Q: My 70-year-old patient is sedated and synchronous with the ventilator; set rate of 12/min, patient rate of 12/min, tidal volume 500 mL, fraction of inspired oxygen (FIO2) 35%, and positive end-expiratory pressure (PEEP) 5 cm H2O. Arterial blood gas (ABG) analysis shows a pH of 7.4, PaCO2 40 mm Hg, PaO2 90 mm Hg, HCO3 24 mEq/L, and SaO2 100%. The FIO2 is mistakenly turned up and left on 100% for 2 hours and the repeat ABG results are the same except the PaO2 is now 180 mm Hg. What should the PaO2 be, and where is the extra oxygen going?

A: Maureen A. Seckel, RN, APN, ACNS-BC, CCNS, CCRN, replies:

We know that PaO2 is a measure of the partial pressure of oxygen dissolved in arterial blood and measured by ABG analysis. Normal PaO2 values on...

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