What is the optimal FiO2 (Fraction of Inspired Oxygen) setting for patients on CPAP (Continuous Positive Airway Pressure) or EPAP (Expiratory Positive Airway Pressure) with supplemental oxygen?

FiO2 Settings for CPAP/EPAP

For patients on CPAP or EPAP requiring supplemental oxygen, start with FiO2 0.6 (60%) at a CPAP pressure of 10 cmH2O, then titrate oxygen flow upward by 1 L/min increments every 15 minutes to maintain SpO2 between 90-96% (or 88-92% if at risk for hypercapnic respiratory failure). 1, 2

Initial Oxygen Settings

• Begin supplemental oxygen at 1 L/min for both adult and pediatric patients when SpO2 falls below target range 2, 1, 3
• Connect oxygen to the PAP device outlet using a T-connector for optimal mixing and to provide a reservoir of oxygen-enriched gas 2, 3
• For patients requiring FiO2 <0.4, low-flow CPAP systems are appropriate 1

Titration Protocol

• Increase oxygen flow by 1 L/min at intervals no shorter than 15 minutes until target SpO2 is achieved 2, 1, 3
• If initial settings prove inadequate, escalate CPAP to 12-15 cmH2O with FiO2 0.6-1.0 (60-100%) 2, 1
• CPAP pressures may be increased up to 15-20 cmH2O if further escalation is needed 2, 1

Target Oxygen Saturation

The target SpO2 depends on the patient's risk for hypercapnic respiratory failure:

For Patients WITHOUT Risk of Hypercapnia

• Target SpO2: 94-98% 2
• This applies to most patients with acute hypoxemic respiratory failure, pneumonia, pulmonary embolism, acute heart failure, and lung cancer without COPD 2
• For patients with strong respiratory drive (low or normal PaCO2), target SpO2 ≥94% 2, 1

For Patients AT RISK of Hypercapnia

• Target SpO2: 88-92% 2, 1
• Risk factors include severe/moderate COPD (especially with previous respiratory failure or on long-term oxygen), severe chest wall or spinal disease, neuromuscular disease, severe obesity, cystic fibrosis, and bronchiectasis 2
• In type 2 respiratory failure with evidence of acute or chronic hypercapnia, titrate to SpO2 88-92% 2, 1

Alternative Conservative Target

• Some guidelines suggest maintaining SpO2 between 90-96% in most patients to avoid both hypoxemia and hyperoxemia 2, 1
• A slightly higher goal of 90-94% may be prudent given that pulse oximetry can overestimate actual arterial oxygen saturation 2, 1, 3

Critical Technical Considerations

Higher CPAP/EPAP pressures reduce the effective FiO2 delivered for a given oxygen flow rate due to increased intentional leak from the circuit 1, 3. This is a crucial pitfall that clinicians must anticipate.

• The effective FiO2 decreases as IPAP or EPAP pressures increase 3
• FiO2 does not vary significantly with respiratory rate or pressure support levels 1, 3
• Maximum oxygen bleed that can be safely used with PAP devices is typically 10-15 L/min, though this requires careful monitoring 3

Monitoring and Reassessment

• Reassess within 1-2 hours of initiating CPAP to determine effectiveness 1
• Monitor SpO2, respiratory rate, heart rate, and mental status continuously during titration 2
• Obtain arterial blood gases if there is doubt about oximetry reliability or if the patient shows signs of respiratory deterioration 2
• Tachypnea and tachycardia are more sensitive early indicators of hypoxemia than visible cyanosis 2

When to Escalate or Intubate

• If target saturation cannot be achieved with reservoir mask at 15 L/min or maximal CPAP settings, seek immediate senior review 2
• Failure to improve or clinical deterioration mandates prompt intubation 1
• Consider invasive ventilation if pH <7.35 with PaCO2 >6.0 kPa despite NIV 2
• Any increase in FiO2 must be followed by repeat blood gases within 1 hour (or sooner if conscious level deteriorates) 2

Special Populations

Pregnant Patients

• Aim for SpO2 92-95% 2

Children with Emergency Signs

• Target SpO2 above 94% 2

Patients with Coexisting COPD

• Even if presenting with acute heart failure or other conditions, maintain target SpO2 88-92% pending blood gas results 2
• Adjust to 94-98% only if PaCO2 is normal and there is no history of previous hypercapnic respiratory failure requiring ventilation 2