This single-center pilot study (Chinese Clinical Trial registration: ChiCTR2300077011) was performed at the Inpatient Unit of the Xuanwu Hospital Capital Medical University, Beijing, China. This study was conducted following the principles outlined in the Declaration of Helsinki and was approved by the Institutional Review Board of the First Affiliated Hospital of Chongqing Medical University. All participants signed a written informed consent form.
Patients who were waiting to undergo CABG were invited to participate in this study. The patients underwent preoperative evaluation, and demographic data (including sex, age, and body mass index (BMI)) and medical history were collected. All patients performed 6MWT. Briefly, the patients were instructed to walk as quickly as possible without running for six minutes in a hallway of 50 m. During the surgery period, all patients were evaluated for lung function (oxygen saturation, partial pressure of oxygen (PaO2), and partial pressure of carbon dioxide (PaCO2). Two surgeons who were not involved in data collection and data analysis screened and recruited the participants in the study through face-to-face interviews. All eligible patients were asked to provide informed consent before enrolling in this study.
Inclusion criteria were as follows: patients who were to undergo selective CABG under general anesthesia; American Society of Anesthesiologists (ASA) grade I ~ IV; expected survival time > three months, could cooperate in observing adverse events and effects; the patient or his/her legal representative signed a written informed consent form. Exclusion criteria were emergency surgery, cognitive dysfunction, neuromuscular diseases, ASA grade V, history of spontaneous pneumothorax, coagulation dysfunction, acute respiratory failure, established respiratory infection, uncontrolled general infection, and failure to obtain informed consent.
Forty patients were included in the study and were randomly assigned to either an intervention or control group. Patients in the intervention group received breathing exercises (including deep breathing, coughing exercises, and balloon-blowing exercises) at least five days before surgery. When patients in the intervention group were admitted to the hospital, they received brochures and a video with instructions describing the method of breathing exercises. The protocol in the intervention group was as follows:
The patient sat down in the chair, inhaled fully through the nose, and held their breath for three seconds. Then, the patient fully exhaled through the mouth into the balloon and held the exhalation for one second. The balloon was immediately covered with fingers, and this counted as one breath cycle. Finally, the balloon was immediately replaced. This was done for three consecutive rounds, counted as one set. In each exercises session, three sets were completed. The patient rested for one minute between sets, and the protocol took approximately 15 minutes. This routine was repeated three to five times per day.
Deep breathing exercises involved taking deep and long breaths through the nose. The patients inhaled air into their lungs and held their breath for three seconds before exhaling through the mouth. Coughing exercises were performed to mobilize lung secretions. Deep breathing and coughing exercises lasted approximately 15 minutes. Patients rested for 30 seconds after each deep breathing and cough. Patients in the sitting position perform deep breathing and coughing exercises, repeated five to ten times daily.
Patients in the control group received standard perioperative care without any breathing exercises. The perioperative care included preoperative education, preoperative smoking cessation, standard anesthetic protocol, early removal of urinary catheter, and encouragement of early ambulation and feeding.
Surgery was performed through median sternotomy. For CABG, saphenous vein grafts and/or left or right internal mammary artery grafts were used [3]. During anesthesia and after surgery, all patients had 40–50% oxygen concentration during inspiration. Postoperatively, patients were artificially ventilated with a positive end-expiratory pressure of 4–6 cmH2O. After tracheal extubation, all patients were subjected to arterial blood gas analysis. Demographic and descriptive data were collected from the medical records.
The primary outcome was the incidence of pulmonary complications, and secondary outcomes were arterial oxygenation, patient satisfaction, and a six-minute walk test (6MWT). According to the guidelines for European perioperative clinical outcome (EPCO), the pulmonary complications including respiratory infection, respiratory failure, pleural effusion, atelectasis, pneumothorax, bronchospasm, aspiration pneumonitis, and pneumonia, as shown in Table 1. [4, 5]. We obtained chest radiographs on the first day postoperatively to detect all relevant postoperative pulmonary complications. Fever, elevated or lowered white cell count, cough, purulent sputum, dyspnea, tachypnea, rales, bronchial breath sounds, and/or worsening gas exchange may indicate pulmonary complications, and chest radiography should be performed promptly. Arterial oxygenation measurements by arterial blood gas were performed at three time points: on the day of admission to the hospital without supplementary oxygen for at least 15 minutes, intraoperatively, and after tracheal extubation. Patient satisfaction was evaluated using the Short-Form 36-item questionnaire (SF-36), chosen for its validity, reliability, and responsiveness across age groups in the heart disease population. The SF-36 includes one multi-item scale that assesses eight health concepts: 1) physical functioning (PF); 2) physical role function (RP); 3) bodily pain (BP); 4) vitality (VT); 5) general health (GH); 6) social functioning (SF); 7) mental health (MH), and 8) emotional role function (RE). The responses for each health concept are standardized on a scale of 0 to 100 [6]. SF-36 was performed at two time points: on the day of admission to the hospital and one month after surgery. All patients performed 6MWT. The patients were instructed to walk as quickly as possible without running in a 50 m hallway for six minutes. This test is currently considered the best indicator to measure functional capacity. It considers the risk of returning to the hospital and observes the patient’s performance based on activities of daily living [7]. Throughout the 6MWT, the patient was monitored so the test could be stopped at any time when the heart rate reached < 20% of baseline; upon an increase in systolic and/or diastolic blood pressure > 30% of baseline; upon an increase in the respiratory rate > 25 breaths/min, and peripheral oxygen saturation < 90% [3]. 6MWT was performed at two-time points: on the day of admission to the hospital and one month after surgery.
Table 1
Definitions of postoperative pulmonary complications
Complication | Definition |
Respiratory infection | Patient has received antibiotics for a suspected respiratory infection and met one or more of the following criteria: new or charged sputum new or changed lung opacities, fever, white blood cell count>12*109/I. |
Respiratory failure | Postoperative PaO2 < 8kPa(60mmHg) on room air, a PaO2:FiO2 ratio < 40kpa(300mmHg )or arterial oxyhemoglobin saturation measured with pulse oximetry < 90% and requiring oxygen therapy. |
Pleural effusion | Chest radiograph demonstrating blunting of the costophrenic angle, loss of sharp silhouette of the ipsilateral hemidiaphragm in upright position, evidence of displacement of adjacent anatomical structures or (in supine position) a hazy opacity in one hemithorax with preserved vascular shadows. |
Atelectasis | Lung opacification with a shift of the mediastinum, hilum or hemidiaphragm toward the affected area, and compensatory over-inflation in the adjacent non-atelectatic lung. |
Pneumothorax | Air in the pleural space with no vascular bed surrounding the visceral pleura |
Bronchospasm | Newly detected expiratory wheezing treated with bronchodilators. |
Aspiration pneumonitis | Acute lung injury after inhalation of regurgitated gastric contents |
Pneumonia | Chest radiograph with at least one of the following: infiltrates, consolidation, cavitation; and at least one of the following: fever (> 38°C) with no other recognized cause, white cell count > 12×109 /l or < 4×109 /l, > 70 years old with altered mental status with no other recognized cause; and at least two of the following: purulent sputum or increased respiratory secretions, cough or dyspnea or tachypnoea, rales or bronchial breath sounds, worsening gas exchange. |
Statistical analysis
The analysis was performed using the SPSS 24.0 software. Normality was assessed using the Shapiro-Wilks test. The variables were expressed as means and standard deviations. Chi-square was used to compare categorical variables. The independent Student’s t-test was used to compare values between groups, and the intragroup comparisons were based on paired Student’s t-test. It was considered as significant at P < 0.05.