Indications for Long-Term Oxygen Therapy
Long-term oxygen therapy (LTOT) is indicated for patients with chronic hypoxemia who have a PaO2 ≤55 mmHg (7.3 kPa) at rest during a stable period, or PaO2 ≤60 mmHg (8.0 kPa) when accompanied by evidence of cor pulmonale, pulmonary hypertension, peripheral edema, or polycythemia (hematocrit >55%). 1, 2, 3
Primary Blood Gas Criteria
The evidence-based indications for LTOT are derived from landmark trials (NOTT and MRC) that demonstrated survival benefits in COPD patients with severe hypoxemia:
Severe hypoxemia: PaO2 ≤55 mmHg (7.3 kPa) measured at rest during a stable period of at least 3-4 weeks on optimal medical therapy 1, 3
Moderate hypoxemia with complications: PaO2 between 56-60 mmHg (7.4-8.0 kPa) when accompanied by any of the following: 1, 2
- Pulmonary hypertension
- Cor pulmonale or signs of right heart failure
- Peripheral edema suggesting right heart strain
- Polycythemia with hematocrit ≥55%
- P pulmonale on ECG
Oxygen saturation criteria: SaO2 ≤88% at rest can be used as a screening tool, but arterial blood gas measurement is mandatory for definitive prescription 1, 3
Critical Requirements for Prescription
Assessment timing is crucial: Never prescribe LTOT during an acute exacerbation or unstable period. 3 The patient must be:
- Clinically stable for at least 3-4 weeks 1, 3
- On optimized medical therapy including bronchodilators and other appropriate medications 1, 3
- Assessed with arterial blood gas measurements, not pulse oximetry alone 3
Duration of use: LTOT must be used for at least 15 hours per day to achieve survival benefit, with continuous use (≥18-24 hours daily) providing superior outcomes. 1, 3 The NOTT trial demonstrated 1.94 times higher mortality with only 12 hours of nocturnal oxygen compared to continuous oxygen therapy. 1, 3
Disease-Specific Applications
While the strongest evidence exists for COPD, the same blood gas criteria apply to other conditions causing chronic hypoxemia:
- COPD: The primary evidence base, with proven survival benefit in severe hypoxemia 1, 2
- Interstitial lung disease: Same PaO2 criteria as COPD 2, 3
- Cystic fibrosis: Same blood gas thresholds 3
- Pulmonary hypertension: When associated with qualifying hypoxemia 1
What Does NOT Qualify for LTOT
No survival benefit has been demonstrated for moderate hypoxemia (PaO2 56-65 mmHg or 7.4-8.7 kPa) without the complications listed above. 1, 3 Specifically:
- Isolated nocturnal desaturation without meeting daytime criteria does not warrant LTOT 2, 3
- Exercise-induced desaturation alone in patients with adequate resting oxygenation (SaO2 89-93%) does not improve mortality, exacerbation rates, or quality of life 1
- Normoxemic patients should not receive LTOT even for symptomatic dyspnea 4
Absolute Contraindications
- Active smoking: LTOT is generally not prescribed to patients who continue to smoke due to safety risks (fire hazard) and reduced efficacy 1, 3, 4
Practical Implementation
Delivery method: Nasal cannulae are the first-line delivery system, typically at 1.5-2.5 L/min to achieve target PaO2 >60 mmHg (8.0 kPa). 1, 2
Target oxygen saturation: Aim for SaO2 ≥90% during oxygen therapy. 1
Follow-up: Reassess arterial blood gases at 3 months after initiating LTOT to confirm ongoing need and adjust flow rates. 2 Annual reassessment is recommended thereafter. 1
Patient education: Formal education from a specialized home oxygen team is essential to ensure adherence and safe use. 2
Common Pitfalls to Avoid
- Prescribing during acute exacerbations: Always wait until clinical stability is achieved 3
- Relying on pulse oximetry alone: Arterial blood gas measurement is mandatory for prescription 3
- Inadequate duration: Prescribing less than 15 hours daily negates survival benefit 1, 3
- Ignoring smoking status: Active smokers face significant safety risks and reduced efficacy 1, 3
- Over-prescribing for moderate hypoxemia: No evidence supports LTOT for PaO2 >55 mmHg without complications 1, 3