Con: Cerebrospinal
Fluid Drainage During Resection
Does Not Afford Spinal of Thoracic Aneurysms
Cord Protection
Salwa A. Shenaq, MD, and Lars G. Svensson
ARAPLEGIA REMAINS the most dreaded complication following surgery of the descending thoracic and throacoabdominal aorta. Several techniques of shunts and bypasses have been used with other adjuncts to prevent paraplegia. However, none of these techniques has completely prevented paraplegia. The reported incidence of paraplegia following occlusion of the descending thoracic aorta ranges from 0.5% to 38%.1-6
P
FACTORS AFFECTING THE INCIDENCE
OF PARAPLEGIA
of the spinal cord that is most vulnerable to ischemia. The origin of the artery of Adamkiewicz is an important determinant of the occurrence of paraplegia following cross-clamping of the descending aorta. Due to variations in the origin of the artery of Adamkiewicz, paraplegia may occur following resection of an abdominal aortic aneurysm if the artery arises from the lower lumbar segment. In 75% of human subjects, the artery arises between T9 and T12.10 METHODS
There are several factors that affect the incidence of paraplegia, and these are described in the sections below. Nature of the Disease (Etiology of the Aneurysm)
Crawford et al6 reported a higher incidence of paraplegia in patients who had aortic dissection than in patients with degenerative aneurysms (no dissection). The higher incidence of paraplegia in the dissection group could be attributed to the lack of developed collateral circulation, resulting in ischemia when the aorta is clamped. This theory may also explain the higher incidence of paraplegia in cases of acute aortic dissection compared with chronic aortic dissection. Extent of the Aneurysm
The extent of the aneurysm determines the extent of the aorta replaced. The longer the aneurysm, the longer is the segment of the aorta that is removed. The removed segment may include a number of intercostal or lumbar arteries that need to be reattached, thus extending the aortic clamp time and increasing the likelihood of paraparesis and paraplegia. Aortic Clamp Time
The longer the aortic cross-clamp time, the higher the incidence of paraplegia. Long aortic occlusion usually occurs with extensive aneurysms. Aortic occlusion longer than 30 minutes carries a higher risk of paraplegia. Availability of Collateral Circulation
In atherosclerotic aneurysms, atheromatous material may obstruct the origins of the intercostal or lumbar arteries. In this type of aneurysm, paraplegia is less likely to occur (5% to lo%), compared with acute dissection or traumatic rupture of the aorta. These acute circumstances do not allow time for the formation of collateral circulation.7
OF PREVENTING
CROSS-CLAMPING
PARAPLEGIA
FOLLOWING
OF THE DESCENDING
THORACIC AORTA
Since paraplegia is multifactorial in origin, it should be expected that no single preventive measure will completely eliminate paraplegia. 7~11~12 The most important factors in developing paraplegia are the degree of ischemia during aortic cross-clamping and failure to reattach the important intercostal and lumbar arteries to the aortic graft. Means of spinal cord protection should involve preservation and enhancement of blood flow to the spinal cord. These are shown in Table 1. CEREBROSPINAL
FLUID DRAINAGE
It is hypothesized that the spinal cord perfusion pressure (SCPP) is equal to the distal aortic blood pressure (DABP) minus the cerebrospinal fluid pressure (CSFP): SCPP = DABP - CSFP.i3J4 This equation is criticized for not accounting for the regional vascular resistance, which is why a high SCPP does not always generate the spinal cord blood flow required to prevent paraplegia.15 Furthermore, Crawford et ali6 and Piano and Gewertz17 have shown that the CSFP correlates well with the central venous pressure and not the arterial blood pressure. Another factor is that the SCPP is not a true, direct measurement of BP in the arteries of the spinal cord, but it is a computation based on speculation. Killen et all8 reported that the distal perfusion pressure did not reflect the spinal cord arteriolar or capillary blood pressures. They added that the higher segmental intercostal or lumbar artery end-pressures were a closer approximation. A critical threshold of SCPP appears not to be an absolute error-free measurement. Individual variability may be based on the degree and type of collateralization, which cannot be properly measured by SCPP alone. Based on that, the assumption that the SCPP equals BP minus CSFP or cisterna magna pressure (SCPP = ABP - CSFP) does not hold true. It has been shown by Griffiths et alI9 that pressure is a more important
Blood Supply of the Spinal Cord
The upper part of the spinal cord receives blood supply via the vertebral and deep cervical arteries. The lower half of the spinal cord is supplied by branches of the intercostal, lumbar, and lateral sacral arteries. There are one or two cervical radicular arteries, two to three thoracic, and one or two lumbar radicular arteries.* The largest and most developed artery is called the artery of Adamkiewicz, which originates between Ts and L4.9 This artery supplies the part
From the Departments of Anesthesiology and Surgery, Baylor College of Medicine, The Methodist Hospital, Houston, TX. Address reprint requests to Salwa A. Shenaq, MD, Service Chief, Cardiovascular Anesthesia, Baylor College of Medicine, Smith Tower, Suite 1003, 6550 Fannin, Houston, TX 77030. Copyright o 1992 by W B. Saunders Company 1053-077019210603-0024$03.00/9 Key words: thoracic aortic aneurysm, spinal cord protection, CSF drainage
Journalof Cardiothoracic and VascularAnesthesia, Vol6, No 3 (June), 1992: pp 369-372
369
SHENAQ AND SVENSSON
370
Table 2. CSF Drainage Studies
Table 1. Methods of Preventing Paraplegia Left heart bypass Study
Heparin-coated shunts
Study
No. of Subjects
Year
Results
Partial cardiopulmonary bypass
Miyamoto25
Dogs
20
1960
Favorable
Left heart bypass with a pump (centrifugal pump)
Blaisdellz3
Dogs
15
1962
Favorable
Hypothermia
Killen’
Dogs
10
1965
Not favorable
Monitoring of spinal cord ischemia by:
Okal
Dogs
12
1984
Favorable
Dasmahapatra3’
Dogs
12
1988
Favorable Favorable
Somatosensory-evoked
potentials
McCullough26
Dogs
40
1988
Reattachment of intercostal and lumbar arteries
Svensson29
Baboons
56
1986
Not favorable
Identification of the blood supply of the spinal cord
Wadouhz8
Pigs
20
1984
Not favorable Favorable
Motor-evoked potentials
Radiographic Hydrogen-induced
current
Enhancement of the perfusion pressure of the spinal cord Use of papaverine
Bowerz7
Dogs
21
1988
WoloszynJ5
Dogs
17
1990
Not favorable
Crawford’”
Human
100
1990
Not favorable
Grankes2
Dogs
21
1991
Favorable
CSF drainage Pharmacologic agents Steroids Sodium thiopental Oxygen radical scavenger Artificial blood (FluosoCDA) Naloxone Calcium channel blockers
determinant of blood flow than the inhibitory effect of increased CSFP, and spinal cord blood flow can accommodate wide fluctuations in CSFP. Lassen and Christensen*O have shown that cerebral blood flow even increased with an increase in intracranial pressure. Regarding the formation and absorption of CSF, the resistance to reabsorption of CSF in dogs is 17 times greater than that of man; thus, any increase in CSFP in man should be more quickly compensated for, compared with dogs.*’ Dunbar et a12*found that the CSFP in the lumbar spinal cord sac decreased during aortic occlusion in dogs, whereas CSFP measured in the cisterna magna or interventricularly increased. This decrease in the CSFP corresponds to the decrease in DABP below the aortic clamp, and the increase in the CSFP corresponds to the increase in BP in the proximal aortic segment. These changes in CSFP disappeared when the aorta was unclamped. If the CSFP in the lumbar region decreases during aortic clamping, then there is no reason for draining CSFP. Other investigators have also shown that the CSFP in the cisterna magna increased during aortic cross-clamping, which confirms Dunbar’s finding.1J,23x24 Thus, it is obvious that the CSFP measured in the cisterna magna may not accurately reflect the CSFP in the lumbar spinal region. Studies in dogs have shown that CSF drainage reduces the incidence of paraplegia during long periods of aortic cross-clamping. 15,23,25-27 However, CSF drainage has not been shown to reduce the incidence of paraplegia in pigs.28 Lumbar CSF drainage alone during aortic cross-clamping in the baboon also has not been accompanied by a reduction in the incidence of paraplegia, although the circulation of the lumbar cord was better maintained.29 This was explained by development of arteriospasm of the spinal arteries associated with a laminectomy, which made a difference between the results of the experiments in dogs versus pigs and baboons.16.29
Results of the experiments on CSF drainage are shown in Table 2. No experiment has been reported either in the dog, pig, baboon, or other animals that duplicates human aortic surgery, which consists of excision and graft replacement with permanent interruption of some or all of the intercostal and lumbar arteries or blind reattachment of these vessels during a long 30- to 60-minute period of aortic cross-clamping. Most of the studies in dogs consisted of aortic cross-clamping for short periods of time. No reattachment of an intercostal artery was performed as in humans, because the aorta was not excised in these experiments. It is also important to realize the difference in anatomy of the blood supply of the spinal cord between humans and dogs. The anterior spinal artery is continuous, but smaller, in dogs than in humans. Dogs also lack the characteristic artery of Adamkiewicz, which makes them more prone to spinal cord ischemia than humans (unpublished data and personal communication with T.G. Bower, 1989). Crawford et all6 performed a prospective randomized study of CSF drainage in 98 patients with extensive aortic disease who were at high risk for developing paraplegia (Crawford type I and II aneurysm) (Fig 1). This study showed that CSF drainage did not improve the incidence of
i
Fig 1. Crawford classification of thoracoabdominal aortic aneurysms according to the extent of involvement of the thoracoabdominal aorta (Reprinted with permission.31)
CON: CSF DRAINAGE
371
paraplegia. This study not only is the largest series in humans, but also was a prospective and randomized one, which gives the study great validity. Most studies performed in animals consisted of a small number (two to 20) of experimental animals. No involvement of the aorta was present and only one clamp was applied to the aorta with no segment of the aorta being isolated. As there was no involvement of the aorta by a disease process, there was no randomization as to the severity of the diseased aorta. In order to select a group of patients who would provide results with adequate statistical power, the number of cases necessary to be enrolled in a study can be calculated by estimating the incidence of paraplegia from the reported studies in the literature in the control group and in the study group. From Fig 2, it can be estimated that the size of the paraplegia study group should be approximately 100 patients. In most of the studies concerning CSF drainage, the number of subjects is much lower than 100, which makes the validity of these studies questionable. In conclusion, no technique has been scientifically proven to prevent paraplegia in humans.30 This can be ascribed to the multifactorial etiology of postoperative paraplegia, the
Fig 2. Nomogram for calculating minimal sample size for a statistically valid study with a dichotomous end-point (u = 0.05, p = 0.2, power = 80%. based on Pearson chi-square test). (Reprinted with permission.“)
failure to take into account the aortic disease process, and not addressing the problem of the spinal cord blood s~pply.~~ Thus, CSF drainage alone will not afford spinal cord protection during aortic cross-clamping.
REFERENCES
1. Crawford ES, Walker HS, Saleh SA, et al: Graft replacement of aneurysm in the descending thoracic aorta: Results without bypass or shunting. Surgery 89:73-85,198l 2. Crawford ES, Fenstermocker JM, Richardson W, et al: Reappraisal of adjuncts to avoid ischemia in the treatment of thoracic aneurysms. Surgery 67:182-196,197O 3. DeBakey ME, McCollum CH, Graham JM: Surgical treatment of aneurysms of the descending thoracic aorta: Long-term results in 500 patients. J Cardiovasc Surg 19571-576, 1978 4. Najafi H, Javid H, Hunter J, et al: Descending aortic aneurysmectomy without adjuncts to avoid ischemia. Ann Thorac Surg 30:326-335, 1980 5. Brewer LA, Fosburg RG, Muldder GA, et al: Spinal cord complication following surgery for coarctation of the aorta: A study of 66 cases. J Thorac Cardiovasc Surg 64:368-381, 1972 6. 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 Vast Surg 3:389-404, 1986 7. Svensson LG, Loop FD: Prevention of spinal cord ischemia in aortic surgery, in Bergan JJ, Yao JST (eds): Arterial Surgery: New Diagnostic and Operative Techniques. New York, NY, Grune & Straton, 1988, pp 273-285 8. Szilagyi DE, Hageman JH, Smith RF, et al: Spinal cord damage in surgery of the abdominal aorta. Surgery 83:38-56,1978 9. Kadyi H: Ueber die Blutgefasse des Menschlichen Ruckenmarkes. Anat Anz 1:303-314,1886 10. Djindjian R, Faure C: Accidents medullaires de1 laortographic. J Bela Radio1 50:207-210,1967 11. Svensson LG, Hinder RA: Hemodynamics of aortic crossclamping. Experimental observations and clinical applications. Surg Annu 19:41-65,1987 12. Svensson LG, Grum DF, Cosgrove DM, et al: Appraisal of cerebrospinal fluid alterations during aortic surgery with intrathecal papaverine administration and cerebrospinal fluid drainage. J Vast Surg 11:423-429,199O 13. Oka Y, Miyamoto T: Prevention of spinal cord injury after cross-clamping of the thoracic aorta. Jpn J Surg 14:159-162,1982
14. Maeda S, Miyamoto T, Murata H, et al: Prevention of spinal cord ischemia by monitoring spinal cord perfusion pressure and somatosensory evoked potentials. J Cardiovasc Surg 30565-571, 1989 15. Woloszyn TT, Marini CP, Coons MS, et al: Cerebrospinal fluid drainage and steroids provide better spinal cord protection during aortic cross-clamping than does either treatment alone. Ann Thorac Surg 49:79-83,199O 16. 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 13:36-46,199O 17. Piano G, Gewertz BL: Mechanism of increased cerebrospinal fluid pressure with thoracic aortic occlusion. J Vast Surg 11:695-701, 1990 18. Killen DA, Edwards RH, Tinsley EA, et al: Effect of low molecular weight dextran, heparin, urea, cerebrospinal fluid drainage, and hypothermia on ischemic injury of the spinal cord secondary to mobilization of the thoracic aorta. J Thorac Cardiovast Surg 50:882-887,1965 19. Griffiths IR, Pitts LH, Crawford RA, et al: Spinal cord compression and blood flow. Neurology 28:1145-1151,1978 20. Lassen NA, Christensen MS: Physiology of cerebral blood flow. Br J Anesth 48:719-734,1976 21. Cutler RW, Page L, Galicich J, Watters GV: Formation and absorption of cerebrospinal fluid in man. Brain 91:707-720, 1968 22. Dunbar HS, Gutherie TC, Karpell B: A study of the cerebrospinal fluid pulse wave. Arch Neurol 14:624-630, 1966 23. Blaisdell FW, Cooley DA: The mechanism of paraplegia after thoracic aortic occlusion and its relationship to spinal fluid pressure. Surgery 51:351-355,1962 24. Grubbs PE, Marini C, Toporoff B, et al: Somatosensory evoked potentials and spinal cord perfusion pressure are significant predictors of postoperative neurologic dysfunction. Surgery 104:216-223,1988 25. Miyamoto K, Veno A, Wada T, et al: A new and simple method of preventing spinal cord damage following temporary
372
occlusion of the thoracic aorta by draining the cerebrospinal fluid. J Cardiovasc Surg 1:188-197,196O 26. McCullough JL, Hollier LH, Nugent M: Paraplegia after thoracic aortic occlusion: influence of cerebrospinal fluid drainage. J Vast Surg 9:153-160, 1988 27. Bower TC, Murray MJ, Glovicki P, et al: Effects of thoracic aortic occlusion and cerebrospinal fluid drainage on regional spinal cord blood flow in dogs: Correlation with neurologic outcome. J Vast Surg 9:135-144, 1989 28. Wadouh F, Lindermann EM, Arndt CF, et al: The arteria radicularis magna as a decisive factor influencing spinal cord damage during aortic occlusion. J Thorac Cardiovasc Surg 88:1-10, 1984 29. Svensson LG, Von Ritter CM, Groeneveld HT, et al: Cross-clamping of the thoracic aorta. Influence of aortic shunts,
SHENAQ AND SVENSSON
laminectomy, papaverine, calcium channel blocker, allopurinol. and superoxide dismutase on spinal cord blood flow and paraplegia in baboons. Ann Surg 204:38-47,1986 30. Svensson LG, Richards E, Core11 A, et al: Relationship of spinal cord blood flow to vascular anatomy during thoracic aortic cross-clamping and shunting. J Thorac Cardiovasc Surg 88:1-10. 1984 31. Himansu K, Dasmahapatra MBBS, Coles JG, et al: Relationship between cerebrospinal fluid dynamics and reversible spinal cord ischemia during experimental thoracic aortic occlusion. J Thorac Cardiovasc Surg 95:920-923,1988 32. Granke K, Hollier LH, Zdrahal P, Moore W: Longitudinal study of cerebral spinal fluid drainage in polyethylene glycolconjugated superoxide dismutase in paraplegia associated with thoracic aortic cross-clamping. J Vast Surg 13:615-621, 1991
Fluid Drainage During Resection
Does Not Afford Spinal of Thoracic Aneurysms
Cord Protection
Salwa A. Shenaq, MD, and Lars G. Svensson
ARAPLEGIA REMAINS the most dreaded complication following surgery of the descending thoracic and throacoabdominal aorta. Several techniques of shunts and bypasses have been used with other adjuncts to prevent paraplegia. However, none of these techniques has completely prevented paraplegia. The reported incidence of paraplegia following occlusion of the descending thoracic aorta ranges from 0.5% to 38%.1-6
P
FACTORS AFFECTING THE INCIDENCE
OF PARAPLEGIA
of the spinal cord that is most vulnerable to ischemia. The origin of the artery of Adamkiewicz is an important determinant of the occurrence of paraplegia following cross-clamping of the descending aorta. Due to variations in the origin of the artery of Adamkiewicz, paraplegia may occur following resection of an abdominal aortic aneurysm if the artery arises from the lower lumbar segment. In 75% of human subjects, the artery arises between T9 and T12.10 METHODS
There are several factors that affect the incidence of paraplegia, and these are described in the sections below. Nature of the Disease (Etiology of the Aneurysm)
Crawford et al6 reported a higher incidence of paraplegia in patients who had aortic dissection than in patients with degenerative aneurysms (no dissection). The higher incidence of paraplegia in the dissection group could be attributed to the lack of developed collateral circulation, resulting in ischemia when the aorta is clamped. This theory may also explain the higher incidence of paraplegia in cases of acute aortic dissection compared with chronic aortic dissection. Extent of the Aneurysm
The extent of the aneurysm determines the extent of the aorta replaced. The longer the aneurysm, the longer is the segment of the aorta that is removed. The removed segment may include a number of intercostal or lumbar arteries that need to be reattached, thus extending the aortic clamp time and increasing the likelihood of paraparesis and paraplegia. Aortic Clamp Time
The longer the aortic cross-clamp time, the higher the incidence of paraplegia. Long aortic occlusion usually occurs with extensive aneurysms. Aortic occlusion longer than 30 minutes carries a higher risk of paraplegia. Availability of Collateral Circulation
In atherosclerotic aneurysms, atheromatous material may obstruct the origins of the intercostal or lumbar arteries. In this type of aneurysm, paraplegia is less likely to occur (5% to lo%), compared with acute dissection or traumatic rupture of the aorta. These acute circumstances do not allow time for the formation of collateral circulation.7
OF PREVENTING
CROSS-CLAMPING
PARAPLEGIA
FOLLOWING
OF THE DESCENDING
THORACIC AORTA
Since paraplegia is multifactorial in origin, it should be expected that no single preventive measure will completely eliminate paraplegia. 7~11~12 The most important factors in developing paraplegia are the degree of ischemia during aortic cross-clamping and failure to reattach the important intercostal and lumbar arteries to the aortic graft. Means of spinal cord protection should involve preservation and enhancement of blood flow to the spinal cord. These are shown in Table 1. CEREBROSPINAL
FLUID DRAINAGE
It is hypothesized that the spinal cord perfusion pressure (SCPP) is equal to the distal aortic blood pressure (DABP) minus the cerebrospinal fluid pressure (CSFP): SCPP = DABP - CSFP.i3J4 This equation is criticized for not accounting for the regional vascular resistance, which is why a high SCPP does not always generate the spinal cord blood flow required to prevent paraplegia.15 Furthermore, Crawford et ali6 and Piano and Gewertz17 have shown that the CSFP correlates well with the central venous pressure and not the arterial blood pressure. Another factor is that the SCPP is not a true, direct measurement of BP in the arteries of the spinal cord, but it is a computation based on speculation. Killen et all8 reported that the distal perfusion pressure did not reflect the spinal cord arteriolar or capillary blood pressures. They added that the higher segmental intercostal or lumbar artery end-pressures were a closer approximation. A critical threshold of SCPP appears not to be an absolute error-free measurement. Individual variability may be based on the degree and type of collateralization, which cannot be properly measured by SCPP alone. Based on that, the assumption that the SCPP equals BP minus CSFP or cisterna magna pressure (SCPP = ABP - CSFP) does not hold true. It has been shown by Griffiths et alI9 that pressure is a more important
Blood Supply of the Spinal Cord
The upper part of the spinal cord receives blood supply via the vertebral and deep cervical arteries. The lower half of the spinal cord is supplied by branches of the intercostal, lumbar, and lateral sacral arteries. There are one or two cervical radicular arteries, two to three thoracic, and one or two lumbar radicular arteries.* The largest and most developed artery is called the artery of Adamkiewicz, which originates between Ts and L4.9 This artery supplies the part
From the Departments of Anesthesiology and Surgery, Baylor College of Medicine, The Methodist Hospital, Houston, TX. Address reprint requests to Salwa A. Shenaq, MD, Service Chief, Cardiovascular Anesthesia, Baylor College of Medicine, Smith Tower, Suite 1003, 6550 Fannin, Houston, TX 77030. Copyright o 1992 by W B. Saunders Company 1053-077019210603-0024$03.00/9 Key words: thoracic aortic aneurysm, spinal cord protection, CSF drainage
Journalof Cardiothoracic and VascularAnesthesia, Vol6, No 3 (June), 1992: pp 369-372
369
SHENAQ AND SVENSSON
370
Table 2. CSF Drainage Studies
Table 1. Methods of Preventing Paraplegia Left heart bypass Study
Heparin-coated shunts
Study
No. of Subjects
Year
Results
Partial cardiopulmonary bypass
Miyamoto25
Dogs
20
1960
Favorable
Left heart bypass with a pump (centrifugal pump)
Blaisdellz3
Dogs
15
1962
Favorable
Hypothermia
Killen’
Dogs
10
1965
Not favorable
Monitoring of spinal cord ischemia by:
Okal
Dogs
12
1984
Favorable
Dasmahapatra3’
Dogs
12
1988
Favorable Favorable
Somatosensory-evoked
potentials
McCullough26
Dogs
40
1988
Reattachment of intercostal and lumbar arteries
Svensson29
Baboons
56
1986
Not favorable
Identification of the blood supply of the spinal cord
Wadouhz8
Pigs
20
1984
Not favorable Favorable
Motor-evoked potentials
Radiographic Hydrogen-induced
current
Enhancement of the perfusion pressure of the spinal cord Use of papaverine
Bowerz7
Dogs
21
1988
WoloszynJ5
Dogs
17
1990
Not favorable
Crawford’”
Human
100
1990
Not favorable
Grankes2
Dogs
21
1991
Favorable
CSF drainage Pharmacologic agents Steroids Sodium thiopental Oxygen radical scavenger Artificial blood (FluosoCDA) Naloxone Calcium channel blockers
determinant of blood flow than the inhibitory effect of increased CSFP, and spinal cord blood flow can accommodate wide fluctuations in CSFP. Lassen and Christensen*O have shown that cerebral blood flow even increased with an increase in intracranial pressure. Regarding the formation and absorption of CSF, the resistance to reabsorption of CSF in dogs is 17 times greater than that of man; thus, any increase in CSFP in man should be more quickly compensated for, compared with dogs.*’ Dunbar et a12*found that the CSFP in the lumbar spinal cord sac decreased during aortic occlusion in dogs, whereas CSFP measured in the cisterna magna or interventricularly increased. This decrease in the CSFP corresponds to the decrease in DABP below the aortic clamp, and the increase in the CSFP corresponds to the increase in BP in the proximal aortic segment. These changes in CSFP disappeared when the aorta was unclamped. If the CSFP in the lumbar region decreases during aortic clamping, then there is no reason for draining CSFP. Other investigators have also shown that the CSFP in the cisterna magna increased during aortic cross-clamping, which confirms Dunbar’s finding.1J,23x24 Thus, it is obvious that the CSFP measured in the cisterna magna may not accurately reflect the CSFP in the lumbar spinal region. Studies in dogs have shown that CSF drainage reduces the incidence of paraplegia during long periods of aortic cross-clamping. 15,23,25-27 However, CSF drainage has not been shown to reduce the incidence of paraplegia in pigs.28 Lumbar CSF drainage alone during aortic cross-clamping in the baboon also has not been accompanied by a reduction in the incidence of paraplegia, although the circulation of the lumbar cord was better maintained.29 This was explained by development of arteriospasm of the spinal arteries associated with a laminectomy, which made a difference between the results of the experiments in dogs versus pigs and baboons.16.29
Results of the experiments on CSF drainage are shown in Table 2. No experiment has been reported either in the dog, pig, baboon, or other animals that duplicates human aortic surgery, which consists of excision and graft replacement with permanent interruption of some or all of the intercostal and lumbar arteries or blind reattachment of these vessels during a long 30- to 60-minute period of aortic cross-clamping. Most of the studies in dogs consisted of aortic cross-clamping for short periods of time. No reattachment of an intercostal artery was performed as in humans, because the aorta was not excised in these experiments. It is also important to realize the difference in anatomy of the blood supply of the spinal cord between humans and dogs. The anterior spinal artery is continuous, but smaller, in dogs than in humans. Dogs also lack the characteristic artery of Adamkiewicz, which makes them more prone to spinal cord ischemia than humans (unpublished data and personal communication with T.G. Bower, 1989). Crawford et all6 performed a prospective randomized study of CSF drainage in 98 patients with extensive aortic disease who were at high risk for developing paraplegia (Crawford type I and II aneurysm) (Fig 1). This study showed that CSF drainage did not improve the incidence of
i
Fig 1. Crawford classification of thoracoabdominal aortic aneurysms according to the extent of involvement of the thoracoabdominal aorta (Reprinted with permission.31)
CON: CSF DRAINAGE
371
paraplegia. This study not only is the largest series in humans, but also was a prospective and randomized one, which gives the study great validity. Most studies performed in animals consisted of a small number (two to 20) of experimental animals. No involvement of the aorta was present and only one clamp was applied to the aorta with no segment of the aorta being isolated. As there was no involvement of the aorta by a disease process, there was no randomization as to the severity of the diseased aorta. In order to select a group of patients who would provide results with adequate statistical power, the number of cases necessary to be enrolled in a study can be calculated by estimating the incidence of paraplegia from the reported studies in the literature in the control group and in the study group. From Fig 2, it can be estimated that the size of the paraplegia study group should be approximately 100 patients. In most of the studies concerning CSF drainage, the number of subjects is much lower than 100, which makes the validity of these studies questionable. In conclusion, no technique has been scientifically proven to prevent paraplegia in humans.30 This can be ascribed to the multifactorial etiology of postoperative paraplegia, the
Fig 2. Nomogram for calculating minimal sample size for a statistically valid study with a dichotomous end-point (u = 0.05, p = 0.2, power = 80%. based on Pearson chi-square test). (Reprinted with permission.“)
failure to take into account the aortic disease process, and not addressing the problem of the spinal cord blood s~pply.~~ Thus, CSF drainage alone will not afford spinal cord protection during aortic cross-clamping.
REFERENCES
1. Crawford ES, Walker HS, Saleh SA, et al: Graft replacement of aneurysm in the descending thoracic aorta: Results without bypass or shunting. Surgery 89:73-85,198l 2. Crawford ES, Fenstermocker JM, Richardson W, et al: Reappraisal of adjuncts to avoid ischemia in the treatment of thoracic aneurysms. Surgery 67:182-196,197O 3. DeBakey ME, McCollum CH, Graham JM: Surgical treatment of aneurysms of the descending thoracic aorta: Long-term results in 500 patients. J Cardiovasc Surg 19571-576, 1978 4. Najafi H, Javid H, Hunter J, et al: Descending aortic aneurysmectomy without adjuncts to avoid ischemia. Ann Thorac Surg 30:326-335, 1980 5. Brewer LA, Fosburg RG, Muldder GA, et al: Spinal cord complication following surgery for coarctation of the aorta: A study of 66 cases. J Thorac Cardiovasc Surg 64:368-381, 1972 6. 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 Vast Surg 3:389-404, 1986 7. Svensson LG, Loop FD: Prevention of spinal cord ischemia in aortic surgery, in Bergan JJ, Yao JST (eds): Arterial Surgery: New Diagnostic and Operative Techniques. New York, NY, Grune & Straton, 1988, pp 273-285 8. Szilagyi DE, Hageman JH, Smith RF, et al: Spinal cord damage in surgery of the abdominal aorta. Surgery 83:38-56,1978 9. Kadyi H: Ueber die Blutgefasse des Menschlichen Ruckenmarkes. Anat Anz 1:303-314,1886 10. Djindjian R, Faure C: Accidents medullaires de1 laortographic. J Bela Radio1 50:207-210,1967 11. Svensson LG, Hinder RA: Hemodynamics of aortic crossclamping. Experimental observations and clinical applications. Surg Annu 19:41-65,1987 12. Svensson LG, Grum DF, Cosgrove DM, et al: Appraisal of cerebrospinal fluid alterations during aortic surgery with intrathecal papaverine administration and cerebrospinal fluid drainage. J Vast Surg 11:423-429,199O 13. Oka Y, Miyamoto T: Prevention of spinal cord injury after cross-clamping of the thoracic aorta. Jpn J Surg 14:159-162,1982
14. Maeda S, Miyamoto T, Murata H, et al: Prevention of spinal cord ischemia by monitoring spinal cord perfusion pressure and somatosensory evoked potentials. J Cardiovasc Surg 30565-571, 1989 15. Woloszyn TT, Marini CP, Coons MS, et al: Cerebrospinal fluid drainage and steroids provide better spinal cord protection during aortic cross-clamping than does either treatment alone. Ann Thorac Surg 49:79-83,199O 16. 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 13:36-46,199O 17. Piano G, Gewertz BL: Mechanism of increased cerebrospinal fluid pressure with thoracic aortic occlusion. J Vast Surg 11:695-701, 1990 18. Killen DA, Edwards RH, Tinsley EA, et al: Effect of low molecular weight dextran, heparin, urea, cerebrospinal fluid drainage, and hypothermia on ischemic injury of the spinal cord secondary to mobilization of the thoracic aorta. J Thorac Cardiovast Surg 50:882-887,1965 19. Griffiths IR, Pitts LH, Crawford RA, et al: Spinal cord compression and blood flow. Neurology 28:1145-1151,1978 20. Lassen NA, Christensen MS: Physiology of cerebral blood flow. Br J Anesth 48:719-734,1976 21. Cutler RW, Page L, Galicich J, Watters GV: Formation and absorption of cerebrospinal fluid in man. Brain 91:707-720, 1968 22. Dunbar HS, Gutherie TC, Karpell B: A study of the cerebrospinal fluid pulse wave. Arch Neurol 14:624-630, 1966 23. Blaisdell FW, Cooley DA: The mechanism of paraplegia after thoracic aortic occlusion and its relationship to spinal fluid pressure. Surgery 51:351-355,1962 24. Grubbs PE, Marini C, Toporoff B, et al: Somatosensory evoked potentials and spinal cord perfusion pressure are significant predictors of postoperative neurologic dysfunction. Surgery 104:216-223,1988 25. Miyamoto K, Veno A, Wada T, et al: A new and simple method of preventing spinal cord damage following temporary
372
occlusion of the thoracic aorta by draining the cerebrospinal fluid. J Cardiovasc Surg 1:188-197,196O 26. McCullough JL, Hollier LH, Nugent M: Paraplegia after thoracic aortic occlusion: influence of cerebrospinal fluid drainage. J Vast Surg 9:153-160, 1988 27. Bower TC, Murray MJ, Glovicki P, et al: Effects of thoracic aortic occlusion and cerebrospinal fluid drainage on regional spinal cord blood flow in dogs: Correlation with neurologic outcome. J Vast Surg 9:135-144, 1989 28. Wadouh F, Lindermann EM, Arndt CF, et al: The arteria radicularis magna as a decisive factor influencing spinal cord damage during aortic occlusion. J Thorac Cardiovasc Surg 88:1-10, 1984 29. Svensson LG, Von Ritter CM, Groeneveld HT, et al: Cross-clamping of the thoracic aorta. Influence of aortic shunts,
SHENAQ AND SVENSSON
laminectomy, papaverine, calcium channel blocker, allopurinol. and superoxide dismutase on spinal cord blood flow and paraplegia in baboons. Ann Surg 204:38-47,1986 30. Svensson LG, Richards E, Core11 A, et al: Relationship of spinal cord blood flow to vascular anatomy during thoracic aortic cross-clamping and shunting. J Thorac Cardiovasc Surg 88:1-10. 1984 31. Himansu K, Dasmahapatra MBBS, Coles JG, et al: Relationship between cerebrospinal fluid dynamics and reversible spinal cord ischemia during experimental thoracic aortic occlusion. J Thorac Cardiovasc Surg 95:920-923,1988 32. Granke K, Hollier LH, Zdrahal P, Moore W: Longitudinal study of cerebral spinal fluid drainage in polyethylene glycolconjugated superoxide dismutase in paraplegia associated with thoracic aortic cross-clamping. J Vast Surg 13:615-621, 1991
