improve survival 1, 3
  • Arterial blood gas measurement is preferred over pulse oximetry for prescribing long-term oxygen therapy 4

Acute Hypoxemia

• Mild hypoxemia: Start with nasal cannulae at 1-2 L/min 2
• Moderate hypoxemia: Simple face mask at 5-6 L/min 2
• Severe hypoxemia: Reservoir mask at 15 L/min 2

Prescription Protocol

1. Always provide a written prescription for oxygen except in emergencies (when it should be documented retrospectively) 1
2. Specify target saturation range rather than fixed concentration or flow rate 1
3. Document delivery device and flow rate alongside SpO₂ on observation charts 1
4. Monitor and adjust to maintain target saturation range 1

Monitoring During Oxygen Therapy

• Use pulse oximetry in all locations where oxygen is being used 1
• Monitor for signs of deterioration:
  • Increasing oxygen requirements
  • Tachypnea
  • Tachycardia
  • Decreasing SpO₂ despite oxygen therapy 2
• For patients at risk of hypercapnic failure, monitor with arterial blood gases to assess for worsening respiratory acidosis 2

Weaning and Discontinuation

1. Step down to 2 L/min via nasal cannulae for most patients 1
   • For hypercapnic risk patients: Step down to 1 L/min or 0.5 L/min via nasal cannulae or 24% Venturi mask 1
2. Stop oxygen when patient is clinically stable and oxygen saturation is within target range on two consecutive observations 1
3. Monitor oxygen saturation on air for 5 minutes after stopping 1
4. Recheck saturation after 1 hour 1
5. If saturation falls below target range, restart at lowest effective concentration 1

Common Pitfalls to Avoid

• Do not rely solely on pulse oximetry for prescribing long-term oxygen therapy; arterial blood gas measurement is required 4
• Avoid hyperoxia in normoxemic patients, which may cause vasoconstriction and increased oxidative stress 5
• Do not discontinue oxygen therapy without monitoring for at least 5 minutes and rechecking after 1 hour 1
• Do not assume all desaturations require correction - transient asymptomatic desaturations may not need treatment 1
• Do not use a fixed concentration of oxygen without considering target saturation ranges 1

Special Considerations

• For post-operative patients, consider discharge when oxygen requirements decrease to ≤2L/min or room air 2
• For COPD patients with FEV₁ <30% predicted, supplemental oxygen for ≥15 hours daily reduces mortality 1
• For patients with heart failure, oxygen is recommended only for hypoxemic patients (SpO₂ <90-94%) 5

By following these guidelines, you can ensure appropriate oxygen prescription that prioritizes patient safety while optimizing clinical outcomes.