Ann Thorac Surg 2001;71:347-349
© 2001 The Society of Thoracic Surgeons
Case report
Thoracoabdominal aortic repair in a 190-kg patient: optimized perfusion with two oxygenators
Erich Gygax, EBPb,
Peter Schüpbach, MDa,
Thierry P. Carrel, MDa
a Clinic for Cardiovascular Surgery, University Hospital, Berne, Switzerland
b University Hospital, Berne, Switzerland
Accepted for publication March 17, 2000.
Address reprint requests to Dr Carrel, Clinic for Cardiovascular Surgery, University Hospital, CH-3010 Berne, Switzerland
e-mail: thierry.carrel{at}insel.ch
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Abstract
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A 190-kg patient was referred because of an acute type B aortic dissection. Conservative management was initially performed but the 34-year-old patient was shown to have an increasing aortic diameter 2 months later and was scheduled for elective repair of the thoracoabdominal aorta. To anticipate potential difficulties with perfusion and oxygenation the cardiopulmonary bypass circuit was constructed with two parallel oxygenators, which allowed an adequate oxygen supply through all phases of the intervention and accelerated the estimated rewarming time.
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Introduction
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Nowadays, the performance of modern oxygenators allows an oxygen transfer of about 350 mL/min. In extremely obese patients, an oxygen debt may appear at any time during extracorporeal circulation, particularly during initial cooling and after deep hypothermic circulatory arrest. This oxygen deficit causes a suboptimal global oxygen supply during rewarming that may not be amenable to adequate correction before weaning from cardiopulmonary bypass.
A 34-year-old patient with a body weight of 190 kg was referred to our hospital because of an acute type B aortic dissection. The initial magnetic resonance imaging (MRI) examination showed a slightly enlarged descending aorta (5 cm) with some pleural effusion. In the absence of complications requiring immediate surgical repair, the patient was initially treated conservatively using antihypertensive drugs and analgesics. Because of the increasing diameter of the aorta up to 7.5 cm at first follow-up of MRI control, associated with diffuse recurrent pain episodes, elective replacement of the thoracoabdominal aorta was found to be indicated 2 months later. At this time the patient presented with hypertension of the upper extremities, resulting from compression of the true aortic channel in the proximal part of the descending aorta. An endovascular stent-graft procedure was rejected because of the extent of the aneurysm up to the suprarenal aorta.
Repair of the thoracoabdominal aorta was performed through a thoracophrenicolaparotomy. Extracorporeal circulation was instituted after cannulation of the external iliac artery and vein as well as the main pulmonary artery to optimize the venous return [1]. Cardiopulmonary bypass was conducted in deep hypothermia and at a core temperature of 20°C, 2 g pentobarbital was administered in the circuit, and the perfusion was interrupted shortly afterward [2, 3]. The proximal anastomosis was performed at the level of the distal aortic arch, which was found to be enlarged and difficult to clamp because of dense periaortic adhesions. Immediately after construction of this anastomosis, reperfusion of the upper extremities and brain was restarted through a cannula introduced into a side arm of the vascular prosthesis (Vaskutek anteflow, Sulzer Medica, Winterthur, Switzerland) and reconstruction of the thoracoabdominal aorta at the level of the visceral arteries was achieved using the distal exsanguination technique [4]. The patient was treated for 4 days in the intensive care unit, recovered well, and was discharged on postoperative day 16.
To anticipate potential difficulties with perfusion and oxygenation the cardiopulmonary bypass circuit was constructed with two parallel oxygenators (Affinity, Medtronic, Minneapolis, MN). At the level of the arterial inflow, a Y connector was introduced into the circuit and connected with two membrane oxygenators. The outflow of the two oxygenators was joined just beyond the outflow ports (Fig 1). Perfusion was performed in alpha-stat regimen with a reduced perfusion index of 1.8 L · min-1 · m-2 (instead of the regular 2.4 L · min-1 · m-2 according to the lean body mass). Twenty-eight French arterial and venous cannulas were used.
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Fig 1. Schematic representation of the constructed bypass circuit with two parallel membrane oxygenators.
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The perfusion was unproblematic during the entire operation and a flow of 6 L/min could be maintained (Table 1). The global oxygen supply was fully satisfactory; the lowest venous oxygen saturation was 62%. Electrolytes remained normal during the whole perfusion period, but the base deficit was as high as -8.9 immediately after restarting the perfusion following the circulatory arrest. This value returned to normal during the rewarming phase (Fig 2). The expected pressure gradient over the oxygenation membrane of 80 to 100 mm Hg could be reduced to 45 to 55 mm Hg with the use of two oxygenators. Phentolamine was given as a vasodilator during the cooling and rewarming phases. The time required for rewarming up to the requested core temperature of 35°C was 42 minutes. Blood loss was 450 mL during the first 12 hours and chest tubes were removed on the 1st postoperative day. The patient received two packed cell units and two fresh frozen plasma units.
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Fig 2. Main perfusion data, blood gas analysis, and evolution of the temperature during the different perfusion phases of the operation. (CPB = cardiopulmonary bypass; HCA = hypothermic circulatory arrest.)
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Comment
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The determination of oxygen transfer in membrane oxygenators is usually based on the perfusion flow rate varying between 1 and 10 L/min. For the commercially available oxygenators, mean oxygen transfer is approximately 250 to 350 mL/min at a flow of 6 L/min.
This case report shows that a patient with severe obesity (body weight 190 kg, theoretical oxygen consumption at rest 350 mL/min) might still be accepted for a major cardiovascular intervention provided the perfusion does not lead to an uncorrectable oxygen debt. In this 34-year-old patient, the use of two parallel oxygenators allowed an adequate oxygen supply during all phases of the intervention and furthermore had the beneficial effect of accelerating the estimated rewarming time, which was 42 minutes, compared with a mean rewarming time of 50 ± 18 minutes observed in the last 38 operations with deep hypothermic circulatory arrest [5].
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References
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Svensson L.G. Anesthesia and perfusion management. In: Svensson L.G., Craword S.E., eds. Cardiovascular and vascular disease of the aorta. Philadelphia: WB Saunders, 1997:248-262.
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Kouchoukos N.T., Daily B.B., Rokkas C.K., Murphy S.F., Bauer S., Abboud N. Hypothermic bypass and circulatory arrest for operations on the descending thoracic and thoraco-abdominal aorta. Ann Thorac Surg 1995;60:67-77.[Abstract/Free Full Text]
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Rokkas C.K., Kouchoukos N.T. Profound hypothermia for spinal cord protection in operations on the descending thoracic and thoracoabdominal aorta. Semin Thorac Cardiovasc Surg 1998;10:57-60.[Medline]
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Cooley D.A. Further experience with exsanguination for descending thoracic aneurysms. J Cardiac Surg 1994;9:625-630.[Medline]
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Carrel T.P., Berdat P.A., Robe J., et al. Outcome of thoracoabdominal aortic operations using deep hypothermia and distal exsanguination. Ann Thorac Surg 2000;69:692-695.[Abstract/Free Full Text]
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Abstract
Introduction
