Partial Cardiopulmonary Bypass for Pericardiectomy and Resection of Descending Thoracic Aortic Aneurysms

Transcription

1 Partial Cardiopulmonary Bypass for Pericardiectomy and Resection of Descending Thoracic Aortic Aneurysms Robert D. Bloodwell, M.D., Grady L. Hallman, M.D., and Denton A. Cooley, M.D. E xtracorporeal circulatory support during extracardiac operative procedures on the cardiovascular system may be used to augment cardiac output, supplement respiratory function, and protect organs distal to sites of temporary aortic occlusion from ischemic injury. Partial cardiopulmonary bypass employing peripheral venous and arterial cannulation and an oxygenator with a small priming volume may be used as an adjunctive perfusion technique in a variety of clinical situations. Preservation of functional integrity of the kidneys and spinal cord is mandatory for the successful conduct of operations for resection and graft replacement of aneurysms of the descending thoracic aorta. Partial cardiopulmonary bypass provides an alternative technique with several advantages over pump bypass from the left atrium to the femoral artery for protection against renal and spinal cord ischemia and for reduction of circulatory load on the heart during temporary aortic occlusion. Partial cardiopulmonary bypass can also provide supplementary respiratory and circulatory function during operations on the heart or lungs which temporarily interfere with their function, such as during pericardiectomy for constrictive pericarditis. This report presents the results of the use of partial cardiopulmonary bypass in 19 patients during operative correction of descending thoracic and thoracoabdominal aneurysms, repair of traumatic transection of the aorta, and pericardiectomy for constrictive pericarditis. From the Texas Heart Institute of the St. Luke s Episcopal-Texas Children s Hospitals and the Cora and Webb Mading Department of Surgery, Baylor University College of Medicine, Houston, Tex. Supported in part by U.S. Public Health Service Grants (HE-03137), (HE-05435), and (HE-05387). Presented at the Fourth Annual Meeting of The Society of Thoracic Surgeons, New Orleans, La., Jan , THE ANNALS OF THORACIC SURGERY

2 Bypass for Pericardiectomy and Aneurysms METHODS During intrathoracic operations either through a median sternotomy or a left lateral thoracotomy, the femoral artery and femoral vein are exposed through an incision in the groin. After initial thoracic dissection, peripheral vascular cannulation is performed just prior to the need for bypass. A standard plastic arterial cannula is inserted through a transverse femoral arteriotomy, and a large catheter is introduced retrograde through a transverse femoral venotomy into the inferior vena cava. Systemic heparinization must be maintained throughout the time that the venous catheter is in place. Catheters usually used for total cardiopulmonary bypass by cannulation of the thoracic venae cavae (ranging in size between #28 and #32 French) will usually provide adequate gravity drainage of venous blood to the extracorporeal system. A disposable plastic bubble oxygenator primed with 5% dextrose in distilled water is inserted into the extracorporeal circuit. Usually a child-sized oxygenator, with a priming volume of 500 ml., is used, but a large adult oxygenator, requiring a priming volume of approximately 1,000 ml., may be used to assure complete oxygenation when a large flow is anticipated. Previous experimental and clinical studies during atrial-femoral bypass and thoracic aortic occlusion demonstrated that 20 ml. per minute per kilogram of body weight was an adequate flow for preservation of renal function [5, 91. Flow during perfusion ranged between 1,000 and 2,000 ml. per minute and ranged in duration between 30 and 60 minutes, with an average of 40 minutes. The opportunity to return heparinized blood lost in the operative field to the oxygenator provides a more stable bypass than when all blood loss is discarded and must be replaced by standard transfusion techniques. Monitoring of blood pressure through an indwelling needle in an accessible artery in the right arm is used as a guide, permitting adjustment of the rate of extracorporeal flow to prevent significant changes in the central circulation during partial bypass. Sudden increase in arterial pressure incident to cross-clamping of the aorta should be avoided, and systolic blood pressure should be maintained approximately 30 mm. Hg above the preocclusion level by regulating the perfusion flow rate. A constant or high flow rate through the bypass is not necessary, and maintenance of a stable arterial blood pressure in the upper body has priority over maintenance of a theoretical optimum flow in the region distal to the site of aortic occlusion. In patients with aneurysms of the descending thoracic aorta a woven Dacron tube graft is inserted to restore aortic flow after incising the aneurysm, controlling bleeding from the intercostal arteries, and fashioning a cuff of aorta for the proximal and distal anastomoses. Bypass is continued during occlusion of the descending thoracic aorta only until completion of the final vascular anastomosis. Early removal of the venous cannula permits reversal of anticoagulation by administration of protamine to facilitate control of bleeding in the operative field. Dissection for pericardiectomy is initially carried out over the anterior and lateral portions of the cardiac chambers and great vessels through a median sternotomy. Peripheral cannulation and bypass is used thereafter during the manipulation and displacement of the heart necessary for thorough removal of the fibrocalcific tissue about the posterior aspects of the heart and pulmonary veins. Conversion to total cardiopulmonary bypass may be accomplished if necessary or to facilitate further the procedure by insertion of an additional catheter into the superior vena cava and occlusion of venous inflow to the heart. CLINICAL MATERIAL AND RESULTS Among 19 patients in whom partial cardiopulmonary bypass was employed, descending thoracic aortic aneurysms were repaired in 17 patients, ranging in age VOL. 6, NO. I, JULY,

3 BLOODWELL, HALLMAN, AND COOLEY T;IBLE 1. PARTIAL CARDIOPULMONARY BYPASS-CLINICAL MATERIAL Operation Pericardiectomy for constrictive pericarditis Correction of aneurysms of descending thoracic aorta Etiology Dissecting Acute Chronic Arteriosclerotic Aortitis Traumatic transection Extent of aneurysm Segment of descending aorta Entire descending aorta Extending into abdominal aorta Ruptured Diagnosis Chest x-ray only (emergency) Angioaortogram Previous thoracotomy Total Ages: 46 and48 years. bage: range = 24 to 74 years; mean = 55 years. No. of Patients % 17b 19 from 24 to 74 years (mean, 55 years), and pericardiectomy was performed in 2 patients (Table 1). The majority of the aneurysms treated were arteriosclerotic in origin and over half involved the entire descending thoracic aorta. A thoracoabdominal aneurysm was present in 1 patient. Dissecting aneurysms were present in 4 patients, in 2 of whom the dissection was acute. In 2 patients, the aneurysm had ruptured prior to operation. Diagnosis was suggested by an x-ray of the chest in all patients, but an angioaortogram was usually performed to substantiate the presence and extent of the aneurysm. In an emergency situation a presumptive diagnosis may be based on an x-ray of the chest alone. Diagnosis in 2 patients in this series was made during a previous thoracotomy performed upon the presumption that a pulmonary lesion existed. Two surviving patients experienced a neurological deficit after operation. One was a 74-year-old man with an aneurysm of the entire descending aorta in whom operation had been previously denied because of the extent of the disease, but in whom operation was subsequently recommended because of persistent chest pain and progressive enlargement of the aneurysm (Fig. 1). He recovered satisfactorily after operation except for leg weakness that improved and permitted ambulation within a month. Another patient, treated for an acute dissecting aneurysm extending below the diaphragm, experienced weakness in one leg after operation. In 1 patient with an aneurysm involving the proximal descending thoracic aorta and base of the aortic arch, hemorrhage necessitated reocclusion of the aorta, including a portion of the arch, and reinstitution of bypass for another 30 minutes without resultant central nervous system or renal functional deficit. One patient who died had paraplegia. 48 THE ANNALS OF THORACIC SURGERY

4 Bypass for Pericardiectomy and Aneurysms A FIG. 1. X-ray of chest (A) and aortogram (B) in 74-year-old man with massive artel-iosclerotic aneurysm of descending thoracic aorta. B A two-staged approach to a complicated combination of cardiovascular lesions was employed in a 46-year-old man with aortic valvular insufficiency and an aneurysm of the descending aorta producing pseudocoarctation. Aortic-valve replacement during total cardiopulmonary bypass was performed 3 weeks after resection and grafting of the descending aorta during partial bypass. He has returned to full-time work as a schoolteacher. Peripheral cannulation and partial cardiopulmonary bypass was particularly useful for repair of a chronic dissecting aneurysm of the descending aorta in a patient who had undergone emergency repair and graft replacement of an acute dissecting aneurysm of the ascending aorta 2 years previously with resultant pericardial adhesions (Fig. 2). This bypass technique was especially applicable in 2 patients with acute dissecting aneurysms and in 1 patient with transection of the thoracic aorta in association with multiple traumatic injuries, including a ruptured viscus requiring laparotomy, pelvic fractures, and several open fractures of the extremities. In this 24-year-old male, who sustained multiple injuries in an auto-pedestrian accident, the only indication of a traumatic aneurysm was a widened superior mediastinum in the x-ray of the chest obtained in the emergency room (Fig. 3). Laparotomy was performed first because of the clinical findings of an acute abdomen. Repair and resection of several segments of ruptured small intestine was done. Immediately following laparotomy the patient was positioned for a lateral thoracotomy. When a large hematoma about the descending thoracic aorta was visualized, peripheral cannulation of the femoral vein and artery was performed for institution of partial bypass. Further dissection demonstrated transection of the aorta just distal to the subclavian artery; repair was accomplished by insertion of a woven Dacron graft. During the same anesthesia, debridement and open reduction of several compound fractures in three extremities was carried out. This patient made a satisfactory recovery following these multiple injuries and illustrates a unique application of this technique. Two patients died in hospital after operation (Table 2). One patient died after correction of a ruptured fusiform aneurysm of the descending thoracic aorta VOL. 6, NO. I, JULY,

5 BLOODWELL, HALLMAN, AND COOLEY 0. I C. I d. I FIG. 2. Diagram (a) and aortogram (b) in 57-year-old man with acute dissecting aneurysm treated 2 years previously by resection and replacement of ascending aorta (c) and resuspension of aortic valve leaflets during total bypass. Diagram (d) and aortogram (e) demonstrate enlarging chronic dissecting aneurysm of descending thoracic aorta which was resected and replaced (f) during partial cardiopulmonary bypass. Recovery satisfactory following abdominal aneurysmectomy 9 months subsequently. associated with massive right-sided hemothorax. The conduct of partial bypass in this 67-year-old patient, who was in shock for 12 hours prior to operation, was not satisfactory since reduction of the total blood volume made little venous blood available for the perfusion circuit although he received 4 liters of blood during the procedure. He died 6 days after operation, having been paraplegic and anuric. During postmortem examination severe coronary atherosclerosis was found as a complicating feature. One patient died during an attempt to replace the entire aortic arch when secondary hemorrhage occurred. Two patients died after hospital discharge: 1 died from intraabdominal hemorrhage 2 months after graft replacement of a thoracoabdominal aneurysm, and the other, a 66-year-old man, died suddenly at home a month after operation, presumably from a myocardial infarction. 50 THE ANNALS OF THORACIC SURGERY

6 Bypass for Pericardiectomy and Aneurysms FIG. 3. X-ray of chest demonstrating widened superior mediastinum in 24-yearold man after auto-pedestrian accident. Peripheral cannulation and partial bypass used during successful repair of traumatic transection of thoracic aorta in conjunction with laparotomy and open reduction of several extremity fractures. Two patients with constrictive pericarditis underwent pericardiectomy through a median sternotomy. Complete decortication of the cardiac chambers, including the venae cavae and pulmonary veins, was facilitated by partial bypass. Circulation was supported during elevation of the heart during dissection of its posterior aspect. In 1 patient inadvertent right atriotomy due to dense adherence of the pericardium to the thin atrial wall resulted in hemorrhage necessitating conversion to total bypass. Cannulation of the superior vena cava and occlusion of venous inflow during bypass permitted repair of the atrial rent and restoration of adequate circulating blood volume. Both patients have recovered satisfactorily. TABLE 2. PARTIAL CARDIOPULMONARY BYPASS-RESULTS CLINICAL EXPERIENCE OF Mortality No. of No. of Operative Procedure Patients Patients % Resection descending thoracic aortic aneurysm Fusiform Dissectinga 4 0 Repair traumatic transection 1 0 of aorta Resection thoracoabdominal 1 0 aneurysm Pericardiectomy for constrictive 2 0 pericardi tis Total "Acute in 2 patients. - VOL. 6, NO. 1, JULY,

7 BLOODWELL, HALLMAN, AND COOLEY COMMENT Numerous techniques have been devised for protection of the spinal cord and kidneys from ischemic damage from cross-clamping of the descending thoracic aorta during resection of aneurysms [l, 51. General body hypothermia [S], temporary vascular shunts depending upon cardiac action to propel blood distally, and left atrial to femoral artery bypass with an extracorporeal pump [5] have been used. The latter perfusion has been the most widely used and provides reliable protection from ischemic injury. A simple alternative technique of perfusion employs a small-volume pump-oxygenator [6, lo]. Systemic venous blood drained from the vena caval system through a peripheral venous cannula is oxygenated and returned via the femoral artery to the distal aortic circulation. Total cardiopulmonary bypass with cannulation of a single peripheral vein and artery has been used experimentally and clinically for intracardiac surgery [3]. In those studies, adequate flow could be obtained through the single venous cannula as shown by swift flow of contrast material introduced into the superior vena cava and right atrium. Accordingly, a partial bypass circuit can provide total cardiopulmonary bypass if circumstances dictate, such as when cardiac failure occurs during the operative procedure. Peripheral cannulation for total bypass has proved clinically useful for circulatory assistance and resuscitation and support of patients with acute massive pulmonary embolism until embolectomy can be performed [Z, 73. Previous studies indicate that a pump flow rate of 20 ml. per minute per kilogram of body weight into the distal aortic circulation is necessary to support renal function during and after periods of temporary occlusion of the thoracic aorta [5, 91. Preservation of spinal cord function also seems to require only a small volume perfusion. Administration of heparin incident to bypass perfusion may provide additional protection from ischemic damage by preventing thrombosis in small vessels in areas of sluggish blood flow. Neurological deficits after operation may be due to spinal cord ischemia incident to temporary aortic occlusion or to permanent interruption of the segmental blood supply through the intercostal arteries. Despite graft replacement of the entire descending thoracic aorta in many of these patients, central nervous system damage occurred in few patients. Partial bypass during pericardiectomy provides the technical advantages of freedom to elevate and compress the heart and to decompress the cardiac chambers while stripping the mat of fibrocalcific material from their walls. By permitting more complete removal of the constricting tissue about the heart, pericardiectomy with the adjunct of partial bypass should provide improved hemodynamic and clinical 52 THE ANNALS OF THORACIC SURGERY

8 Bypass for Pericardiectomy and Aneurysms results and reduce the risk of operation which is reported to be between 11 and 15% [4, 111. Several advantages of partial cardiopulmonary bypass over left atrial to femoral artery bypass exist. Partial bypass (1) obviates operative damage to the left atrium from catheter insertion, (2) removes bypass tubing from the operative field, (3) eliminates postoperative pericardial complications which may increase morbidity in older patients, (4) is readily employed when pericardial and pleural cavities are obliterated by adhesions, (5) facilitates perfusion in thoracoabdominal aneurysms or with a median sternotomy incision, (6) may be employed for resuscitation before thoracotomy in cases of ruptured aneurysm or traumatic aortic transection, and (7) may be converted to total cardiopulmonary bypass if necessary. Precautions which should be considered when using partial cardiopulmonary bypass include: (1) perfusion may be unsatisfactory if blood volume is depleted, (2) venous return may be inadequate if a large catheter is not inserted into the inferior vena cava (as might happen with stenosis with the common iliac veins or narrowing of the femoral vein due to phlebitis), and (3) excess removal of vena caval blood may interfere with cardiac output. SUMMARY Partial cardiopulmonary bypass with femoral vein and femoral artery cannulation and a small-volume bubble oxygenator with the hemodilution technique may be used for extracorporeal circulatory support during extracardiac operative procedures on the cardiovascular system. Partial bypass was used during pericardiectomy for constrictive pericarditis in 2 patients and resection and replacement of aneurysms of the descending thoracic aorta in 17 patients. While providing protection from ischemic damage to the kidneys and spinal cord and preventing strain of the left side of the heart during thoracic aortic occlusion, this alternative technique has certain advantages over left atrial to femoral artery bypass without oxygenation in the management of patients with aneurysms of the descending aorta. Use of partial bypass during pericardiectomy for constrictive pericarditis permits more extensive and thorough removal of the constricting fibrocalcific tissue and should provide improved clinical and hemodynamic results following this operation. While facilitating the operative dissection, the perfusion protects the patient from periods of decreased cardiac output during operation by assuring adequate blood flow to vital organs. Partial cardiopulmonary bypass with peripheral cannulation provides a convenient and flexible means for management of a variety of VOL. 6, NO. 1, JULY,

9 BLOODWELL, HALLMAN, AND COOLEY extracardiac lesions which require interruption of arterial circulation or interference with cardiac output. REFERENCES 1. Austen, W. G., and Shaw, R. S. Experimental studies with extracorporeal circuits as a method to enable surgical attack on thoracic aneurysms. J. Thorac. Cardiovasc. Surg. 39: 337, Beall, A. C., Jr., Al-Attar, A. S., Mani, P., and Tuttle, L. L. D., Jr. Resuscitation after acute massive pulmonary embolism. J. Thorac. Cardiovasc. Surg. 49:419, Berger, R. L., and Barsamian, E. M. Iliac or femoral vein-to-artery total cardiopulmonary bypass: An experimental and clinical study. Ann. Thorac. Surg. 2:281, Chamblis, J. R., Jaruszewski, E. J., Brofman, B. L., Martin, J. R., andfeil, H. Chronic cardiac compression (chronic constrictive pericarditis): A critical study of sixty-one operated cases with follow-up. Circulation 4:816, Cooley, D. A., De Bakey, M. E., and Morris, G. C., Jr. Controlled extracorporeal circulation in surgical treatment of aortic aneurysm. Ann. Szirg. 146:473, Dillon, M. L., Young, W. G., and Sealy, W. C. Aneurysms of the descending thoracic aorta. Ann. Thorac. Szirg. 3:430, Goldman, A., Boszormenyi, E., Utsu, F., Enescu, V., Swan, H. J. C., and Corday, E. Veno-arterial pulsatile partial bypass for circulatory assist. Dis. Chest 50:633, Morris, G. C., Jr., Moyer, J. H., Cooley, D. A., and Brockman, H. L. The renal hemodynamic response to hypothermia and to clamping of the thoracic aorta with and without hypothermia. Surg. Forum 5:219, Morris, G. C., Jr., Witt, R. R., Cooley, D. A., Moyer, J. H., and De Bakey, M. E. Alterations in renal hemodynamics during controlled extracorporeal circulation in the surgical treatment of aortic aneurysm. J. Thorac. Surg. 34:590, Neville, W. E., Thomason, R. D., Peacock, H., and Colby, C. Cardiopulmonary bypass during noncardiac surgery. Arch. Surg. (Chicago) 92:576, Wood, P. Chronic constrictive pericarditis. Amer. J. Cardiol. 7:48, DISCUSSION DR. WILLIAM E. NEVILLE (Hines, Ill.): We have been using a technique similar to that described by Dr. Bloodwell for several years, but with some deviation from that which he has shown. I am particularly happy to discuss this because it is the only time in my life when I will be able to present more cases than Dr. Cooley. Dr. Bloodwell has covered the subject so thoroughly that it is probably superfluous for me to present our data. We have operated upon 23 patients using partial perfusion through the groin, with 3 deaths occurring in the postoperative period. Three patients had dissecting aneurysms, 19 had aneurysms of the chronic variety, and in 1 patient with a coarctation without evidence of collaterals we used a femoral vein to femoral artery oxygenation perfusion. Our technique is similar to Dr. Bloodwell s with the exception that we use gravity drainage into the 13-inch disc oxygenator primed with Ringer s lactate solution. One group of surgeons prepares the femoral vessels for cannulation while another team is working in the chest. The perfusion is begun commensurate with clamping the aorta proximal and distal to the aneurysm. we rely on the arterial pressure and the appearance of the electroenceph- 54 THE ANNALS OF THORACIC SURGERY

10 Bypass for Pericardiectomy and Aneurysms alogram as to the effectiveness of the blood supply to the upper half of the body. If too much venous blood is removed, the radial arterial pressure will fall and evidence of hypoxia will be manifest on the electroencephalogram. An adjustable screw clamp on the venous outflow line effectively limits the drainage of blood into the oxygenator. As a rule, a flow rate of 1500 ml. per minute is adequate to prevent kidney damage and paraplegia. It is important to emphasize that it is unnecessary to mobilize the entire aneurysm. Only proximal and distal aortic isolation is needed for the placement of the clamps and a cuff to accept the graft. By leaving the mediastinal surface of the aneurysm undisturbed and suturing the intercostal vessels from within the aorta, postoperative bleeding is markedly diminished. DR. LARI A. ATTAI (Bronx, N.Y.): I would like to congratulate the authors on a very excellent presentation and call your attention to a problem that we encountered during pericardiectomy for constrictive pericarditis. A 64-year-old male patient was admitted to Montefiore Hospital and Medical Center with clinical manifestations of constrictive pericarditis, characterized by massive ascites, edema of the lower extremities, and marked elevation of the venous pressure. The preoperative chest x-rays showed egg-shell calcification involving both anterior and posterior aspects of the ventricles. Cardiac catheterization showed elevation of the end diastolic pressure in the right ventricle to 18 mm. Hg and the characteristic M wave appearance on the right atrial tracing with elevation of the mean pressure to 16 mm. Hg. Operation was performed through a bilateral anterior thoracotomy with transection of the sternum at the level of the fourth intercostal space. During dissection of the heavily calcified pericardium from the diaphragmatic surface of the right ventricle, an inadverent rent was made into the ventricle, and control of bleeding was difficult because of our inability to deliver the heart from the pericardial sac because of unyielding adhesions posteriorly. While pressure controlled the bleeding, cardiopulmonary bypass was prepared. A Bentley Temptrol disposable oxygenator was assembled and primed with Ringer s lactate solution. A single cannula was inserted into the right atrium for venous drainage. The right femoral artery was used for arterial return. Cardiopulmonary bypass was instituted, the rent was repaired, and the pericardiectomy was then completed. We were impressed with the ease with which we could accomplish pericardiectomy in a decompressed heart, particularly in the posterior aspect of the ventricles and the venae cavae. We believe that this method should be used routinely and electively for surgical treatment of constrictive pericarditis. DR. VINCENT L. GOTT (Baltimore, Md.): A year ago at this meeting, in discussion of Dr. Dillon s paper, we presented our technique for bypassing thoracic aneurysms using a graphite-benzalkonium-heparin (GBH) shunt bypass. I shall bring you up to date on the current status of this simplified bypass technique. It does eliminate the need for a pump, and it also eliminates the need for systemic heparinization which, I think, greatly simplifies the procedure. We have now used this technique on a total of 6 patients during the last 22 months; 4 patients had elective resections of thoracic aneurysms and 2 had emergency resections of ruptured aneurysms. Our first patient, who was mentioned last year, was a 78-year-old woman; she is now doing very well 22 months after surgery. All 4 of these patients had extensive aneurysms of the descending thoracic aorta and the bypass was achieved in each case either from the subclavian artery or the transverse arch of the aorta above into the iliac artery or the distal aorta below the aneurysm. All 4 patients who had elective resections are doing well at this time. There were 2 patients who had emergency surgery for ruptured aneurysms using this technique. In the first patient, the aneurysm had partially sealed, and the resection went satisfactorily; however, this patient had a myocardial infarction postoperatively and died 3 weeks after surgery. The second patient with a VOL. 6, NO. 1, JULY,

11 BLOODWELL, HALLMAN, AND COOLEY ruptured aneurysm came to surgery with a fistula from the aorta into the pulmonary artery as deqonstrated on an aortogram. At the time of induction of anesthesia, this aneurysm ruptured into the bronchus, with massive hemorrhage from the endotracheal tube, and on opening the chest, there was massive bleeding into the thoracic cavity. We lost this patient on the table, and I would say that this is the type of case that should be managed with a pump bypass or system such as Dr. Neville s or Dr. Bloodwell s so that you have a coronary suction unit in the system and blood can be retrieved from the open chest. For the elective resection of thoracic aneurysms, however, we think that the GBH shunt bypass is the preferred technique since it considerably simplifies the overall operative procedure. Finally, I can say that in the laboratory, we are now working with some new nongraphited, heparinized tubing. This tubing is not opaque, as is the case with the GBH tubing, and I think may offer a number of advantages over our present tubing. We hope that this will be available in the near future. DR. COOLEY: I would like to thank the discussants for their remarks. In regard to Dr. Attai s remarks, I think the one thing that deserves emphasis is that median sternotomy is a very convenient incision for doing pericardiectoniy. However, we have experienced the limitations of this approach in trying to free up the apex of the left ventricle. Planned partial pulmonary bypass will permit the extreme cardiac manipulation necessary to accomplish a complete pericardiectomy. We are in favor of median sternotomy. In regard to Dr. Gott s remarks, our difficulty with this technique has always been with the proximal cannulation of the subclavian artery or aorta directly. He alluded to this possibility. We have found that when one clamps at the level of the left subclavian artery or just distal to the left common carotid artery, proximal cannulation is not satisfactory and may lead to bleeding around the cannula. Another hazard in Dr. Gott s technique results from plunging a catheter into an atherosclerotic aorta which releases debris which might enter the carotid arteries or left subclavian artery. Dr. Gott apparently expressed an objection to using heparin in aortic surgery. We believe that heparin offers an additional protective effect upon the organs distal to the point of clamping. In this relatively low-pressure area heparin prevents microscopic thrombi which may be more serious than anoxic or ischemic damage. 56 THE ANNALS OF THORACIC SURGERY