With acute onset, somnolence, confusion, mental status changes, asterixis, and myoclonus may develop. Severe hypercapnia increases cerebral blood flow, cerebrospinal fluid pressure, and intracranial pressure; papilledema and idiopathic intracranial hypertension (pseudotumor cerebri) may be seen.
Arterial pH is low and PCO2 is increased. Serum HCO3– is elevated but does not fully correct the pH. If the disorder is chronic, hypochloremia is seen. Respiratory etiologies of respiratory acidosis usually have a wide A-a gradient; a relatively normal A-a gradient suggests a nonpulmonary (eg, central) etiology.