Optimal PaO2 Target Range in Respiratory Disorders
The optimal target PaO2 range for patients with respiratory disorders should be 55-80 mmHg (corresponding to SpO2 88-92%), especially for patients at risk of hypercapnic respiratory failure such as those with COPD. 1
Evidence-Based Rationale
Target PaO2 Ranges by Condition
The British Thoracic Society (BTS) guidelines provide clear recommendations for oxygen therapy targets based on patient condition:
Patients at risk of hypercapnic respiratory failure (COPD, chest wall disorders, neuromuscular disease):
- Target PaO2: 55-80 mmHg
- Target SpO2: 88-92% 1
Patients without risk of hypercapnic respiratory failure:
- Target PaO2: 70-90 mmHg
- Target SpO2: 94-98% 1
Physiological Basis for Lower Targets in Certain Conditions
Patients with COPD and other conditions that predispose to carbon dioxide retention require careful oxygen management:
- 20-50% of patients with acute exacerbations of COPD or obesity-hypoventilation syndrome are at risk of carbon dioxide retention if given excessive oxygen 1
- Excessive oxygen can lead to acidosis and, in severe cases, coma 1
- The mechanism is more complex than simply reducing hypoxic drive - it involves multiple physiological pathways 1
Evidence from Clinical Trials
Recent research has investigated optimal oxygenation targets with mixed results:
The LOCO2 trial (2020) compared conservative oxygen therapy (PaO2 55-70 mmHg; SpO2 88-92%) with liberal oxygen therapy (PaO2 90-105 mmHg; SpO2 ≥96%) in ARDS patients 2
- The trial was stopped early due to safety concerns
- At 90 days, mortality was higher in the conservative-oxygen group (44.4% vs 30.4%)
- Five mesenteric ischemic events occurred in the conservative-oxygen group 2
A 2020 Cochrane review concluded that the evidence comparing higher versus lower oxygen targets in ARDS is of very low certainty 3
Clinical Implementation
Monitoring Recommendations
- Use pulse oximetry for continuous monitoring, recognizing it may misrepresent arterial saturation by up to 7% in certain conditions 1
- Perform regular arterial blood gas measurements to monitor for worsening respiratory acidosis in at-risk patients 4
- Compare SpO2 readings with SaO2 values to avoid discrepancies and hidden hypoxemia 5
Oxygen Delivery Devices
| Clinical Scenario | Initial Device | Initial Flow Rate | Target SpO₂ |
|---|---|---|---|
| Mild hypoxemia | Nasal cannulae | 1-2 L/min | 94-98% |
| Moderate hypoxemia | Simple face mask | 5-6 L/min | 94-98% |
| COPD/hypercapnic risk | Venturi mask 24-28% | 2-6 L/min | 88-92% |
| Severe hypoxemia | Reservoir mask | 15 L/min | 94-98% |
| [4] |
Special Considerations
ARDS Management
For ARDS patients, the National Heart, Lung, and Blood Institute ARDS Clinical Trials Network recommends:
- Target PaO2: 55-80 mmHg 2
- However, recent evidence suggests potential risks with targeting the lower end of this range 2
Balancing Risks
- Hypoxemia risks: Cardiovascular and hemodynamic stress, limited oxygen delivery to tissues, potential neuropsychological impairment 1
- Hyperoxemia risks: Increased lung inflammation, adverse microcirculation effects, increased mortality in certain patient categories 1
Long-term Considerations
Some researchers have proposed considering higher PaO2 targets (85-110 mmHg) to potentially improve long-term cognitive outcomes in ARDS survivors 6, but this must be balanced against the risk of oxygen toxicity, especially in the presence of lung inflammation 7
Conclusion
When managing oxygen therapy in patients with respiratory disorders, clinicians should:
- Identify patients at risk for hypercapnic respiratory failure
- Set appropriate target ranges based on patient condition
- Use the minimum FiO2 necessary to achieve targets
- Monitor closely with both pulse oximetry and arterial blood gases
- Be vigilant for signs of oxygen toxicity or inadequate oxygenation
Remember that there is no known benefit to hyperoxemia, and clinicians should aim for saturation values in the normal range appropriate for the patient's condition 1.