Mr. P., age 65 years, was transferred to the critical care unit from the emergency department after successful resuscitation from a cardiac arrest sustained out of the hospital. Initial diagnosis...

Mr. P., age 65 years, was transferred to the critical care unit from the emergency department after successful resuscitation from a cardiac arrest sustained out of the hospital. Initial diagnosis based on laboratory results and electrocardiography is acute anterior myocardial infarction. It is suspected that Mr. P. aspirated gastric contents during the cardiac arrest. He opens his eyes to painful stimuli. He is orally intubated and receiving mechanical ventilation. He is on assist-control ventilation, respiratory rate set at 12 breaths/min, FiO₂
of 0.40, PEEP 5 cm H₂O, V_T
700 mL. An arterial blood gas is drawn upon arrival to the critical care unit and shows the following values: pH, 7.33; PaCO₂, 40 mm Hg; HCO₃
^_, 20 mEq/L; PaO2, 88 mm Hg; and SaO₂, 99%. A decision is made to maintain the initial ventilator settings. The following day, Mr. P.’s chest radiograph shows progressive infiltrates. His oxygen saturation is dropping below 90% and he is demonstrating signs of hypoxemia: increased heart rate and premature ventricular contractions. Arterial blood gas analysis at this time shows pH, 7.35; PaCO₂, 43 mm Hg; HCO₃
^_, 20 mEq/L; PaO₂, 58 mm Hg; and SaO₂, 88%. The physician orders the FiO₂
increased to 0.50, and PEEP increased to 10 cm H₂O.

Questions

1. What were the results of Mr. P.’s first arterial blood gas analysis? What factors are contributing to these results?

2. What factor is contributing to Mr. P.’s worsening condition the day after hospital admission?

3. Interpret the arterial blood gases done the day after the cardiac arrest.

4. Why did the physician change the ventilator settings after the second set of arterial blood gases?

5. What must the nurse assess after the addition of the PEEP? Why is this especially important for Mr. P.?