Asian Cardiovasc Thorac Ann 1998;6:28-33
© 1998 Asia Publishing EXchange Pte Ltd
Spirometric Changes Following Open-Heart Surgery on Rheumatic Mitral Valves
Abha Chandra, MCh,
Shashi Srivastava, MD1,
Dronamraju Dilip, FRCS
Department of Cardiovascular and Thoracic Surgery
1 Department of Anaesthesiology Sri Venkateswara Institute of Medical Sciences Tirupati, Andhra Pradesh, India
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Abha Chandra, MCh Department of Cardiovascular and Thoracic Surgery Sri Venkateswara Institute of Medical Sciences Tirupati 517507, Andhra Pradesh, India Tel:91 8574 51222 Ext. 2378 or 2289 Fax:91 8574 28803
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ABSTRACT
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Evaluation of pulmonary function by spirometry in adult patients undergoing cardiac surgery is a simple test to assess pulmonary reserve that has important implications in the operative morbidity. Pulmonary function was studied preoperatively, before discharge, and at the 3-month follow-up in 22 randomly selected patients who underwent open-heart surgery for rheumatic mitral valve disease (2 reconstructions, 20 replacements). The mean preoperative cardiothoracic ratio was 0.58. Lung function was found to be impaired preoperatively in all 22 patients and the majority suffered from restrictive lung disease. Better preoperative lung function was seen in nonsmokers, patients with a cardiothoracic ratio of less than 0.50, and those with a normal pulmonary artery pressure. After mitral valve surgery, the mean pulmonary artery pressure was 20.6 ± 2.9 mm Hg, the mean mitral valve pressure gradient was 3.6 ± 2.4 mm Hg, and the mean cardiothoracic ratio was 0.52 ± 0.09. A significant deterioration was seen in the predischarge spirometric values of forced vital capacity, forced expiratory volume in one second, peak expiratory flow rate, flow rate at 25% to 75% of expired vital capacity, and maximum volume ventilation. The deterioration was greater in smokers and those who had prolonged cardiopulmonary bypass (more than 80 minutes). No correlation was found with ventilation because all patients were electively ventilated overnight. There was an overall improvement in spirometric parameters at the 3-month follow-up although the values remained lower than predicted. Spirometry was found to be useful for assessing lung function in patients undergoing mitral valve surgery and we recommended it as a routine test.
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INTRODUCTION
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Pulmonary function tests have been used routinely for decades to predict operative morbidity and postoperative outcome in patients undergoing thoracotomy mainly for lung resection or to assess the degree of respiratory impairment caused by chest deformities such as pectus excavatum.1–3 Most studies of pulmonary function tests in cardiac diseases have concentrated on patients with mitral valve disease who have restrictive ventilatory impairment and abnormal perfusion of the lung.4,5 However, the existing reports of pulmonary function after mitral commissurotomy or mitral valve replacement range from no improvement to significant improvement.6–8 There are studies showing the impact of anesthesia and thoracotomy on lung function, but the adverse effects of smoking and prolonged cardiopulmonary bypass time have not been studied much.9,10 This prompted us to study the spirometeric changes in mitral valve disease in relation to smoking, cardiopulmonary bypass time, and surgical technique.
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PATIENTS AND METHODS
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Eleven male and 11 female patients who underwent open-heart surgery for rheumatic mitral valve disease were randomly selected for this study. The mean age was 33.32 ± 12.14 years (range 14 to 52 years). Six (27%) were smokers. Eighteen (81.8%) were in New York Heart Association (NYHA) functional class III and the other 4 were in class IV. Preoperative congestive cardiac failure was treated in 4 patients and pulmonary hypertension was noted in 16. Patients with a previous history of lung disease or alcoholism were excluded from the study. All patients were receiving digoxin and diuretics. None of the patients was in cardiac failure at the time of surgery. Mitral valve morphologic features included mitral stenosis in 7, mitral regurgitation in 8, and mixed mitral lesions in 7 cases. Tricuspid regurgitation was found in 9 patients but none had evidence of early aortic disease.
PULMONARY FUNCTION TESTS
Pulmonary function tests were carried out using a Spirolite 201 (Vise Medical Co., Tokyo, Japan). The Spirolite 201 analyzes pulmonary function by means of a Fleisch flow sensor and a pressure-differential transducer. It incorporates a microcomputer that processes the measurements and displays the calculated data. Criteria for ventilatory parameters established by the American Thoracic Society were followed.11 The measurements consisted of forced vital capacity (FVC), forced expiratory volume in one second (FEV1), maximum mid-expiratory flow rate at 25%, 50%, and 75% of exhaled vital capacity (MEF 25, MEF 50, MEF 75), peak expiratory flow rate (PEFR) and maximum volume ventilation (MVV). Pulmonary function tests were carried out prior to surgery, at the time of discharge, and at the 3-month follow-up. Reference values of ventilatory parameters described by Rastogi and colleagues12 for the normal Indian population were taken into consideration. Values were expressed as mean ± standard deviation of the measured and the predicted values.
Ventilatory disturbances were categorized into three types: restrictive type (observed values less than 80% of the predicted values); obstructive type (observed vital capacity values more than 80% of predicted values but FEV1: FVC ratio less than 70%); mixed type (observed vital capacity values less than 80% of the predicted and FEV1: FVC ratio less than 70%).13 These were further graded into mild pulmonary impairment (observed values 61% to 79% of predicted), moderate (observed values between 40% and 60% of predicted), and severe (observed values less than 40% of predicted) according to Conrad's criteria.14
SURGERY AND FOLLOW-UP
Mitral valve surgery was performed through a median sternotomy with heparinization under cardiopulmonary bypass using aortic and bicaval cannulation and a bubble oxygenator in 4 cases (Baxter Healthcare Corp., Bentley Laboratories Division, Irvine, CA, USA). A membrane oxygenator was used in 18 cases (Terumo Europe N.V., Leuven, Belgium). A single period of aortic cross-clamping during systemic normothermia was employed in all patients. Myocardial protection was achieved with continuous topical cooling and cold crystalloid cardioplegia administered every 20 minutes through the aortic root. Two patients underwent mitral valve reconstruction. Twenty patients underwent mitral valve replacement; the conventional technique was used in 7 patients and the modified technique with preservation of the posterior mitral leaflet complex was employed in the other 13. Nineteen patients received a Starr-Edwards prosthetic mitral valve model 6120 (Baxter Edwards AG, Horw, Switzerland) and one received a Biomed valve (Biomedica Medicana, S.A., Mexico City, Mexico). Prostheses were seated with interrupted 2/0 pledgetted Ethibond (Ethibond Ltd., Edinburgh, UK) sutures. Concomitant tricuspid valve annuloplasty was carried out in one patient.
Follow-up was conducted every month after discharge for 3 months. Patients were queried on respiratory system symptoms and the degree of breathlessness. Pulmonary function tests were performed at the 3-month follow-up. A chest skiagram (posteroanterior view) was obtained to assess the cardiothoracic ratio. None of the patients underwent repeat surgery during this period.
STATISTICAL ANALYSIS
The measured and the predicted values of the various spirometric parameters were expressed as the mean ± standard deviation. Tests of significance were carried out on pooled t test on data. The paired t test was used to assess the statistical significance of the difference between matched samples.
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RESULTS
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The mean weight was 43.54 ± 7.82 kg, mean height 159.95 ± 8.91 cm, and the mean body mass index was 17.28 ± 3.37 indicating generally poor nutrition in this group of patients. Cardiorespiratory symptoms were present in all and smoking (6 patients) was the only risk factor noted. There was no operative mortality. All patients were electively ventilated for over 14 hours (mean 16.34 ± 1.5 hours; range 16 to 19 hours). Following surgery, there was a decrease in the mean pulmonary artery pressure, mitral valve pressure gradient, and cardiothoracic ratio as seen in Table 1
. There was a significant improvement in mitral valve area and the resting heart rates and systemic arterial pressures were similar before and after surgery. One patient with atrial fibrillation reverted to normal sinus rhythm postoperatively (Table 1).
The pulmonary function tests performed preoperatively were found to be impaired in all cases (Table 2). The majority of patients (16/22) had restrictive changes, obstructive changes were noticed in 4 of the 6 smokers, and 2 patients had mixed pulmonary dysfunction. A further deterioration was seen immediately after surgery in all patients, with an overall improvement at the 3-month follow-up, although the values remained less than predicted (Table 2). The lung function tests returned to normal after surgery in 6 non-smokers (Table 3). Five of these 6 patients were in NYHA functional class I and one was in class II. Significantly better respiratory function was found in nonsmokers (p < 0.05). The immediate postoperative deterioration was worse in the smokers with significant changes in FVC and FEV1. NYHA functional class correlated well with the pulmonary function tests (Tables 4 and 5). One patient in NYHA class III postoperatively had a minimal improvement in most lung function tests at the 3-month follow-up and two patients who persisted in NYHA class IV showed a further deterioration but the findings were not significant. The other patients showed an improvement in lung function parameters at follow-up (Tables 4 and 5).
Overall preoperative pulmonary function tests were found to be better in patients with a cardiothoracic ratio below 0.50. The difference was significant for FVC, FEV1, and PEFR (p < 0.05) as shown in Table 6. There was a significant deterioration in most pulmonary function tests in individuals who were on cardiopulmonary bypass for more than 80 minutes (Table 7). Lung function parameters did not correlate with the surgical procedure and we observed an overall deterioration in the spirometric parameters after both types of surgery. At the 3-month follow-up, an improvement was seen in FVC, FEV1, PEFR, MEF 75, and MVV values in patients who underwent mitral valve replacement with preservation of the posterior mitral leaflet but these changes were not significant. Patients who underwent mitral valve replacement by the conventional technique had a reduction in these parameters.
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DISCUSSION
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The severity and duration of pulmonary hypertension and its organic sequela determine the degree of pulmonary impairment in patients with mitral stenosis.5 The subjective improvement of individual symptoms is dependent on the degree of postoperative normalization of the hemodynamics, especially of pressures in the pulmonary circulation. Various abnormalities have been described and attributed to chronic congestion of the lung.6 Blaunt and colleagues15 reported decreased arterial oxygen saturation in patients with mitral stenosis, which was attributed to impairment of the diffusion of oxygen across the membrane and impairment of ventilation-perfusion in the lung, leading to decreased maximum breathing capacity and vital capacity.16 Changes in the distribution of perfusion have been observed, which indicate diminished perfusion in the dependent lung zone as a result of constricted vasculature and the organic sequela resulting from pulmonary hypertension.4,5,17
Over the last decade there have been very few studies on lung function in mitral valve disease and none have included patients who smoked. Previously, the report by Palmer and colleagues4 included smokers and suggested airway obstruction to be the cause of poor lung function. In our study, we observed that the impairment of lung function was greater in smokers, obstructive in nature, and with significant deterioration in FVC and FEV1 after surgery. Neale and Demers10 included data on respiratory symptoms and dysfunction in 864 individuals in a voluntary health screening program and found impaired pulmonary function in smokers. Other studies in nonsmoking patients with mitral valve disease reported that the more severe the valve defect, the more abnormal were the lung function results in terms of reduced spirometric volumes and increased residual volumes.8,18 The combination of long-standing severe valvular disease and smoking was associated with impaired preoperative pulmonary function in the present study.
The hemodynamic data in our patients improved after surgery. The pulmonary function data correlated well with the NYHA functional class, in agreement with other reports9,19 However, although we found symptomatic improvement in terms of functional class, the pulmonary function parameters were lower than predicted. Two patients remained in NYHA functional class IV after mitral valve replacement and did not show any improvement at the 3-month follow-up. They both continued to have severe pulmonary arterial hypertension in spite of normal mitral valve pressure gradients. Both had significantly reduced pulmonary function and required longer periods of ventilation. Since the chronic nature of the disease is important in changes in pulmonary function as well as in the degree of cardiac dysfunction, pulmonary function tests should be included in the assessment of patients with mitral valve disease. Vaidya and colleagues19 showed a similar correlation between the severity of clinical symptoms and pulmonary function data.
There was a deterioration in the mean values of pulmonary function tests at discharge that could be attributed to thoracotomy and cardiopulmonary bypass.9,19 Patients who were on cardiopulmonary bypass for a longer time had significantly reduced postoperative FVC and FEV1. During cardiopulmonary bypass, leucocytosis and platelet dysfunction are induced, leading to pulmonary endothelial damage with increased permeability of the alveolar capillary membrane and increased interstitial fluid and lung water resulting in pulmonary edema.16,20,21 Previous studies have also noted similar deterioration in pulmonary function soon after cardiopulmonary bypass.9,19
At the 3-month follow-up, only 6 patients had normal pulmonary function and 12 continued to have restrictive changes. Kral and colleagues21 noticed a decrease in the pulmonary blood flow index after operation in patients with the greatest abnormality of pulmonary blood flow distribution before operation, perhaps caused by vasoconstriction in the lower parts of the lung and its immediate release after surgery. Improvement after surgery was not seen in some cases and this was attributed to thickening of the alveolar capillaries in mitral stenosis leading to a decrease in vital capacity postoperatively.16,19 Patients with mitral valve disease may have inspiratory muscle weakness that contributes to the restriction of lung volume in cases of pulmonary vascular congestion.22 Our experience confirms the suggestion that in long-standing mitral valve disease the inspiratory muscles are compromised as a result of poor nutritional status resulting in decreased muscle mass, decreased work in breathing, and decreased respiratory muscle strength.14,16,22 Other studies reported that the time-span of the disease might be equally important as cardiac dysfunction in determining the improvement after surgery.18,21 Our patients had a history of long-standing disease with evidence of poor nutrition, which could be the cause of poor preoperative pulmonary function and minimal improvement at the short-term follow-up. We agree with the conclusions of Vaidya and colleagues19 that patients with deranged preoperative lung function should not be denied surgery. With better understanding of ventilation and the availability of arterial blood gas measurements in the intensive care unit, such patients can be offered prolonged ventilation in the postoperative period.
This study suggests that pulmonary function may be impaired in all patients with rheumatic mitral valve disease and that it deteriorates further after surgery, especially in smokers, but improves gradually in the postoperative period. Spirometry can evaluate respiratory reserve in cardiac patients and it is simple and reproducible. Thus, a routine evaluation of pulmonary function in patients undergoing mitral valve replacement is recommended.
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Acknowledgments
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The authors would like to gratefully acknowledge the staff of the cardiothoracic unit and department of anaesthesia at Sri Venkateswara Institute of Medical Sciences hospital for their diligence and cooperation during this project.
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ABSTRACT
INTRODUCTION
