What are the criteria for long-term oxygen (O2) support?

Criteria for Long-Term Oxygen Support

Long-term oxygen therapy (LTOT) should be prescribed for patients with stable chronic respiratory disease who have severe resting hypoxemia with PaO2 ≤7.3 kPa (55 mmHg), or PaO2 ≤8.0 kPa (60 mmHg) in the presence of peripheral edema, polycythemia (hematocrit ≥55%), or pulmonary hypertension, measured during a stable period of at least 3-4 weeks despite optimal medical therapy. 1

Primary Blood Gas Criteria

Absolute Indication

• PaO2 ≤7.3 kPa (55 mmHg) during stable state with optimal therapy 1
• Measurements must be obtained during a stable 3-4 week period, not during acute exacerbations 1
• Two separate measurements at least 3 weeks apart are required to confirm chronic hypoxemia 2

Conditional Indication

• PaO2 7.3-8.0 kPa (55-60 mmHg) when accompanied by any of the following 1:
  • Peripheral edema or clinical signs of cor pulmonale 1
  • Polycythemia with hematocrit ≥55% 1
  • Evidence of pulmonary hypertension 1
  • Severe nocturnal hypoxemia 1

Disease-Specific Applications

COPD Patients

• The criteria above apply directly to COPD patients, with the strongest survival benefit demonstrated in this population 1
• LTOT improves survival, pulmonary hemodynamics, and quality of life in severe hypoxemia 1
• Hypercapnia is not a contraindication; LTOT should be prescribed if blood gas criteria are met 1

Interstitial Lung Disease

• Apply the same blood gas criteria: PaO2 ≤7.3 kPa or PaO2 ≤8.0 kPa with complications 1
• Consider palliative oxygen therapy for severe breathlessness even if blood gas criteria not met 1

Cystic Fibrosis

• Use identical criteria: PaO2 ≤7.3 kPa or PaO2 ≤8.0 kPa with peripheral edema, polycythemia, or pulmonary hypertension 1

Sjögren's-Related ILD

• Prescribe LTOT for resting hypoxemia defined as oxygen saturation <88%, PaO2 <55 mmHg, or PaO2 <60 mmHg with complications of chronic hypoxemia such as cor pulmonale 1

Duration Requirements

LTOT must be used for at least 15 hours per day, with continuous use (≥18 hours/day) providing greater survival benefit. 1

• The landmark NOTT study demonstrated 1.94 times higher mortality with 12-hour nocturnal oxygen compared to continuous oxygen 1
• Survival benefit correlates directly with hours of daily use 1, 2

Oxygen Delivery Specifications

• Flow rate: 1.5-2.5 L/min via nasal cannulae typically achieves target PaO2 >8.0 kPa (60 mmHg) 1
• Adjust flow based on arterial blood gas measurements or oximetry to maintain adequate oxygenation 1
• Reassess oxygen dose at least annually 1

Critical Exclusions and Contraindications

Moderate Hypoxemia

• No survival benefit demonstrated for PaO2 >7.3 kPa (55 mmHg) 1, 3, 4
• LTOT is not routinely recommended for moderate hypoxemia (PaO2 55-65 mmHg) without complications 3, 4

Isolated Desaturation

• Exercise-induced hypoxemia alone: insufficient evidence to support LTOT 2, 5
• Sleep hypoxemia alone: controversial, not routinely recommended without resting hypoxemia 2, 4, 5

Active Smoking

• LTOT is generally not prescribed for patients who continue to smoke due to safety concerns and reduced efficacy 1

Assessment Protocol

Timing of Measurements

• Never assess for LTOT during acute exacerbations 1
• Wait at least 3-4 weeks after stabilization on optimal medical therapy 1
• Many COPD patients have low PaO2 at hospital discharge but normalize at follow-up 1

Required Testing

• Arterial blood gas measurements are mandatory; pulse oximetry alone is insufficient for LTOT prescription 6
• Document stability with repeat measurements at least 3 weeks apart 2
• Assess for complications: echocardiography for pulmonary hypertension, complete blood count for polycythemia 1

Common Pitfalls

• Prescribing during acute illness: Blood gas criteria must be met during stable periods, not during exacerbations or hospitalizations 1
• Insufficient duration: Prescribing less than 15 hours/day negates survival benefit 1
• Relying on oximetry alone: Arterial blood gas measurements are required for accurate assessment 6
• Extending indications without evidence: No proven benefit for moderate hypoxemia or isolated exercise/sleep desaturation 3, 4, 5