What are the criteria for prescribing long‑term oxygen therapy (LTOT) in patients with chronic stable hypoxemia?

Criteria for Long-Term Oxygen Therapy (LTOT)

Prescribe LTOT for patients with chronic stable hypoxemia when resting PaO₂ is ≤7.3 kPa (≤55 mmHg), or when PaO₂ is ≤8 kPa (≤60 mmHg) with evidence of end-organ damage including peripheral edema, polycythemia (hematocrit ≥55%), or pulmonary hypertension. 1

Core Eligibility Criteria by Disease State

COPD (Strongest Evidence - Grade A)

• Prescribe LTOT when resting PaO₂ ≤7.3 kPa (≤55 mmHg) in clinically stable patients, as this provides survival benefit and improves pulmonary hemodynamics 1
• Prescribe LTOT when resting PaO₂ ≤8 kPa (≤60 mmHg) if any of the following are present: 1
  • Peripheral edema
  • Polycythemia with hematocrit ≥55%
  • Pulmonary hypertension
• Prescribe LTOT for patients with hypercapnia if they meet all other LTOT criteria 1

The British Thoracic Society provides Grade A evidence (the highest level) specifically for COPD patients, based on landmark trials showing five-year survival improved from 25% to 41% with oxygen therapy ≥15 hours daily. 1

Interstitial Lung Disease (Grade D Evidence)

• Prescribe LTOT when resting PaO₂ ≤7.3 kPa (≤55 mmHg) 1
• Prescribe LTOT when resting PaO₂ ≤8 kPa (≤60 mmHg) with peripheral edema, polycythemia (hematocrit ≥55%), or pulmonary hypertension 1
• Consider palliative oxygen therapy (not LTOT) for severe breathlessness in ILD patients 1

Cystic Fibrosis (Grade D Evidence)

• Prescribe LTOT when resting PaO₂ ≤7.3 kPa (≤55 mmHg) 1
• Prescribe LTOT when resting PaO₂ ≤8 kPa (≤60 mmHg) with peripheral edema, polycythemia (hematocrit ≥55%), or pulmonary hypertension 1

Pulmonary Hypertension (Grade D Evidence)

• Prescribe LTOT when PaO₂ ≤8 kPa (≤60 mmHg), including idiopathic pulmonary hypertension 1

Advanced Cardiac Failure (Grade D Evidence)

• Prescribe LTOT when resting PaO₂ ≤7.3 kPa (≤55 mmHg) 1
• Prescribe LTOT when resting PaO₂ ≤8 kPa (≤60 mmHg) with peripheral edema, polycythemia (hematocrit ≥55%), or pulmonary hypertension on ECG or echocardiograph 1

Neuromuscular or Chest Wall Disorders

• Prescribe non-invasive ventilation (NIV) as first-line treatment for type 2 respiratory failure 1
• Add LTOT only if hypoxemia persists despite NIV 1

Assessment Protocol

Initial Screening

• Refer patients with resting stable SpO₂ ≤92% for arterial blood gas assessment to determine LTOT eligibility 1, 2
• Consider referral at SpO₂ ≤94% if clinical evidence of peripheral edema, polycythemia (hematocrit ≥55%), or pulmonary hypertension exists, as these patients may have PaO₂ ≤8 kPa 1, 2

Confirmation Requirements

• Obtain two arterial blood gas measurements at least 3 weeks apart during clinical stability and optimal medical treatment 1, 2
• Wait at least 8 weeks after the last exacerbation before formal LTOT assessment 1, 2
• Failure to assess during stability results in inappropriate LTOT prescriptions 1

Critical caveat: Patients who exacerbate frequently and cannot achieve 8 weeks of stability may need earlier assessment, but counsel them that LTOT may be discontinued once stability is achieved. 1

Blood Gas Titration

• Measure blood gases with supplemental oxygen to ensure the prescribed flow achieves PaO₂ >8 kPa (>60 mmHg) without unacceptable PaCO₂ rise 1
• Initial arterial blood gas is mandatory; capillary blood gases can be used for subsequent oxygen titration 2

LTOT Delivery Specifications

Duration and Flow

• Prescribe LTOT for at least 15-16 hours daily to achieve mortality benefit, with 24 hours daily being optimal 1, 3
• Set oxygen concentrator flow at 2-4 L/min based on blood gas assessments 1
• Use nasal cannulae as first-line delivery device 2
• Consider Venturi masks for patients at risk of hypercapnic respiratory failure or with cognitive problems 2

Special Populations and Contraindications

Active Smokers

• Discuss limited clinical benefit with patients who continue smoking before prescribing LTOT 1, 2
• Strongly encourage smoking cessation due to increased fire risk and reduced therapeutic benefit 2
• LTOT remains an option but with explicit counseling about reduced effectiveness 1

Moderate Hypoxemia (PaO₂ >55 mmHg)

• Do not prescribe LTOT for moderate hypoxemia (PaO₂ 56-65 mmHg or >7.3 kPa) without additional qualifying criteria 4, 5
• Evidence does not support LTOT for normoxemic patients 3
• The Long-term Oxygen Treatment Trial (LOTT) evaluated mild-moderate hypoxemia but robust data supporting routine use remain lacking 1

Exercise or Sleep Desaturation Alone

• Do not prescribe LTOT based solely on exercise desaturation in patients with normal resting oxygenation 4, 5
• Do not prescribe LTOT based solely on sleep desaturation in patients with normal resting oxygenation 4, 5
• Evidence for nocturnal-only oxygen remains controversial and does not demonstrate mortality benefit 5

Short-Burst Oxygen Therapy (SBOT)

• Do not prescribe SBOT before or after exercise in hypoxemic or normoxic COPD patients 2
• Do not prescribe SBOT on discharge for non-hypoxemic patients with severe COPD 2
• Exception: Prescribe SBOT with high-flow oxygen (12 L/min via non-rebreather mask) for acute cluster headache attacks 2

Palliative Oxygen Therapy (POT)

• Do not provide POT for non-hypoxemic patients (SpO₂ ≥92%) with cancer or end-stage cardiorespiratory disease 2
• Prioritize assessment for opiates and non-pharmacological treatments for intractable breathlessness 2
• Consider POT only by specialist teams for intractable breathlessness unresponsive to all other treatments 2

Follow-Up and Discontinuation

Monitoring

• Conduct risk assessments before installation and every 6 months thereafter 2
• Monitor oxygen saturation for 5 minutes after stopping oxygen therapy and recheck at 1 hour when considering discontinuation 2
• Patients with borderline saturations (93-94%) should have oxygen saturations monitored at annual review or sooner if exacerbation occurs 1

Weaning Protocol

• Step down to 2 L/min via nasal cannulae before cessation in most stable patients 2
• Step down to 1 L/min or 24% Venturi mask for patients at risk of hypercapnic respiratory failure 2
• Discontinue oxygen once patient is clinically stable and maintains target saturation on room air 2

Common Pitfalls to Avoid

• Never prescribe LTOT during acute exacerbations - wait for clinical stability 1, 2
• Never rely on pulse oximetry alone - arterial blood gas confirmation is mandatory 1, 2
• Never prescribe based on single blood gas measurement - two measurements 3 weeks apart are required 1, 2
• Never assume benefit in non-COPD conditions without meeting blood gas criteria - evidence is extrapolated from COPD studies 4, 6
• Educate patients about fire risks and avoiding naked flames near oxygen 2
• Secure cylinders properly when transported in vehicles 2