Anticholinergic versus beta 2-agonist on gas exchange in COPD: a comparative study in 15 patients

beta-agonist bronchodilators are known to influence gas exchange and ventilation-perfusion relationships in asthmatic patients, where they induce hypoxaemia via hypoxic vasoconstriction. As this effect could have serious consequences in chronic obstructive pulmonary disease (COPD) patients with chronic hypoxaemia, alternative agents have been sought. It has been shown that inhaled anticholinergic drugs may be of value in this condition. In the present study, we compared the effects of salbutamol (Sb) and ipratropium bromide (IB) inhalation on gas exchange in 15 patients with stable COPD. All patients had a history of COPD (mean arterial oxygen tension (Pa,O2) = 8.2 +/- 1.0 kPa (61.8 +/- 7.3 mmHg) forced expiratory volume in one second (FEV1) = 39 +/- 12%; FEV1/vital capacity (VC) = 42 +/- 6%) and no evidence of acute respiratory failure. Haemodynamic and gas exchange data were recorded after right catheterization by the multiple inert gas elimination technique. Measurements were made under basal conditions, after two puffs of freon propellant (placebo) and after two puffs of either 200 micrograms Sb or 200 micrograms IB in a randomized design. Sb and IB reduced airway resistances to the same extent, but had no significant influence on the haemodynamic and ventilation parameters. There was a slight but significant decrease in arterial carbon dioxide tension (Pa,CO2) = 6.0 +/- 0.8 versus 6.4 +/- 0.8 kPa (45.4 +/- 5.9 versus 47.9 +/- 6.3 mmHg) p < 0.05 with an enhanced perfusion distribution heterogeneity and a slight improvement in ventilation homogeneity shown by a decrease of the decimal logarithm of SD of the ventilation distribution (LogSDV) after inhalation of IB relative to control. Since these alterations did not affect arterial oxygen tension we concluded that inhalation of these doses of salbutamol or ipratropium bromide do not affect gas exchange in patients with stable chronic obstructive pulmonary disease. The normal home treatment: inhalation of two puffs of these bronchodilating drugs thus appears to be safe. The choice of agent will depend on the extent of the bronchodilator effect in a given individual.