What is the desired Fraction of Inspired Oxygen (FiO2) for an adult patient requiring oxygen therapy?

Desired FiO2 for Adult Patients Requiring Oxygen Therapy

The desired FiO2 depends critically on the clinical context: for cardiac arrest, use 100% oxygen (FiO2 1.0) immediately; for patients at risk of hypercapnic respiratory failure (COPD, neuromuscular disease, obesity hypoventilation), target SpO2 88-92% using controlled oxygen delivery (typically 24-28% Venturi mask); for other acutely ill patients without hypercapnic risk, target SpO2 94-98%. 1, 2

Cardiac Arrest and Resuscitation

During cardiopulmonary resuscitation, 100% inspired oxygen (FiO2 1.0) should be administered as soon as it becomes available to optimize arterial oxyhemoglobin content and oxygen delivery. 1 Although prolonged exposure to 100% oxygen has potential toxicity, there is insufficient evidence that this occurs during brief periods of CPR. 1 The 1998 European Resuscitation Council similarly recommends providing FiO2 of 1.0 during resuscitation. 1

Acute Hypercapnic Respiratory Failure (AHRF)

For patients with conditions predisposing to hypercapnic respiratory failure, a saturation range of 88-92% is strongly recommended regardless of whether they are spontaneously breathing or receiving non-invasive ventilation (NIV). 1 This Grade A recommendation is based on Level 1+ evidence showing that targeted oxygen therapy (SpO2 88-92%) reduces mortality in AHRF. 1

At-Risk Populations for Hypercapnic Respiratory Failure:

• Moderate-to-severe COPD 1, 2
• Severe chest wall or spinal disease 2
• Neuromuscular disease 2
• Severe obesity 2
• Cystic fibrosis and bronchiectasis 2

Initial Oxygen Delivery Methods:

Start with controlled oxygen therapy using:

• 24% Venturi mask at 2-3 L/min, OR 2
• 28% Venturi mask at 4 L/min, OR 2
• Nasal cannulae at 1-2 L/min 2

Critical pitfall: Do not give FiO2 >28% via Venturi mask or >2 L/min via nasal cannulae until arterial blood gases are known in patients with suspected COPD aged ≥50 years. 1 PaO2 above 10.0 kPa increases the risk of respiratory acidosis in hypercapnic patients. 2

FiO2 Achieved with Different Flow Rates:

When oxygen is delivered near the NIV mask, the mean FiO2 achieved is:

• 31% at 1 L/min 1
• 37% at 2 L/min 1
• 40% at 3 L/min 1
• 44% at 4 L/min 1

Flow rates >4 L/min provide minimal additional FiO2 increase and may cause mask leak and delayed ventilator triggering, risking patient-ventilator asynchrony. 1 A ventilator with an integral oxygen blender is recommended if oxygen at 4 L/min fails to maintain SpO2 >88%. 1

Monitoring Requirements:

• Check arterial blood gases within 60 minutes of starting oxygen and within 60 minutes of any change in inspired oxygen concentration 1
• Obtain ABGs immediately for all patients with suspected hypercapnic respiratory failure 2
• Repeat ABGs after 30-60 minutes of oxygen therapy or sooner if clinical deterioration occurs 2

Acute Respiratory Distress Syndrome (ARDS)

For patients with ARDS, lung protective ventilation strategies should limit tidal volume to 4-8 mL/kg predicted body weight and inspiratory pressures (plateau pressure ≤30 cm H2O). 1 The guideline recommends using higher PEEP strategies in moderate to severe ARDS but does not specify a single target FiO2. 1 The focus is on achieving adequate oxygenation while minimizing ventilator-induced lung injury through protective ventilation strategies.

General Acute Illness (Non-Hypercapnic Risk)

For acutely ill patients without risk factors for hypercapnic respiratory failure, target SpO2 94-98% and wean oxygen gradually as the patient recovers. 1 Most stable convalescent patients will eventually be stepped down to 2 L/min via nasal cannulae prior to cessation of oxygen therapy. 1

Important Caveats

Variability with nasal cannulae: Studies show considerable variation in FiO2 achieved with nasal cannulae both within and between patients, with average FiO2 at 2 L/min ranging from 23.7% to 34.9% in COPD patients. 3 This mode is unsatisfactory when precise control of inspired oxygen is required. 3

Avoid hyperoxygenation: Recent evidence suggests that higher FiO2 or oxygenation targets may increase mortality (RR 1.18,95% CI 1.01-1.37) and serious adverse events (RR 1.13,95% CI 1.04-1.23) compared to lower targets in ICU patients. 4 This reinforces the importance of avoiding excessive oxygen supplementation.

Nebulizer considerations in COPD: Nebulized bronchodilators should be driven by compressed air (not oxygen) in patients with COPD exacerbations to avoid worsening hypercapnia. 2 If compressed air is unavailable, limit oxygen-driven nebulizers to 6 minutes and provide supplemental oxygen via nasal cannulae at 1-2 L/min during nebulization. 2