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Ann Thorac Surg 2003;75:853-857
© 2003 The Society of Thoracic Surgeons

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Original article: cardiovascular

Intraoperative and postoperative risk factors for respiratory failure after coronary bypass

^a Division of Cardiothoracic Surgery, The Heart Institute, Albany Medical College, Albany, New York, USA

Accepted for publication September 16, 2002.

^* Address reprint requests to Dr Canver, Division of Cardiothoracic Surgery, The Heart Institute, Albany Medical College, Mail Code 55, 47 New Scotland Ave, Albany, NY 12208, USA
e-mail: canverc{at}mail.amc.edu

	Abstract

Top Abstract Introduction Patients and methods Results Comment Acknowledgments References

 
BACKGROUND: Unlike preoperative events, the influence of intraoperative or postoperative events on respiratory failure after coronary artery bypass grafting (CABG) remains unclear. The purpose of this study was to identify intraoperative and postoperative risk factors that predispose respiratory impairment after CABG.

METHODS: A single institutional database combined with a mandatory report submitted to the Cardiac Surgery Registry of the New York State Department of Health was used. A total of 8,802 consecutive patients who underwent primary CABG with or without a concomitant cardiac operation from January 1993 through December 2000 were included. Respiratory failure was defined as the need for postoperative mechanical ventilatory support longer than 72 hours. Univariate and multivariate logistic regression model was used in the analysis.

RESULTS: Of 8,802 consecutive patients (6,234 males and 2,568 females) who underwent CABG with or without a concomitant operation, 491 patients (5.6%) suffered from postoperative respiratory failure. Although univariate analysis identified 39 statistically significant preoperative risk factors for post-CABG respiratory failure, only six preoperative risk factors were statistically significant by multivariate analysis (p < 0.001). CPB time (in 30 minutes increments) was the only validated intraoperative variable that increased the risk of postrespiratory failure (odds ratio [OR], 1.2; p less than 0.0001). Postoperative events contributing significantly to an increased risk of post-CABG respiratory failure were (1) sepsis and endocarditis (OR, 90.4; p < 0.0001), (2) gastrointestinal bleeding with or without infarction and perforation (OR, 38.8; p < 0.0001), (3) renal failure (OR, 30.7; p < 0.0001), (4) deep sternal wound infection (OR, 11.3; p < 0.0001), (5) new stroke, intraoperative at 24 hours (OR, 9.3; p < 0.0001), and (6) bleeding that required reoperation (OR, 5.5; p < 0.0001). All perioperative variables together accounted for only 28.6% (R²) of the variation.

CONCLUSIONS: Respiratory function after CABG is readily influenced by postoperative occurrence of extracardiac organ or system complications.

	Introduction

Top Abstract Introduction Patients and methods Results Comment Acknowledgments References

 
Respiratory failure is common after coronary artery bypass grafting (CABG) and continues to be a major cause of potentially fatal morbidity after CABG [1–3]. Recent advances in anesthesia, myocardial protection, and surgical techniques have led to fast-track CABG, in which patients have been extubated within a few hours and discharged within 3 to 5 days of operation [4]. At the same time, because of the increasing age and comorbidity of the CABG population, a subset of these patients will require prolonged ventilation in the postoperative period [5, 6].

Most cardiac surgical patients, presenting for either elective or emergent operations, have adequate pulmonary function. For other types of operations, patients would not require prolonged mechanical ventilation; a general rule of thumb is that if a patient was not intubated preoperatively, the need for prolonged postoperative mechanical ventilatory support is unlikely [7]. Importantly, patients undergoing emergent cardiac operation typically do not behave differently when compared with elective postoperative patients. Those patients who require prolonged intensive care unit stay with mechanical ventilatory support are similar to those who might require such support in other operative settings [8].

Since the widespread use of CABG for the treatment of ischemic heart disease, several investigators have attempted to define preoperative characteristics that predict postoperative survival, but the reliability of their predictive value has been controversial [9]. It is possible that an individual with adequate pulmonary function before CABG may have severe respiratory failure develop postoperatively secondary to other organ dysfunction or failure. Therefore our aim in this study was to identify intraoperative and postoperative risk factors that predispose pulmonary impairment after CABG.

	Patients and methods

Top Abstract Introduction Patients and methods Results Comment Acknowledgments References

 
All patient variables and perioperative events were obtained from the Cardiac Surgery Registry of the New York State Department of Health combined with our institutional perfusion database. A total of 8,802 consecutive patients (6,234 males and 2,568 females) who underwent CABG with or without a concomitant cardiac operation from January 1993 through December 2000 at Albany Medical Center (Albany, NY) were included in the analysis to determine their impact on postoperative respiratory failure.

Respiratory failure was defined as pulmonary insufficiency requiring intubation and ventilation for a period of 72 hours or more at any time during the postoperative stay. For patients who were placed on and taken off ventilation several times, the total of these episodes were 72 hours or more. Chronic obstructive pulmonary disease (COPD) was assumed in patients who require chronic (more then 3 months) bronchodilator therapy to avoid disability from obstructive airway disease, or have a forced expiratory volume in one second of less than 75% of the predicted value or less than 1.25 L, or have a room air PO₂ less than 60 or PCO₂ more than 50 mm Hg. In analysis, COPD was not included unless the patient’s record contained documented evidence of the criteria previously described regardless of how much the patient may have smoked. In the database, smoking history was separately recorded if the patient has smoked any tobacco products or used chewing tobacco within the past 2 weeks or within the past year.

A complete list of the preoperative variables in the database is shown in the Appendix and in Table 1. Intraoperative variables within the database were type of operation, aortic cross-clamp time, cardiopulmonary bypass (CPB) time, type of cardioplegia (cold or warm crystalloid or blood), delivery method of cardioplegia (antegrade, retrograde, or both), use of blood products, need for inotropic agents, vasodilators, phosphodiesterase inhibitors, or antiarrhythmic agents. Postoperative variables were return to operating room for hemodynamic decompensation, stroke, transmural or nontransmural myocardial infarction, bleeding required reoperation, deep sternal wound infection, use of insertion of intraaortic balloon pump during and after operation, gastrointestinal (GI) bleeding with or without infarction and perforation, renal failure, implantation of permanent pacemaker caused by heart block, malignant ventricular tachycardia, and septic endocarditis.

Statistical analysis
Statistical analysis was done by using the software StatView version 5.0.1 (SAS Institute Inc, San Francisco, CA). Preoperative, intraoperative, and postoperative variables were analyzed separately by applying univariate logistic regression (Tables 1, 2, 3, and 4). A multivariable logistic regression analysis was used to validate the risk factors for respiratory failure after CABG (Table 5). Survival was calculated as either early (30-day) or hospital discharge. A p value less than 0.05 was considered statistically significant.

	Results

Top Abstract Introduction Patients and methods Results Comment Acknowledgments References

Table 1 shows univariate analysis of preoperative patient variables with their relationship to respiratory failure after CABG. The influence of any other operation combined with CABG on the risk of developing respiratory dysfunction is depicted in Table 2. The effects of commonly used vasoactive or antiarrhythmic agents on post-CABG respiratory complications is shown on Table 3. The association between postoperative respiratory impairment and other postoperative events are displayed in Table 4.

Cardiopulmonary bypass time significantly increased the risk of respiratory failure. Patients undergoing a concomitant procedure with CABG also had significant risk of respiratory failure. Nonuse of arterial conduit was also a strong predictor of respiratory failure. However none of these variables had been validated by multivariate analysis. Use of vasopressin, norepinephrine, nitroglycerin, phenylephrine, and sodium nitroprusside in the postoperative intensive care unit were strongly associated with development of respiratory failure. Nonuse of antiarrhythmics was inversely related to respiratory failure. However none of them was identified as a risk factor for respiratory failure by multivariate analysis.

Table 5 lists the multivariate analysis of preoperative, intraoperative, and postoperative variables. In decreasing order of importance, factors validated by multivariate analysis that contributed significantly to an increased risk of post-CABG respiratory failure were (1) postoperative septic endocarditis; (2) postoperative gastrointestinal bleeding with or without infarction and perforation; (3) postoperative renal failure; (4) postoperative new stroke (intraoperative, 24 hours); (5) postoperative deep sternal wound infection; (6) bleeding requiring reoperation; (7) preoperative insertion of intraaortic balloon pump; (8) congestive heart failure at current admission; (9) COPD; (10) age in 10-year increments; and (11) CPB time in 30-minute increments. All perioperative variables together accounted for only 28.6% (R²) of the variation.

	Comment

Top Abstract Introduction Patients and methods Results Comment Acknowledgments References

 
Prolonged ventilatory support after cardiac operation occurs in 5% to 22% of patients [3]. Postoperative respiratory failure had been documented in 5.6% of our patients who underwent CABG with or without a concomitant cardiac operation. The preoperative risk factors associated with prolonged ventilation after CABG have been addressed in a number of studies. These studies have shown left ventricular dysfunction, COPD, reoperation, unstable angina, age, peripheral vascular disease, impaired renal function, and associated valvular disease as risk factors for respiratory dysfunction [3, 5, 6].

With the number of CABG surgical procedures approaching 600,000 per year in the United States, a complication such as respiratory failure can significantly increase hospital costs and diminish overall quality of life [10]. Postoperative incidence of respiratory failure (17.1%) is common in septuagenarians [11]. As in our study, it is not surprising that the risk of postoperative respiratory failure increases with increasing age, because these patients generally have more preoperative comorbid conditions and less physiologic reserve [10, 12–14]. Increased operative risk in women has been noted before [9, 15]. Although we did not find the impact of female gender as an independent risk factor of respiratory failure, male gender in our patient population had a significantly less chance of respiratory failure after CABG (Table 1).

Although patients with COPD (irrespective of age) stay in the intensive care unit and in the hospital longer after coronary artery bypass grafting [16], hospital mortality in most patients with mild-to-moderate COPD undergoing CABG is similar to those without COPD [17]. Postoperative cardiac function and the occurrence of complications are more significant than preoperative pulmonary function in determining the duration of endotracheal intubation after cardiac operation. Routine spirometry is probably unnecessary for most adult cardiac patients [18]. It is interesting to note that among our patients the risk of postoperative respiratory failure was only modestly increased by the presence of COPD; nevertheless, multivariate analysis identified COPD as a significant independent predictor of respiratory failure. Although univariate analysis showed slightly increased risk of respiratory failure in diabetic patients, multivariate analysis failed to show any significant relationship between diabetes and postoperative respiratory failure.

A well-recognized risk factor for operative morbidity and mortality is the history of previous cardiac operation [11, 12]. Reoperation seemed to have mild increased risk of respiratory failure only on univariate analysis in our study. Coronary artery bypass grafting is technically a more difficult procedure in the setting of prior cardiac operation, given the areas of scarring that must be crossed, the limited options for graft vessels, and the generally more advanced stage of coronary disease found in such patients. Patients undergoing CABG emergently or urgently had a significant and independent elevation in risk for postoperative respiratory failure by univariate analysis.

Intraaortic balloon pumps are effective both prophylactically and intraoperatively in patients who would not otherwise survive cardiac operations. The use of preoperative intraaortic balloon pump in high-risk patients lowers hospital mortality and shortens the stay in intensive care unit due to improved cardiac performance. Although the procedure is cost-beneficial, intraaortic balloon pump does not significantly affect the outcome in terms of postoperative morbidity or hospital mortality [19]. In our patients, preoperative intraaortic balloon pump was a strong independent predictor of respiratory failure, as it was identified by both univariate and multivariate analyses.

It has been suggested that pulmonary diagnosis, lung mechanics, and blood gas values do not offer the clinician definite rules in predicting postoperative respiratory outcome, and these should not be used as exclusion criteria for CABG operations [20]. It has been postulated that myocardial revascularization with or without CPB causes a similar degree of pulmonary dysfunction, and the deterioration in pulmonary gas exchange associated with cardiac operation conceivably is due to factors other than the use of CPB [1].

We do not document the specific reasons for development of respiratory failure in each patient, but note that, in addition to causes of isolated respiratory failure, many patients had multiple organ system involvement. However, recent research would demonstrate that even very sick, high-risk patients may derive significant survival benefit from CABG [21–26]. Although we comment on increased risk associated with these factors, we make no suggestion that CABG should be withheld from any particular patient, but rather that these conditions should be addressed before operation when possible.

In summary, our study has identified intraoperative and postoperative risk factors in addition to preoperative ones predicting post-CABG respiratory failure. The major limitation of this study is that it includes a large set of variables into one multiple logistic regression analysis which is somewhat overwhelming. However, the novel aspect of this work is primarily the evaluation of intraoperative and immediate postoperative events as risk factors for post-CABG respiratory failure. In addition, having a large number of patients in the analysis is consistent with ensuring reliable results at a single institution. These data lend support to further emphasizing the practice of preoperative optimization of acute and chronic extracardiac problems before CABG to minimize the risk of postoperative respiratory failure.

	Acknowledgments

Top Abstract Introduction Patients and methods Results Comment Acknowledgments References

 
The authors express their gratitude to Bradley VanKeuren and Sandy Sheldrick for data collection.

	Appendix

 
Other variables in the database
Age, gender, body mass index (kg/m²), left ventricular ejection fraction, preoperative myocardial infarction, use of intravenous nitroglycerin, stroke, previous cardiac operation, diabetes, hypertension, renal failure (serum creatinine > 2.5 mg/dL), renal failure requiring dialysis, current congestive heart failure, congestive heart failure before current admission, COPD, intraaortic balloon pump, arrhythmia, prior percutaneous transluminal coronary angioplasty more than 6 months ago, percutaneous transluminal coronary angioplasty before admission, use of thrombolytics, coronary artery stent thrombosis, angina (Canadian Cardiovascular Society, CCS class), different degree of stenosis of coronary arteries, pathology of heart valves, active endocarditis, carotid and cerebrovascular disease, calcified ascending aorta, aorto-iliac disease, femoropopliteal disease diagnosed during cardiac catheterization, urgency of operation, and smoking history.

	References

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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 Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Canver, C. C. Articles by Chanda, J. Search for Related Content PubMed PubMed Citation Articles by Canver, C. C. Articles by Chanda, J. Related Collections Coronary disease