Determining When a Patient Needs Oxygen Therapy
Oxygen therapy should be initiated when a patient's oxygen saturation falls below 94% for most acutely ill patients, or below 88% for patients at risk of hypercapnic respiratory failure. 1, 2
Assessment Criteria for Oxygen Therapy Initiation
Primary Assessment Tools
- Pulse oximetry measurement (SpO₂) - considered the "fifth vital sign" 1
- Arterial blood gas analysis - gold standard for confirming hypoxemia 3
- Type 1 respiratory failure: PaO₂ < 60 mmHg with normal/low PaCO₂
- Type 2 respiratory failure: PaO₂ < 60 mmHg AND PaCO₂ > 45 mmHg 2
Clinical Scenarios Requiring Immediate Oxygen
Critical illness situations - use reservoir mask at 15 L/min initially 1:
- Cardiac arrest/resuscitation
- Shock, sepsis, major trauma
- Drowning, anaphylaxis
- Major pulmonary hemorrhage
- Status epilepticus
- Major head injury
- Carbon monoxide poisoning
Acute respiratory distress - when SpO₂ cannot be reliably measured 2, 3
Device Selection Algorithm
| 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% |
Monitoring Requirements
- Record oxygen saturation and delivery system (including flow rate) on monitoring chart 1
- Perform clinical assessment if saturation falls by ≥3% or below target range 1
- For stable patients: monitor SpO₂ at least four times daily 2
- For unstable patients: continuous monitoring 2
- Arterial blood gas analysis when:
- Initial assessment of severe hypoxemia
- Suspected hypercapnia
- Poor response to oxygen therapy
- Deteriorating clinical status 3
Common Pitfalls to Avoid
- Overreliance on pulse oximetry: While sensitive for detecting hypoxemia, it has low specificity 3
- Inappropriate targets for COPD patients: Using high-concentration oxygen can worsen hypercapnia in these patients 2, 3
- Failure to monitor: Lack of regular assessment can lead to undetected deterioration 1
- Misclassification of respiratory failure type: Can lead to inappropriate treatment 2
- Delayed recognition: Can result in tissue hypoxia and organ damage 2
- Inaccurate readings: Pulse oximetry may be less reliable in anemia or poor peripheral perfusion 2
Escalation Criteria
- Failure to maintain target SpO₂ despite increasing oxygen delivery
- Increasing work of breathing despite adequate oxygenation
- Development of respiratory acidosis on blood gas analysis
- Clinical signs of deterioration (tachypnea, accessory muscle use, altered mental status)
- Consider high-flow nasal oxygen (HFNO) or non-invasive ventilation if conventional oxygen therapy is insufficient 2, 4
Remember that while the British Thoracic Society recommends a target range of 94-98% for most patients 1, some evidence suggests that a slightly lower target of 92-96% may be preferable 5, and the American Association for Respiratory Care also supports the 94-98% target range 4.