Effects of rac-albuterol on arterial blood gases in patients with stable hypercapnic chronic obstructive pulmonary disease.

AIMS

Many patients with chronic obstructive pulmonary disease (COPD) are treated with high dose beta(2)-adrenoceptor agonists, which can increase ventilation/perfusion mismatching, and tremor and cardiac output, thereby increasing oxygen uptake and carbon dioxide output (VCO(2)). Patients with severe COPD and hypercapnia may be unable to increase ventilation in response to increased VCO(2), in which case arterial carbon dioxide tension (P(a)CO(2)) may rise. Our aim was to determine whether high dose nebulized rac-albuterol could increase P(a)CO(2) in patients with COPD, limited bronchodilator reversibilty and hypercapnia.

METHODS

We compared 10 mg and 400 microg rac-albuterol, given in two doses 1 h apart on nonconsecutive days, in a double-blind randomized crossover study in 14 patients with severe COPD. P(a)CO(2), arterial oxygen tension (P(a)O(2)) and heart rate were measured over 120 min and change from baseline was plotted against time to obtain an area under the curve.

RESULTS

Mean P(a)CO(2) fell slightly over 120 min, with no difference between treatments (0.03 kPa h(-1) (95% confidence interval 0.02, 0.04)) and only three subjects had an increase in P(a)CO(2) after high dose rac-albuterol. High dose rac-albuterol caused a greater fall in P(a)O(2)[0.1 kPa h(-1) (95% confidence interval 0, 0.2)] and increase in heart rate than the low dose, although the differences were small.

CONCLUSIONS

Under stable conditions most subjects with severe COPD and hypercapnia will have a fall in P(a)CO(2) and P(a)O(2) following 10 mg rac-albuterol, suggesting that they maintain capacity to respond to any increase in VCO(2) and prevent a rise in P(a)CO(2).