Influence of FIO2 on PaCO2 During Noninvasive Ventilation in Patients With COPD.

BACKGROUND: The administration of a high F_IO2 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 F_IO2 of 1.0 for 40 min, after having been noninvasively ventilated with an F_IO2 of ≤ 0.50 for 40 min. RESULTS: The mean ± SD baseline findings were: P_aO2 101.4 ± 21.7 mm Hg, P_aCO2 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. P_aO2 significantly increased (P < .001) when F_IO2 was increased to 1.0, but there was no significant change in P_aCO2, breathing frequency, tidal volume, or Glasgow coma score. CONCLUSIONS: During noninvasive ventilation with an F_IO2 sufficient to maintain a normal P_aO2, a further increase in F_IO2 did not increase P_aCO2 in our CO₂ -retaining COPD patients. [ABSTRACT FROM AUTHOR]