Question . 1. A 3-yr-old boy is undergoing mechanical ventilation 12 hr after repair of an

atrial septal defect. Opioids and benzodiazepines are being used for analgesia and

sedation. The mandatory ventilatory rate has been decreased from 20 to 10 breaths/min in

preparation for removal of the endotracheal tube. The arterial PO2 is 120 mm Hg and the

arterial PCO2 is 75 mm Hg. The arterial pH is 7.13. The child has no spontaneous

respirations. Auscultation of the chest demonstrates that the breath sounds are slightly

reduced on the left side. Occasional crackles can be heard over both bases.

The most likely reason for this child's acidosis is:

A. Pulmonary edema

B. Pneumonia

C. Cardiogenic shock

D. Respiratory depression

Explanation: As a result of sedation and analgesia, he is hypoventilating, which is

manifested by an acute respiratory acidosis and hypercarbia.Oxygenation may not

be affected if he is breathing enriched oxygen.The reduced breath sounds and

crackles could be due to atelectasis. (See Chapter 357 in Nelson, 17th ed.)

E. Pneumothorax