Although patients at MAC-awake levels of anesthesia may have patent airways, they will have depression of other reflexes such as cough and gag reflexes. Patients with Chronic Obstructive Pulmonary Disease (COPD) or other causes may become increasingly hypercarbic in the PACU. Patients can and do oxygenate and not ventilate, i.e., they can get enough oxygen and not expel enough carbon dioxide. The degree of painful stimuli can determine the degree of vigorousness in the respiratory effort. In the patient that has had an exploratory laparatomy splinting will occur further decreasing the ability to breathe deeply and subsequently become hypercarbic.

Response to Oxygen

Patients in a PACU are frequently predisposed to hypoxemia; causes might include airway obstruction, central hypoventilation, atelectasis, an dimished tidal volume secondary to pain, tight dressings, or casts. Because the patient might be significantly somnolent from the anesthetic agents, they might not arouse and lapse into unconsciousness.

A strong argument may be made for using supplemental oxygen routinely to prevent this episodic hypoxemia, which might occur even in routine cases.

Use of high concentrations of oxygen must be judicious and should be given due consideration due to the potential risks of retinopathy in premies.