GAS-EXCHANGE RESPONSE TO INTRAVENOUS AMINOPHYLLINE IN PATIENTS WITH ASEVERE EXACERBATION OF ASTHMA

In patients with acute exacerbations of asthma, the intravenous admini stration of bronchodilators, such as salbutamol, entails the potential risk of worsening pulmonary gas exchange, despite an amelioration of airflow obstruction, The present study was designed to investigate the effect of intravenous aminophylline on pulmonary gas exchange in pati ents hospitalized with a severe exacerbation of asthma. We studied 12 patients (aged 41+/-13 yrs) admitted to the hospital because of an I e xacerbation of asthma. The study was of a randomized, double-blind, pl acebo-controlled design. Six patients were treated with intravenous am inophylline and six received placebo, in addition to standard treatmen t with inhaled salbutamol and intravenous corticosteroids, Forced spir ometry, respiratory gas exchange, ventilation-perfusion relationships assessed with the multiple inert gas elimination technique, and system ic haemodynamics were measured at baseline and 60 min after treatment started. In the aminophylline-treated group, mean theophylline plasma levels increased to 15.2+/-3.6 mu g . ml(-1), forced expiratory volume (FEV(1)) increased by 17+/-12%, and forced vital capacity (FVC) by 16 +/-10%. The mean changes in FEV(1) and FVC in the aminophylline-treate d group were significantly higher than in the placebo-treated group. L ikewise, minute ventilation increased by 23+/-14% and arterial carbon dioxide tension (PaCO2) decreased by 0.4+/-0.3 kPa (3+/-2 mmHg) during aminophylline infusion. No significant changes in arterial oxygen ten sion (PaO2) or in ventilation-perfusion distributions were shown in am inophylline-treated patients. In contrast, a moderate worsening in ven tilation-perfusion relationships developed in placebo-treated patients , as assessed by an increase of the dispersion of blood flow distribut ion (logSD Q, from 1.18+/-0.26 to 1.25+/-0.28, these changes in pulmon ary gas exchange were not significantly different between the groups. We conclude that intravenous aminophylline, given at therapeutic plasm a levels in severe exacerbations of asthma, produces a moderate increa se in airflow rates without disturbing pulmonary gas exchange.