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Ann Thorac Surg 1998;66:144-147
© 1998 The Society of Thoracic Surgeons

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Original articles: cardiovascular

Influence of age-specific lung function on survival after coronary bypass

^a Section of Cardiothoracic Surgery, William S. Middleton Memorial Veterans Hospital, University of Wisconsin School of Medicine, Madison, Wisconsin, USA

Accepted for publication March 4, 1998.

Address reprint requests to Dr Canver, Division of Cardiothoracic Surgery, University of Wisconsin School of Medicine, H4/352, Clinical Science Center, 600 Highland Ave, Madison, WI 53792
e-mail: (cccanver{at}facstaff.wisc.edu)

	Abstract

Top Abstract Introduction Patients and methods Results Comment Acknowledgments References

 
Background. Respiratory complications after successful coronary artery bypass grafting influence the immediate recovery of a patient; however, whether they influence the longevity of a patient is largely unknown. The aim of this study was to examine the effects of preoperative pulmonary risk factors in younger patients and older patients on outcome after coronary artery bypass grafting.

Methods. A retrospective chart review was performed on 939 patients who underwent primary coronary artery bypass grafting between July 1987 and November 1996. For better comparison, they were arbitrarily divided by age into two groups: group 1, less than 70 years old (n = 710), and group 2, 70 years old or older (n = 229). The variables collected for each patient included history of chronic obstructive pulmonary disease, active smoking, forced expiratory volume, and ventilatory support for more than 48 hours. These variables were compared with postoperative length of stay in the intensive care unit, length of stay in the hospital, and the midterm survival up to 5 years. The data were analyzed by the use of univariate/multivariate log-rank tests and the method of Kaplan-Meier survival estimates.

Results. The presence of chronic obstructive pulmonary disease was associated with increased length of stay in the intensive care unit and in the hospital for both groups. Preoperative forced expiratory volume in 1 second, significantly affected length of stay in the hospital only in the patients less than 70 years old (p = 0.0001). Delayed extubation beyond 48 hours of ventilatory support resulted in prolonged length of stay in the intensive care unit and in the hospital for patients less than 70 years old (p = 0.0001, p = 0.0001, respectively) and patients 70 years old or older (p = 0.0001, p = 0.0001, respectively). The 5-year survival after coronary artery bypass grafting for both groups was significantly influenced by the level of preoperative forced expiratory volume in 1 second (p = 0.0004, p = 0.0282, respectively).

Conclusions. Patients with chronic obstructive pulmonary disease, irrespective of age, stay in the intensive care unit and in the hospital longer after coronary artery bypass grafting. In addition, preoperative forced expiratory volume in 1 second is a significant predictor of 5-year survival in the young and aged individuals undergoing coronary artery bypass grafting.

	Introduction

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Respiratory failure after a successful coronary artery bypass grafting (CABG) operation continues to have an influence on the immediate recovery of a patient. Life-threatening pulmonary complications after CABG are more likely to occur in patients with chronic obstructive pulmonary disease (COPD), which has largely been regarded as a risk factor for early mortality [1]. In fact, reduced forced expiratory volume in 1 second (FEV₁) has been shown to be an independent risk factor for early mortality [2]. We have recently shown acceptable early mortality and long-term survival equal to those of an age-matched population in the elderly as sound outcome measures that support the justification of CABG in older patients irrespective of age [3, 4]. However, little is known about the influence of pulmonary dysfunction on outcome of CABG patients of different ages and about midterm CABG survival of young or old patients with preexisting impaired lung function. Therefore, the purpose of this study was to provide a comparative analysis between preoperative pulmonary risk factors and outcome after CABG for patients of different ages.

	Patients and methods

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We performed a chart review on 939 patients who underwent primary CABG at the William S. Middleton Memorial Veterans Hospital (Madison, Wisconsin) between July 1987 and November 1996. Because of the retrospective nature of the study, only the following variables were complete on each patient: age, sex, preoperative ejection fraction, number of grafts, use of internal thoracic artery, ischemia time, perfusion time, history of COPD, current smoking, FEV₁, duration of ventilatory support after CABG, and postoperative length of stay (LOS) in the intensive care unit (ICU), LOS in the hospital, early mortality (defined as death within 30 days of the CABG operation), and current status (dead or alive). This study excluded patients who underwent repeat CABG and patients who had undergone CABG incidental to heart valve repair or replacement, resection of a ventricular aneurysm, or other surgical procedures.

For comparison purposes, patients were arbitrarily divided into two different age groups: group 1, included patients less than 70 years old (n = 710; range = 37 to 69 years), and group 2, included patients 70 years old or older (n = 229; range = 70 to 82 years). Most patients had class III or class IV angina according to the Canadian Cardiovascular Society. The indications for bypass grafting included unstable angina or angina after recent (<6 weeks) myocardial infarction. Most of the patients had three-vessel occlusive coronary disease at angiography. Most operations were performed by one of two cardiac surgeons (C.C.C. or G.M.K.). Cardiopulmonary bypass was established by the use of a membrane oxygenator. Cold blood cardioplegia was used predominantly.

The definitions of preoperative pulmonary variables were according to the protocol of the Department of Veterans Affairs Continuous Improvement in Cardiac Surgery [2]. The presence of COPD was recorded if the chart of the patient indicated COPD resulting in functional disability, hospitalization, required chronic bronchodilator therapy, FEV₁ less than 75% of predicted value, or a combination of these factors. The patient was an active smoker if the patient or the chart indicated that the patient had smoked tobacco in any form (eg, cigarettes, pipe, or cigar) in the 2 weeks before the operation. The actual values for FEV₁ were recorded from the most recent pulmonary function testing before the operation. The exact number of patients with various characteristics is shown in Table 1 for both groups.

Data are presented in the text and tables as simple percentage and frequency distributions. Statistical analysis was performed by the use of univariate or multivariate log-rank tests on SAS software program (SAS Inc, Cary, NC), and values were expressed as mean ± standard error of the mean. Patient survival estimates were calculated by actuarial analysis according to the method of Kaplan and Meier [5] and plotted at semiannual intervals using the day of CABG as the starting time. Significant differences were considered to exist when calculated p values were less than 0.05.

	Results

Top Abstract Introduction Patients and methods Results Comment Acknowledgments References

 
Characteristics of the patient population are shown in Table 2. In group 1, there were 705 men and 5 women, and in group 2, there were 228 men and 1 woman. The mean preoperative ejection fraction was comparable in both age groups (p = 0.0997). The number of grafts during the CABG was unaffected by the age (p = 0.2330). Aortic cross-clamp time (p = 0.6035) and the cardiopulmonary perfusion time (p = 0.3857) were similar in both groups. The use of ITA in group 1 was substantially higher than in group 2 (p < 0.0001).

View larger version (15K): [in this window] [in a new window]   Fig 1. Relationship between patient variables and duration of intensive care unit care after coronary bypass (mean ± standard error of the mean). (COPD = chronic obstructive pulmonary disease; Vent = ventilator; FEV1 = forced expiratory volume in 1 second; *p < 0.05.)

View larger version (18K): [in this window] [in a new window]   Fig 2. Relationship between patient variables and length of hospital stay after coronary bypass (mean ± standard error of the mean). (COPD = chronic obstructive pulmonary disease; Vent = ventilator; FEV1 = forced expiratory volume in 1 second; *p < 0.05).

View larger version (19K): [in this window] [in a new window]   Fig 3. Comparison of lung function with survival of coronary artery bypass grafting patients less than 70 years old, with confidence intervals of 95% (dotted lines). (FEV1 = forced expiratory volume in 1 second.)

View larger version (18K): [in this window] [in a new window]   Fig 4. Comparison of lung function with survival of coronary artery bypass grafting patients 70 years old or older, with confidence intervals of 95% (dotted lines). (FEV1 = forced expiratory volume in 1 second.)

	Comment

Top Abstract Introduction Patients and methods Results Comment Acknowledgments References

Coronary bypass operation for ischemic heart disease is associated with significant risk of postoperative pulmonary complications. Although static pulmonary function tests have been used to assess the risk of respiratory complications after CABG, these tests have limited sensitivity and specificity [6]. Some patients estimated to be at high risk experience no difficulties, whereas others predicted to be at low risk, with only mild or moderate abnormalities of pulmonary function, have serious complications. Prior studies have reported conflicting results on the use of routine pulmonary function testing in an attempt to identify patients at higher risk for serious respiratory complciations after CABG [1, 7–9]. Recent emphasis on curbing the cost of a coronary bypass operation has led to selective use of preoperative screening pulmonary function testing at many hospitals. The Department of Veterans Affairs Continuous Improvement in Cardiac Surgery Study was initiated in 1987 to develop risk-adjusted outcome models of continuous quality improvement and to evaluate the efficacy of this approach on the quality of all cardiac surgical procedures performed in Veterans Administration medical centers [10]. Therefore, all patients in our study had routine screening preoperative pulmonary function testing because our Veterans Administration hospital was required to complete a single-page data form (73 patient-care variables) for each patient undergoing a cardiac operation [10].

Previous studies have not provided a definite clarification for the predictive value of preoperative FEV₁ on patient survival after CABG. We found a relationship between preoperative level of FEV₁ and reduced 5-year survival in patients undergoing CABG regardless of their age. We believe that the knowledge of a patient’s preoperative baseline pulmonary function might help to predict patients’ longevity after successful CABG.

Coronary bypass operation is not risk free for any age group. In our analysis, the perioperative mortality was comparable for the young and the elderly. However, it is necessary to reiterate that most patients in this analysis were veteran men with normal left ventricular function, and the results also pertain primarily to men. Conclusions of this study may not be completely applicable to women or to those individuals undergoing cardiac operations other than primary CABG.

With recognition of its retrospective nature, this study does not separate the patient groups according to other incremental risks, but affirms that impaired lung function before CABG is of predictive value irrespective of age. Performance of pulmonary function testing in patients with COPD before CABG is probably worthwhile. Such testing can be part of cost-effectiveness programs specifically dealing with patients who have impaired lung function, to minimize the expenditure for these patients in the health care delivery system.

	Acknowledgments

Top Abstract Introduction Patients and methods Results Comment Acknowledgments References

 
We appreciate the statistical assistance provided by Glen E. Leverson, PhD, and the assistance provided by Stephenia D. Cooler, MS, and by Wanda L. Stroyny, BS.

	References

Top Abstract Introduction Patients and methods Results Comment Acknowledgments References

 

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3. Canver C.C., Nichols R.D., Cooler S.D., et al. The influence of increasing age on long-term survival after coronary bypass. Ann Thorac Surg 1996;62:1123-1127.[Abstract/Free Full Text]
4. Canver C.C., Kroncke G.M., Nichols R.D., Heisey D.M., Murray E.L., Mentzer R.M., Jr Coronary artery bypass surgery in older patients. Cardiol Elderly 1994;2:442-447.
5. Kaplan E.L., Meier P. Nonparametric estimation from incomplete observations. J Am Stat Assoc 1958;53:457-461.
6. Zibrak J.D., O’Donnell C.R., Marton K. Indications for pulmonary function testing. Ann Intern Med 1990;112:763-771.
7. Durand M., Combes P., Eisele J.H., Contet A., Blin D., Girardet P. Pulmonary function tests predict outcome after cardiac surgery. Acta Anaesthesiol Belg 1993;44:17-23.[Medline]
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10. Grover F.L., Johnson R.R., Marshall G., Hammermeister K.E., Department of Veterans Affairs Cardiac Surgeons. Factors predictive of operative mortality among coronary artery bypass subsets. Ann Thorac Surg 1993;56:1296-1307.[Abstract]

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This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Personal Folders Download to citation manager Author home page(s): Charles C. Canver George M. Kroncke Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Canver, C. C. Articles by Kroncke, G. M. Search for Related Content PubMed PubMed Citation Articles by Canver, C. C. Articles by Kroncke, G. M.