Descending thoracic aortic aneurysms Madhusudan Rao Puchakayala MB BS, MD, FRCA

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1 Descending thoracic aortic aneurysms Madhusudan Rao Puchakayala MB BS, MD, FRCA Wei C Lau MD Key points The natural course of the majority of aortic aneurysms is rupture and death. Patients usually have co-morbidities involving the heart, lung and kidneys: these must be identified and optimized appropriately. Surgical access is best achieved by a left thoracotomy and using one lung ventilation. Distal perfusion techniques reduce the incidence of complications. After operation, the mean arterial pressure should be maintained between 80 and 100 mm Hg to prevent spinal cord hypoperfusion. The main postoperative complications are renal failure and ischaemic spinal cord injury. The incidence of thoracic aortic aneurysms is estimated to be 5.9 compared with 350 cases for abdominal aortic aneurysms per person-years. Of the thoracic aortic aneurysms, the ascending aorta is affected in 50% of cases, the aortic arch in 10% and the descending thoracic aorta (DTA) in 40%. 1 A DTA aneurysm is defined as involving any portion of the thoracic aorta distal to the origin of the left subclavian artery. It can involve varying parts of the DTA and may extend to the abdominal aorta. Thoracoabdominal aneurysms (TAAs) are divided into five groups according to the modified TAA classification 2 (Fig. 1). Classification is crucial because it allows risk stratification based on the extent of aorta involved. The majority of aneurysms are degenerative; other causes include traumatic, mycotic and pseudo-aneurysms. The mean age of diagnosis is yr with a male predominance of 2:1 4:1. The 5-yr survival rates of patients with thoracic and abdominal aortic aneurysms not surgically treated is 20 and 16 19%, respectively. 1 3 The most common cause of death is rupture. Those who survive operation sustain significant morbidity, prolonged hospital course and a poor quality of life. Aneurysm growth is exponential with a rate of 0.12 cm per yr for aneurysms >5.2 cm in diameter. Predisposing factors for rupture include: aneurysm diameter >5 cm, hypertension, smoking and chronic obstructive pulmonary disease, pain, chronic aortic dissection and age. Although complications after thoracic aortic surgery remain a threat, the overall operative mortality is 5 12% with a 5 yr survival of 70 79% for DTA aneurysm and 59% for TAA surgery. 4 Major postoperative complications include renal failure (5 13% 5 ) and spinal cord ischaemic injury (4 30%, depending on the extent of repair and the use of adjuncts 6 ). Madhusudan Rao Puchakayala MB BS MD FRCA Consultant Cardiac Anaesthetist Guy s and St Thomas NHS Foundation Trust Lambeth Palace Road London SE1 7EH UK Tel: Fax: madhusudan.puchakayala@gstt.nhs.uk (for correspondence) Wei C Lau MD Associate Professor and Director of Cardiac Anaesthesia Department of Anaesthesiology University of Michigan Medical Center 1500 East Medical Center Drive Ann Arbor MI USA Fig. 1 Modified TAA classification. Extent I: from distal to the left subclavian artery to above the renal arteries. Extent II: from distal to the left subclavian artery to the aortic bifurcation. Extent III: from the sixth intercostals space to the aortic bifurcation. Extent IV: from the diaphragm to the aortic bifurcation (total abdominal aorta). Extent V: from the sixth intercostals space to above the renal arteries. (Reproduced from Safi and colleagues, 2 with permission.) 54 Continuing Education in Anaesthesia, Critical Care & Pain Volume 6 Number ª The Board of Management and Trustees of the British Journal of Anaesthesia [2006]. All rights reserved. For Permissions, please journals.permissions@oxfordjournals.org doi: /bjaceaccp/mkl002

2 Preoperative investigations Thoracic aneurysm patients are generally elderly and have one or more co-morbidities involving the heart, lungs and kidneys that must be identified and optimized appropriately. In addition to full blood counts, clotting and renal function, liver function should be evaluated if deep hypothermic circulatory arrest (DHCA) is planned during surgery. The presence of preoperative renal insufficiency and the development of postoperative renal failure are associated with increased morbidity, mortality and neurological deficit. Liver dysfunction is associated with bleeding problems and has increased mortality. Preoperative CT scan and transoesophageal echocardiography (TOE) are required to delineate the extent of aneurysm and in planning the operative strategy. MRI and MR angiography scans do not require radiocontrast dyes and are now being used more often than aortography and contrast CT scans, because of safety concerns in patients with impaired renal function. All patients should undergo imaging studies to assess myocardial ischaemic risk and ventricular function because of the high incidence of coronary artery disease (CAD) and the haemodynamic stress placed on the heart during proximal aortic crossclamping. Coronary angiography is performed in all patients and, if intervention is indicated, undergo either coronary angioplasty, stenting, or both or bypass surgery, as appropriate. Echocardiography is used to evaluate ventricular function and concomitant valvular abnormalities. Chest X-ray may detect the presence of left bronchial distortion because of the aneurysm. Pulmonary function tests and room-air arterial blood gas determinations are performed to evaluate respiratory reserve as one lung ventilation (OLV) is necessary for surgical exposure. Patients should stop smoking for at least 2 weeks before surgery and bronchodilator therapy maximized. Intraoperative management Anaesthetic management of these patients is extremely challenging and requires skill and expertise in: (i) haemodynamic monitoring; (ii) patient positioning; (iii) OLV; (iv) proximal and distal aortic perfusion management; (v) end-organ (renal, mesenteric and spinal cord) function monitoring and prevention of dysfunction; and (vi) massive blood loss and coagulopathy. Haemodynamic monitoring A right radial or brachial artery catheter is required to assess blood pressure proximal to the aneurysm because the left subclavian artery may be compromised by the proximal cross-clamp. The right femoral arterial pressure is monitored for distal perfusion. The left femoral vessels are needed for femoral bypass. Ventricular function can be monitored using a pulmonary artery catheter (PAC) and TOE. The limitations of PAC include passage into the left PA and use of OLV with the left lung collapsed resulting in overestimation of the left ventricular end-diastolic pressure (LVEDP). The left internal jugular vein is preferred for easy access under the drapes in the left lateral position. TOE dynamically monitors left ventricular (LV) function, confirms the diagnosis of any associated dissection, confirms correct position right atrial cannula, defines the quality of repair and assesses the adequacy of retrograde perfusion via femoral femoral bypass. Patient positioning The left lateral decubitus position is used with a slight tilt to the left to access the femoral vessels for femoral femoral bypass. After induction of anaesthesia and placement of invasive lines, the left femoral vessels are surgically exposed. The patient is then turned to the right and the arms, shoulder and knees are padded. One lung ventilation Surgical access is best achieved via a left thoracotomy. Repair is greatly facilitated by using a double lumen tube (DLT) especially for types 1 and 2 and some type 3 repairs. The right lung is isolated and protected in the event of an intrapulmonary bleed or rupture of the aneurysm into the left main bronchus. The ability to have the left lung collapsed improves visualization of the surgical field. This decreases the cross-clamp time, thereby reducing the likelihood of spinal cord, renal and visceral ischaemic injury and also reduces left lung retraction and trauma. It is not unusual for an aneurysm to distort the left main stem bronchus, which can make the usual left-sided tube positioning difficult; right-sided DLT placement may be required. Therefore, the chest X-ray should be examined. Performing a fibreoptic bronchoscopy before insertion of the DLT can confirm distortion of the left main bronchus. Other methods for lung isolation may have to be used including univent tubes and bronchial blockers. Consideration must be given for anaesthesia under OLV and management of hypoxaemia as these patients frequently have chronic lung disorders. At the end of surgery, provided there is no facial swelling, airway oedema or evidence of bleeding, the DLT should be changed for a single lumen tube. Leaving the DLT for h is beneficial only if there is any possibility of re-exploration. Surgical technique Exposure of the DTA is accomplished via a left thoracotomy usually between the 4th and the 5th ribs. However, double intercostal incision may be required for full exposure. For a full thoracoabdominal exposure, the incision begins above the symphysis pubis, goes midline to the umbilicus, and curves across the costal cartilage to the bed of the 6th rib. The surgical technique involves cross-clamps insertion above and below the lesion, opening of the aneurysm and replacing the aneurysm with a graft. Diaphragmatic preservation, defined as division of only the muscular portion with preservation of the tendinous portion of the diaphragm, leads to early ventilator weaning when compared with complete diaphragmatic division. Continuing Education in Anaesthesia, Critical Care & Pain Volume 6 Number

3 Pathophysiology of aortic cross-clamp Cross-clamping of the DTA produces proximal hypertension and distal hypoperfusion. The cardiac filling pressures, myocardial wall stress and oxygen consumption (VO 2 ) increase; cardiac output (CO) and ejection fraction decrease. The degree of hypertension depends on the location of the clamp, degree of collaterals, and the pre-occlusion aortic flow. There is typically a 40% increase and 85% decrease in mean arterial pressure (MAP) above and below the cross-clamp respectively with distal aortic pressures typically ranging between 11 and 30 mm Hg. In an attempt to limit the degree of hypertension, there is reflex slowing of the heart rate, decreased contractility and peripheral vasodilatation. Distal to the cross-clamp, there is decreased oxygen consumption and conversion to anaerobic metabolism. In addition, hepatic and renal hypoperfusion greatly attenuates the elimination of lactic acid. Partial bypass and shunt techniques reduce lactate accumulation. Declamping can result in severe hypotension because of hypovolaemia, decreased systemic vascular resistance and myocardial depression. Sudden increases in intravascular volume and sequestration of blood, wash out of acid metabolites and vasodilators, hyperkalaemia, increased vasoactive intestinal peptide and reactive hyperaemia contribute to hypotension. Pharmacological management of the period of aortic cross-clamping When isolated cross-clamp and repair is used without distal perfusion techniques, pharmacological interventions are necessary to treat proximal hypertension and to protect the myocardium. Arterial vasodilators such as sodium nitroprusside can result in dangerously low pressures distal to the lowest clamp leading to steal phenomenon and possibly spinal cord injury. Venodilators such as nitroglycerine reduce preload and cardiac filling pressures and limit ventricular dilatation and wall tension. Nitroglycerine alone is usually not sufficient to control proximal arterial hypertension; it is best used in combination with vasodilators and deepening levels of anaesthesia. Isoflurane causes vasodilatation of both resistance and capacitance vessels and has been safely used for anaesthesia and blood pressure control. Esmolol infusion decreases proximal arterial pressure by reducing contractility and heart rate. It is shortacting and its effects do not persist after unclamping of the aorta. Before clamping of the aorta, it is helpful to keep the patient in a slightly hypovolaemic state to help decrease the extent of arterial hypertension. Shortly before cross-clamp application, vasodilator therapy is started. During the period of crossclamping, intravascular volume must be maintained and replaced with the crystalloids, colloids and blood transfusion to increase the pulmonary artery wedge pressure (PCWP) to above its baseline status by 2 4 mm Hg. All infusions of vasodilator agents should be discontinued before unclamping. Ventilation should be increased in anticipation of an increased acid load from the distal circulation. Vasopressor substances, including phenylephrine hydrochloride and norepinephrine, should be available to treat declamping hypotension. Even though each patient should be treated individually, the usual aim is to have a haematocrit >27% at the end of surgery. Because of concomitant coronary artery disease in these patients and the risk of spinal cord, renal and splanchnic ischaemia, anaemia may decrease oxygen delivery to vital organs. Blood volume replacement should be guided by monitoring of filling pressures and CO and by TOE. Cross-clamp must be released slowly to help adapt to the sudden increase in intravascular space. If necessary, the surgeon can partially or totally reclamp the aorta until appropriate therapy is instituted. Proximal and distal aortic perfusion management The methods used for upper- and lower-body blood flow control are: simple aortic cross-clamping, passive shunts, atriofemoral bypass, partial cardiopulmonary bypass (CPB) and DHCA. The advantages and disadvantages for the use of distal aortic perfusion techniques are described in Table 1. 7 There are no established criteria for the selection of one technique over another. Simple aortic cross-clamping consists of clamping the DTA proximal and distal to the aneurysm without the use of a shunt or pump. The main disadvantages of this technique are distal organ ischaemia, and the incidence of ischaemic complications increases with prolonged clamp times especially with times exceeding 30 min. Simple cross-clamping results in lower morbidity and mortality than shunt and bypass techniques, provided that surgery is expeditious. Passive shunts divert blood from proximal to distal aortic sites or femoral artery and control proximal hypertension primarily by decreasing left ventricular afterload. For the shunt to be effective it has to carry 60% or more of the baseline descending aortic flow. The most commonly used shunt is the 9 mm heparin-coated conduit (Gott shunt) that does not require systemic anticoagulation. The proximal end of the shunt is typically placed in the ascending aorta attributable to high flow rates, although the Table 1 Advantages and disadvantages of distal perfusion techniques (Reproduced from O Connor and Rothenberg, 7 with permission) Advantages Effective control of proximal hypertension Protection against myocardial, renal and visceral ischaemia Prevention of acidosis and declamping shock Potential reduction in the incidence of spinal cord ischaemic injury Ability to rapidly warm patients Access for rapid volume infusion Potential reduction in the incidence of DIC Supplementary oxygenation with extracorporeal oxygenators Disadvantages Possible atrial, ventricular aortic or femoral artery injury Technical difficulty with atrial or proximal aortic cannulation Risk of air emboli/embolic stroke Interference and cluttering of the operative field Increased operative time Potential for excess haemorrhage with anticoagulation Bleeding from cannulation sites Shunt dislodgement 56 Continuing Education in Anaesthesia, Critical Care & Pain Volume 6 Number

4 aortic arch and the proximal DTA can be other suitable sites. Use of the left subclavian artery for proximal cannulation should be avoided because it may cause subclavian steal phenomenon with flow reversal in the vertebral artery (from which the anterior spinal artery is derived) and in the internal mammary artery. The disadvantages include technical difficulties, bleeding, dislodgement, embolic stroke and death. Atriofemoral centrifugal bypass or left heart bypass are most commonly used in TAA surgery. The bypass is established from the left atrium to the left common femoral artery with an interposed centrifugal pump. Centrifugal pumps are non-occlusive and non-traumatic to blood cells and thus require minimal or no heparin, provided that the flow is >800 ml min 1. Diversion of blood from the left atrium to the bypass on cross-clamping decreases LV preload, CO, proximal aortic pressure and left ventricular stroke work. The ACT should be maintained between 150 and 200 s. With this technique, the need for vasodilators and sodium bicarbonate is almost eliminated, because proximal arterial hypertension, metabolic acidosis and splanchnic organ ischaemia do not occur. Bypass flow should be adjusted to maintain a distal mean aortic pressure of mm Hg. Because about 50% of total CO is distributed to organs below the diaphragm, pump flow is typically set at 2 3 litre min 1. Bypass flow rates of ml kg 1 min 1 are sufficient to normalize proximal aortic pressure, maintain distal aortic perfusion and provide satisfactory renal and spinal cord blood flow. Adjustments in pump flow rates and circulating blood volume are guided by the careful interpretation of haemodynamic data, including ventricular filling pressures and end-diastolic area, along with proximal and distal aortic pressures. Current evidence indicates that left atriofemoral centrifugal pump bypass may be beneficial in patients with poor left ventricular function, CAD, pre-existing renal disease, or anticipated prolonged aortic cross-clamping time. Partial CPB (femoral vein or right atrial femoral artery bypass) uses oxygenators and requires full heparinization. Partial CPB results in the reduction of venous return and CO, which helps control proximal hypertension. The arterial cannula in the femoral artery provides distal perfusion to the lower extremities, spinal cord and splanchnic viscera. A flow rate of ml kg 1 min 1 is usually adequate to control proximal hypertension and maintain mean distal aortic pressure of mm Hg. Partial CPB is useful in patients who require a long duration of aortic cross-clamping. Increased blood loss and haemorrhagic complications can occur with this technique because of heparinization, CPB-related coagulopathy and haemorrhage from cannulation sites. DHCA is always used if there is difficulty in application of the proximal cross-clamp. DHCA has been used to protect vital organs, especially the spinal cord, from ischaemic injury during thoracic aortic clamping. The CMRO 2 at 37 C is 2.2 times that at 27 C. The decrease in spinal cord temperature can significantly improve its tolerance to ischaemia. Advantages of DHCA include minimal aortic dissection, avoidance of proximal aortic crossclamping, bloodless surgical field and increased tolerable ischaemic time. The period of cerebral circulatory arrest should still be limited to min to minimize the risk of cerebral injury. The use of DHCA to 15 C can decrease spinal cord injury and renal failure compared with simple cross-clamping. A major disadvantage is the substantial increase in blood loss and transfusion requirements. Initial studies have not shown a consistent improvement in outcome with the use of distal aortic perfusion compared with the clamp-and-sew technique, provided that aortic occlusion time is <30 min. However, distal perfusion techniques, along with adjuncts such as CSF drainage and hypothermia, have shown significant improvement in neurological outcome. 4 End-organ assessment and protection Renal The incidence of acute renal failure after DTA and TAA surgery is 5 13%. 5 Because of the increased mortality associated with postoperative renal failure after DTA repair, high-risk patients must be identified and protective measures instituted. Acute renal failure is usually because of decreased renal blood flow and reperfusion injury. Increased cross-clamp time (>30 min) is the main risk factor. Other predisposing factors include advanced age, preoperative renal dysfunction, sustained perioperative hypotension and low CO, and failure to use atriofemoral bypass during operation. Renal protective measures that are most effective include minimal cross-clamp times and maintenance of adequate intravascular volumes, CO and perfusion pressures. Adjuncts such as distal perfusion and hypothermia (both selective renal and systemic) have also shown to improve renal outcome. Methods to increase urine output using low dose dopamine, furosemide and mannitol may limit renal dysfunction. Low dose dopamine (1 3 mg kg 1 min 1 ) was found to be ineffective in reversing renal injury after thoracic aortic surgery. Although loop diuretics can theoretically improve renal tolerance to ischaemia by reducing tubular oxygen requirement, its use has not shown to affect renal outcome. Mannitol, in addition to being an osmotic diuretic, causes renal vasodilatation and is a free radical scavenger. Current available data do not support the use of these agents. Spinal cord Ischaemic neurological injury usually presents as paraplegia; it is a devastating complication with an incidence of 5 30% depending on the extent of surgery and the use of adjuncts. 6 This may result from prolonged ischaemia (prolonged cross-clamp times, particularly >30 45 min) or the resection of the artery of Adamkiewcz. Other important contributing factors are the presence of aortic dissection, the extent of the aneurysm, whether intercostal arteries were implanted and age. Distal aortic hypoperfusion, Continuing Education in Anaesthesia, Critical Care & Pain Volume 6 Number

5 perioperative hypotension and hypoxaemia are risk factors for developing postoperative delayed paraplegia. Collateral blood flow to the spinal cord influences the degree of spinal cord injury. Renal dysfunction and hyperglycaemia can also increase the risk of injury. Aortic cross-clamping decreases the distal MAP and increases the CSF pressure (CSFP) because of increased central venous pressure (CVP) and CSF production. Thus, the spinal cord perfusion pressure (SCPP) is decreased (MAP CSFP). In addition to decreasing aortic cross-clamp time, different methods and adjuncts have been used to reduce the frequency of paraplegia. CSF drainage using spinal drains improves SCPP by decreasing CSFP. However, although CSF drainage alone does not appear to have substantial benefit, it is proven useful if combined with maintenance of distal aortic perfusion. 89 The use of spinal drains has increased because of low morbidity and significant benefits. 910 They are inserted under general anaesthesia and kept to overflow at a CSFP of 10 cm H 2 O. CSF drainage should be continued in the immediate postoperative period for at least h. After surgery, MAP should be maintained between 80 and 100 mm Hg. Delayed neurological deficit can occur. The signs include unstable arterial blood pressure, hypoxaemia post extubation and CSF pressure >10 mm Hg. CSF drainage is discontinued usually after the second postoperative day. If delayed neurological deficit occurs, the CSF drainage catheter should be reinserted and CSF drained for another 3 days. Other spinal cord protective measures are distal aortic perfusion, hypothermia, surgical implantation of critical intercostal arteries, intrathecal papaverine and drugs such as steroids, barbiturates, calcium channel blockers, perfluorocarbons and naloxone. Distal aortic perfusion protects the spinal cord only if the artery of Adamkiewcz originates beyond the distal clamp. It also decreases vasodilator use by preventing proximal hypertension thus preventing steal phenomenon. Hypothermia increases ischaemic tolerance because neural oxygen consumption decreases by 5% for every degree centigrade reduction in body temperature. Mild to moderate hypothermia, DHCA and regional spinal cord cooling have shown to be spinal cord protective. Regional spinal cord cooling is achieved by infusion of iced saline (4 C) through an epidural catheter or perfusion of the aortic area between the cross-clamps with iced solutions. However, epidural infusions may increase intraspinal pressure and attenuate the beneficial effects of hypothermia. Spinal cord function monitoring, such as somatosensory evoked potentials (SSEP), does not reliably assess function during cross-clamping. The technique monitors the posterior column (sensory function) of the spinal cord and not the anterior motor column which is at risk. Therefore, paraplegia may occur despite intact SSEPs. In addition, anaesthetic agents suppress SSEPs. The use of motor evoked potentials that monitor anterior horn cells have shown some success; however, this requires partial neuromuscular block, it is cumbersome and seizures can be triggered. Mesentery DTA cross-clamping results in ischaemia and reperfusion injury to the mesenteric circulation. To attenuate the effects of mesenteric hypoperfusion, rapid reimplantation of the celiac trunk and superior mesenteric artery is required in TAA surgery. Bleeding abnormalities and depletion of coagulation factors can occur after supracoeliac cross-clamping and the severity correlates with prolonged clamp times. Arterial blood gas levels should be monitored at regular intervals, and acidosis corrected with an i.v. continuous infusion of sodium bicarbonate. Maintenance of perfusion of the gut, liver and kidneys with the use of distal perfusion techniques reduces the severity of these complications. The use of mesenteric shunts to perfuse the viscera can significantly reduce visceral ischaemic time. Massive blood loss and coagulopathy Intraoperative haemorrhage is a major cause of early mortality after thoracic aortic surgery. Blood loss is increased because of hypothermia and acidosis, heparinization and disseminated intravascular coagulation (DIC) after hypoperfusion. Hepatic hypoperfusion leads to citrate accumulation and hypocalcaemia. Massive blood transfusion leads to dilutional thrombocytopaenia and factor deficiencies. Techniques for monitoring coagulation including thromboelastogram, platelet function analyser, and prothrombin time and activated partial thromboplastin time should be used. Blood, platelets, fresh frozen plasma and cryoprecipitate should be readily available in addition to a cell saver. Depending on the preoperative haemoglobin, up to 2 units (350 ml per unit) of blood can be removed before heparinization and stored at room temperature with frequent agitation. The autologous blood is a good source of platelets and is retransfused after heparin reversal with protamine. Management of anaesthesia There are no randomized controlled studies identifying the beneficial effects of any particular anaesthetic technique. Induction is usually performed by a slow administration of i.v. anaesthetic such as etomidate, propofol or thiopental followed by a nondepolarizing neuromuscular blocking agent. Opioids such as fentanyl are used to blunt the haemodynamic response to laryngoscopy and intubation. Maintenance of anaesthesia is achieved with inhalation agents and intermittent opioids. The use of combined general and epidural anaesthesia for thoracic aortic surgery is still debatable and this practice varies among different centres. Beneficial effects of epidural anaesthesia include excellent postoperative pain relief, and decreased stress response and pulmonary and cardiac morbidity. The cardiovascular response to proximal aortic cross-clamping can also be blunted. The risk of epidural haematomata is minimal if low dose heparin is used. Side-effects include excessive hypotension after cross-clamp release, epidural haematomata associated with anticoagulation and coagulation abnormalities. 58 Continuing Education in Anaesthesia, Critical Care & Pain Volume 6 Number

6 Postoperative management After operation, patients are nursed in the supine posture with a slight reversed Trendelenburg tilt if a CSF drainage catheter is in situ. A single lumen tracheal tube is exchanged for the DLT. The MAP is maintained between 80 and 90 mm Hg to prevent a decrease in SCPP. Patients are woken up and extubation is attempted as soon as possible to evaluate the neurological status. Even if there is no immediate neurological deficit, be alert for delayed deficit (see above). CSF drainage is discontinued usually after 48 h. Pain management can be achieved by continuous opioid infusions titrated to effect or epidural infusions of low dose local anaesthetic and opioid mixtures. Patients must be closely monitored for any neurological and haemodynamic changes. References 1. Bickerstaff LK, Pairolero PC, Hollier LH, et al. Thoracic aortic aneurysms: a population-based study. Surgery 1982; 92: Safi HJ, Huynh TTT, Estera AL, Miller CC III, Porat EE. Thoracoabdominal aortic aneurysm. In: Franco KL, Verrier ED, eds. Advanced Therapy in Cardiac Surgery. Hamilton: BC Decker Inc., 2003; Szilagyi DE, Smith RF, DeRusso FJ, et al. Contribution of abdominal aneurysmectomy to prolongation of life. Ann Surg 1966; 164: Crawford ES, Crawford JL, Safi HJ, et al. Thoracoabdominal aortic aneurysms: preoperative and intraoperative factors determining immediate and long-term results of operations in 605 patients. J Vasc Surg 1986; 3: Kashyap VS, Cambria RP, Davison JK, et al. Renal failure after thoracoabdominal aortic surgery. J Vasc Surg 1997; 26: Safi HJ, Miller CC III, Huynh TT, et al. Distal aortic perfusion and cerebrospinal fluid drainage for thoracoabdominal and descending thoracic aortic repair: ten years of organ protection. Ann Surg 2003; 238: O Connor CJ, Rothenberg DM. Anesthetic considerations for descending thoracic aortic surgery: part II. J Cardiothorac Vasc Anesth 1995; 9: Ling E, Arellano R. Systematic overview of the evidence supporting the use of cerebrospinal fluid drainage in thoracoabdominal aneurysm surgery for the prevention of paraplegia. Anesthesiology 2000; 93: Estrera AL, Rubenstein FS, Miller CC III, Huynh TT, Letsou GV, Safi HJ. Descending thoracic aortic aneurysm: surgical approach and treatment using the adjuncts cerebrospinal fluid drainage and distal aortic perfusion. Ann Thorac Surg 2001; 72: Cheung AT, Pochettino A, Guvakov DV, Weiss SJ, Shanmugan S, Bavaria JE. Safety of lumbar drains in thoracic aortic operations performed with extracorporeal circulation. Ann Thorac Surg 2003; 76: Please see multiple choice questions 6 9. Continuing Education in Anaesthesia, Critical Care & Pain Volume 6 Number