Incentive spirometry with expiratory positive airway pressure reduces pulmonary complications, improves pulmonary function and 6-minute walk distance in patients undergoing coronary artery bypass graft surgery

Article Outline

• Abstract
• Methods
  • Patients and design
  • Preoperative assessment
  • Randomization, intervention, and follow-up
  • Primary outcome measures
    • Respiratory muscle strength
    • Lung function
    • Six-minute walk test
    • Chest x-ray
  • Statistical analysis and sample size
• Results
  • Patients and baseline characteristics
  • Primary outcomes
    • Respiratory muscle strength
    • Pulmonary function
    • Six-minute walk test
    • Chest x-ray
  • Secondary outcomes
    • Length of hospital stay
• Discussion
• References
• Copyright

Background

The use of the incentive spirometry (IS) with expiratory positive airway pressure (EPAP) to prevent postoperative pulmonary complications (PPC) after coronary artery bypass graft (CABG) is not well established. This study sought to determine the effects of IS + EPAP after CABG.

Methods

Thirty-four patients undergoing CABG were randomly assigned to a control group or IS + EPAP group. Maximal respiratory pressures, pulmonary function test, 6-minute walk test and chest x-ray were performed at baseline as well as 1 week and 1 month after CABG.

Results

Maximal inspiratory pressure was significantly higher in the IS + EPAP group compared to controls at both 1 week and 1 month (P < .001). Maximal expiratory pressure was significantly higher at 1 month compared to 1 week in IS + EPAP group (P < .01). At 1 month, forced vital capacity and forced expiratory volume in 1 second was significantly higher in IS + EPAP compared to controls (P < .05). Inspiratory capacity was higher at 1 month in IS + EPAP group compared to controls (P < .05). The distance walked in 6-minute walk test was higher at 1 month in IS + EPAP group (P < .001) compared to controls. Lastly, radiological injury score at 1 week was lower in IS + EPAP compared to controls (P < .004).

Conclusions

In patients undergoing CABG, IS + EPAP results in improved pulmonary function and 6-minute walk distance as well as a reduction in PPC.

Coronary artery bypass graft (CABG) surgery is performed daily on a worldwide basis in patients with coronary artery disease. Despite advances in anesthesia protocols,¹ cardiopulmonary bypass techniques² and pre and postoperative care,³ CABG is still associated with the frequent development of postoperative pulmonary complications (PPC).⁴ The incidence of PPC will most likely continue to remain problematic⁵ secondary to CABG procedures being more frequently performed in patients with multiple comorbidities.⁵ In addition, perioperative factors such as the reduction in functional residual capacity,⁶ pulmonary gas exchange,⁷ and cough strength as well as the increase in pleural effusion, pain with breathing, and retention of secretions all contribute to increased PPC risk.⁸ Postoperative pulmonary complications are particularly concerning given its link to increased patient morbidity and mortality and resource utilization.⁵, ⁹, ¹⁰

Respiratory physiotherapy has been proposed to improve lung function and prevent or treat pulmonary complications in the postoperative period of CABG. Incentive spirometry (IS) is currently used with the intention to PPC prevention.¹¹ Earlier studies have compared the effect of different respiratory physiotherapy interventions, such as breathing and coughing exercises, incentive spirometry, and expiratory positive airway pressure (EPAP), on PPC after CABG.¹², ¹³ Recently, 2 systematic reviews concluded there is no conclusive evidence indicating that patients undergoing CABG benefit from respiratory physiotherapy¹⁴ or incentive spirometry.¹⁵ However, the past investigations in this area were typically performed in small cohorts and possessed methodological limitations such as poor control of confounding factors. In addition, most of these studies included patients at low risk for postsurgical complications and did not perform adequate follow-up. Several recent, well-controlled, studies have demonstrated beneficial effects of respiratory physiotherapy in patients at higher risk for developing PPC.⁹, ¹⁶, ¹⁷ As a result of the lack of consistent positive evidence, respiratory physiotherapy for patients undergoing CABG remains controversial. Clearly more work, expanding upon traditional respiratory physiotherapy treatment approaches, is needed in this area of research. To our knowledge, there are no published studies related to use of incentive spirometry in combination with expiratory positive airway pressure after CABG. An application of expiratory positive airway pressure can promote collateral ventilation, prevent airway collapse during expiration and thus reduce gas trapping and enhancing airway secretion clearance.

We therefore conducted a randomized controlled clinical trial with 1 month follow-up to test the hypothesis that the combination of IS and EPAP (IS + EPAP) will result in reduced PPC and improved pulmonary function and 6-minute walk distance in patients undergoing CABG.

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Methods 

Patients and design 

This study was a prospective, controlled, randomized clinical trial conducted in patients undergoing CABG at the Hospital de Clínicas de Porto Alegre (HCPA, Porto Alegre, Rio Grande do Sul, Brazil). Entry criteria for the study were a previous history of tobacco use, >50 years of age, and use of mammary artery graft. To minimize the potential impact of comorbidities, exclusion criteria consisted of chronic heart failure, diabetes mellitus, peripheral neuropathy, obesity (body mass index ≥30 kg/m²), neurologic, or musculoskeletal diseases. Patients that required mechanical ventilation for >24 hours or reintubation were also excluded from the study. In all patients, the surgical approach was through a median sternotomy, with cardiopulmonary bypass, and the postoperative routine was the same. The protocol was approved by the Committee for Ethics in Research of the HCPA and all subjects signed an informed consent form.

Preoperative assessment 

Demographic and preoperative risk factors, clinical history, and presence of symptoms were recorded by means of a standardized interview. Spirometry, body pletismography, chest x-ray, respiratory muscle function testing, and 6-minute walk test (6-MWT) were also performed. All included patients were closely monitored daily during their entire hospital stay until discharged.

Randomization, intervention, and follow-up 

The patients were assigned to undergo IS + EPAP or usual care (control group) by a computer-generated randomization table. The patients in the IS + EPAP group were submitted to a protocol, with the use of incentive spirometry associated with EPAP. The control group received only instructions about coughing technique, early mobilization, and deep breathing exercises. Two hours after extubation, the intervention group started the IS + EPAP protocol consisting of breathing exercises, using an incentive volumetric spirometry (Voldyne 5000, Salt Lake City, UT) associated to the EPAP (Vital Signs, Totowa, NJ) simultaneously. The intervention group trained twice a day (15-20 minutes per session) everyday of the week under the supervision of a physical therapist. During the IS + EPAP protocol, patients were instructed to maintain diaphragmatic breathing, at a rate of 12 to 18 breaths per minute. The expiratory pressure was increased progressively in the following fashion: days 1 and 2, 5 cm H₂O; day 3, 6 cm H₂O; days 4 and 5, 8 cm H₂O; days 6 and 7, 10 cm H₂O; and on the days after hospital discharge, 15 cm H₂O. After hospital discharge, the IS + EPAP group received their equipment to continue the protocol at home, twice each day, 15 minutes each session, without supervision. To monitor protocol compliance and performance, patients were contacted by phone on a weekly basis.

Primary outcome measures 

All patients underwent the same evaluation procedures in the preoperative period as well as 1 week and 1 month after CABG. All tests were performed by investigators blinded to study group assignment.

Respiratory muscle function testing was performed using a pressure transducer (MVD-500 V.1.1 Microhard System, Globalmed, Porto Alegre, Rio Grande do Sul, Brazil), connected to a system with 2 unidirectional valves. Maximal inspiratory pressure (MIP) was determined by deep inspiration from residual volume against an occluded airway with a minor air leak (2 mm), preventing undesirable glotic closure. Measurement of maximal expiratory pressure (MEP) consisted of slow inspiration to the point of total lung capacity, followed by a forced expiration against a closed circuit.

Lung function was measured by a spirometric computerized test (Eric Jaeger GmbH, Wüerzburg, Germany) and body pletismography test (Master Screen Body, Jaeger, Germany). The values are expressed as absolute and predicted as recommended by the American Thoracic Society.¹⁸

The maximum distance covered during a standardized walk test was used to assess submaximal functional capacity.

Chest x-ray analysis were done by radiologists in the radiology department of the HCPA. The presence of atelectasis, pleural effusion, and/or lung consolidation were quantified through the score of 0 to 4, as previously described.²

Statistical analysis and sample size 

Statistical analysis assessed between- and within-group differences, with intention-to-treat basis. To detect a minimum difference of 15% in the forced vital capacity among the IS + EPAP group and the control group, with a probability of error type II of 20% (β = .2) and error type I of 99% (α = .01), 20 patients were required in each group. After an interim analysis, the study was interrupted with 17 patients in each group. The data were initially plotted in Excel spreadsheets (Microsoft Corp, Redmond, WA [XP version]) and converted into either SPSS (version 14.0, SPSS, Chicago, IL) or Graph Pad format (Graph Pad Prism, version 4.0, San Diego, CA) for statistical analysis. Continuous data with a normal distribution were expressed as mean ± SD. Nonparametric variables are expressed in median and percent values. The basal data between the groups were analyzed with the Student t test for independent samples. The effect of the intervention on continuous variables were compared by 2-way analysis of variance (ANOVA) for repeated measures, and post-hoc analysis was conducted by the Student-Newmann-Keuls test. Nonparametric data were compared through the Mann-Whitney U test. All differences with a P value ≤.05 were considered significant.

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Results 

Patients and baseline characteristics 

From January of 2005 to January of 2007, 194 patients with ischemic heart disease were screened. Forty-three patients met entry criteria and were selected for the study. Nine patients were excluded (1 death due to stroke; 1 myocardial infarction, 2 reintubations; 1 developed symptoms of psychomotor disturbance, 1 had extensive subcutaneous emphysema, 1 had mediastinitis, and 2 patients did not return for the 1-month evaluation). Therefore, 34 patients were included in the final analysis: 17 in the control group and 17 in the IS + EPAP group (Figure 1). Their general baseline characteristics are summarized in Table I. There are no differences in baseline characteristics between groups. Likewise, the patients in both groups received the same surgical and anesthetic protocol. All patients received a left internal mammary artery graft with pleural opening. Beyond the 2 daily supervised sessions, patients carried out an average of 2 additional unsupervised sessions. Furthermore, no patient in the IS + EPAP experienced any adverse effects during the protocol. Both groups had a similar treatment regimen, prescribed by medical staff in accordance to standard intensive care unit guidelines for the postoperative period of CABG.

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• Figure 1. 

  Flow of participants in the study.

Table I. Patients' characteristics at study entry

Values are expressed as mean ± SD. FVC, Forced vital capacity; FEV₁, forced expiratory volume in 1 second.

Primary outcomes 

The inspiratory muscle strength at 1 week and 1 month after CABG was significantly higher in the IS + EPAP group compared to controls (P < .0001, for the interaction and time effects, Figure 2, A). In contrast, in the control group, MIP remained significantly decreased at both 1 week and 1 month compared with the preoperative measurement (P < .05, Figure 2, A). Expiratory muscle strength was reduced in both groups 1 week after CABG. However, the IS + EPAP group demonstrated a better recovery from 1 week to 1 month of the postoperative period (P < .01, Figure 2, B). In the control group, MEP was still reduced at 1 month post CABG compared to baseline (P < .05, Figure 2, B).

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• Figure 2. 

  Values are expressed as mean ± SD. Intervention group (IS + EPAP) and control group. A, *IS + EPAP group versus control group (P < .001); ^†One week versus baseline in the control group (P < .05); **One month versus baseline in the control group (P < .05). B, *One week versus baseline in IS + EPAP (P < .01) and 1 week versus baseline in control group (P < .001); ^†One month versus 1 week (P < .01); **One month versus baseline (P < .05). Two-way ANOVA for repeated measures and Student-Newmann-Keuls as post hoc.

Pulmonary function decreased significantly after CABG in both groups (Table II and Figure 3). There was no significant difference between groups at 1 week after CABG (Figure 3). However, the IS + EPAP group demonstrated improvement in pulmonary function at 1 month post CABG compared with baseline (Figure 3, A and B). In the control group, however, pulmonary function did not recover completely at 1 month post CABG (P < .05 for the interaction and time effects). Likewise, recovery of inspiratory capacity (Figure 3, C) was better in the IS+EPAP group compared to the control group at 1 month post CABG (P < .0002 for the interaction and time effects). Furthermore, inspiratory capacity remained significantly reduced 1 month post CABG in the control group compared with the baseline (P < .05, Figure 3, C). Similarly, there was a significant reduction in total lung capacity (TLC) compared to baseline at the 1 week postoperative assessment in both groups. After 1 month, TLC in IS + EPAP group returned to baseline values, whereas in the control group, the values remains significantly reduced at 1 month (Table II). In addition, the lung diffusion capacity of the carbon monoxide (DLCO) was lower in control group compared with IS + EPAP group at 1 month post CABG (P < .001 for the interaction and time effects). The DLCO values between baseline and 1 month assessments were similar in IS + EPAP group (Figure 3, D). There were no differences between groups in peak expiratory flow, residual volume, functional residual capacity, and airway resistance at the 1-week and 1-month postoperative evaluation (Table II).

Table II. Pulmonary function test

Values are expressed as mean ± SD. PEF, Peak expiratory flow; FRC, functional residual capacity; R, resistance.

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• Figure 3. 

  Values are expressed as mean ± SD. Intervention group (IS + EPAP) and control group. A, FVC, Forced vital capacity. B, FEV₁, Forced expiratory volume in 1 second. *One week versus baseline in both groups (P < .01; ^†IS + EPAP group versus control group at 1 month (P < .05); **One month versus baseline in the control group (P < .05). C, IC, inspiratory capacity, *One week versus baseline in both groups (P < .001); ^‡IS + EPAP group versus control group (P < .05); ^†One month versus 1 week (P < .05); **One month versus baseline (P < .05). D, *One week versus baseline in both groups (P < .001); **One month versus 1 week (P < .001); ^†One month versus baseline (P < .05). Two-way ANOVA for repeated measures and Student-Newmann-Keuls as post hoc.

Functional capacity assessed by the distance covered during the 6-MWT was higher in IS + EPAP group at both the 1 week and 1 month postoperative evaluation compared with the control group (P < .0001 for the interaction, time, and group effects) (Figure 4, A).

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• Figure 4. 

  Values are expressed as mean ± SD. Intervention group (IS + EPAP) and control group. A, 6-MWT, distance covered in 6-MWT on baseline, 1 week and 1 month after CABG. *IS + EPAP group versus control group (P < .0001); ^†One week versus baseline in control group (P < .001). Two-way ANOVA for repeated measures and Student-Newmann-Keuls as post hoc. B, Score of pulmonary alterations in chest x-ray 1 week after CABG, *IS + EPAP group versus control group (P < .0004, Mann-Whitney U test).

Chest x-rays, evaluated 1 week after CABG, showed that the score indicating with the presence of lung radiological alterations was significantly lower in IS + EPAP group compared to controls (P < .0004, Figure 4, B).

Secondary outcomes 

The duration of postoperative hospitalization was higher in the control group compared with the IS + EPAP group (7.47 vs 7 days, P < .002). In addition, 4 patients of the control group developed pneumonia, whereas no patient in the IS + EPAP group was diagnosed with this condition (P < .001).

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Discussion 

To the best of our knowledge, this is the first randomized, controlled clinical trial assessing the efficiency of IS in conjunction with EPAP. The main results of the present study is the demonstration that the use of IS + EPAP restores respiratory muscle strength, reduces PPC and improve functional capacity 1 month after CABG. It is noteworthy that patients in both groups were submitted to a similar anesthesia and surgical procedure. In addition, the vessels used for bypass, level of ischemia as well as mechanical ventilation and intubation times were similar. Moreover, the amount of analgesics, anti-inflammatory and diuretics administered to patients were not different, minimizing confounding factors that may have influenced the results of the present study.

Respiratory muscle dysfunction after CABG surgery may lead to alveolar hypoventilation due to a reduction in tidal volume, vital capacity, and total lung capacity. Few studies designed to test the respiratory muscle strength and endurance after CABG have been published.⁸ Surgical trauma, internal mammary artery dissection, the presence of chest tubes for pleural and mediastinum drainage, and pain¹⁹, ²⁰ can all contribute to respiratory muscle dysfunction during the postoperative period. In the present study, there was a 26.4% reduction in MIP and 26.9% reduction in MEP in the control group 1 week after CABG. Conversely, in the IS + EPAP group, the reduction in MIP and MEP was only 15.5% and 18.2%, respectively. Moreover, we found a complete recovery of respiratory muscle strength in the IS + EPAP group 1 month after CABG, whereas in the control group, muscular strength was still reduced (25.5% for MIP and 15.8% for MEP). A recent study have shown that respiratory muscle training is associated with a significant recovery of the respiratory muscle strength and that this recovery is directly related to the improvement of the pulmonary function,⁹ with a reduction of pulmonary complications and length of hospital stay.⁹ Although the present study was not designed to increase force production of the respiratory musculature, the use of an incentive spirometry, which, through visual feedback stimulates maximum sustained inspiration, coupled with positive expiratory pressure in the airway, which is related with alveolar recruitment and lung reexpansion, may induce respiratory muscle training, as demonstrated by the increase in MIP and MEP.

In our study, a marked reduction (20%-27%) in lung function was present on the 1 week postoperative evaluation in both groups, which is consistent with previous findings.¹⁶, ²¹, ²² Regarding pulmonary function, the main positive result of the present study, was obtained 1 month after CABG. In our study, the IS + EPAP group demonstrated a complete recovery in functional vital capacity, forced expiratory volume on first second, inspiratory capacity, and DLCO at the 1-month postoperative evaluation. In contrast, the control group did not show a complete recovery in pulmonary function variables at 1 month, remaining 10% to 26% lower compared to baseline values. A significant restrictive pulmonary impairment, persisting up to 4 months after CABG has been previously reported.²³ Furthermore, persistent respiratory asymmetry was found 3 months after CABG.²⁴ Therefore, the aforementioned data and the results of the present report, supports the hypothesis that IS + EPAP after CABG, facilitates a complete recovery of the lung volumes and capacities 1 month after surgery, which may be associated with a significant reduction in PPC and resource utilization.

Patients who participated in IS + EPAP presented with a better recovery in functional capacity 1 month after CABG, as shown by >70 m increase in distance covered during 6-MWT, which is considered clinically important to the patients.²⁵ In addition, we demonstrated a 23.5% reduction of distance covered during 6-MWTin the control group 1 week after CABG. In contrast, the IS + EPAP group demonstrated a smaller reduction (12.5%) in distance covered at the 1-week assessment. Furthermore, there was an additional increase (32%) of the distance covered at the 1-month assessment compared to the 1 week assessment in the IS + EPAP group, whereas in the control group, the distance covered was 7% below the baseline assessment at 1 month post CABG. These results indicate that IS + EPAP may be associated with an improvement in functional capacity after CABG.

Chest x-ray alterations observed during the postoperative period of CABG is associated with modifications in lung volume and capacity, as previously discussed. In patients undergoing CABG, IS + EPAP resulted in a significant reduction in atelectasis, pleural effusion, and pulmonary consolidation, which is consistent with other studies.¹⁷, ²⁶ In the present study, 64.7% of the patients in control group showed atelectasis, and 23.52% had pulmonary consolidation on the day of the hospital discharge, whereas in the IS + EPAP group, atelectasis incidence was lower (29.41%) and there was no occurrence of pulmonary consolidation. Presence of atelectasis, contributes to post surgical pulmonary dysfunction, diminishing of lung compliance and gas exchange, leading to hypoxemia.²⁷ The lower incidence of chest x-ray alterations through IS + EPAP use may be secondary to a lower incidence of pulmonary infections. In the present study, 23.5% of patients in the control group developed pneumonia, requiring treatment with antibiotics. In contrast, in the IS + EPAP group, there were no cases of lung infection. An increase in the lung volume during the inspiration (IS) and, at the same time, an increase in the lung volume at the end of the expiration (EPAP) may have resulted in increased alveolar ventilation, thereby reducing the incidence of atelectasis. Moreover, in our study, length of hospital stay was reduced in the IS + EPAP group compared to controls. The higher length of hospital stay in control group may have been secondary to a higher incidence of pulmonary infections and the use of antibiotics, increasing resource use in these patients.

Generalization of our findings may be restricted because of inherent study limitations. To better ensure the likelihood of homogeneity between the intervention and control groups, subjects with chronic heart failure, diabetes mellitus, peripheral neuropathy, obesity, and neurologic or musculoskeletal diseases were excluded. Extrapolation of our findings to patients with these comorbidities is therefore not recommended. Furthermore, because of the difficulty in the sampling, the patients included in this study did not have severe lung disease. However, ex-smokers and active smokers were included. Lastly, at the moment of hospital discharge, all individuals showed some difficulty in walking, secondary to the graft incision in 1 of the lower limbs. This may limit the performance during the walking test. Finally, during the fulfillment of the protocol after hospital discharge at the patient's home, we were not able to personally supervise the IS + EPAP protocol. Even so, patients reported excellent compliance with IS + EPAP during the weekly phone calls.

In conclusion, this randomized, controlled trial demonstrated that IS + EPAP results in faster recovery of inspiratory muscle strength, lung function and functional capacity after CABG. Moreover, we found that IS + EPAP administered to patients undergoing CABG is associated with diminish postoperative pulmonary alterations by chest x-ray, pneumonias, and length of hospital stay. Future investigations should be directed toward confirming our findings and expanding this area of research. Because of the simplicity of and low risk associated with IS + EPAP use, we consider this to be an important intervention that appears to be effective in improving the clinical outcome in this patient population.

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