Oxygen Therapy and Respiratory Failure
BTS Guideline for oxygen use in adults in healthcare and emergency settings. Published: May 2017.
Background Information
Definition
There are 2 main types of respiratory failure:
- Type 1 respiratory failure: hypoxia (PaO2 <8 kPa) with normal PaCO2
- Type 2 (hypercapnic) respiratory failure: hypercapnia (PaCO2 >6 kPa) irrespective of oxygen level (PaO2 is usually low but can be normal)
Type 2 Respiratory Failure Risk Factors
- COPD – main risk factor
- Cystic fibrosis
- Bronchiectasis
- Severe chest wall or spinal disease (e.g. kyphoscoliosis)
- Neuromuscular disease (e.g. ALS)
- Severe obesity
Oxygen Delivery Devices
| Device | Flow Rate | Indications | Advantages | Disadvantages / Cautions |
|---|---|---|---|---|
| Nasal Cannulae | 1-6 L/min (FiO2 ~24% to ~50%). |
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| Simple face mask (aka ‘Hudson mask’) | 5-10 L/min (FiO2 40-60%) |
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| Non-rebreather mask (reservoir mask) | Up to 15 L/min (FiO2 60-90% at 15L/min) |
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| Venturi mask | Refer to individual mask packaging for flow rate and FiO2 |
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Further options (if patients remain hypoxic on 15 L/min of non-rebreather mask):
- High-flow nasal cannulae
- CPAP / NIV
- Endotracheal intubation + mechanical ventilation
Guidelines
Oxygen Therapy in Critical Illness
Initial oxygen therapy (ALL patients):
- Device: non-rebreather (reservoir) mask
- Flow rate: 15 L/min
- SpO2 target: 94-98% (unless in carbon monoxide poisoning where the target is 100%)
BTS defined the following conditions as ‘critical illness’:
- Cardiac arrest or resuscitation
- Shock
- Sepsis
- Major trauma
- Anaphylaxis
- Status epilepticus
- Major head injury
- Carbon monoxide poisoning
In patients who are at risk of type 2 respiratory failure and are critically ill → the same initial oxygen therapy (15 L/min via non-rebreather, targeting 94-98%) should be given (instead of the controlled oxygen therapy, aiming for 88-92%, as “hypoxia kills”).
Urgently perform a blood gas and adjust oxygen therapy accordingly:
- If blood gas shows acidotic hypercapnia (↓ pH and ↑ pCO2) or chronic CO2 retention (↑ HCO3–) → adjust target to 88-92% and use controlled oxygen therapy
- If none of the above → maintain target as 94-98%
Oxygen Therapy in Non-Critical Illness
Oxygen therapy depends on whether the patient is at risk of type 2 respiratory failure (see above for risk factors).
Patients at Risk of Type 2 Respiratory Failure
The most important investigation in these patients are ABG to guide oxygen therapy, as it definitively gives information on whether the patient is a chronic retainer and if hypercapnia exists.
Initial Oxygen Therapy (Prior ABG Results Available)
SpO2 target: 88-92%
Device:
- Venturi mask (preferred), or
- Nasal cannulae
Flow rate:
- Venturi mask: 24% (2-3 L/min) or 28% (4 L/min)
- Nasal cannulae: 1-2 L/min
If the patient’s SpO2 remains <88% respite a 28% (4 L/min) Venturi mask, escalate with either of the following:
- Nasal cannulae up to 6 L/min, or
- Simple face mask at 5 L/min
NB that the SpO2 target remains the same (88-92%).
Specifically applying to COPD exacerbation, escalation to 15 L/min via non-rebreather (reservoir) mask is indicated in ANY of the following:
- Profound hypoxaemia (SpO2 <85%) – due to the high immediate risk of death (“hypoxia kills”)
- Peri-arrest situations
- Failed nasal cannulae or simple face mask
But one should still aim for SpO2 88-92% (the only reason the aim for 94-98% from the start in someone at risk of type II respiratory failure, is if they are critically ill – see definition above).
Oxygen Therapy Based on ABG Results
- ↑ PCO2 (>6.0 kPa) +/- low pH → maintain 88-92% target with venturi mask (24-28%) or nasal cannulae (consider NIV if there is respiratory acidosis)
- Normal PCO2 and pH → increase target to 94-98% (no restriction on the oxygen delivery device)
Patients NOT at Risk of Type 2 Respiratory Failure
SpO2 target: 94-98%
Oxygen delivery device:
- SpO2 <85% → 15 L/min via non-rebreather (reservoir) mask
- SpO2 ≥85% → nasal cannulae at 2-6 L/min or simple face mask at 5-10 L/min