The effect of preoperative deep breathing exercise with incentive spirometer initiated in the preoperative period on respiratory parameters and complications in patients underwent open heart surgery: a randomized controlled trial
Coronary artery bypass grafting (CABG) is a surgical procedure that involves bypassing blocked coronary arteries with the objective of restoring blood flow to the heart . Patients who have undergone cardiac surgery are at an elevated risk of developing postoperative pulmonary complications (PPCs) . Furthermore, approximately one-quarter of patients who have undergone cardiac surgery and do not have chronic pulmonary dysfunction develop a PPC. PPCs range from a mild respiratory infection to acute respiratory failure, which may necessitate the use of oxygen therapy and invasive or non-invasive mechanical ventilation (MV) support . PPCs have been demonstrated to result in elevated healthcare expenditures , extended periods of hospitalisation, and an increased prevalence of morbidity and mortality . The development of a PPC is influenced by a number of factors. Contributing factors have included surgical stress and anaesthesia, the systemic inflammatory response and oxidative stress from cardiopulmonary bypass, the type of surgery performed, inadequate pain management, the anaesthesia protocol employed, the use of blood products, and diaphragmatic dysfunction . A significant contributing factor to the development of PPCs is preoperative respiratory muscle weakness . A variety of respiratory physiotherapy techniques are employed with the objective of alleviating muscle weakness and preventing PPCs in patients who have undergone cardiac surgery. The main aims of respiratory physiotherapy are to improve ventilation-perfusion compliance, increase lung volumes, improve mucociliary clearance, and reduce pain . The most commonly used methods are incentive spirometry (IS) and deep breathing exercises (DBE), which are easy to use, straightforward, and inexpensive . IS is a method that provides visual feedback based on the patient's motivation and cooperation in deep breathing  to maintain alveolar patency after cardiac surgery , improve lung volumes by ensuring oxygen delivery and proper ventilation , ensure maximum bronchial dilatation, and produce an effective cough . In clinical practice, DBEs with IS is usually initiated in the post-operative period . However, it has been reported that inadequate physical adaptation and respiratory muscle weakness in the preoperative period are closely associated with PPCs leading to a prolonged hospital stay and increased mortality . There are limited studies investigating the efficacy of preoperative IS application only in patients undergoing open-heart surgery . In addition, the literature evaluating the effect of IS and DBEs on respiratory complications in patients undergoing open-heart surgery is inconsistent. Some studies have found a statistically significant lower incidence of atelectasis with IS and DBEs , while others have found no effect . The aim of this study was to determine the effects of preoperative DBE and IS on respiratory parameters and complications in patients undergoing open-heart surgery. It is anticipated that the data obtained from this study will contribute to the existing literature on the effects of initiating IS and DBE in the preoperative period in patients undergoing open-heart surgery. Furthermore, it may shed light on preoperative nursing care practices to prevent PPCs. 

Study design and participants The randomized controlled study was conducted at the Cardiovascular Surgery Unit (CVSU) of a training and research hospital between June 2022 and January 2023. This study was registered in a clinical trial database (NCT05428722||( https://www.clinicaltrials.gov/ ) (June 17, 2022). The G*Power (version 3.1.9.4) test was used to determine sample size. A priori analysis was based on the mean hypoxic events (intervention: 9.4 ± 7.6 vs. control 30.9 ± 26.2) in 89 patients underwent for elective cardiac surgery in the study by Alwekhyan et al. . It was determined that a total of 62 patients (31 patients in each group) should be included when the Independent Sample t-test was two-tailed, with a predicted effect size of 1.11 and a (type 1 or 2) error level of 5% with a power of 99%. Considering that the dropout rate was 15% in the reference study, 72 patients (36 in each group) were included in this study. Three patients who died in the deep breathing group, one patient who did not comply with the exercises and two patients who died in the control group were excluded from the study. Thus, the study included 66 patients (32 in the deep breathing group; and 34 in the control group). The study flowchart according to the Consolidated Standards of Reporting Trials (2010) is shown in Fig. . Inclusion criteria were (a) 18 years or older; (b) Turkish speaking and understanding; (c) conscious, oriented, and cooperative; (d) undergoing cardiac surgery for the first time; (e) undergoing CABG, valve surgery or combined open-heart surgery; (f) did not require oxygen support in the preoperative period; and (g) had a Medical Research Council Scale (MRCS) score of 1. Patients were excluded if they (a) underwent emergency surgery, (b) had complete (100%) occlusion of the left and right main coronary arteries, (c) had a concomitant vascular aneurysm, (d) had a chronic respiratory disease (asthma, chronic obstructive pulmonary disease, bronchiectasis, etc.), (e) refused to participate in the study, (f) had heart failure, and (g) had incomplete data. Patients who (a) died during surgery and (b) did not comply with IS and exercises were considered patients lost to follow-up. Randomization and blinding In this study, 72 patients who met the inclusion criteria were assigned to groups using the block randomization method (36 patients in the deep breathing group and 36 patients in the control group). The assignment of patients to groups by block randomization method was performed through a computer program . A coin was tossed to determine whether Groups A and B represented the deep breathing and control groups, respectively. Group A was the deep breathing group and Group B was the control group. It was not possible for the patients and the researcher to be blinded to the study. Data collection tools Medical Research Council Scale (MRCS) The Medical Research Council Scale (MRCS) was used to determine the severity of dyspnea in the patients included in the study. It is a five-item scale ranging from 1 (no dyspnea) to 5 (very severe dyspnea) based on various physical activities that cause dyspnea . In this study, the items on the scale were read to patients, who were then asked to choose the number that best described their dyspnoea. According to the scale, patients with a "1", or no dyspnoea, were included in the study. Sociodemographic and medical data form The Sociodemographic and Medical Data Form, which was prepared by the researchers, consists of a total of 13 items including sociodemographic and medical questions . Sociodemographic and medical data forms were administered to all patients on the first day of hospitalisation. Patient follow-up form Finally, the Patient Follow-up Form was a researcher-administered form used to monitor respiratory rate (RR), oxygen saturation (SpO 2 ), arterial blood gas parameters (pH, pO 2 , pCO 2 , SaO 2 , HCO 3 ), and posteroanterior (PA) Chest X-ray during different phases of the patient's care. Observation indicators The measurement times of the observation indicators are given in Fig. . Primary outcomes Assessment of respiratory parameters (RR, SpO 2 level, arterial blood gas parameters, Chest X-ray), and PPCs development. The RR was counted four times daily by the research nurse. RR was measured by the research nurse for one minute after a rest period of at least 15 min. SpO 2 levels were determined four times a day, after a 15-min interval in patients receiving oxygen support, using a Braun YK-81CEU Pulse oximeter (China) (pulse and oxygen meter), and the mean value was recorded. SpO 2 was measured on room air. The pulse oximetry device was disinfected, and the same device was used for all patients. The calibration of the device was verified at the beginning of the study. To avoid measurement error (or bias), assessments were conducted by a single researcher. A pulse oximeter was placed over the nail bed. Arterial blood gas analysis was routinely performed at (First day of hospitalisation, before surgery, postoperative 1st day and discharge day) certain times in the CVSU clinic and studied on the same device in the laboratory. PA Chest X-rays of the patients were evaluated. All patients were evaluated by a medical doctor researcher on the first day of hospitalisation if complications developed and were deemed necessary, and the last PA chest X-ray was taken before discharge. A PPC was defined as the occurrence of at least one pulmonary complication among atelectasis, pleural effusion, respiratory failure, pneumonia, pneumothorax, bronchospasm, or aspiration pneumonia. The diagnosis of one of these conditions by a medical doctor was determined as the criterion. Classification of PPCs was made according to the Dindo-Clavien postoperative surgical complications classification. According to this classification, postoperative complications were classified as Grade I, II, IIIA, IIIB, IVA, IVB, and V . Secondary outcomes MV time, postoperative length of intensive care unit (ICU) stay, and duration of hospital stay were considered secondary outcomes in our analysis . MV duration was recorded in hours from the moment the patient was admitted to the postoperative intensive care unit until extubation. The day of admission to the ICU after surgery was considered the patient's first postoperative day. The time from this day until the day the patient was transferred to the CVSU was recorded as the postoperative intensive care unit stay. The number of days from the first hospitalisation to discharge was recorded as the length of hospital stay. Implementation of the initiative Each patient was included in the study on the day of admission to the CVSU. All patients were followed up until discharge. Routine treatment and care All patients included in the study received routine cardiovascular surgical care. In addition, all patients included in the study received routine treatment and care in the ICU. Postoperatively, in the ICU patients were first administered MV with a fraction of inspired oxygen (FiO2) of 45–50%, tidal volumes of 6–8 ml/kg and RR adjusted (according to arterial blood gases) in the Synchronized Intermittent Mandatory Ventilation and Continuous Positive Airway Pressure modes, respectively. A routine chest X-ray was performed after the patient was transferred to the ICU to examine the location of the endotracheal tube and the overall condition of the lungs. Close monitoring was performed daily for the development of PPCs. In the CVSU DBEs with IS were started after open-heart surgery for all patients. Deep breathing group In this study, in addition to routine treatment and care, patients in the deep breathing group received DBE training with IS on the first day of hospitalisation (preoperative period). IS training was given practically by the nurse at the bedside using an IS. The nurse first introduced the IS and explained how it is used. Then, the nurse demonstrated how to properly position and hold the IS during the exercise. Finally, the steps of inspiration, holding the breath in and expiration were demonstrated. The patient performed DBEs with IS in front of the study nurse. Areas where the patient made mistakes during the exercise were corrected. All questions asked by the patient were answered. The first training took approximately 30–45 min. The need for retraining was assessed. None of the patients required retraining. Subsequently, the patients performed DBE with the IS until the time of surgery. Thus, patients were made to do deep breathing exercises from the first day they were admitted to the CVSU. After the patient was extubated in the ICU postoperatively, DBE with IS was re-started in the ICU after their clinical condition stabilized and continued until discharge. DBEs with IS were performed as inspiration 5–10 times per hour, holding the breath in for 3–5 s and then expiration 5–10 times. Patients were instructed to start the morning after breakfast and to inspire 5–10 times per hour with IS, hold their breath for 3–5 s, and then expire 5–10 times per hour until they fell asleep in the CVSU. The research nurse instructed patients that they should exercise every hour, and the alarms of the patients' cell phones were set to ring every hour as reminders. The start and end times of the exercise were decided together with the patient; usually, the patient's waking and bedtimes were considered. No side effects of the intervention were observed in patients in the deep breathing group. Control group Patients in the control group received hospital routine physiotherapy. No additional intervention was applied. Patients in this group began DBE with IS after surgery as part of their routine care in the CVSU. Statistical analysis Data analysis was performed using the Statistical Package for Social Sciences 25 (IBM SPSS Statistics Version 25, USA). A normality test was performed to determine the tests used in the data analysis. The mean and standard deviation values were used for age, body mass index (BMI), and duration of smoking, and number and percentage values were used for all other variables. An independent sample t-test was used for intergroup comparisons of age, BMI, smoking duration, duration of surgery (hours), MV time (hours), length of hospital stay (days), postoperative length of ICU stay (days), aortic cross-clamp (AXC) duration (min), cardiopulmonary bypass pump (CBP) duration (min), arterial blood gas parameters, RR and SpO 2 levels. A paired sample t-test was used for intragroup comparisons of RR, O 2 , CO 2 , and SpO 2 levels. A chi-square test was used to determine the relationship between the presence of a PPC, the presence of complications other than a PPC, and postoperative PA chest X-ray features. A Pearson correlation test was used to determine the relationship between MV time (hours), duration of surgery (hours), postoperative length of ICU stay (days), CBP duration (min), and length of hospital stay (days). Pearson correlation tests were also used to determine the relationship between MV time (hours), duration of surgery (hours), CBP duration (min), AXC duration (min), and postoperative length of ICU stay (days). 

The randomized controlled study was conducted at the Cardiovascular Surgery Unit (CVSU) of a training and research hospital between June 2022 and January 2023. This study was registered in a clinical trial database (NCT05428722||( https://www.clinicaltrials.gov/ ) (June 17, 2022). The G*Power (version 3.1.9.4) test was used to determine sample size. A priori analysis was based on the mean hypoxic events (intervention: 9.4 ± 7.6 vs. control 30.9 ± 26.2) in 89 patients underwent for elective cardiac surgery in the study by Alwekhyan et al. . It was determined that a total of 62 patients (31 patients in each group) should be included when the Independent Sample t-test was two-tailed, with a predicted effect size of 1.11 and a (type 1 or 2) error level of 5% with a power of 99%. Considering that the dropout rate was 15% in the reference study, 72 patients (36 in each group) were included in this study. Three patients who died in the deep breathing group, one patient who did not comply with the exercises and two patients who died in the control group were excluded from the study. Thus, the study included 66 patients (32 in the deep breathing group; and 34 in the control group). The study flowchart according to the Consolidated Standards of Reporting Trials (2010) is shown in Fig. . Inclusion criteria were (a) 18 years or older; (b) Turkish speaking and understanding; (c) conscious, oriented, and cooperative; (d) undergoing cardiac surgery for the first time; (e) undergoing CABG, valve surgery or combined open-heart surgery; (f) did not require oxygen support in the preoperative period; and (g) had a Medical Research Council Scale (MRCS) score of 1. Patients were excluded if they (a) underwent emergency surgery, (b) had complete (100%) occlusion of the left and right main coronary arteries, (c) had a concomitant vascular aneurysm, (d) had a chronic respiratory disease (asthma, chronic obstructive pulmonary disease, bronchiectasis, etc.), (e) refused to participate in the study, (f) had heart failure, and (g) had incomplete data. Patients who (a) died during surgery and (b) did not comply with IS and exercises were considered patients lost to follow-up. 

In this study, 72 patients who met the inclusion criteria were assigned to groups using the block randomization method (36 patients in the deep breathing group and 36 patients in the control group). The assignment of patients to groups by block randomization method was performed through a computer program . A coin was tossed to determine whether Groups A and B represented the deep breathing and control groups, respectively. Group A was the deep breathing group and Group B was the control group. It was not possible for the patients and the researcher to be blinded to the study. 

Medical Research Council Scale (MRCS) The Medical Research Council Scale (MRCS) was used to determine the severity of dyspnea in the patients included in the study. It is a five-item scale ranging from 1 (no dyspnea) to 5 (very severe dyspnea) based on various physical activities that cause dyspnea . In this study, the items on the scale were read to patients, who were then asked to choose the number that best described their dyspnoea. According to the scale, patients with a "1", or no dyspnoea, were included in the study. Sociodemographic and medical data form The Sociodemographic and Medical Data Form, which was prepared by the researchers, consists of a total of 13 items including sociodemographic and medical questions . Sociodemographic and medical data forms were administered to all patients on the first day of hospitalisation. Patient follow-up form Finally, the Patient Follow-up Form was a researcher-administered form used to monitor respiratory rate (RR), oxygen saturation (SpO 2 ), arterial blood gas parameters (pH, pO 2 , pCO 2 , SaO 2 , HCO 3 ), and posteroanterior (PA) Chest X-ray during different phases of the patient's care. 

The Medical Research Council Scale (MRCS) was used to determine the severity of dyspnea in the patients included in the study. It is a five-item scale ranging from 1 (no dyspnea) to 5 (very severe dyspnea) based on various physical activities that cause dyspnea . In this study, the items on the scale were read to patients, who were then asked to choose the number that best described their dyspnoea. According to the scale, patients with a "1", or no dyspnoea, were included in the study. 

The Sociodemographic and Medical Data Form, which was prepared by the researchers, consists of a total of 13 items including sociodemographic and medical questions . Sociodemographic and medical data forms were administered to all patients on the first day of hospitalisation. 

Finally, the Patient Follow-up Form was a researcher-administered form used to monitor respiratory rate (RR), oxygen saturation (SpO 2 ), arterial blood gas parameters (pH, pO 2 , pCO 2 , SaO 2 , HCO 3 ), and posteroanterior (PA) Chest X-ray during different phases of the patient's care. 

The measurement times of the observation indicators are given in Fig. . Primary outcomes Assessment of respiratory parameters (RR, SpO 2 level, arterial blood gas parameters, Chest X-ray), and PPCs development. The RR was counted four times daily by the research nurse. RR was measured by the research nurse for one minute after a rest period of at least 15 min. SpO 2 levels were determined four times a day, after a 15-min interval in patients receiving oxygen support, using a Braun YK-81CEU Pulse oximeter (China) (pulse and oxygen meter), and the mean value was recorded. SpO 2 was measured on room air. The pulse oximetry device was disinfected, and the same device was used for all patients. The calibration of the device was verified at the beginning of the study. To avoid measurement error (or bias), assessments were conducted by a single researcher. A pulse oximeter was placed over the nail bed. Arterial blood gas analysis was routinely performed at (First day of hospitalisation, before surgery, postoperative 1st day and discharge day) certain times in the CVSU clinic and studied on the same device in the laboratory. PA Chest X-rays of the patients were evaluated. All patients were evaluated by a medical doctor researcher on the first day of hospitalisation if complications developed and were deemed necessary, and the last PA chest X-ray was taken before discharge. A PPC was defined as the occurrence of at least one pulmonary complication among atelectasis, pleural effusion, respiratory failure, pneumonia, pneumothorax, bronchospasm, or aspiration pneumonia. The diagnosis of one of these conditions by a medical doctor was determined as the criterion. Classification of PPCs was made according to the Dindo-Clavien postoperative surgical complications classification. According to this classification, postoperative complications were classified as Grade I, II, IIIA, IIIB, IVA, IVB, and V . Secondary outcomes MV time, postoperative length of intensive care unit (ICU) stay, and duration of hospital stay were considered secondary outcomes in our analysis . MV duration was recorded in hours from the moment the patient was admitted to the postoperative intensive care unit until extubation. The day of admission to the ICU after surgery was considered the patient's first postoperative day. The time from this day until the day the patient was transferred to the CVSU was recorded as the postoperative intensive care unit stay. The number of days from the first hospitalisation to discharge was recorded as the length of hospital stay. 

Assessment of respiratory parameters (RR, SpO 2 level, arterial blood gas parameters, Chest X-ray), and PPCs development. The RR was counted four times daily by the research nurse. RR was measured by the research nurse for one minute after a rest period of at least 15 min. SpO 2 levels were determined four times a day, after a 15-min interval in patients receiving oxygen support, using a Braun YK-81CEU Pulse oximeter (China) (pulse and oxygen meter), and the mean value was recorded. SpO 2 was measured on room air. The pulse oximetry device was disinfected, and the same device was used for all patients. The calibration of the device was verified at the beginning of the study. To avoid measurement error (or bias), assessments were conducted by a single researcher. A pulse oximeter was placed over the nail bed. Arterial blood gas analysis was routinely performed at (First day of hospitalisation, before surgery, postoperative 1st day and discharge day) certain times in the CVSU clinic and studied on the same device in the laboratory. PA Chest X-rays of the patients were evaluated. All patients were evaluated by a medical doctor researcher on the first day of hospitalisation if complications developed and were deemed necessary, and the last PA chest X-ray was taken before discharge. A PPC was defined as the occurrence of at least one pulmonary complication among atelectasis, pleural effusion, respiratory failure, pneumonia, pneumothorax, bronchospasm, or aspiration pneumonia. The diagnosis of one of these conditions by a medical doctor was determined as the criterion. Classification of PPCs was made according to the Dindo-Clavien postoperative surgical complications classification. According to this classification, postoperative complications were classified as Grade I, II, IIIA, IIIB, IVA, IVB, and V . 

MV time, postoperative length of intensive care unit (ICU) stay, and duration of hospital stay were considered secondary outcomes in our analysis . MV duration was recorded in hours from the moment the patient was admitted to the postoperative intensive care unit until extubation. The day of admission to the ICU after surgery was considered the patient's first postoperative day. The time from this day until the day the patient was transferred to the CVSU was recorded as the postoperative intensive care unit stay. The number of days from the first hospitalisation to discharge was recorded as the length of hospital stay. 

Each patient was included in the study on the day of admission to the CVSU. All patients were followed up until discharge. Routine treatment and care All patients included in the study received routine cardiovascular surgical care. In addition, all patients included in the study received routine treatment and care in the ICU. Postoperatively, in the ICU patients were first administered MV with a fraction of inspired oxygen (FiO2) of 45–50%, tidal volumes of 6–8 ml/kg and RR adjusted (according to arterial blood gases) in the Synchronized Intermittent Mandatory Ventilation and Continuous Positive Airway Pressure modes, respectively. A routine chest X-ray was performed after the patient was transferred to the ICU to examine the location of the endotracheal tube and the overall condition of the lungs. Close monitoring was performed daily for the development of PPCs. In the CVSU DBEs with IS were started after open-heart surgery for all patients. Deep breathing group In this study, in addition to routine treatment and care, patients in the deep breathing group received DBE training with IS on the first day of hospitalisation (preoperative period). IS training was given practically by the nurse at the bedside using an IS. The nurse first introduced the IS and explained how it is used. Then, the nurse demonstrated how to properly position and hold the IS during the exercise. Finally, the steps of inspiration, holding the breath in and expiration were demonstrated. The patient performed DBEs with IS in front of the study nurse. Areas where the patient made mistakes during the exercise were corrected. All questions asked by the patient were answered. The first training took approximately 30–45 min. The need for retraining was assessed. None of the patients required retraining. Subsequently, the patients performed DBE with the IS until the time of surgery. Thus, patients were made to do deep breathing exercises from the first day they were admitted to the CVSU. After the patient was extubated in the ICU postoperatively, DBE with IS was re-started in the ICU after their clinical condition stabilized and continued until discharge. DBEs with IS were performed as inspiration 5–10 times per hour, holding the breath in for 3–5 s and then expiration 5–10 times. Patients were instructed to start the morning after breakfast and to inspire 5–10 times per hour with IS, hold their breath for 3–5 s, and then expire 5–10 times per hour until they fell asleep in the CVSU. The research nurse instructed patients that they should exercise every hour, and the alarms of the patients' cell phones were set to ring every hour as reminders. The start and end times of the exercise were decided together with the patient; usually, the patient's waking and bedtimes were considered. No side effects of the intervention were observed in patients in the deep breathing group. Control group Patients in the control group received hospital routine physiotherapy. No additional intervention was applied. Patients in this group began DBE with IS after surgery as part of their routine care in the CVSU. 

All patients included in the study received routine cardiovascular surgical care. In addition, all patients included in the study received routine treatment and care in the ICU. Postoperatively, in the ICU patients were first administered MV with a fraction of inspired oxygen (FiO2) of 45–50%, tidal volumes of 6–8 ml/kg and RR adjusted (according to arterial blood gases) in the Synchronized Intermittent Mandatory Ventilation and Continuous Positive Airway Pressure modes, respectively. A routine chest X-ray was performed after the patient was transferred to the ICU to examine the location of the endotracheal tube and the overall condition of the lungs. Close monitoring was performed daily for the development of PPCs. In the CVSU DBEs with IS were started after open-heart surgery for all patients. 

In this study, in addition to routine treatment and care, patients in the deep breathing group received DBE training with IS on the first day of hospitalisation (preoperative period). IS training was given practically by the nurse at the bedside using an IS. The nurse first introduced the IS and explained how it is used. Then, the nurse demonstrated how to properly position and hold the IS during the exercise. Finally, the steps of inspiration, holding the breath in and expiration were demonstrated. The patient performed DBEs with IS in front of the study nurse. Areas where the patient made mistakes during the exercise were corrected. All questions asked by the patient were answered. The first training took approximately 30–45 min. The need for retraining was assessed. None of the patients required retraining. Subsequently, the patients performed DBE with the IS until the time of surgery. Thus, patients were made to do deep breathing exercises from the first day they were admitted to the CVSU. After the patient was extubated in the ICU postoperatively, DBE with IS was re-started in the ICU after their clinical condition stabilized and continued until discharge. DBEs with IS were performed as inspiration 5–10 times per hour, holding the breath in for 3–5 s and then expiration 5–10 times. Patients were instructed to start the morning after breakfast and to inspire 5–10 times per hour with IS, hold their breath for 3–5 s, and then expire 5–10 times per hour until they fell asleep in the CVSU. The research nurse instructed patients that they should exercise every hour, and the alarms of the patients' cell phones were set to ring every hour as reminders. The start and end times of the exercise were decided together with the patient; usually, the patient's waking and bedtimes were considered. No side effects of the intervention were observed in patients in the deep breathing group. 

Patients in the control group received hospital routine physiotherapy. No additional intervention was applied. Patients in this group began DBE with IS after surgery as part of their routine care in the CVSU. 

Data analysis was performed using the Statistical Package for Social Sciences 25 (IBM SPSS Statistics Version 25, USA). A normality test was performed to determine the tests used in the data analysis. The mean and standard deviation values were used for age, body mass index (BMI), and duration of smoking, and number and percentage values were used for all other variables. An independent sample t-test was used for intergroup comparisons of age, BMI, smoking duration, duration of surgery (hours), MV time (hours), length of hospital stay (days), postoperative length of ICU stay (days), aortic cross-clamp (AXC) duration (min), cardiopulmonary bypass pump (CBP) duration (min), arterial blood gas parameters, RR and SpO 2 levels. A paired sample t-test was used for intragroup comparisons of RR, O 2 , CO 2 , and SpO 2 levels. A chi-square test was used to determine the relationship between the presence of a PPC, the presence of complications other than a PPC, and postoperative PA chest X-ray features. A Pearson correlation test was used to determine the relationship between MV time (hours), duration of surgery (hours), postoperative length of ICU stay (days), CBP duration (min), and length of hospital stay (days). Pearson correlation tests were also used to determine the relationship between MV time (hours), duration of surgery (hours), CBP duration (min), AXC duration (min), and postoperative length of ICU stay (days). 

Seventy-two patients were enrolled, 66 patients completed the study. Two patients in the deep breathing group died of bleeding and cardiac tamponade, while one patient in this group died of arrhythmia; one patient from the control group died of arrhythmia and one patient from the control group died of bleeding. In this study, patients in the deep breathing and control groups were similar in terms of mean age, mean BMI, sex, marital status, education, history of smoking, duration of smoking, surgical intervention, presence of chronic disease, presence of complications other than PPC, and chronic disease characteristics (Table ). It was determined that 3.1% ( n = 1) of the patients in the deep breathing group developed pneumonia and had a pathologic postoperative chest X-ray. In the control group, 23.5% ( n = 8) of the patients developed a PPC, of which 8.8% had atelectasis and had a pathological postoperative chest X-ray. PPCs occurring in the deep breathing and control groups were classified as Grade I and Grade II according to the Dindo-Clavien classification . When comparing the deep breathing and control groups, there was a statistically significant difference in terms of the development of PPCs ( p < 0.05). There was a statistically significant higher number of patients in the control group with a pathological postoperative PA chest X-ray ( p < 0.05) (Table ). A comparison of the surgical intervention-related characteristics and arterial blood gas parameters of the patients is presented in Table . There was no significant difference between the mean duration of surgery, AXC duration, and CBP duration ( p > 0.05) between groups. MV time (16.58 ± 8.94), duration of hospital stay (18.97 ± 6.26), and postoperative length of ICU stay (4.47 ± 1.87) of patients in the deep breathing group were significantly shorter than those in the control group (11.59 ± 5.04; 16.03 ± 4.99; 3.51 ± 1.54, respectively) ( p < 0.05). When examining blood gases; the mean pCO 2 on the first day in the CVSU (33.63 ± 3.31), and on the day of discharge (32.73 ± 4.87) of patients in the deep breathing group were significantly lower than those in the control group (36.43 ± 4.71; 35.34 ± 4.01, respectively) ( p < 0.05). The difference between the mean values of all other parameters and at different timepoints were not significant ( p > 0.05). A comparison of mean RR and SpO 2 levels between groups is presented in Table . The mean SpO 2 values of the patients in the deep breathing group before surgery (97.59 ± 0.91), on the first day in the CVSU (93.15 ± 3.71), and on the day of discharge (96.37 ± 1.87) were significantly higher than the control group ( p < 0.05). Moreover, it was found that the mean RR of the patients in the deep breathing group on the first day in the CVSU (20.43 ± 2.36) was significantly lower than in the control group ( p < 0.05). A comparison of respiratory rate, O 2 , CO 2 , and SpO 2 levels intra-group at patient follow-up is presented in Table . In the deep breathing group, the mean SpO 2 (97.59 ± 0.91) and PaO 2 (88.07 ± 8.44) levels before surgery were significantly higher than those on the first day of hospitalisation (96.84 ± 1.24, 84.83 ± 10.42, respectively) ( p < 0.05). The SpO 2 levels on the day of discharge were significantly higher than those on the first day in the CVSU. The RR levels on the day of discharge were statistically significantly lower than those on the first day in the CVSU in both the intervention and the control groups ( p < 0.05). The correlation between some characteristics of the patients and the length of hospital stay and postoperative length of ICU stay is presented in Table . Accordingly, it was determined that there was a weak positive correlation between the postoperative length of ICU stay and MV time ( r :0.23; p < 0.05) as well as AXC duration ( r :0.29; p < 0.05). Also, there was a weak positive relationship between the postoperative length of ICU stay and MV time ( r: 0.23; p < 0.05) and AXC duration ( r: 0.29; p < 0.05). 

Cardiopulmonary bypass is responsible for a systemic inflammatory response that causes pulmonary ischemia–reperfusion injury . Additionally, factors such as patient respiratory function, type of surgery, type of pain management, anaesthesia protocol, and use of blood products are associated with the development of PPCs . Atelectasis is a well known complication of general anesthesia which may persist for several days for a variety of reasons . In this sense, DBEs have been shown to improve postoperative lung expansion and ventilation  and reduce the occurrence and severity of PPCs . Incentive spirometry is used in lung expansion therapy to maintain alveolar patency and improve pulmonary volumes in postoperative cardiac surgical patients . A meta-analysis showed that the use of IS alone had little or no effect on reducing pulmonary complications after cardiac, thoracic, and lower abdominal surgery . Similarly, in other studies, it was determined that respiratory exercise initiated with IS in the preoperative period had no effect on atelectasis and hypoxemia after CABG , and it was determined that there was no significant difference in PPCs between the patients in the IS group and the patients in the DBE and control group . In a study conducted with patients who underwent lung resection, it was determined that compliance with postoperative IS use was better and the incidence of PPCs was significantly lower in the group that received preoperative DBE with IS . In our study, preoperative DBE combined with IS had a statistically significant lower incidence of atelectasis in patients after open-heart surgery. This is similar to the findings of a meta-analysis which examined the effect of preoperative exercise training on PPCs in patients who underwent a major surgical intervention (cardiac, lung, esophageal, or abdominal surgery). Preoperative exercise training resulted in significantly reduced development of PPCs in the postoperative period . Additionally, our results are in agreement with a previous study in CABG patients in which DBE with IS in the preoperative period significantly reduced the incidence of postoperative atelectasis . In this study, it was found that the number of PPCs in the deep breathing group was lower than that in the control group. Moreover, no atelectasis was seen in the patients in the deep breathing group, only one patient in the deep breathing group developed pneumonia, whereas most of the patients with PPCs in the control group developed atelectasis. The results of this study lend support to the findings of other studies that have reported that preoperative DBE with IS has a statistically significant lower incidence of atelectasis in patients undergoing open-heart surgery . Deconditioning and respiratory muscle weakness in the preoperative period are closely associated with PPCs, which lead to a prolonged hospital stay and increased mortality . Our findings are consistent with those of previous studies that have shown that preoperative DBEs with IS have positive effects on respiratory function in patients undergoing open-heart surgery and subsequently reduces the development of PPCs. Mechanical ventilation plays an important role in pulmonary injury and is considered to be an independent risk factor for the development of PPCs after cardiac surgery . MV duration was significantly shorter in patients in the deep breathing group than in the control group. This is consistent with other studies in CABG patients that have shown that the duration of MV was significantly shorter in patients who started DBE with IS preoperatively . Yet another study of preoperative DBE and IS in CABG patients reported that there was no difference in MV duration . It is likely that the difference between the results of these studies may be due to differences in care protocols in the different countries and institutions in which these previous trials have been performed. The results of this study suggest that DBE with IS initiated in the preoperative period in patients undergoing open-heart surgery contributes to a shorter-term termination of MV support in the postoperative period. It is important that patients stay in the hospital for a short time to avoid additional complications and increased healthcare costs. In our study, the duration of hospitalisation was found to be significantly shorter in the deep breathing group. A study of CABG patients showed that the length of hospital stay was significantly shorter in patients who underwent DBE with IS prior to surgery . A meta-analysis of the effects of preoperative exercise training in patients undergoing major surgery (heart, lung, oesophageal or abdominal surgery) found that the length of hospital stay was significantly reduced . In a study of patients undergoing CABG, the postoperative hospital stay was shorter in the group that received preoperative inspiratory muscle training compared with the control group . One study found that there was no significant difference in the length of hospital stay between patients in a DBE with IS group versus a DBE alone control group . These results can be interpreted as meaning that starting DBE with IS in the preoperative period may shorten the recovery time of patients after CABG and help them to return to their normal life in a shorter time. One study found that the length of ICU stay of patients who underwent breathing exercises with nurse-guided IS in the postoperative period was significantly shorter than patients with self-administered IS . In this study, the length of postoperative ICU stay was significantly shorter in the DBE and IS group as compared to the control group. In our data, there was a weak positive relationship between the length of postoperative ICU stay and the length of hospitalisation as well as a weak positive relationship between the length of postoperative ICU stay and AXC duration. AXC duration is an important metric in cardiac surgery. A complication associated with AXC duration is myocardial ischemia. Although hypothermia and cardioplegia solutions are used to prevent this complication, it still remains an important problem . The increased myocardial ischemia from increased AXC durations may lead to increased need for longer ICU stays postoperatively. There are many factors that lead to prolongation of a ICU stay. The results of this study show that the duration of stay in the ICU is shorter in patients in whom DBE with IS was started in the preoperative period. The presumed benefits of DBE and IS of increased respiratory muscle strength and lung capacity in the preoperative period can affect all other systems by increasing oxygenation. This increased oxygenation can lead to reduced length of stays in the ICU and may contribute to shortening the overall hospital stay and recovery period. Decreased oxyhemoglobin saturation level is a common pulmonary complication after CABG surgery . Hypoxia causes deterioration in tissue perfusion. Decreased tissue perfusion leads to tissue hypoxia by disruption of cellular metabolism. Tissue hypoxia leads to decreased perfusion of vital organs and cell death. All body systems are significantly affected by impaired tissue oxygenation . In our study, it was found that the mean pCO 2 levels of the patients in the deep breathing group on the first day in the CVSU and on the day of discharge were significantly lower than those in the control group. Moreover, it was found that the mean SpO 2 values of the patients in the deep breathing group evaluated before surgery, on the first day in the CVSU, as well as on the day of discharge were significantly higher than those in the control group. In a study conducted in patients undergoing CABG, it was found that the duration of dependence on oxygen therapy was shorter in the group receiving preoperative inspiratory muscle training compared to the control group . In another study, it was determined that the incidence of hypoxic events was significantly less in patients who underwent breathing exercises with nurse-guided IS in the postoperative period . In a study conducted with patients who underwent CABG, it was shown that the median of the amount arterial blood oxygen and SpO 2 of patients who underwent DBE with IS before surgery significantly improved than the control group . In another study, it was determined that SpO 2 was higher and RR was lower in patients who performed DBE with IS compared to patients who performed deep breathing alone . The findings of this study are concurrent with the current literature, suggesting that starting DBEs with IS in the preoperative period can provide an increase in oxygenation and a decrease in carbon dioxide levels following surgery. Strengths and limitations of the study This study has several limitations. First, at the time of the study, the COVID-19 pandemic rules were strictly applied, especially for this high-risk group of patients. Pulmonary function tests were not routinely performed at our institution due to COVID-19 restrictions. Additionally, the device that allows bedside pulmonary function testing could not be purchased due to its high cost. Given this set of circumstances, preoperative pulmonary function testing could not be performed and respiratory parameters had to be assessed using RR, arterial blood gas parameters, PA chest X-ray, and SpO 2 values. Second, participants were not blinded in this trial. However, the researcher who performed the randomisation, processed the data, and performed the statistical analysis was blinded. This design is inferior to a double-blind randomised controlled trial because it makes it difficult to control for the placebo effect. Thirdly, since many mechanisms are involved in achieving these functional and clinical improvements, further studies are needed to investigate the timing of IS intervention and its effect on maximum inspiratory/expiratory pressure. This study could not evaluate the effects of other complications such as acute renal failure, atrial fibrillation, and reintubation on the development of PPCs. It would be useful in future studies to investigate these effects in a sufficient sample. Despite these limitations, this study provides evidence that DBEs with IS would be beneficial if started preoperatively in patients undergoing open-heart surgery as opposed to the current standard of care of being initiated in the postoperative period in Turkey. 

This study has several limitations. First, at the time of the study, the COVID-19 pandemic rules were strictly applied, especially for this high-risk group of patients. Pulmonary function tests were not routinely performed at our institution due to COVID-19 restrictions. Additionally, the device that allows bedside pulmonary function testing could not be purchased due to its high cost. Given this set of circumstances, preoperative pulmonary function testing could not be performed and respiratory parameters had to be assessed using RR, arterial blood gas parameters, PA chest X-ray, and SpO 2 values. Second, participants were not blinded in this trial. However, the researcher who performed the randomisation, processed the data, and performed the statistical analysis was blinded. This design is inferior to a double-blind randomised controlled trial because it makes it difficult to control for the placebo effect. Thirdly, since many mechanisms are involved in achieving these functional and clinical improvements, further studies are needed to investigate the timing of IS intervention and its effect on maximum inspiratory/expiratory pressure. This study could not evaluate the effects of other complications such as acute renal failure, atrial fibrillation, and reintubation on the development of PPCs. It would be useful in future studies to investigate these effects in a sufficient sample. Despite these limitations, this study provides evidence that DBEs with IS would be beneficial if started preoperatively in patients undergoing open-heart surgery as opposed to the current standard of care of being initiated in the postoperative period in Turkey. 

The use of deep breathing exercises with IS represents a cost-effective, accessible, and easily applied method for improving postoperative respiratory parameters. In patients who are planned to undergo open heart surgery, the initiation of DBEs with IS in the preoperative period may contribute to a reduction in the incidence of PPCs, the duration of MV, the length of stay in the ICU, the duration of hospitalisation, and an improvement in pre- and postoperative oxygenation. Implication for nursing In patients undergoing open heart surgery, it is crucial to commence DBEs with an IS under the guidance of a nurse in the preoperative period. This approach can enhance respiratory parameters, minimise or avert PPCs, and abbreviate the length of hospitalisation. 

In patients undergoing open heart surgery, it is crucial to commence DBEs with an IS under the guidance of a nurse in the preoperative period. This approach can enhance respiratory parameters, minimise or avert PPCs, and abbreviate the length of hospitalisation. 

Supplementary Material 1 

