During transport of a patient with pneumonia who is ventilated on SIMV (Vt 380, f 16, FiO2 0.5, PEEP 5), the SpO2 falls to 82% despite correct connections. Which ventilator adjustment should be tried first?

• A. Increase PEEP
• B. Increase FiO2
• C. Decrease tidal volume
• D. Increase rise-time

Answer: (B)

When a patient who is ventilated shows a drop in SpO2, the quickest and most direct way to improve oxygenation is to raise the fraction of inspired oxygen. Increasing FiO2 increases the amount of oxygen available for diffusion in the lungs, which can rapidly raise arterial oxygen saturation, especially in pneumonia with alveolar involvement. The current FiO2 is 0.5, so increasing it toward higher levels (up to the device limits or until SpO2 improves) is the appropriate first step.

Adjusting PEEP could help recruit collapsed alveoli and improve oxygenation, but it typically comes after ensuring FiO2 is optimized. Decreasing tidal volume would reduce ventilation and can worsen oxygenation in a patient already hypoxemic. Increasing rise-time mainly affects the flow pattern rather than the amount of oxygen delivered to the lungs. Therefore, raising FiO2 is the best initial adjustment to address the hypoxemia.