How often should the fractional inspired oxygen (FIO2) of an adult be measured?

• A. Every hour
• B. Every 4 hours
• C. Only at initial setup
• D. Every patient-ventilator system check

Answer: (D)

The important idea is that the oxygen concentration delivered to the patient can drift in the breathing circuit for several reasons— leaks, changes in the gas blender, circuit disconnections, humidity, or sensor drift. Because of that, FiO2 should be confirmed whenever you perform a patient-ventilator system check. Verifying FiO2 at each system check ensures the patient is actually receiving the intended oxygen level and helps catch any drift or malfunction before it harms the patient.

Relying on initial setup alone leaves room for changes later in the course of care, and fixed hourly or four-hour intervals may miss transient shifts. While modern ventilators often display FiO2 continuously, a formal check during every system check provides a safety confirmation that the delivered and displayed FiO2 match after any adjustments or circuit changes. If the patient’s condition changes or signs of desaturation appear, FiO2 should be verified immediately regardless of the schedule.