A mechanically ventilated patient on an FIO2 of 1.0 has an A-a gradient of 275 mmHg. What does this finding indicate?

The finding of a high A-a gradient, particularly at a FIO2 of 1.0, is indicative of a significant impairment in oxygenation, often due to a shunting of blood. A shunt refers to a portion of blood that bypasses the alveoli where gas exchange occurs, resulting in hypoxemia that cannot be corrected by simply increasing the FIO2.

In this context, the A-a gradient of 275 mmHg is markedly elevated, suggesting that despite administering pure oxygen, there is still inadequate oxygenation occurring. This is typically reflective of either intrapulmonary or extrapulmonary shunting. PEEP (Positive End-Expiratory Pressure) can be an effective intervention for such scenarios, as it helps open collapsed alveoli and improves ventilation-perfusion matching, ultimately enhancing oxygenation.

Thus, the correct choice highlights the need for PEEP to better manage the patient’s respiratory status in light of the shunting. The other options, while potentially relevant in other circumstances, do not directly address the specific pathophysiology indicated by such a high A-a gradient under high FIO2 conditions.