Objectives: To investigate the response of CO2-retaining chronic obstructive pulmonary disease (COPD) patients to an increase in FIO2 following a period of mechanical ventilation with PaO2 in the normal range. The administration of a high FIO2 to chronic obstructive pulmonary disease (COPD) patients may result in hypercapnia. Recent evidence indicates that the hypercapnia may be due to reversal of preexisting regional hypoxic pulmonary vasoconstriction resulting in a greater deadspace. This effect would be more pronounced in patients whose initial PaO2 was <60 torr (<7.9 kPa)
Design: Single blinded, prospective study.
Setting: A medical surgical intensive care unit in a tertiary care, teaching hospital.
Patients: COPD CO2-retaining patients.
Interventions: FIO2 increased to 0.7.
Measurements and Main Results: Twelve intubated COPD patients weaned from mechanical ventilation were studied both at their baseline FIO2 (0.3 to 0.4), and following a 20-min period of exposure to an FIO2 of 0.7. Mean baseline values were: PaO2 of 85 torr (11.3 kPa), PCO2 of 56 torr (7.5 kPa), deadspace of 73%, and respiratory drive normal, as measured by P0.1. Statistical analysis using the paired Student's t-test showed that the PaO2 increased significantly when the FIO2 was increased to 0.7, but there was no significant change in PaCO2, deadspace, or respiratory drive.
Conclusion: These results show that following a period of mechanical ventilation with an FIO2 sufficient to maintain a normal PaO2, a further increase in FIO2 does not result in an increased PaCO2 in this group of CO2-retaining COPD patients. (Crit Care Med 1997;25:1522-1526)
From the Department of Anaesthesia, The Toronto Hospital, Western Division, 399 Bathurst Street, Toronto, ON, Canada.