Influence of F IO 2 on P aCO 2 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 8m L, 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. Key words: noninvasive ventilation; obstructive lung disease; oxygen; PaCO2 ;P aO2 ; carbon dioxide; hypercapnia. [Respir Care 2014;59(3):383–387. © 2014 Daedalus Enterprises]