A 59-kg IBW female patient is being mechanically ventilated in the CMV mode, f = 12/min, VT = 400 mL, PEEP = 5 cm H2O, FIO2 = 0.5. The ABG results on these settings show a respiratory acidosis and severe hypoxemia

The respiratory therapist increases the set VT and increases the PEEP to 12 cm H2O. The resulting ABGs show improved oxygenation, but the patient still has a respiratory acidosis. The respiratory acidosis may be due to which of the following?
a. Tissue hypoxia
b. Increased dead space
c. Increased cardiac output
d. Continued hypoventilation

ANS: B
If an increase in alveolar ventilation does not correct a respiratory acidosis, the condition is usu-ally caused by pulmonary embolism, low pulmonary perfusion, or increased dead space. The re-duction in pulmonary blood flow caused by high alveolar pressures can increase dead space. In this patient's case, the increase in PEEP is most likely the reason for the continued respiratory acidosis.