Atelectasis

Study objectives: To investigate the effects of deep-breathing exercises on pulmonary function, atelectasis, and arterial blood gas levels after coronary artery bypass graft (CABG) surgery.

Design, setting, and patients: In a prospective, randomized trial, patients performing deep-breathing exercises (n = 48) were compared to a control group (n = 42) who performed no breathing exercises postoperatively. Patient management was similar in the groups in terms of assessment, positioning, and mobility.

Interventions: The patients in the deep-breathing group were instructed to perform breathing exercises hourly during daytime for the first 4 postoperative days. The exercises consisted of 30 slow, deep breaths performed with a positive expiratory pressure blow-bottle device (+ 10 cm [H.sub.2]O).

Measurements and results: Spirometric measurements, spiral CT (three transverse levels), arterial blood gas analysis, and scoring of subjective experience of the breathing exercises were performed on the fourth postoperative day. Atelectasis was only half the size in the deep-breathing group compared to the control group, amounting to 2.6 [+ or -] 2.2% vs 4.7 [+ or -] 5.7% (p = 0.045) at the basal level and 0.1 [+ or -] 0.2% vs 0.3 [+ or -] 0.5% (mean [+ or -] SD) [p = 0.01] at the apical level. Compared to the control subjects, the patients in the deep-breathing group bad a significantly smaller reduction in FVC (to 71 [+ or -] 12%, vs 64 [+ or -] 13% of the preoperative values; p = 0.01) and FE[V.sub.1] (to 71 [+ or -] 11%, vs 65 [+ or -] 13% of the preoperative values; p = 0.01). Arterial oxygen tension, carbon dioxide tension, fever, or length of ICU or hospital stay did not differ between the groups. In the deep-breathing group, 72% of the patients experienced a subjective benefit from the exercises.

Conclusions: Patients performing deep-breathing exercises after CABG surgery had significantly smaller atelectatic areas and better pulmonary function on the fourth postoperative day compared to a control group performing no exercises.

Key words: atelectasis; breathing exercises; cardiac surgery; coronary artery bypass; CT; physical therapy; postoperative care; postoperative complications; thoracic surgery

Abbreviations: BMI = body mass index; CABG = coronary artery bypass graft; FRC functional residual capacity; HU = Hounsfield unit; IC = inspiratory capacity; PEP = positive expiratory pressure; VC = vital capacity

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Atelectasis and arterial hypoxemia are commonly seen after cardiac surgery. Chest physical therapy is widely used postoperatively for the prevention of pulmonary complications.

A variety of treatment techniques are used, and there are differences in the management between countries. In later years, the routine use of breathing exercises after cardiac surgery has been questioned. Breathing exercises combined with physical therapy after coronary artery bypass graft (CABG) surgery have been reported not to be more effective than physical therapy, including early mobilization alone in reducing atelectasis, (1) pneumonia, (2) gas exchange and lung function impairment, (3) or other kinds of pulmonary complications. (4,5) Pasquina et al (6) concluded that evidence is lacking on benefit from any method of prophylactic respiratory physical therapy after cardiac surgery, and that it is more comprehensive than justified by findings of clinical research.

We have shown (7) an immediate effect of a single session of voluntary deep-breathing exercises on atelectasis and oxygenation on the second postoperative day after CABG surgery. Incentive spirometry remains a frequently used technique for the prophylaxis and treatment of respiratory complications in postsurgical patients, but the evidence does not support the use of incentive spirometry for decreasing the incidence of atelectasis and pulmonary complications following cardiac surgery. (1,8,9) The objective of this study was to evaluate the effectiveness of voluntary deep-breathing exercises performed with a positive expiratory pressure (PEP) blow-bottle device on pulmonary function, atelectasis, arterial blood gas levels, and subjective experience in CABG patients compared to a control group who performed no breathing exercises.

MATERIALS AND METHODS

Patients

A sample of 115 patients undergoing CABG surgery at a university hospital were invited to participate in the study. Patients who had an emergency operation, previous cardiac surgery, severe renal dysfunction, or difficulties in cooperating during measurements were not included. Three patients declined participation. The patients were randomized to a deep-breathing group (n = 57) that performed deep-breathing exercises postoperatively and to a control group (n = 55) that performed no breathing exercises. Informed consent was obtained from each patient, and the study was approved by the local research ethics committee.

Surgical and Postoperative Procedure

All patients received general anesthesia, and the CABG was performed with saphenous veins and in most cases the left internal mammary artery. During anesthesia and following surgery, all patients inspired oxygen with a concentration of 40 to 80%. The surgical approach was through a median sternotomy. Cold-blood cardioplegia and occasionally topical cooling of the heart were used. An insulation pad was used to protect the phrenic nerve. The pericardium, the mediastinum and, occasionally one or both pleura were drained, usually < 24 b after surgery. Postoperatively, the patients received mechanical ventilation with a positive end-expiratory pressure of 5 to 10 cm [H.sub.2]O. The patients were extubated when they had resumed normothermia, were hemodynamically stable, had adequate diuresis and no severe bleeding in the drain, and were able to breathe normally without distress, in accordance with the ordinary clinical routines.

Pain

All patients were administered pain relief according to standard routines at the clinic. At the time of the pulmonary function test on the fourth postoperative day, the patients were asked to quantify the pain from the median sternotomy incision. A continuous visual analog scale from 0 (no pain) to 10 (the worst imaginable pain) was used.

Study Groups and Chest Physical Therapy

The day before the operation, or the week before if operated on a Monday, the patients received general information about postoperative routines by one of three physical therapists. All patients received chest physical therapy once or twice daily as normally performed at the clinic during the first 4 postoperative days. Therapy consisted of early mobilization, instructions in efficient coughing techniques, daily active exercises of the shoulder girdle and upper back and instructions, and assistance to turn from side to side and get out of bed. The patients were mobilized as early as possible by the nursing staff. The patients were sitting out of bed and/or standing on the first postoperative day, walked in the room or a short distance in the corridor on the second day, and walking a longer distance in the corridor on the third postoperative day. On the third and fourth postoperative days, the patients participated in a sitting group exercise program.

The patients in the deep-breathing group were informed and practiced the breathing technique preoperatively. The exercises were started approximately 1 h after extubation, and the patients were encouraged to perform 30 deep breaths once per hour when awake (in daytime) for the first 4 postoperative days. The exercise included three sets of 10 deep breaths with a 30- to 60-s pause between each set. If needed, the patients were asked to cough during the pause to mobilize secretions. The patients were instructed to perform the deep breathing in the sitting position, if possible. A 50-cm plastic tube (1 cm in internal diameter) in a bottle containing 10 cm of water (the "blow-bottle") was used to create an expiratory resistance of + 10 cm [H.sub.2]O. If the patient initially was unable to expire through the tube, a PEP/respiratory muscle training facemask (Astra Tech AB; Molndal, Sweden) was used to create the expiratory pressure. One of three experienced physical therapists supervised the breathing exercises, and the patients were instructed to perform slow maximal inspirations, while expiration was aimed to end approximately at functional residual capacity (FRC) to minimize airway closure and alveolar collapse. Compliance with treatment was documented in the patient record until the morning of the second postoperative day, and after that it was self-reported. The patients in the control group were not instructed to do any breathing exercises.

Measurements

Pulmonary function measurements were performed preoperatively and on the fourth postoperative day (Jaeger MasterScreen PFT/Bodybox; Spiropharma Cardiopulmonary Diagnostics; Klampenborg, Denmark) with proprietary software. The equipment was calibrated every morning prior to measurements. Six medical laboratory technicians who were unaware of the patient's randomization performed the tests. The patients were in a sitting position, and a nose clip was used. Predicted values for pulmonary function were related to age, sex, and height according to the values reported by Quanjer et al. (10) Spirometry was performed according to the recommendations of the European Respiratory Society. The highest value of three technically satisfactory maneuvers was retained. First an inspiratory maneuver was obtained for measurement of vital capacity (VC). Then measurements of FVC and FE[V.sub.1] were performed, followed by recording of the inspiratory capacity (IC) and FRC. Total lung capacity (TLC) was calculated as FRC + IC.

Atelectasis and aeration of the lungs were assessed by spiral CT (Philips CT Secura; Philips Medical Systems; Eindhoven, the Netherlands) (11,13) on the fourth postoperative day. The patients were transported to the Department of Radiology in a wheelchair. One radiologist and one radiographer who were blinded to study group assignments made all measurements. The patients lay in the supine position with their arms raised above their heads, and the examination was made during apnea at FRC. First, a frontal scanogram covering the chest was obtained for positioning. The scan time was 9 s for a 12-cm volume scan at 280 mA and 120 kV. Slice thickness was 1.0 cm, and a matrix of 512 x 512 elements was used. The total estimated effective dose was 1.5 millisieverts. Three of the CT scans were used for subsequent analysis, positioned 1 era, 5 cm, and 9 cm above the top of the right diaphragm. A radiologist delineated the lung area manually from the inner margins of the thoracic cage, excluding pleural fluid and tissue between the ribs, mediastinum, or any part of the diaphragm. The computer identified the border between inflated lung tissue and atelectasis. Aerated lung area was defined as volume elements with attenuation values between - 100 Hounsfield units (HU) and - 1,000 HU, and atelectasis was defined as values between + 100 and - 100 HU. (12,14) The most eephalad point of the diaphragm was determined in relation to the carina.

Arterial blood gas measurements were done before induction of anesthesia and on the fourth postoperative day for blood gas analysis (Radiometer ABL .505; Inter Bio-Lab; Orlando, FL). The patients had been without supplementary oxygen for [greater than or equal to] 15 min.

Body temperature was measured preoperatively and on postoperative days 1, 2, 3, and 4. On the fourth postoperative day, the patients in the deep-breathing group were asked to score their subjective benefit and/or discomfort of the breathing exercise on an arbitrary scale.

Statistical Analysis

All data were collected and analyzed in a statistical computer program (StatView; Abacus Concepts; Berkeley, CA) and presented as mean values [+ or -] SD. Baseline data were compared by unpaired t test or by [chi square] test. The relative decrease in pulmonary function after the operation, the atelectatic area, and arterial blood gases were compared by an unpaired t test. Including 45 patients per group would yield 80% power ([alpha] = 0.05) to detect a decrease from 2.5 to 1.9% (percentage reduction, 20 to 25%) in bilateral atelectatic area in percentage of total lung area between groups, assuming a SD of 1.0%. This difference is assumed by the authors to be of clinical relevance. Dropout was anticipated to be up to 20% and hence another 10 patients were included in each group. All results refer to two-sided tests, and p < 0.05 was considered significant.

RESULTS

Five women and 17 men (mean age [+ or -] SD, 68 [+ or -] 11 years) were excluded for various reasons, as reported in Table 1. In total, 90 patients (23 women and 67 men) were investigated. Demographic (Table 2) and surgical (Table 3) data did not significantly differ between the two groups. Pain from the sternotomy did not differ between the two groups. Mean value for the visual analog scale at rest was 1.4 [+ or -] 1.6 cm; while taking a deep breath, 2.5 [+ or -] 2.1 cm; while coughing, 4.3 [+ or -] 2.8 cm; and during pulmonary function testing, 2.4 [+ or -] 2.2 cm. No significant differences in length of ICU stay (deep-breathing group, 17.9 [+ or -] 5.3 h; control group, 18.8 [+ or -] 4.0 h), postoperative hospital stay (5.5 [+ or -] 2.8 days vs 5.3 [+ or -] 2.6 days), or fever (mean value for the 4 postoperative days, 37.5 [+ or -] 0.3[degrees]C vs 37.6 [+ or -] 0.4[degrees]C) were noticed. None of the patients had signs of pneumonia during the hospital stay. One of the excluded patients received antibiotics because of a sternal infection.

Pulmonary Function

The preoperative lung function showed a VC at or below - 2 SD in five patients in the treatment group and one patient in the control group. There was no significant difference between the two groups. On the fourth postoperative day, the patients in the deep-breathing group had a significantly smaller reduction in FVC, down to 71 [+ or -] 12% of the preoperative value, than patients in the control group (64 [+ or -] 1.3%; p = 0.01). Similarly, FE[V.sub.1] was reduced less in the deep-breathing group than the control group, to 71 [+ or -] 11% vs 65 [+ or -] 13% of the preoperative values (p = 0.01; Fig 1).

[FIGURE 1 OMITTED]

Atelectasis

Four days after CABG surgery, all examined patients had signs of atelectasis (missing data in the treatment group [n = 11] and in the control group [n = 6] because of technical and scheduling difficulties). The atelectatic area was largest at the basal level, close to the diaphragm, and minor at the upper level, near the apex. A significantly smaller atelectatic area in the deep-breathing group, of one half the size, compared to the control group (p < 0.05) was found at the basal and apical levels. The mean values from both lungs at the three CT levels are shown in Table 4, and examples of CT scans are shown in Figure 2. The amount of atelectasis at the basal level (in percentage of the total lung area) correlated to FE[V.sub.1] on the fourth postoperative day (r = -0.32, [r.sup.2] = 0.10, p < 0.01) as well as to the postoperative relative decrease in FE[V.sub.1] (r = -0.37, [r.sup.2] = 0.14, p < 0.01). Patients with a body mass index (BMI) > 30 (n = 19) had the same amount of atelectasis as those with a BMI < 30; there no significant differences in the results of breathing exercises between the groups. The distance between the diaphragm and the carina did not differ between the treatment group (7.8 [+ or -] 1.6 cm in the right lung and 9.9 [+ or -] 1.3 cm in the left lung) and in the control group (7.9 [+ or -] 1.6 cm and 9.2 [+ or -] 1.8 cm, respectively).

[FIGURE 2 OMITTED]

Arterial Blood Gas Levels

No significant differences in Pa[O.sub.2], arterial oxygen saturation, or PaC[O.sub.2] between the two groups were found (Table 5).

Subjective Experience and Self-Report of the Breathing Exercises

All 46 patients (2 patients with missing data) in the deep-breathing group answered that the breathing technique was easy to perform. Of these, 33 patients (72%) experienced a subjective benefit of the exercises, 2 patients found no benefit, and 11 patients had no opinion. Only five patients experienced discomfort during the exercises. The patients answered that they had performed the deep-breathing exercises 7 [+ or -] 2 times per day (range, 2 to 12 times per day) postoperatively and that each session had consisted of 25 [+ or -] 8 breaths (range, 8 to 30 breaths).

DISCUSSION

In the present investigation, it was found that chest physical therapy including deep-breathing exercises significantly decreased atelectasis and improved spirometry values compared to a regime without breathing instructions following CABG surgery. Atelectasis on the fourth postoperative day was decreased by one half compared to the control group. The amount of atelectasis in the lungs expressed in percentage of the total transverse lung area was less in the present study (2 to 5% just above the diaphragm) than in a study (7) performed on the second postoperative day (10 to 12%) after CABG surgery. A decrease of atelectasis during the succeeding postoperative days has been shown after abdominal surgery, (15) and a similar spontaneous recovery after cardiac surgery could be expected. Another possible explanation could be better preservation of pulmonary function because of shorter operation and extracorporeal circulation time in the present study.

However, between the two groups we saw no difference in ICU or hospital stay, and there were no records of pulmonary infection in any patient. It must be clear that the study was not designed to evaluate clinical outcome: the material was too small and limited by the inclusion of CT in the study. Atelectasis could be a reason for pneumonia, but the diagnosis should be based on the presence of clinical signs and symptoms of pneumonia coupled with the identification of pathogenic bacteria, rather than radiographic identification of atelectasis. (16,17)

Despite the common use of breathing exercises in the management of CABG patients in many countries, scientific evidence for the efficacy of this treatment has been lacking. (1,4,5,9) The physical therapy treatment has even been considered to cause adverse effects and costs only. (6)

In a previous investigation, (7) we showed an immediate decrease in atelectatic area and an increase in oxygenation after a session of 30 deep breaths performed on the second postoperative day after CABG surgery. The effect was achieved by just one series of deep breathing; however, no significant differences between patients performing the breathing with or without a PEP device were present. In the present investigation, we examined deep breathing performed with a blow-bottle device because it is the standard technique at the university hospital where the study took place. The focus was to facilitate deep breaths, and the patients were instructed to perform maximal slow inspirations. The expiration was relaxed, and an expiratory pressure of 10 cm [H.sub.2]O was achieved if the patients were breathing out correctly. It is possible that the same results could have been obtained even without using the blow-bottle device. (7)

The patients were encouraged to perform the deep-breathing exercises once per hour throughout the day. The frequency (three sets of 10 breaths) was chosen according to the ordinary routines at the clinic. Compliance with the suggested exercises was not objectively measured, but it was self-reported by the patients in the deep-breathing group. The reported number of exercise sessions performed each day might be considered acceptable and is in accordance with what one can achieve in a clinical situation. At present, it is not known if increasing the frequency and intensity of the exercises is likely to be more efficacious. All patients found the breathing technique easy to perform, and most of the patients experienced a subjective benefit of the exercises; this is important for completion of the treatment.

In our study, pulmonary function measurement was performed preoperatively and repeated on the fourth postoperative day. A marked reduction in lung volumes was present on the fourth postoperative day, which was of the same extent as found in previous investigations after CABG surgery. (18-20) A slightly better preservation of spirometric variables was also seen in the deep-breathing group compared to the control group on the fourth postoperative day; however, the effect on atelectasis was more obvious than the spirometric results. However, a correlation was found between atelectasis and worsening in FE[V.sub.1], similar to a previous study (15) on postoperative atelectasis after abdominal surgery.

CT can give reliable measurement of atelectasis, but it is worth noting that up to this time CT has not been used in the evaluation of prophylactic chest physical therapy following cardiac surgery. Clear effects of deep breathing on pulmonary function parameters after cardiac surgery have earlier not been documented, and this could possibly be explained by the choice of outcome measures. Studies including control group patients who did not receive chest physiotherapy at all have been limited, (3,4) and none of these studies have shown benefits from treatment regimens. Even though our patients were seen by a physical therapist daily and were instructed in active exercises and mobilized early, the patients in the deep-breathing group still had better pulmonary function and smaller atelectatic areas.

A weak correlation between atelectatic areas and Pa[O.sub.2] has earlier been presented, (7) but in the present study no significant difference in oxygenation was apparent between the deep-breathing group and the control group. Recruited lung tissue is most likely converted from a shunt region to a zone with low ventilation in relation to perfusion, still contributing to poor oxygenation of blood. (21,22) Arterial oxygenation is also influenced by nonpulmonary factors such as mixed venous oxygen tension or cardiac output and efficiency of hypoxic pulmonary vasoconstriction. (23)

It should also be emphasized that atelectasis is a locus for inflammation. A variety of signs and symptoms can identify a postoperative pulmonary complication. The presence of atelectasis in combination with other chosen factors is often a criterion for the definition. Whether a reduced amount of atelectasis can decrease postoperative lung complications, if atelectasis is not considered a complication, remains to be tested.

CONCLUSION

Patients who performed deep-breathing exercises after CABG surgery showed a significantly smaller amount of atelectasis and had less reduction in FVC and FE[V.sub.1] on the fourth postoperative day compared to patients who performed no breathing exercises.

ACKNOWLEDGMENT: We thank the staff at the Departments of Cardiothoracic Surgery, Physiotherapy, and Clinical Physiology for support and measurements, and Martin Gustavsson, Department of Radiology, Orebro University Hospital, for performing all CT measurements.

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* From the Department of Medical Sciences, Clinical Physiology (Drs. Westerdahl and Hedenstierna) and Department of Neuroscience, Section of Physiotherapy (Dr. Lindmark), University Hospital, Uppsala; the Departments of Cardiothoracic Surgery (Dr. Friberg) and Radiology (Dr Eriksson), Orebro University Hospital, Orebro; and the Department of Cardiothoracic Anesthesia (Dr Tenling), Karolinska University Hospital Huddinge, Sweden.

This study was supported by financial grants from the Heart and Lung Patients National Association, Sweden: the Karolinska Institute, Stockholm; the Research Committee of Orebro County Council, Orebro: and the Swedish Heart Lung Foundation and Uppsala University.

Manuscript received July 9, 2004; revision accepted June 9, 2005.

Reproduction of the article is prohibited without written permission from the American College of Chest Physicians (www.chestjournal. org/misc/reprints.shtml).

Correspondence to: Elisabeth Westerdahl, RPT, PhD, Department of Physiotherapy, Orebro University Hospital, SE-701 85 Orebro, Sweden; e-mail: elisabeth.westerdahl@orebrull.se

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