The Effect of Inhaled Salbutamol on Residual Capacity in Patients with Chronic Obstructive Pulmonary Disease

Background: It is now hypothesized that anti-asthmatic agents such as bronchodilators can reduce residual capacity and Residual Volume (RV) along with inducing no change in Total Lung Capacity (TLC). In the present study, an attempt was made to assess RV following administration of salbutamol inhaled in patients with Chronic Obstructive Pulmonary Disease (COPD). Methods: This prospective interventional case series was conducted on 119 patients with COPD who referred to Rasoul-e-Akram Hospital in Tehran, Iran in 2015. At the beginning of the study, the patients were assessed using spirometer and plethysmograph (BodyBox) and RV was measured. Then, inhaled 400 μg salbutamol (Four puffs) was administered and the RV, TLC and the ratio of RV to TLC (RV/TLC) was measured again 15 min later. Results: Regarding the change in parameters of lung volumes after salbutamol administration, although Forced Expiratory Volume in one second (FEV1) and FEV1/FVC (Forced Vital Capacity-FVC) ratio is significantly increased, the deduction of RV and TLC would be much more. RV decreased from 217.02±123.72% before intervention to 167.50±30.91% after that (p 0.001). There was also no difference between men and women in the change of RV (142.99±52.30% vs. 37.78±36.99%, p=0.37). Compared to smokers, nonsmokers had experienced more reduction in RV (142.50±60.06% vs. 57.79±11.20% p=0.01). The change in RV was adversely associated with age. There was no relation between COPD severity and the change in RV and also RV to TLC. Conclusion: The use of salbutamol inhaled in COPD patients even 15 min after administration leads to significant decrease in RV and RV to TLC ratio even more than increment in FEV1 and FEV1/FVC ratio.