Long term Oxygen therapy (LTOT)

⚠️ Safety Note: Oxygen supports combustion - it is not itself flammable but intensifies fire risk. Patients must stop smoking completely before starting home oxygen.

ℹ️ About

• Long-Term Oxygen Therapy (LTOT) is prescribed for patients with chronic hypoxaemia to prolong survival, improve exercise tolerance, sleep quality, and reduce pul­monary hypertension.
• It is not a symptom reliever alone - oxygen therapy corrects chronic low PaO₂ and prevents right heart strain (“cor pulmonale”).
• Initiation requires a clinical review using the Home Oxygen Order Form (HOOF).
• Assessment should be when the patient is clinically stable - typically 6 weeks after an acute exacerbation.
• Evidence from the NOTT (Nocturnal Oxygen Therapy Trial) and MRC trials demonstrated significant survival benefit with ≥15 hours/day of oxygen in stable hypoxaemic patients.

🧬 Physiology and Rationale

• Chronic alveolar hypoxia causes pulmonary vasoconstriction → pulmonary hypertension → right ventricular hypertrophy and failure.
• LTOT reverses hypoxic vasoconstriction, lowers haematocrit (polycythaemia), and improves neurocognitive and exercise function.
• Excess oxygen in hypercapnic COPD patients can worsen CO₂ retention by reducing hypoxic drive and increasing V/Q mismatch - therefore careful titration is mandatory.

📊 Evidence Level A – NICE Criteria

• PaO₂ < 7.3 kPa (55 mmHg) when stable = LTOT indicated.
• PaO₂ 7.3 – 8.0 kPa (55–60 mmHg) plus any of: 
  • Secondary polycythaemia (Hb > 17 g/dL or Hct > 55%)
  • Peripheral oedema / signs of cor pulmonale
  • Pulmonary hypertension (on echo)
  • Nocturnal desaturation < 90% for > 30% of sleep

Measurements should be made with the patient on optimal medical therapy, breathing room air for ≥20 min, at rest, and in a stable clinical state.

⏱️ Duration and Targets

• Use ≥ 15 hours/day including overnight (sleep period). 
  • Survival benefit plateaus around 15–19 hours/day; no significant gain beyond 24 hours.
• Target PaO₂ > 8 kPa (≈ SaO₂ ≥ 90%) without raising PaCO₂ beyond acceptable limits.
• Re‑check ABG or O₂ saturations every 3–6 months and after each flare or treatment change.

📋 NICE / Department of Health Eligibility Guidance

• Stable COPD with < 30% predicted FEV₁ or < 1.5 L absolute FEV₁ and hypoxaemia (PaO₂ < 7.3 kPa).
• Evidence of right heart strain – raised JVP, hepatomegaly, ankle oedema.
• Polycythaemia (Hb > 17 g/dL) indicative of chronic hypoxia.
• SpO₂ < 92% on room air during stability period → ABG assessment.
• Exclude coexisting sleep apnoea or obesity hypoventilation which require different management (e.g. CPAP / BiPAP).

🧪 Assessment and Titration Process

• Perform ABGs on two occasions ≥ 3 weeks apart during stability.
• Commence trial oxygen at 1 or 2 L/min via nasal cannulae and re‑measure PaCO₂/PaO₂ to ensure CO₂ does not rise > 1 kPa or pH < 7.35.
• If significant hypercapnia develops, refer for non‑invasive ventilation (“LTOT + NIV” combined therapy).
• Patients with nocturnal desaturation should have overnight oximetry or capnography to titrate night‑time O₂ flow (usually 1–2 L/min higher).

🏥 Oxygen Delivery Systems

• Stationary Oxygen Concentrator: Mainstay of LTOT - extracts O₂ from air (≈ 90–95%) and delivers continuous flow 1–4 L/min.
• Portable Concentrators: Lightweight battery‑powered devices for ambulatory use; deliver continuous or pulse‑dose oxygen.
• Compressed Gas Cylinders: Backup source for short term use or when power outage occurs.
• Liquid Oxygen Systems: Used for patients needing >5 L/min - higher density O₂ allows longer duration portable supply.
• Interface: Nasal cannula for flows ≤ 4 L/min; simple mask ≥ 5 L/min to prevent CO₂ rebreathing.

🏠 Home Oxygen Safety & Follow‑Up

• Provide written and verbal education:
  • 🚭 No smoking or open flames near oxygen.
  • Keep equipment ≥ 1 m from heat sources, cookers, candles etc.
  • Ensure fire alarms present and household members aware.
• Check filters and tubing regularly for obstruction or condensation build‑up.
• Annual service by oxygen provider and home visit from respiratory team.
• Regular review of adherence (hours logged on machine meter) and re‑assessment of continuing need (especially after smoking relapse or disease progression).
• Advise patients to travel with documentation (airlines require fit‑to‑fly testing and approval of portable devices).

🚫 Contraindications / Precautions

• Active smoking - fire risk and therapy inefficacy.
• Unstable clinical conditions (e.g. acute exacerbation of COPD - repeat ABG after recovery).
• Poor adherence or cognitive impairment without support person - risk of misuse or hypoventilation.
• Uncontrolled hypercapnia - requires assessment for NIV before LTOT.

📋 Summary Table – Key Principles of LTOT

📚 References

• NICE Guidelines – COPD & LTOT
• BTS Home Oxygen Guideline, Thorax 2020
• NOTT Trial – Effect of Continuous Oxygen on COPD Survival