What is the Fraction of Inspired Oxygen (FiO2)?

From the Guidelines

The fraction of inspired oxygen (FiO2) should be titrated to maintain an oxygen saturation (SpO2) of 94-98% in most patients, with the exception of those at risk of hypercapnic respiratory failure, who should target an SpO2 of 88-92%. According to the BTS guideline for oxygen use in adults in healthcare and emergency settings 1, the initial FiO2 can be started at 28% or 24% oxygen or 1-2 L/min nasal oxygen, and then adjusted based on the patient's response and blood gas results. It is essential to carefully measure respiratory rate and heart rate, as tachypnoea and tachycardia are more common than cyanosis in hypoxaemic patients 1.

Key considerations for FiO2 adjustment include:

• The patient's underlying condition, such as severe or moderate COPD, which may increase the risk of hypercapnic respiratory failure
• The patient's oxygen saturation level, with a target range of 94-98% for most patients and 88-92% for those at risk of hypercapnic respiratory failure
• The results of blood gas analysis, which can help guide adjustments to FiO2 and identify potential complications such as respiratory acidosis or metabolic acidosis
• The need for regular monitoring of oxygen saturation and arterial blood gases to ensure that the patient is receiving the appropriate level of oxygen therapy.

In patients with respiratory acidosis or hypercapnia, it is crucial to seek immediate senior review and consider non-invasive ventilation (NIV) or invasive ventilation 1. Additionally, any increase in FiO2 must be followed by repeat blood gases in 1 hour (or sooner if the patient's condition deteriorates) to ensure that the patient is not experiencing oxygen toxicity or other complications.

From the Research

Fio2 Overview

• Fio2, or fraction of inspired oxygen, is a critical parameter in oxygen therapy, referring to the percentage of oxygen in the air a patient breathes in.
• The optimal Fio2 target can vary depending on the patient's condition, such as those with chronic obstructive pulmonary disease (COPD) or acute hypoxemic respiratory failure 2, 3.

Oxygen Therapy Targets

• For most hospitalized patients, the recommended oxygen saturation target range is 94-98%, while for those with COPD, it is 88-92% 2.
• In critically ill patients, the same target range of 94-98% is often applied 2.
• Avoiding both hypoxemia and hyperoxemia is crucial, as exposure to hyperoxemia can be associated with adverse outcomes in acutely ill adults 3.

Noninvasive Oxygenation Strategies

• Various noninvasive oxygenation strategies, including high-flow nasal cannula (HFNC), helmet continuous positive airway pressure (CPAP), and bilevel ventilation, have been evaluated for treating acute hypoxemic respiratory failure 4.
• Helmet CPAP may reduce mortality compared to standard oxygen therapy, while HFNC may reduce the need for invasive mechanical ventilation 4.

Automatic Oxygen Titration

• Automatic oxygen titration devices can help maintain target oxygen saturation levels and avoid periods of hypoxemia and hyperoxemia 5.
• Compared to manual oxygen titration, automatic titration may decrease the length of hospital stay and oxygen therapy, and increase the percentage of time spent within the target saturation range 5.

Factors Affecting Fio2

• The actual Fio2 delivered to a patient can be affected by factors such as the type of CO2 exhalation system and leaks in the circuit 6.
• Using a leak port circuit or introducing artificial leakage into the circuit can decrease the oxygen concentration at the mask and negatively impact gas exchange 6.