ABSTRACT
When present severe hypercapnia depresses the central nervous system and decreases respiratory motor output. A vicious cycle can arise, whereby hypercapnia causes depressed drive leading to more hypercapnia.1 Hypercapnia can decrease diaphragmatic contractility, although not consistently.3 Acidosis may be more important than hypercapnia in causing respiratory muscle impairment (mortality is more closely related to acidosis than to hypercapnia).3 Even this last possibility is uncertain because diaphragmatic contractility was not affected by acidosis in one study.4
