Room Air Baseline — Chronic Hypoxemia
Untreated chronic lung disease drives SpO2 and PaO2 below safe levels.
- ~82%: Room air SpO2 (below 88% threshold)
- ~48: Room air PaO2 (mmHg, hypoxemic)
- ≤55: LTOT qualifying PaO2 (mmHg on room air)
- 0: O2 flow (L/min, none given)
Why chronic hypoxemia happens
COPD, fibrosis, and other diseases impair alveolar gas exchange.
Diagnostic thresholds
PaO2 ≤55 mmHg or SpO2 ≤88% qualifies for long-term oxygen therapy.
Two measurements, weeks apart, confirm chronic need before prescribing.
Risks of untreated hypoxemia
Pulmonary hypertension, polycythemia, and cognitive decline can follow.
Low-Flow Oxygen — 1 to 2 L/min
A nasal cannula at low flow nudges saturation upward gently.
- 1-2: Typical starting flow (L/min nasal cannula)
- ~86%: SpO2 after start (modest rise)
- ~4%: FiO2 added per L/min (above room air 21%)
- 20-30: Reassessment window (minutes post-start)
Starting conservatively
Low flow avoids overshooting in CO2-retaining patients.
Cannula delivery mechanics
Each added liter per minute raises inspired oxygen fraction slightly.
Monitoring response
Pulse oximetry guides the next titration step.
Rapid retesting after any flow change prevents under- or over-correction.
Titrated Flow Adjustment
Flow is raised stepwise, watching SpO2 climb toward target.
- 0.5-1: Titration step size (L/min increments)
- 90-96%: Target SpO2 range (for most patients)
- ~15: Recheck interval (minutes per step)
- 6-10: Max typical LTOT flow (L/min ceiling)
Stepwise titration protocol
Small flow increases are tested and reassessed before the next step.
Balancing correction and risk
Overshooting flow can blunt hypoxic drive in CO2 retainers.
Titrate to the lowest flow that meets the SpO2 target.
Individualized targets
COPD patients often target a slightly lower SpO2 ceiling.
Target Achieved — Stable Oxygenation
SpO2 at or above 90% and PaO2 at or above 60 mmHg, sustained.
- ≥90%: Target SpO2 (maintained at rest)
- ≥60: Target PaO2 (mmHg maintained)
- ~2: Maintenance flow (L/min typical)
- Low: CO2 risk at target (with titrated flow)
Confirming a stable target
Repeat measurements confirm the flow rate holds steady.
Prescribing for home use
The titrated flow becomes the resting home oxygen prescription.
Ongoing reassessment
Targets are re-checked periodically as disease progresses.
A stable target today does not mean a fixed prescription forever.
Ambulatory & Exertional Titration
Activity raises oxygen demand, requiring a higher walking flow.
- +1-3: Exertional flow bump (L/min above resting)
- Standard: 6-minute walk test (exertional assessment)
- <88%: Desaturation trigger (during activity)
- 2-3: Separate prescriptions (rest / activity / sleep)
Why exertion changes demand
Muscles consume more oxygen, dropping SpO2 during movement.
The 6-minute walk test
Ambulatory flow is titrated while walking under monitoring.
Many patients need a distinct flow setting just for activity.
Portable delivery systems
Portable concentrators or conserving devices support ambulatory dosing.