Lack of effect of airway anesthesia on hypoxic ventilation.

Airway anesthesia causes an increase in ventilation (VE) during hypercapnia. However, it is unclear if that is related to an effect of the anesthesia on all forms of stimulated V.E or just hypercapnic VE. After airway anesthesia, an increase in hypoxic VE would suggest the former, whereas absence of an increase would suggest the latter. Thus we compared VE before and after airway anesthesia during hypoxic VE. Normal subjects performed hypoxic rebreathing plus additional periods of sham hyperoxic rebreathing. There was no effect of airway anesthesia on the slope of the line relating VE and arterial O2 saturation. However, there was an upward shift in the line, attributable to an effect of anesthesia on hypercapnic VE present during rebreathing. Additional normal subjects performed eucapnic hypoxic breathing, and there was no effect of airway anesthesia on VE. We conclude that airway anesthesia has little or no effect on hypoxic VE. To date, only hypercapnic VE has been shown to be increased after airway anesthesia.