Final answer:
To improve the blood oxygen levels of a patient with ARDS and a P/F ratio of 90, it is important to increase the ventilator oxygen concentration (FIO₂), as this will help address the physiological shunt caused by potential lung obstructions and improve gas exchange.
Step-by-step explanation:
When a patient with acute respiratory distress syndrome (ARDS) who is receiving mechanical positive pressure ventilation has a PaO₂/FIO₂ (P/F) ratio of 90, the most appropriate action to take would be to increase the ventilator O₂ concentration (FIO₂). This is because a P/F ratio of 90 indicates severe hypoxemia, and increasing the oxygen concentration would help to improve the patient's blood oxygen levels.
A physiological shunt occurs when there is an obstruction in the lung such as from infection or edema. This leads to a decrease in ventilation that does not affect perfusion, impacting the V/Q ratio and thereby compromising gas exchange. To address a physiological shunt and improve oxygenation, increasing the FIO₂ is necessary.
It is also important to consider adjusting other ventilator settings such as PEEP and tidal volume, as well as monitoring the resultant changes in respiratory parameters, to ensure the patient's ventilation is optimized and to prevent further lung injury.