Uncontrolled Oxygen Administration and Respiratory Failure in Acute Asthma

Abstract

To determine if 100% oxygen administration adversely influences gas exchange in acutely ill asthmatic subjects. Prospective preinterventional and postinterventional comparison. University hospital emergency department. Thirty-seven asthmatic subjects seeking care for symptomatic exacerbations. Twenty minutes of 100% oxygen administration by face mask. Arterial blood gases and FEV(1) were measured before and during the last minute of oxygen administration. On presentation, the subjects had moderately severe airway obstruction (FEV(1), 49.1 +/- 3.6% of predicted); hypocarbia (PaCO(2), 36.8 +/- 1.1 mm Hg); hypoxemia (PaO(2), 70.2 +/- 2.5 mm Hg); and respiratory alkalosis (pH, 7.43 +/- 0.01). During oxygen breathing, 25 patients (67.6%) experienced elevations in PaCO(2) 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, < or = 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 (PaCO(2) before oxygen, 39.6 +/- 0.6; during oxygen, 44.7 +/- 0.7 mm Hg; p = 0.005), and in six patients (40%), it worsened (PaCO(2) 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. Our data demonstrate that the administration of 100% oxygen to acutely ill asthmatics may adversely influence carbon dioxide elimination.