PRO AND CON J. Earl Wynands, MD, Editor
Pro: Cerebrospinal
Fluid
Drainage
Prevents
Paraplegia
Michael Nugent, MD
M
ORTALITY RATES for repair of thoracic aortic aneurysms remain approximately 10% and paraplegia rates in survivors are reported to exceed 6..5%.‘J The largest published series of 605 patients reported more than 20% of patients with paraplegia after repair of large aneurysms extending from the left subclavian artery and including the abdominal aorta. These large aneurysms, which carry a particularly high risk of paraplegia, accounted for more than one-fourth of all aneurysms repaired in the series.2 The location and extent of the aneurysm, patient age, and prolonged aortic cross-clamp time have all been correlated with an increased incidence of paraplegia.‘J Spinal cord injuries complicating repair of a descending thoracic aneurysm result in neurologic findings similar to the anterior spinal artery syndrome seen after occlusion of the arteria radicularis magna anterior or artery of Adamkiewicz. Motor function is lost in the lower extremities, while pain, temperature, vibratory, and position senses remain intact. The origin of the artery of Adamkiewicz is variable, occurring only 60% of the time in the expected Tg to T12 region. The origin of the artery can be as high as T3 or as low as L5.3 For this reason, during the repair of any given aneurysm, the surgeon does not know which intercostal arteries to preserve or anastamose to the graft. Until the surgeon knows the blood supply of the spinal cord for each individual patient, no intervention such as cerebrospinal fluid (CSF) drainage will completely prevent paraplegia, but such interventions may help maintain the viability of anterior horn cells of the spinal cord during aortic clamping. If surgical resection of the artery of Adamkiewicz has occurred, paraplegia still may or may not result, depending on the adequacy of collateral blood supply through the anterior spinal arteries. Recent reports of late paraplegia often associated with postoperative hypotension may represent patients in whom the artery of Adamkiewicz has been resected, but intraoperative preventive measures have preserved function during the surgery, only to have spinal cord ischemia occur postoperatively. In addition to CSF drainage, two other interventions that are strongly supported in laboratory models and can be applied with minimal risk will be discussed. These are mild hypothermia and the avoidance of glucose-containing solutions. A short discussion of shunting procedures will be
From the Department of Anesthesia, Medical College of Ohio, Toledo, OH. Address reprint requests to Michael Nugent, MD, Department of Anesthesia, Medical College of Ohio, 3000 Arlington Ave, PO 10008, Toledo, OH 43699. Copyright o 1992 by W.B. Saunders Company 1053-0770/9210603-0029$03.0010 Key words: arteries, aorta aneuqsrns, paralysis
366
presented, because their absence or presence may reflect on nitroprusside usage and the effectiveness of CSF drainage for spinal cord protection. Vicanti and Ames have shown that mild hypothermia to 34°C combined with intravenous magnesium doubled the cross-clamp time that could be tolerated without paraplegia in a laboratory modeL4 Allowing the patient to cool to 34°C could theoretically cause problems with hemostasis, because enzymatic coagulation reactions are slowed, but with good surgical hemostasis coagulopathies usually are not a major problem. Several studies have addressed the deleterious consequences of adding modest amounts of glucose to intravenous solutions prior to cerebral ischemia.5 One study in rabbits has demonstrated similar deleterious effects of glucose loading on spinal cord ischemia.h The decision to use a shunt to pressurize the aorta distal to the lower cross-clamp is a surgical one. In 1973, Crawford and Rubio showed that shunting procedures to pressurize the distal aorta below the cross-clamp would not prevent paraplegia from occurring.7 However, this was not a prospective randomized study to answer the question if shunting procedures decrease the incidence of paraplegia. It only demonstrated that, despite having shunts in place, paraplegia still occurred. One retrospective study has shown that shunting procedures do decrease the incidence of paraplegia when a dissecting aneurysm is present.8 Shunts do greatly facilitate anesthetic management of these cases, attenuating the tremendous hemodynamic effects of crossclamping the aorta just below the left subclavian artery. Shunts also minimize the need for large doses of nitroprusside. Nitroprusside may have deleterious effects on spinal cord preservation, because it not only results in an increase in CSF pressure, but it also decreases aortic pressure below the cross-clamp.‘-” The concept of CSF drainage was first suggested by Blaisdell and Cooley in 1962 in a canine model.‘? Their findings that CSF drainage prevented paraplegia during aortic cross-clamping have consistently been reconfirmed.13J4 Svensson et al have shown that CSF drainage in combination with intrathecal papaverine is effective against paraplegia in a primate model.14 The first documentation of a patient becoming paraparetic in association with a marked elevation in CSF pressure after aortic cross-clamping was reported during a coarctation repair by Berendes et al in 1982.1s They suggested that CSF drainage may be helpful. Concerns regarding CSF drainage are that (1) it is not proven effective in man; (2) it could theoretically result in cerebral herniation if CSF were drained at a time when the CSF pressure was very high; (3) if postoperative paraplegia occurs, the possibility that it may have resulted from an epidural hematoma must be ruled out; and (4) medical legal concerns may discourage placement of a subarachnoid
Journal of Cardiothoracic and
Vascular
Anesthwa,
Vol6, No 3 (June), 1992: pp 366-368
PRO: CSF DRAINAGE
367
catheter in a patient with a significant risk of postoperative paraplegia. The mechanism by which aortic cross-clamping results in increased CSF pressure may be large increases in arterial pressure that exceed the limits of cerebral autoregulation, increasing cerebral blood flow and cerebral blood volume. If arterial pressure increases are attenuated with vasodilators, such as sodium nitroprusside, this would decrease cerebral vascular resistance, resulting in an increase in cerebral blood flow, cerebral blood volume, and CSF pressure. Nitroprusside is of particular concern, because it not only results in an increase in CSF pressure, but also in a decrease in aortic pressure below the aortic cross-clamp, and possibly in a decreased perfusion gradient from the distal aorta to the spinal cord.lOJ1 As stated earlier, CSF drainage in laboratory models has been effective in attenuating increases in CSF pressure and also improving neurologic outcome during aortic crossclamping. An additional study has shown that CSF drainage is not effective in improving neurologic outcome in the presence of high doses of nitroprusside.i6 These authors suggest that CSF drainage may fail to be effective in the presence of nitroprusside, because it is technically difficult to remove adequate volumes of CSF when spinal cord edema occurs. An additional factor may be that decreases in distal aortic pressure may have more deleterious effects than improvements gained in spinal cord perfusion pressure by decreasing CSF pressure. A randomized prospective study by Crawford et al looked at the effectiveness of CSF drainage in 99 patients and found an equally high 20% rate of paraplegia with or without CSF drainage.” Certainly, anyone considering CSF drainage has to give serious consideration to this study, which shows CSF drainage to be ineffective. One confounding issue is that 60% of the patients in this study did not have shunts placed, and, therefore, it is assumed that large doses of sodium nitroprusside were used, which may have attenuated the effectiveness of CSF drainage.i7 Although greater than 50 mL of CSF was removed from those patients having CSF drainage, CSF pressures still remained high in many patients, similar to the findings of Woloszyn et al using CSF drainage in dogs in the presence of nitroprusside.16 High doses of nitroprusside can be avoided by using shunts or by accept-
ing higher aortic pressures above the cross-clamp. As long as the surgeon feels that the aorta can withstand the higher pressures, and acute left ventricular failure or myocardial ischemia does not occur, nitroprusside usage can be minimized. Mutch and Thomson have recently shown in the barbiturate anesthetized dog that phlebotomy can reverse the hemodynamic and cerebrospinal fluid pressure effects of thoracic aortic cross-clamping.18 Phlebotomy may not be practical during repair of thoracic aortic aneurysms, but elevations in cerebrospinal pressure occurring after thoracic aortic cross-clamping might be attenuated if the central venous pressure is kept to a minimum when replacing volume losses. The final answer to the problem of paraplegia after thoracic aortic aneurysm repair will not center around interventions such as mild hypothermia, avoidance of glucose-containing solutions, and CSF drainage, but will be resolved when the surgeon has full knowledge of the blood supply of the spinal cord and can alter the surgical techniques by either adjusting the placement of the aortic cross-clamps or by anastamosing the intercostal artery that supplies the artery of Adamkiewicz to the graft. The first published series of 45 patients with angiographically defined blood supply to the spinal cord reported good results in patients in whom they could identify the artery of Adamkiewicz, but a high paraplegia rate in the 20% of patients in whom they were unable to locate this artery.i9 A preliminary report of intraoperative localization of spinal cord blood supply in eight patients has also been reported.” In the interim, interventions such as mild hypothermia to 34°C the avoidance of glucose-containing solutions, and CSF drainage (when large doses of sodium nitroprusside are avoided) should be used. Murray et al have reported 50 patients undergoing thoracic aortic aneurysm repair with mild hypothermia to 33.5”C and CSF drainage (47 f 7 mL of CSF); three deaths occurred, and there was only one case of immediate postoperative paraplegia and three cases of late paraparesis, two of which resolved before discharge.21 The risks of avoiding solutions with added glucose, mild hypothermia, and CSF drainage are low when compared with the risk of paraplegia.
REFERENCES
1. Livesay JJ, Cooley DA, Ventemiglia RA, Montro CG, et al: Surgical experience in descending thoracic aneurysmectomy with and without adjuncts to avoid ischemia. Ann Thorac Surg 39:37-46, 1985 2. Crawford ES, Crawford JL, Safi HJ, Coselli JS, et al: Thoracoabdomina! aortic aneurysms: Preoperative and intraoperative factors determining immediate and long-term results of operations in 605 patients. J Vast Surg 3:389-404, 1986 3. Wadouh F, Lindemann EM, Arndt CF, Hetzer R, et al: The arteria radicularis magna anterior as a decisive factor influencing spinal cord damage during aortic occlusion. J Thorac Cardiovasc Surg 88:1-lo,1984 4. Vacanti FX, Ames A III: Mild hypothermia and Mg++ protect against irreversible damage during CNS ischemia. Stroke 15695698, 1984
5. Lanier WL, Stangland KJ, Scheithauer BW, Milde JH, et al: The effects of dextrose infusion and head position on neurologic outcome after complete cerebral ischemia in primates: Examination of a model. Anesthesiology 66:39-48, 1987 6. Drummond JC, Moore SS: The influence of dextrose administration on neurologic outcome after temporary spinal cord ischemia in the rabbit. Anesthesiology 70:64-70, 1989 7. Crawford ES, Rubio PA: Reappraisal of adjuncts to avoid ischemia in the treatment of aneurysms of descending thoracic aorta. J Thorac Cardiovasc Surg 66:693-704,1973 8. Jex RK, Schaff HV, Piehler JM, King RM, et al: Early and late results following repair of dissections of the descending thoracic aorta. J Vast Surg 3:226-237, 1986 9. Gelman S, Reves JG, Fowler K, Samuelson PN, et al: Regional blood flow during cross-clamping of the thoracic aorta
368
and infusion of sodium nitroprusside. J Thorac Cardiovasc Surg 85:287-291,1983 10. Shine T, Nugent M: Sodium nitroprusside decreases spinal cord perfusion pressure during descending thoracic aortic crossclamping in the dog. J Cardiothorac Anesth 4:185-193,199O 11. Marini CP, Grubbs PE, Toporoff B, Woloszyn TT, et al: Effect of sodium nitroprusside on spinal cord perfusion and paraplegia during aortic cross-clamping. Ann Thorac Surg 47:379383,1989 12. Blaisdell FW, Cooley DA: The mechanism of paraplegia after temporary thoracic aortic occlusion and its relationship to spinal fluid pressure. Surgery 51:351-355, 1962 13. McCullough JL, Hollier LH, Nugent M: Paraplegia after thoracic aortic occlusion: Influence of cerebrospinal fluid drainageExperimental and early clinical results. J Vast Surg 7:153-160,1988 14. Svensson LG, Von Ritter CM, Groenevld HT, Richards ES, et al: Cross-clamping of the thoracic aorta: Influence of aortic shunts, laminectomy, papaverine, calcium channel blocker, allopurinol, and superoxide dismutase on spinal cord blood flow and paraplegia in baboons. Ann Surg 204:38-47,1986 15. Berendes JN, Bredee JJ, Schipperheyn JJ, et al: Mechanisms of spinal cord injury after cross-clamping of the descending thoracic aorta. Circulation 66:1112-1116,1982 (suppl) 16. Woloszyn T, Corrado P, Marini P, et al: Cerebrospinal fluid
MICHAEL
NUGENT
drainage does not counteract the negative effect of sodium nitroprusside on spinal cord perfusion pressure during aortic crossclamping. Curr Surg 489-492,1989 17. Crawford ES, Svensson LG, Hess KR, et al: A prospective randomized study of cerebrospinal fluid drainage to prevent paraplegia after high-risk surgery on the thoracoabdominal aorta. J Vast Surg 13:36-45,199l 18. Mutch WAC, Thomson IR, Teskey JM, Thiessen D, et al: Phlebotomy reverses the hemodynamic consequences of thoracic aortic cross-clamping: Relationship between central venous pressure and cerebrospinal fluid pressure. Anesthesiology 74:320-324, 1991 19. Kieffer E, Richard T, Chivas J, et al: Preoperative spinal cord arteriography in aneurysmal disease of the descending thoracic and thoracoabdominal aorta: Preliminary results in 45 patients. Ann Vast Surg 3:34-46,1989 20. Svensson LG, Pate1 V, Robinson MF, et al: Influence of preservation or perfusion of intraoperatively identified spinal cord blood supply on spinal motor evoked potentials and paraplegia after aortic surgery. J Vast Surg 13:355-365,199l 21. Murray MJ, Werner E, Oliver WC, et al: Anesthetic management of thoracoabdominal aortic aneurysm repair: effects of CSF drainage and mild hypothermia. Anesthesiology 71:A62, 1989
Pro: Cerebrospinal
Fluid
Drainage
Prevents
Paraplegia
Michael Nugent, MD
M
ORTALITY RATES for repair of thoracic aortic aneurysms remain approximately 10% and paraplegia rates in survivors are reported to exceed 6..5%.‘J The largest published series of 605 patients reported more than 20% of patients with paraplegia after repair of large aneurysms extending from the left subclavian artery and including the abdominal aorta. These large aneurysms, which carry a particularly high risk of paraplegia, accounted for more than one-fourth of all aneurysms repaired in the series.2 The location and extent of the aneurysm, patient age, and prolonged aortic cross-clamp time have all been correlated with an increased incidence of paraplegia.‘J Spinal cord injuries complicating repair of a descending thoracic aneurysm result in neurologic findings similar to the anterior spinal artery syndrome seen after occlusion of the arteria radicularis magna anterior or artery of Adamkiewicz. Motor function is lost in the lower extremities, while pain, temperature, vibratory, and position senses remain intact. The origin of the artery of Adamkiewicz is variable, occurring only 60% of the time in the expected Tg to T12 region. The origin of the artery can be as high as T3 or as low as L5.3 For this reason, during the repair of any given aneurysm, the surgeon does not know which intercostal arteries to preserve or anastamose to the graft. Until the surgeon knows the blood supply of the spinal cord for each individual patient, no intervention such as cerebrospinal fluid (CSF) drainage will completely prevent paraplegia, but such interventions may help maintain the viability of anterior horn cells of the spinal cord during aortic clamping. If surgical resection of the artery of Adamkiewicz has occurred, paraplegia still may or may not result, depending on the adequacy of collateral blood supply through the anterior spinal arteries. Recent reports of late paraplegia often associated with postoperative hypotension may represent patients in whom the artery of Adamkiewicz has been resected, but intraoperative preventive measures have preserved function during the surgery, only to have spinal cord ischemia occur postoperatively. In addition to CSF drainage, two other interventions that are strongly supported in laboratory models and can be applied with minimal risk will be discussed. These are mild hypothermia and the avoidance of glucose-containing solutions. A short discussion of shunting procedures will be
From the Department of Anesthesia, Medical College of Ohio, Toledo, OH. Address reprint requests to Michael Nugent, MD, Department of Anesthesia, Medical College of Ohio, 3000 Arlington Ave, PO 10008, Toledo, OH 43699. Copyright o 1992 by W.B. Saunders Company 1053-0770/9210603-0029$03.0010 Key words: arteries, aorta aneuqsrns, paralysis
366
presented, because their absence or presence may reflect on nitroprusside usage and the effectiveness of CSF drainage for spinal cord protection. Vicanti and Ames have shown that mild hypothermia to 34°C combined with intravenous magnesium doubled the cross-clamp time that could be tolerated without paraplegia in a laboratory modeL4 Allowing the patient to cool to 34°C could theoretically cause problems with hemostasis, because enzymatic coagulation reactions are slowed, but with good surgical hemostasis coagulopathies usually are not a major problem. Several studies have addressed the deleterious consequences of adding modest amounts of glucose to intravenous solutions prior to cerebral ischemia.5 One study in rabbits has demonstrated similar deleterious effects of glucose loading on spinal cord ischemia.h The decision to use a shunt to pressurize the aorta distal to the lower cross-clamp is a surgical one. In 1973, Crawford and Rubio showed that shunting procedures to pressurize the distal aorta below the cross-clamp would not prevent paraplegia from occurring.7 However, this was not a prospective randomized study to answer the question if shunting procedures decrease the incidence of paraplegia. It only demonstrated that, despite having shunts in place, paraplegia still occurred. One retrospective study has shown that shunting procedures do decrease the incidence of paraplegia when a dissecting aneurysm is present.8 Shunts do greatly facilitate anesthetic management of these cases, attenuating the tremendous hemodynamic effects of crossclamping the aorta just below the left subclavian artery. Shunts also minimize the need for large doses of nitroprusside. Nitroprusside may have deleterious effects on spinal cord preservation, because it not only results in an increase in CSF pressure, but it also decreases aortic pressure below the cross-clamp.‘-” The concept of CSF drainage was first suggested by Blaisdell and Cooley in 1962 in a canine model.‘? Their findings that CSF drainage prevented paraplegia during aortic cross-clamping have consistently been reconfirmed.13J4 Svensson et al have shown that CSF drainage in combination with intrathecal papaverine is effective against paraplegia in a primate model.14 The first documentation of a patient becoming paraparetic in association with a marked elevation in CSF pressure after aortic cross-clamping was reported during a coarctation repair by Berendes et al in 1982.1s They suggested that CSF drainage may be helpful. Concerns regarding CSF drainage are that (1) it is not proven effective in man; (2) it could theoretically result in cerebral herniation if CSF were drained at a time when the CSF pressure was very high; (3) if postoperative paraplegia occurs, the possibility that it may have resulted from an epidural hematoma must be ruled out; and (4) medical legal concerns may discourage placement of a subarachnoid
Journal of Cardiothoracic and
Vascular
Anesthwa,
Vol6, No 3 (June), 1992: pp 366-368
PRO: CSF DRAINAGE
367
catheter in a patient with a significant risk of postoperative paraplegia. The mechanism by which aortic cross-clamping results in increased CSF pressure may be large increases in arterial pressure that exceed the limits of cerebral autoregulation, increasing cerebral blood flow and cerebral blood volume. If arterial pressure increases are attenuated with vasodilators, such as sodium nitroprusside, this would decrease cerebral vascular resistance, resulting in an increase in cerebral blood flow, cerebral blood volume, and CSF pressure. Nitroprusside is of particular concern, because it not only results in an increase in CSF pressure, but also in a decrease in aortic pressure below the aortic cross-clamp, and possibly in a decreased perfusion gradient from the distal aorta to the spinal cord.lOJ1 As stated earlier, CSF drainage in laboratory models has been effective in attenuating increases in CSF pressure and also improving neurologic outcome during aortic crossclamping. An additional study has shown that CSF drainage is not effective in improving neurologic outcome in the presence of high doses of nitroprusside.i6 These authors suggest that CSF drainage may fail to be effective in the presence of nitroprusside, because it is technically difficult to remove adequate volumes of CSF when spinal cord edema occurs. An additional factor may be that decreases in distal aortic pressure may have more deleterious effects than improvements gained in spinal cord perfusion pressure by decreasing CSF pressure. A randomized prospective study by Crawford et al looked at the effectiveness of CSF drainage in 99 patients and found an equally high 20% rate of paraplegia with or without CSF drainage.” Certainly, anyone considering CSF drainage has to give serious consideration to this study, which shows CSF drainage to be ineffective. One confounding issue is that 60% of the patients in this study did not have shunts placed, and, therefore, it is assumed that large doses of sodium nitroprusside were used, which may have attenuated the effectiveness of CSF drainage.i7 Although greater than 50 mL of CSF was removed from those patients having CSF drainage, CSF pressures still remained high in many patients, similar to the findings of Woloszyn et al using CSF drainage in dogs in the presence of nitroprusside.16 High doses of nitroprusside can be avoided by using shunts or by accept-
ing higher aortic pressures above the cross-clamp. As long as the surgeon feels that the aorta can withstand the higher pressures, and acute left ventricular failure or myocardial ischemia does not occur, nitroprusside usage can be minimized. Mutch and Thomson have recently shown in the barbiturate anesthetized dog that phlebotomy can reverse the hemodynamic and cerebrospinal fluid pressure effects of thoracic aortic cross-clamping.18 Phlebotomy may not be practical during repair of thoracic aortic aneurysms, but elevations in cerebrospinal pressure occurring after thoracic aortic cross-clamping might be attenuated if the central venous pressure is kept to a minimum when replacing volume losses. The final answer to the problem of paraplegia after thoracic aortic aneurysm repair will not center around interventions such as mild hypothermia, avoidance of glucose-containing solutions, and CSF drainage, but will be resolved when the surgeon has full knowledge of the blood supply of the spinal cord and can alter the surgical techniques by either adjusting the placement of the aortic cross-clamps or by anastamosing the intercostal artery that supplies the artery of Adamkiewicz to the graft. The first published series of 45 patients with angiographically defined blood supply to the spinal cord reported good results in patients in whom they could identify the artery of Adamkiewicz, but a high paraplegia rate in the 20% of patients in whom they were unable to locate this artery.i9 A preliminary report of intraoperative localization of spinal cord blood supply in eight patients has also been reported.” In the interim, interventions such as mild hypothermia to 34°C the avoidance of glucose-containing solutions, and CSF drainage (when large doses of sodium nitroprusside are avoided) should be used. Murray et al have reported 50 patients undergoing thoracic aortic aneurysm repair with mild hypothermia to 33.5”C and CSF drainage (47 f 7 mL of CSF); three deaths occurred, and there was only one case of immediate postoperative paraplegia and three cases of late paraparesis, two of which resolved before discharge.21 The risks of avoiding solutions with added glucose, mild hypothermia, and CSF drainage are low when compared with the risk of paraplegia.
REFERENCES
1. Livesay JJ, Cooley DA, Ventemiglia RA, Montro CG, et al: Surgical experience in descending thoracic aneurysmectomy with and without adjuncts to avoid ischemia. Ann Thorac Surg 39:37-46, 1985 2. Crawford ES, Crawford JL, Safi HJ, Coselli JS, et al: Thoracoabdomina! aortic aneurysms: Preoperative and intraoperative factors determining immediate and long-term results of operations in 605 patients. J Vast Surg 3:389-404, 1986 3. Wadouh F, Lindemann EM, Arndt CF, Hetzer R, et al: The arteria radicularis magna anterior as a decisive factor influencing spinal cord damage during aortic occlusion. J Thorac Cardiovasc Surg 88:1-lo,1984 4. Vacanti FX, Ames A III: Mild hypothermia and Mg++ protect against irreversible damage during CNS ischemia. Stroke 15695698, 1984
5. Lanier WL, Stangland KJ, Scheithauer BW, Milde JH, et al: The effects of dextrose infusion and head position on neurologic outcome after complete cerebral ischemia in primates: Examination of a model. Anesthesiology 66:39-48, 1987 6. Drummond JC, Moore SS: The influence of dextrose administration on neurologic outcome after temporary spinal cord ischemia in the rabbit. Anesthesiology 70:64-70, 1989 7. Crawford ES, Rubio PA: Reappraisal of adjuncts to avoid ischemia in the treatment of aneurysms of descending thoracic aorta. J Thorac Cardiovasc Surg 66:693-704,1973 8. Jex RK, Schaff HV, Piehler JM, King RM, et al: Early and late results following repair of dissections of the descending thoracic aorta. J Vast Surg 3:226-237, 1986 9. Gelman S, Reves JG, Fowler K, Samuelson PN, et al: Regional blood flow during cross-clamping of the thoracic aorta
368
and infusion of sodium nitroprusside. J Thorac Cardiovasc Surg 85:287-291,1983 10. Shine T, Nugent M: Sodium nitroprusside decreases spinal cord perfusion pressure during descending thoracic aortic crossclamping in the dog. J Cardiothorac Anesth 4:185-193,199O 11. Marini CP, Grubbs PE, Toporoff B, Woloszyn TT, et al: Effect of sodium nitroprusside on spinal cord perfusion and paraplegia during aortic cross-clamping. Ann Thorac Surg 47:379383,1989 12. Blaisdell FW, Cooley DA: The mechanism of paraplegia after temporary thoracic aortic occlusion and its relationship to spinal fluid pressure. Surgery 51:351-355, 1962 13. McCullough JL, Hollier LH, Nugent M: Paraplegia after thoracic aortic occlusion: Influence of cerebrospinal fluid drainageExperimental and early clinical results. J Vast Surg 7:153-160,1988 14. Svensson LG, Von Ritter CM, Groenevld HT, Richards ES, et al: Cross-clamping of the thoracic aorta: Influence of aortic shunts, laminectomy, papaverine, calcium channel blocker, allopurinol, and superoxide dismutase on spinal cord blood flow and paraplegia in baboons. Ann Surg 204:38-47,1986 15. Berendes JN, Bredee JJ, Schipperheyn JJ, et al: Mechanisms of spinal cord injury after cross-clamping of the descending thoracic aorta. Circulation 66:1112-1116,1982 (suppl) 16. Woloszyn T, Corrado P, Marini P, et al: Cerebrospinal fluid
MICHAEL
NUGENT
drainage does not counteract the negative effect of sodium nitroprusside on spinal cord perfusion pressure during aortic crossclamping. Curr Surg 489-492,1989 17. Crawford ES, Svensson LG, Hess KR, et al: A prospective randomized study of cerebrospinal fluid drainage to prevent paraplegia after high-risk surgery on the thoracoabdominal aorta. J Vast Surg 13:36-45,199l 18. Mutch WAC, Thomson IR, Teskey JM, Thiessen D, et al: Phlebotomy reverses the hemodynamic consequences of thoracic aortic cross-clamping: Relationship between central venous pressure and cerebrospinal fluid pressure. Anesthesiology 74:320-324, 1991 19. Kieffer E, Richard T, Chivas J, et al: Preoperative spinal cord arteriography in aneurysmal disease of the descending thoracic and thoracoabdominal aorta: Preliminary results in 45 patients. Ann Vast Surg 3:34-46,1989 20. Svensson LG, Pate1 V, Robinson MF, et al: Influence of preservation or perfusion of intraoperatively identified spinal cord blood supply on spinal motor evoked potentials and paraplegia after aortic surgery. J Vast Surg 13:355-365,199l 21. Murray MJ, Werner E, Oliver WC, et al: Anesthetic management of thoracoabdominal aortic aneurysm repair: effects of CSF drainage and mild hypothermia. Anesthesiology 71:A62, 1989
