INFLUENCE OF INSPIRED OXYGEN CONCENTRATION ON DEADSPACE, RESPIRATORY DRIVE, AND PA-CO2 IN INTUBATED PATIENTS WITH CHRONIC OBSTRUCTIVE PULMONARY-DISEASE

Objectives: To investigate the response of CO2-retaining chronic obstr uctive pulmonary disease (COPD) patients to an increase in Fio(2) foll owing a period of mechanical ventilation with Pao(2) in the normal ran ge. The administration of a high Fio(2) to chronic obstructive pulmona ry disease (COPD) patients may result in hypercapnia. Recent evidence indicates that the hypercapnia may be due to reversal of preexisting r egional hypoxic pulmonary vasoconstriction resulting in a greater dead space. This effect would be more pronounced in patients whose initial Pao(2) was <60 torr (<7.9 kPa). Design: Single blinded, prospective st udy. Setting: A medical surgical intensive care unit in a tertiary car e, teaching hospital. Patients: COPD CO2-retaining patients. Intervent ions: Fio(2) increased to 0.7. Measurements and Main Results: Twelve i ntubated COPD patients weaned from mechanical ventilation were studied both at their baseline Fio(2) (0.3 to 0.4), and following a 20-min pe riod 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 anal ysis using the paired Student's t-test showed that the Pao(2) increase d significantly when the Fio(2) was increased to 0.7, but there was no significant change in Paco(2) deadspace, or respiratory drive. Conclu sion: These results show that following a period of mechanical ventila tion 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 gro up of CO2-retaining COPD patients.