Although the use of incentive spirometry with a deep breathing exercise (DBE) is widely used in clinical practice in patients who have undergone coronary artery bypass graft (CABG) surgery, the effect of this combination therapy has not been conclusively elucidated. The aim of this study was to investigate the effect of postoperative combined incentive spirometry and DBE versus DBE alone on inspiratory muscle strength following CABG.

This randomised clinical trial was conducted in patients scheduled to undergo CABG surgery at Siriraj Hospital, Bangkok Thailand. The study group received incentive spirometry and DBE, and the control group received DBE only. Maximal inspiratory pressure (MIP) before surgery and at day 4 after surgery was assessed by a respiratory pressure meter. Secondary outcomes, including postoperative pulmonary complication and duration of postoperative hospitalisation, were obtained from the medical records.

Ninety (90) patients were included, with 47 and 43 patients assigned to the study and control groups, respectively. In both groups, there was a significant reduction in MIP from preoperative baseline to postoperative day 4; however, the MIP in the incentive spirometry group had a significantly smaller reduction in MIP compared with the control group (33.0±23.2% vs 47.2±20.1%, respectively; p=0.006, 95% confidence interval, 3.9-23.3). There was no difference between groups regarding secondary outcomes.

Patients in the study group had significantly better recovery of inspiratory muscle strength on day 4 post-CABG than patients in the control group. There was no significant difference between groups for either postoperative pulmonary complications or length of hospital stay.