Influence of inspired oxygen concentration on deadspace, respiratory drive, and PaCO2 in intubated patients with chronic obstructive pulmonary disease
Crossley, D.J.; McGuire, G.P.; Barrow, P.M.; Houston, P.L.
Critical Care Medicine 25(9): 1522-1526
1997
ISSN/ISBN: 0090-3493 PMID: 9295826 Document Number: 483479
Objectives: To investigate the response of CO-2-retaining chronic obstructive pulmonary disease (COPD) patients to an increase in FIO-2 following a period of mechanical ventilation with PaO-2 in the normal range.The administration of a high FIO-2 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 Pao-2 was lt 60 torr ( lt 7.9 kPa) Design: Single blinded, prospective study. Setting. A medical surgical intensive care unit in a tertiary care, teaching hospital. Patients: COPD CO-2-retaining patients. Interventions: FIO-2 increased to 0.7. Measurements and Main Results: Twelve intubated COPD patients weaned from mechanical ventilation were studied both at their baseline FIO-2 (0.3 to 0.4), and following a 20-min period of exposure to an FIO-2 of 0.7. Mean baseline values were: Pao-2 of 85 torr (11.3 kPa), Pco-2 of 56 torr (7.5 kPa), deadspace of 73%, and respiratory drive normal, as measured by P-0.1. Statistical analysis using the paired Student's t-test showed that the Pao-2 increased significantly when the FIO-2 was increased to 0.7, but there was no significant change in Paco-2, deadspace, or respiratory drive. Conclusion: These results show that following a period of mechanical ventilation with an FIO-2 sufficient to maintain a normal Pao-2, a further increase in FIO-2 does not result in an increased Paco-2 in this group of CO-2-retaining COPD patients.