The study of ten patients, mean age, 56 years, with a mean forced expiratory volume in one second (FEV1), 0.41 liters (range, 0.31 to 0.67), and mean level of carbon dioxide in the arterial blood (Paco2) of 90 mm Hg (range, 75 to 110 mm Hg) reveals that this chronic steady state can exist for many months (mean survival of 17 months after first determination of Paco2 > 74 mm Hg) and that it is well tolerated. Elevated CO2, per se, does not seem to cause central nervous system dysfunction with the possible exception of a fine tremor in some patients. Well oxygenated "steady state" chronically severely hypercapnic patients have the ability to maintain a high plasma bicarbonate level; mean, 45 mEq/liter; and, therefore, nearly normal arterial pH; mean, 7.32. The judicious use of corticosteroid and diuretic therapy did not produce a primary metabolic alkalosis.
Neff TA, Petty TL. Tolerance and Survival in Severe Chronic Hypercapnia. Arch Intern Med. 1972;129(4):591-596. doi:10.1001/archinte.1972.00320040067008