Ann Thorac Surg 2002;73:149-152
© 2002 The Society of Thoracic Surgeons
Original article: cardiovascular
Left pleural effusion after coronary artery bypass decreases with a supplemental pleural drain
Maryann Payne, MDa,
George J. Magovern, Jr, MD*a,
Daniel H. Benckart, MDa,
Alexander Vasilakis, MDa,
Gary W. Szydlowski, MDa,
John C. Cardone, MDa,
Gary C. Marrone, MDa,
John A. Burkholder, MDa,
James A. Magovern, MDa
a Department of Cardiothoracic Surgery, Allegheny General Hospital, Pittsburgh, Pennsylvania, USA
Accepted for publication September 13, 2001.
* Address reprint requests to Dr Magovern, Department of Cardiothoracic Surgery, Allegheny General Hospital, Pittsburgh, PA 15212, USA
e-mail: jmagover{at}wpahs.org
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Abstract
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Background. This prospective study was undertaken to determine the incidence of symptomatic left pleural effusion after coronary artery bypass grafting, and to determine if routine drainage of the pleural cavity with a supplemental flexible drain reduces this incidence.
Methods. The clinical course of study patients was prospectively recorded during the initial hospitalization and at 6-weeks after surgery. All patients had a mediastinal and a left pleural tube, which were removed on the 1st postoperative day. The supplemental drain system was implanted in a subset of patients and remained in place for 3 to 5 days. A symptomatic effusion was defined as one that required thoracentesis, tube thoracostomy, or readmission for treatment.
Results. A total of 460 patients were studied, of whom 115 had a supplemental drain. The two groups (supplemental drain versus control) were equivalent with respect to age, gender distribution, and comorbid diseases. The incidence of symptomatic left pleural effusion for the entire group was 9.8% (45 of 460). Symptomatic left pleural effusion occurred in 11.9% (41 of 345) patients when only chest tubes were used, and in 3.5% (4 of 115) when a supplemental drain was placed. This difference was significant (F ratio 7.583, p < 0.005). There were no complications from the supplemental drain.
Conclusions. The incidence of symptomatic left pleural effusion can be greatly reduced with the use of a supplemental pleural drain that remains in place for several days after surgery.
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Introduction
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Pleural effusion is a common occurrence following heart surgery, but in most cases the fluid collection is small and not clinically significant. Some patients, however, develop a significant effusion during the initial hospitalization or after hospital discharge, which requires drainage to relieve respiratory symptoms. The reported incidence of symptomatic effusion varies widely in the literature, but there is relatively little published data that deals specifically with this topic [1–6].
We have been concerned that fast-track protocols may increase the incidence of postoperative pleural effusion, because early chest tube removal might cause incomplete pleural drainage. In response to this issue, several surgeons in this surgical practice group began to employ a supplemental pleural drain system in all cases, in addition to standard chest tubes (Fig 1). The other surgeons in the group did not adopt this practice and never used the supplemental drain. This provided an opportunity to study the effect of these supplemental drains on the development of postoperative pleural effusion. This study was undertaken to address three questions: (1) What is the incidence of symptomatic pleural effusion after coronary artery bypass grafting (CABG)? (2) Can this incidence be reduced with the use of a supplemental drain? (3) What perioperative factors are associated with the development of symptomatic pleural effusion?
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Fig 1. The flexible drainage system, consisting of a silastic drain and a collection bulb. The quarter is shown as a size reference.
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Patients and methods
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Patient population
The study analyzed the clinical outcome of 460 patients, in which the left internal mammary artery was used for CABG (412) or CABG plus valve surgery (48). The patients in the study were operated on at three hospitals in the Pittsburgh region by a single group practice which performs all of the cardiac operations at these hospitals. The institutions were: (1) Allegheny General Hospital, Pittsburgh, PA; (2) The Medical Center at Beaver, Beaver, PA; and (3) Westmoreland Regional Hospital, Greensburg, PA. The study period was July 1999 to January 2, 2000. The mean age of the patients was 65 ± 10 years and 66% were male. A clinical risk score was calculated for each patient, based on a published risk prediction model (Allegheny General Hospital preoperative risk stratification model) that uses preoperative data to estimate the probability of postoperative major morbidity and mortality. The mean risk score for the entire patient population was 4.4 ± 3.2, which predicted an operative mortality of less than 2% for this group.
Study design and data collection
This was a prospective, nonrandomized observational study of two methods for mediastinal/pleural drainage after CABG. The primary endpoint was the incidence of symptomatic left pleural effusion (SLPE), as defined by the need for thoracentesis, tube thoracostomy, or hospital readmission for resolution. Inclusion criteria were: (1) nonemergent operative status, and (2) an operation that included use of the left internal mammary artery. Preoperative and postoperative data were obtained from the Allegheny General Hospital cardiothoracic database. Information on events after hospital discharge was obtained by a questionnaire completed during a 6-week postoperative office visit.
Operative technique and postoperative care
All patients in the study had CABG or CABG plus valve operations, all of which utilized cardiopulmonary bypass and cold blood cardioplegia. The mean number of grafts for the entire group was 2.8 ± 1.0 (range 1 to 5 grafts). The mean cardiopulmonary bypass time and aortic occlusion periods were 93 ± 34 minutes and 65 ± 26 minutes, respectively. All patients received epsilon aminocaproic acid (amicar) during surgery as an antifibrinolytic agent. Each patient had the mediastinum and the left pleural cavity drained with two 32F chest tubes. The chest tubes were removed on the first postoperative day, if the drainage was less than 100 cc in the previous 8 hours. Otherwise, the tubes were left in place for another 12 to 24 hours. The study group patients had a flexible plastic drain (Blake drain, Ethicon, Somerville, NJ) placed in the left pleural cavity; this drain was removed 3 to 5 days after surgery (Fig 2). The criteria for removal of the supplemental drain was a daily drainage of less than 100 mL/day. All patients were started on aspirin (325 mg/day) on the 1st postoperative day, but heparin and coumadin were not used. All patients had at least three chest roentgenograms during hospitalization, one immediately after surgery, one on the 1st postoperative day, and one after chest tube removal. Thereafter, roentgenograms were not routinely obtained unless a clinical indication existed.
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Fig 2. A cross-section of the chest tube (left), the silastic drain (center), and the section of the silastic drain that exits through the skin (right). The silastic drain is smaller and softer than the chest tube.
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Statistical analysis
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Univariate analysis
The data were analyzed by occurrence of postoperative SLPE (SLPE versus no SLPE groups). Univariate analysis was performed using selected preoperative and intraoperative variables in an effort to identify factors associated with the development of SLPE following CABG. Patient data was also grouped by usage of the supplemental drain system (flexible drain versus standard drain groups), to evaluate the efficacy of the supplemental drain in reducing the rate of development of SLPE. In each analysis, groups were compared using Student’s t test and the Mann-Whitney rank sum test for continuous variables. Rates and proportions were compared using two-tailed 
2 and Fisher’s exact tests.
Multivariate analysis
Multivariate analysis was conducted using preoperative and postoperative variables to determine if there was an association between the supplemental drain system and the occurrence of SLPE. Regression analysis was performed to determine if significant differences were present between the supplemental drain and the standard groups with respect to SLPE.
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Results
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Factors associated with development of SLPE
The overall incidence of symptomatic pleural effusion in the study was 9.8% (45 of 460), approximately two-thirds of the effusions occurred during the initial hospitalization, but another one-third occurred after hospital discharge. Patients who developed SLPE had a significantly higher incidence of insulin dependent diabetes (13 of 45, 29% versus 59 of 415, 14%, p = 0.02), and chronic obstructive pulmonary disease (12 of 45, 27% versus 49 of 415, 12%, p = 0.01). There were no differences in the groups with respect to age, gender, preoperative risk score, cardiopulmonary bypass time, or aortic cross-clamp time (Table 1).
Effect of supplemental drain system on incidence of SLPE
Patients with and without the supplemental drain system were similar with respect to age, gender, comorbid diseases, risk score, and number of grafts (Table 2).
The incidence of comorbid diseases, such as renal insufficiency, peripheral vascular disease, diabetes, and chronic obstructive pulmonary disease was not different between the 2 groups. The incidence of symptomatic pleural effusion was 11.9% (41 of 345) in patients drained with standard chest tubes and 3.5% (4 of 115) in those patients who had a flexible pleural drain in addition to chest tubes (p = 0.005). This difference was highly significant using the Student’s t test and Mann-Whitney rank sum test (p = 0.006). In addition, there was a strong association between use of the supplemental drain and the incidence of SLPE (correlation coefficient 0.758). Regression analysis also confirmed a significant difference between the drain versus no drain groups with respect to SLPE (F ratio 7.583, p < 0.005). There were no complications caused by, or attributed to, the flexible drain in this study.
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Comment
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Pleural effusion is very common after CABG surgery, occurring in up to 50% to 75% of patients in the 1st week after operation, depending on the definition of effusion and the method used to measure it [1]. Most of these effusions are small and not clinically significant. This study focuses on symptomatic effusion, defined here as a collection of pleural fluid that requires drainage by thoracentesis or tube thoracotomy, or readmission to the hospital, for relief of symptoms. This study shows that SPLE occurs in about 12% of CABG or CABG/valve patients during a 6-week postoperative observation period, when traditional chest tubes are used for a 12 to 24 hour period after surgery.
The causes of pleural effusion after CABG are not known, but several factors have been associated with this problem. Some authors have reported that pleural effusion is more common following left internal mammary artery harvest [2, 7, 8]. This may be due to pleurotomy, which allows blood to enter the pleural cavity, or to the left internal mammary artery harvest itself, which leaves a raw surface that can be the source of serous fluid [8, 9]. Other studies, however, have found that pleural effusion occurs with the same frequency after CABG, even in the absence of left internal mammary artery harvest [3, 4, 10]. Other contributing factors may include postoperative pericarditis/pleuritis, congestive heart failure, atelectasis, and an incompletely drained hemothorax. We could not identify any patient-related or procedure-related factors that were associated with effusion, except for a higher incidence of insulin-dependent diabetes and chronic obstructive pulmonary disease in patients who subsequently develop a symptomatic effusion. The mechanism by which these factors could mediate pleural effusion are not clear. We have consistently noted that the fluid that drains with the flexible system is sanguinous or serosanguinous in nature. This leads us to believe that residual pleural blood is an important cause of subsequent pleural effusion, but the data do not prove this point.
This study also shows that symptomatic effusion is greatly reduced when a supplemental pleural drain remains in place for several days after surgery. We have used a soft silastic drain (Blake drain) connected to a suction bulb for this purpose. This system is comfortable for the patient, allows ambulation and is easy to remove. Initially, there was concern about the risk of pneumothorax, because this is not an underwater seal system. However, the collection bulb has a one-way valve which prevents retrograde entry of air when the bulb is opened, and this appears to prevent this problem. This system is intended to drain fluid, but is not effective if there is an air leak from the lung. In this study, we did not have any drain-related complications, such as pneumothorax or pleural infection.
There are several study limitations. This was a prospective study, but it was not randomized, which raises the question of selection bias. The 2 groups were equivalent with respect to all preoperative factors, including age, gender, comorbid diseases, and clinical risk score. The decision to use a supplemental drain was surgeon-determined. Several surgeons used the drain in all cases and other surgeons did not use the drain at all. It is possible that some surgeons have a higher incidence of pleural effusion. Our analysis of the data demonstrates no evidence of this and we believe that the difference in the incidence of symptomatic effusion between the groups reflects a genuine effect of the supplemental drain.
Routine postoperative chest roentgenograms were obtained after surgery and after chest tube removal, but not before hospital discharge. Therefore, we do not know the actual incidence of pleural effusion in the 2 groups during the hospitalization, but this information would not answer our question since most of the effusions would be small and asymptomatic. We have used symptomatic effusion, which is a functional definition, as a study endpoint rather than the presence of pleural fluid, which is an anatomic definition. The decision on what constitutes a symptomatic effusion is somewhat subjective, but the performance of thoracentesis or insertion of a chest tube is a clearly definable, easily determined endpoint.
We have not analyzed this data from an economic viewpoint. This was a preliminary study to determine whether the supplemental drain was safe and effective. The supplemental drain is inexpensive, with an approximate cost of $25 per patient. It is likely that this approach will be cost-saving, not merely cost-effective, but this will need to be confirmed in future studies.
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References
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Abstract
Introduction
