Study objectives: To determine if 100% oxygen
administration adversely influences gas exchange in acutely ill
preinterventional and postinterventional comparison.
Setting: University hospital emergency department.
Patients: Thirty-seven asthmatic subjects seeking care for
minutes of 100% oxygen administration by face mask.
Measurements and results: Arterial blood gases and
FEV1 were measured before and during the last minute of
oxygen administration. On presentation, the subjects had moderately
severe airway obstruction (FEV1, 49.1 ± 3.6% of
predicted); hypocarbia (Paco2, 36.8 ± 1.1 mm
Hg); hypoxemia (Pao2, 70.2 ± 2.5 mm Hg); and
respiratory alkalosis (pH, 7.43 ± 0.01). During oxygen breathing, 25
patients (67.6%) experienced elevations in
Paco2 ranging from 1 to 10 mm Hg (mean,
4.1 ± 0.6 mm Hg; p = 0.0003). The increase was considered to be a
physiologic manifestation of the Haldane effect (ie,≤
2 mm Hg) in 10 subjects, but in the remaining 15 subjects (40.5%
of the total studied), the elevation represented worsening gas
exchange. In seven of these patients (46.7%), hypercapnic respiratory
failure developed (Paco2 before oxygen,
39.6 ± 0.6; during oxygen, 44.7 ± 0.7 mm Hg; p = 0.005), and in
six patients (40%), it worsened (Paco2 before
oxygen, 46.8 ± 1.9; during oxygen, 52.0 ± 3.1 mm Hg; p = 0.03).
In general, the tendency toward hypercarbia was the greatest in the
participants with the most severe airway obstructions.
Conclusions: Our data demonstrate that the administration
of 100% oxygen to acutely ill asthmatics may adversely influence
carbon dioxide elimination.