Influence of FIO2 on PaCO2 during noninvasive ventilation in patients with COPD.

BACKGROUND The administration of a high FIO2 to COPD patients breathing spontaneously may result in hypercapnia, due to reversal of preexisting regional hypoxic pulmonary vasoconstriction, resulting in a greater dead space. Arterial blood gas trends have not been reported in these patients. In a 31-bed medical ICU in a teaching hospital we prospectively investigated the response of 17 CO2-retaining COPD patients, after acute respiratory crisis stabilization with noninvasive ventilation, to an FIO2 of 1.0 for 40 min, after having been noninvasively ventilated with an FIO2 of ≤ 0.50 for 40 min. RESULTS The mean ± SD baseline findings were: PaO2 101.4 ± 21.7 mm Hg, PaCO2 52.6 ± 10.4 mm Hg, breathing frequency 17.8 ± 3.7 breaths/min, tidal volume 601 ± 8 mL, and Glasgow coma score of 14.8 ± 0.3. PaO2 significantly increased (P < .001) when FIO2 was increased to 1.0, but there was no significant change in PaCO2, breathing frequency, tidal volume, or Glasgow coma score. CONCLUSIONS During noninvasive ventilation with an FIO2 sufficient to maintain a normal PaO2, a further increase in FIO2 did not increase PaCO2 in our CO2-retaining COPD patients.