What is the first step in increasing a low PaO2?

Increasing the FIO2 (fraction of inspired oxygen) by 5-10% is commonly considered the first step in addressing a low partial pressure of oxygen in arterial blood (PaO2). This approach is straightforward and directly enhances the oxygen concentration available for the patient to inhale, which can rapidly improve arterial oxygenation. When a patient's oxygen saturation is low, simply increasing the FIO2 can often lead to immediate improvements in PaO2, making it an effective initial response to hypoxemia.

Adjusting FIO2 is typically the first line of intervention before making changes to other parameters, as it is usually the most direct and least disruptive method to improve oxygen delivery. Increasing PEEP levels can also help improve oxygenation by recruiting collapsed alveoli and enhancing ventilation-perfusion matching, but it can also lead to complications such as reduced cardiac output or barotrauma. Decreasing FIO2 would be counterproductive when trying to improve a low PaO2. Increasing tidal volume may also assist in improving ventilation and gas exchange, but it is a more complex change that can have effects on ventilation mechanics and should follow initial oxygen adjustments.

Thus, increasing the FIO2 by 5-10% is the most immediate and effective way to start