Ann Thorac Surg 2001;71:39-41
© 2001 The Society of Thoracic Surgeons
Original article: cardiovascular
Choice of venous cannulation for bypass during repair of traumatic rupture of the aorta
Riyad Karmy-Jones, MDa,
Yvonne Carter, MDa,
Mark Meissner, MDa,
Michael S. Mulligan, MDa
a Division of Cardiothoracic Surgery, University of Washington, Seattle, Washington, USA
Accepted for publication June 26, 2000.
Address reprint requests to Dr Karmy-Jones, Department of Surgery, Box 359796, Harborview Medical Center, 325 Ninth Ave, Seattle, WA 98104
e-mail: karmy{at}u.washington.edu
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Abstract
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Background. Choices for venous cannulation for left heart bypass, to assist repair of traumatic rupture of the thoracic aorta, are between the left atrial appendage and pulmonary veins.
Methods. A retrospective chart review was performed of patients who underwent operative repair of ruptured aorta.
Results. Over a 15-year period between March 1985 and February 2000, 133 patients were admitted to a level I trauma center with aortic rupture. Of the 50 procedures performed with left heart bypass, the left atrial appendage was cannulated in 19 and pulmonary veins in 31 (four superior, 27 inferior). Complications occurred in 7 of the 19 patients who underwent venous cannulation via the atrial appendage (two ventricular fibrillation, three atrial fibrillation, one pericardial effusion leading to tamponade, and one phrenic nerve injury). Complications occurred in 2 patients who underwent cannulation via pulmonary vein (one atrial fibrillation, one pericardial effusion requiring tapping) (p = 0.02).
Conclusions. Cannulation via the pulmonary veins is associated with a decrease in complication rates compared with cannulation of the atrial appendage.
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Introduction
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The use of extracorporeal circulatory support to maintain distal perfusion during repair of traumatic rupture of the thoracic aorta has been recognized as an important factor in decreasing the incidence of paralysis [1–4]. Currently, left heart bypass using a centrifugal pump is the most commonly employed technique. Most authors report obtaining venous inflow for left heart bypass via the left atrial appendage [1, 2]. In some settings, this may be hazardous, and obtaining venous access via the pulmonary veins may be both safer and easier [5]. We reviewed our experience with left heart bypass primarily to determine whether or not we could identify differences in the complication rates between pulmonary venous and left atrial appendage cannulation.
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Patients and methods
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A 15-year retrospective chart review of 133 patients identified by the trauma registry as having been admitted to Harborview Medical Center with traumatic rupture of the thoracic aorta between March 1985 and February 2000 was performed. Approval from the Institutional Review Board was obtained before starting data gathering. Data regarding injury severity score, initial systolic blood pressure, TRISS-derived probability of survival, hospital course, and complications was obtained from the trauma registry, medical records, and, where appropriate, medical examiner reports [6, 7]. The TRISS score incorporates both injury severity score, initial revised trauma score, age, and mechanism of injury, and thus provides an overall assessment of both anatomic injury severity as well as physiologic derangement [7]. Paraplegia was determined by documented neurological exam only in those patients who survived long enough to be evaluable.
Results are expressed as the mean ± standard deviation. Univariate analysis was performed using the 
2 test and the independent pairs t test for categorical and continuous variables, respectively. All variables significant at a level of p less than or equal to 0.1 were entered into a logistic regression model to determine predictors of outcome. Statistical significance was taken to be p less than 0.05. All statistical analyses were performed with SPSS 7.5 for Windows (SPSS Inc, Chicago, IL).
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Results
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Of 133 patients admitted (age 39.5 ± 18.4 years), 16 were not or have not yet been operated on due to concurrent injuries or morbidities. Etiology included motor vehicle crash (106), motorcycle crash (16), pedestrian struck (8), and fall (3). Of the 117 patients who did undergo operative repair, circulatory arrest was used in three cases due to extension of the injury into the arch (one death), standard right atrial-ascending aortic cardiopulmonary bypass (CPB) in one case of ascending aortic injury (died), and in three cases, femoral-femoral bypass with oxygenator due to inability to tolerate one lung ventilation was used (one death). Fifty patients underwent left heart bypass with centrifugal pump (six deaths). Of all patients who underwent repair with some form of mechanical support, 4 (all fatalities) presented in extremis with systolic blood pressure less than 60 mm Hg. Twenty-seven of the 60 patients (including 11 patients who presented in severe shock with systolic blood pressure less than or equal to 60 mm Hg or who experienced rupture before proximal aortic control in the operating room) who underwent repair without any extracorporeal circulatory support ("clamp and sew") died. Thus, the overall mortality was 27%. Comparing the "clamp and sew" group with all patients who underwent repair with some form of mechanical circulatory support, the "clamp and sew" group presented with lower systolic blood pressure (110.4 ± 41.4 vs. 129.3 ± 35.9 mm Hg, p = 0.01), higher injury severity score (34.7 ± 17.1 vs 29.6 ± 9.9, p = 0.04), and overall lower TRISS probability of survival (0.65 ± 0.4 vs 0.83 ± 0.24, p = 0.02). While the mortality among those who were operated on without bypass (45%) was significantly greater than those who underwent repair with some form of bypass (16%) (p = 0.001 if include all patients, p = 0.013 if exclude patients presenting in shock), mortality was also significantly associated by TRISS score (0.45 ± 0.39 nonsurvivors vs 0.90 ± 0.16 survivors, p = 0.0001). When entered into a logistic regression, only TRISS score retained significance (p = 0.0002).
Eight of the 33 (24%) survivors of traumatic aortic rupture who underwent repair without extracorporeal circulatory support developed paralysis, while none of the 48 survivors who had repair supported by mechanical bypass (of all forms) experienced paralysis (p = 0.01). Cross-clamp time was not significantly different between these groups (43.4 ± 23.1 minutes paralysis vs 33.6 ± 18.0 minutes no paralysis, p = 0.4). When analyzing only those patients who underwent repair without any form of circulatory support, there was again no significant difference in cross-clamp times between both those who suffered paralysis and those who did not (43.4 ± 23.1 minutes paralysis vs 26.6 ± 10.7 minutes no paralysis, p = 0.18). Patients who suffered paralysis did have greater injury severity score (39.8 ± 15.7) than those without (29.4 ± 9.4, p = 0.04). There were no differences in terms of TRISS probability of survival between both groups. Logistic regression did not identify mechanical support as being independently associated with a significant reduction in paralysis.
The Biomedicus was used for all left heart bypass procedures. In the last 2 years of the study, heparin-bonded tubing was used. Partial heparinization using 2,000 units intravenously was employed because of concerns about clot formation around the cannula themselves. Arterial cannulation was obtained using the thoracic aorta in 44 cases, the femoral artery in six. No arterial complications were noted. Venous inflow to the device was obtained by cannulating the left atrial appendage in 19 and pulmonary veins in 31 (superior vein in four, inferior in 27). Seven (36.8%) patients cannulated via atrial appendage experienced a complication, compared with 2 (6.5%) cannulated via the pulmonary veins (p = 0.02) (Table 1). The dysrythmias occurred either immediately upon cannulation or shortly thereafter. The patient in the pulmonary vein cannulation group who experienced pericardial effusion requiring tapping was the only patient in whom the pericardium was opened to allow cannulation. No bleeding complications occurred. There was no difference in the mortality between atrial appendage (3 [15.8%]) and pulmonary vein (3 [9.6%]). The causes of death included cardiac arrest (one), complications from rupture (two), multiple organ failure (one), and closed head injury (two).
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Comment
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Mechanical circulatory support, usually left heart bypass, has been identified as an important adjunct in the surgical management of traumatic rupture of the thoracic aorta. While it has been questioned whether mechanical support independently reduces the risk of paralysis, it is still recommended in most circumstances [1–11]. Our data indicate that while circulatory support is important in this regard, the overall severity of injury and condition of the patient also affect outcomes. In addition, although the cross-clamp times were not statistically significantly different, type II error can not be entirely excluded. The observation of a clear trend towards less paralysis with bypass would perhaps reach statistical significance with a larger number of patients. Furthermore, the fact that the use of cardiopulmonary bypass was not found to be significant by multivariate analysis could reflect a combination of factors. The most important variable is that sicker patients, including those in shock and/or impending or actual rupture, would have been operated on without the benefit of circulatory support and not survived, thus potentially reducing the incidence of paralysis overall. Indeed, the "clamp and sew" group presented with worse physiology (lower initial systolic blood pressure) and greater injury severity than those patients who underwent repair with mechanical support. These considerations have been addressed by a contemporary multicenter study of thoracic aortic injury [4]. That study noted that mortality among patients who experience rupture or who were in extremis was 100%, and documented an overall mortality of 31% and paraplegia rate of 8.7%. Considering only patients who underwent "elective repair," however, the mortality rate was 25% (15.1% among "clamp and sew," 14.9% if circulatory support was employed). Considering only those patients who survived, the overall incidence of paraplegia was 11.3% (19% in "clamp and sew," 5.2% when circulatory support was employed). Our results are consistent with the findings of this study.
Our primary goal was to evaluate whether or not there was a difference in complication rate between cannulating a pulmonary vein as compared with atrial appendage. Left heart bypass has been most commonly employed using the left atrial appendage. In some circumstances, such as a large hematoma obscuring the proximal descending aorta, cannulation may be safer utilizing the pulmonary veins [5]. Our data indicate that avoiding opening the pericardium and handling the left atrial appendage reduces complications. We now use straight venous and arterial cannulas, and expose the inferior pulmonary vein by mobilizing the inferior ligament. This gives the added advantages of allowing a dissection in an area removed from the hematoma and placing the cannula away from the operative field.
Combining this technique with early institution of left heart bypass, of the last 24 patients admitted with traumatic rupture of the aorta, the only three fatalities occurred in patients who arrested before thoracotomy could be performed. The remaining 21 patients have all been discharged neurologically intact.
Conclusions
Left heart bypass and other forms of mechanical circulatory support are important adjuncts to reduce the risk of paralysis after operative repair of traumatic rupture of the thoracic aorta. However, the risk of paralysis and death is not determined by the use or lack of use of extracorporeal circulatory support alone. When establishing left heart bypass, complication rates are lower by obtaining venous access via the pulmonary veins.
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References
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Abstract
Introduction
