41

Eur J Cardio-thorac Surg (1992)6:36-41

European Journal of

0 Springer-Verlag 1992

Deep hypothermic systemic circulatory arrest and continuous retrograde cerebral perfusion for surgery of aortic arch aneurysm Y. Ueda, S. Miki, K. Kusuhara, Y. Okita, T. Tahata, and K. Yamanaka Department

of Cardiovascular

Surgery, Tenri Hospital, Tenri, Nara, Japan

Abstract. From 1987 to February 1991, we have repaired or replaced the aortic arch in ten patients using deep hypothermic systemic circulatory arrest with continuous retrograde cerebral perfusion (CRCP). CRCP can be implemented using the bypass connecting the arterial and venous lines of the extracorporeal circuit to reverse the flow into the superior vena cava cannula after induction of circulatory arrest. CRCP flow required to maintain an internal jugular vein pressure of 20 mmHg ranged from 100 to 500 ml/min. After completion of suturing of the aortic arch graft, air is evacuated retrogradely from the open arch vessels prior to reestablishing the usual arterial return. Two patients died, one from sepsis and the other from liver cirrhosis 1 month postoperatively. CRCP times ranged from 11 to 56 min, and minimal nasopharyngeal temperatures ranged from 16’ to 18OC. The difference in oxygen content between the perfused blood and the blood draining from the arch vessels during CRCP most likely reflected the steady-state metabolism of the brain during the deep hypothermic state. This technique offers advantages including the need for dissecting and clamping the arch branches, providing sufficient metabolic support to the brain during deep hypothermia, and eliminating embolism of particulate debris from the aortic arch. [Eur J Cardio-thorac Surg (1992) 6:36-411 Key words: Aortic arch aneurysm - Aortic dissection - Deep hypothermia perfusion

Surgical treatment of aneurysm or dissection involving the aortic arch remains one of the most complicated technical and tactical challenges in cardiovascular surgery. Deep hypothermic circulatory arrest [2,4-9, 11-17, 201 or various partial cerebral perfusion techniques [lo, 181 have been widely used for intraoperative protection of the central nervous system. The use of deep hypothermic circulatory arrest offers important advantages, providing a dry, quiet surgical field unencumbered by clamps and cannulas for repairing the aneurysm or dissection of the aortic arch. Deep hypothermic circulatory arrest, however, entails problems relating to preservation of cerebral function and avoiding air embolism. In 1986, we introduced systemic deep hypothermic circulatory arrest, with intermittent retrograde cerebral perfusion via the superior vena cava. The clinical results with that method were satisfactory in six patients 1241.We expanded the method of retrograde cerebral perfusion from intermittent to continuous in November

Presented at the 5th Annual Meeting of the European Association for Cardio-thoracic Surgery, London, UK, September 23-25,1991

- Circulatory arrest - Retrograde cerebral

1987 [24, 251. We now report our recent experience in treating aortic arch lesions using the continuous retrograde cerebral perfusion (CRCP) technique. We also studied the extent of cerebral protection via intraoperative electroencephalography and monitoring somatosensory-evoked potentials.

Patients and methods Subjects included five female and five male patients who underwent replacement or repair of the aortic arch under hypothermic circulatory arrest with CRCP between November 1987 and February 1991. The mean age was 66.6 years, with a range of 46 to 81 years. Atherosclerotic aneurysm was present in five (including distal arch aneurysm after replacement of the ascending aorta and proximal aortic arch), aortic dissection in five (all in the acute phase, and two patients in shock) (Fig. 1). One patient with atherosclerotic aneurysm had a history of cerebral and myocardial infarction. One patient underwent replacement of the ascending aorta and proximal aortic arch under deep hypothermic circulatory arrest and intermittent retrograde cerebral perfusion 4 years prior to reoperation for a distal arch aneurysm. The other patients had no history of neurological disease.

31

1

1 Fig. 1. Illustrations

I

of the type of disease and number of patients

Operative technique Option I. The femoral artery was cannulated after systemic heparinization for the patients with aortic dissection or atherosclerotic aneurysm involving the ascending aorta and aortic arch. The sternum was then split at the midline and the pericardium was carefully opened. Cardiopulmonary bypass was then established via transatria1 bicaval drainage and femoral arterial return. The superior vena cava was snared. The heart was vented through the right upper pulmonary vein or main pulmonary artery. While the patient was core-cooled to 15”-18 “C, the ascending aorta was cross-clamped just proximal to the brachiocephalic artery. The ascending aorta was opened longitudinally, and the right and left coronary arteries were selectively perfused with cold cardioplegic solution (St. Thomas Hospital solution) to protect the myocardium. Topical hypothermia was also applied to the heart with an ice slush. The ascending aorta was transected in its midportion. The proximal end was then anastomosed at the supracoronary level to a woven Dacron graft with ultra-low porosity of an appropriate size, or the aortic valve and ascending aorta were replaced with a composite graft and the coronary arteries reimplanted. The graft was preclotted with fibrin glue. Before induction of systemic circulatory arrest, the superior vena cava cannula was clamped and the arterial return was continued until the pressure in the internal jugular vein reached 15 mm Hg to prevent air embolism into the cerebral vessels (Fig. 2). Clamps were then applied to both the arterial and venous lines to accomplish total circulatory arrest and to prevent introduction of air into the perfusion circuit. The arch aneurysm was opened without clamping any branches of the aortic arch or the distal thoracic aorta. The patient was placed flat in the usual cardiac surgery position. The inside of the aortic arch was inspected. CRCP can be implemented using the bypass connecting the arterial and venous lines of the extracorporeal circuit to reverse the flow into the superior vena cava cannula after induction of circulatory arrest. CRCP flow required to maintain an internal jugular vein pressure of 20 mmHg ranged from 100 to 500 ml/min. Blood draining into the aortic arch was removed by suction. The peripheral end of the graft was anastomosed to the beveled aortic arch or, preferably, to the intact lumen of the distal aorta. All aortic anastomoses were done with continuous 3/O polypropylene suture. After completion of suturing of the aortic arch graft, air was evacuated retrogradely from the open arch vessels and backflushed through the femoral artery by releasing the clamp on the arterial line before reestablishing the usual arterial return (Fig. 2). Conventional cardiopulmonary bypass was then restarted and the patients were rewarmed.

Fig. 2. Cardiopulmonary bypass circuit and technique of CRCP. Cannulation of the ascending aorta illustrated by the broken lines is only for operative technique Option 2: (1) Before induction of systemic circulatory arrest, the superior vena cava (s) is clamped until the internal jugular vein pressure reaches 15 mmHg. Clamps are then applied to the arterial (Ri) and inferior vena cava (R2) to accomplish total circulatory arrest. (2) CRCP can be implemented by clamping the venous line (R3) and releasing the clamp (5’) on the superior vena cava through the bypass connecting the arterial and venous lines by releasing the clamps (N). Reverse flow into the superior vena cava is indicated by broken arrows. (3) Just before completion of the aortic arch graft suturing, air is evacuated retrogradely from the open arch vessels and backflushing through the femoral artery by releasing the clamp (Ri) on the arterial line. (4) Conventional cardiopulmonary bypass is restarted by clamping the bypass (N) and releasing the clamps (R2, R3) on the venous line. CRCP = continuous retrograde cerebral perfusion; FA = femoral artery; IVC = inferior vena cava; SVC = superior vena cava; Heat Ex= heat exchanger. (This figure is reproduced with permission from Japanese Association for Thoracic Surgery [25])

Option 2. In the patients with atherosclerotic aortic arch aneurysm and an intact ascending aorta, the ascending aorta was also cannulated for arterial return, and the femoral arterial line was clamped during core-cooling (Fig. 2). As the atherosclerotic aneurysm usually contains mural thrombus or atheroma, backflushing of thrombus by femoral arterial return and clamping of the aorta and tributaries were eliminated. The aortic arch was opened without any clamping after deep hypothermic systemic circulatory arrest using the same method previously described in Option 1. CRCP was then also commenced. After inspection of the inside of the ascending aorta, it was clamped and cardioplegic solution was perfused for myocardial protection. The distal end of a woven Dacron graft with ultra-low porosity was anastomosed initially and then the branches of the aortic arch were implanted, together with an oval base patch, in the vascular graft. The proximal end of the graft was anastomosed to the ascending aorta last. The operation was completed by careful expulsion of air from the opened aorta and arch vessels, using the same method as described in option 1. At this stage, the cannula in the femoral artery was used for backflushing by releasing the clamp on the arterial line. Core-rewarming and heart resuscitation were commenced by conventional extracorporeal perfusion via the ascending aortic return alone (Fig. 2). The femoral arterial line was clamped to eliminate backflushing of emboli.

38 Monitoring Electroencephalography (EEG) and somatosensory-evoked potentials (SEP) were recorded in eight patients during the operation. SEPs following stimulation of the left median nerve were recorded from the right post-central hand area with a Neuropack II (MEB5100, Nihon Koden, Japan). Stimuli used were square-wave pulses of 0.3 ms duration; intensity was increased until an evoked potential wave was recorded. An average of 250 or 500 samples were obtained intraoperatively. Samples of the blood perfused into the superior vena cava and that drained from the arch vessels were collected during CRCP about every 10 min in eight patients for measurements of the oxygen content difference.

No.

of

CRCP

Patients time(min)

(mean)

I

3

4 36-56

13-24

(45)

(20)

II

\/Lr ‘Y.

JV

.;

. “x,,

i. J p1

Results

No. of Patients CRCP

Circulatory arrest times ranged from 11 to 56 min; average 35.6 min and 95% of confidence limits (CL) of mean were 22 and 44 min (Fig. 3). Minimal nasopharyngeal temperatures ranged from 16” to 18 “C. Core cooling times ranged from 32 to 95 minutes; average 64.8 min and 95% of CL of mean were 47 and 83 minutes. Times for rewarming ranged from 50 to 158 min; average 84.2 min and 95% CL of mean were 59 and 109 min. Total extracorporeal bypass times ranged from 127 to 282 min; average 180 min and 95% CL of mean are 142 min and 218 min. The mode of operation was as follows; total replacement of the aortic arch with a woven Dacron tube graft of ultra-low porosity in four, replacement of the ascending aorta and proximal portion of the aortic arch with a beveled anastomosis in three, replacement of the aortic valve and ascending aorta with a composite graft in one, resuspension of the aortic valve and replacement of the ascending aorta and aortic arch combined with right coronary artery bypass grafting (CABG) in one, and replacement of the distal aortic arch and triple CABG using saphenous vein in one (Fig. 3). Two patients died 1 month postoperatively, one from sepsis and the other from liver cirrhosis. Hospital mortality was 20% (70% of CL were from 7 to 41%). The patient who died from sepsis had multiple systemic emboli due to massive atheroma in the aortic arch aneurysm. His EEG and SEP diminished during rewarming bypass through the femoral artery. Although he recovered consciousness, he died 1 month postoperatively. The other patient with acute aortic dissection and liver cirrhosis recovered almost completely; however, she developed fatal hepatic failure 2 weeks postoperatively. Acute renal failure developed in one patient who underwent aortic valvuloplasty and replacement of the ascending aorta with CABG while in shock, but this patient recovered fully. The convalescence of the remaining seven patients was uneventful and six patients were extubated the day after the operation. Routine postoperative conventional angiograms or digital subtraction angiograms were obtained in seven patients. The results obtained were satisfactory (Fig. 4). Intraoperative SEP monitoring revealed a low amplitude during hypothermia and no potentials throughout the period of circulatory arrest, except in one patient. The

time(min)

ti

I

I

32

48

Fig. 3. Illustrations of the main operative procedures, number of patients, and CRCP times in minutes. CRCP=continuous retrograde cerebral perfusion

5/l:

Fig. 4a, b. Pre- and postoperative digital subtraction aortogram of the patients who underwent aortic arch replacement with a Dacron tube graft. Arrows indicate the margin of the aneurysm and mural thrombi

patient underwent replacement of the ascending aorta and proximal arch for acute dissection, and her SEP was faintly maintained and recovered immediately after rewarming bypass. The recovery of SEP was observed at a body temperature of 25” to 30°C in the other patients (Fig. 5). The EEG became isoelectric during deep hypothermia and circulatory arrest and recovered activity after rewarming bypass, except in one patient. That patient whose EEG did not recover completely had massive atheroma in the arch aneurysm as described previously, and multiple systemic emboli were developed from the femoral arterial return during the rewarming stage.

39

SEP

9:46

control

s.Y.

,2:48

73~.

M

90.9.6

‘VP I

ECC

II

lo:42 32.3”C

, 13:25

lo:48

11:13 CABG

13:32

26.4%

24.8”C

ii:46

14:08

18.5%

11154 14127

18.7%

15:20

12:24

12:41

15:56 fqy L.

1

(/+++TW~ ., a - --___

Fig. 5. Intraoperative SEP monitoring in the patient who underwent replacement of the distal aortic arch and triple coronary artery bypass grafting. CABG = coronary artery bypass grafting; CRCP = continuous retrograde cerebral perfusion; ECC = extracorooreal circulation; ‘SEP = somatosensory evoked potentials

The difference in oxygen content (DO,) between the perfused blood and the blood draining from the arch vessels at the beginning of CRCP ranged from 1.2 to 5.8 ml/dl. After 10 to 30 min of CRCP, DO, tended to decrease but remained in the 1.5 to 5 ml/d1 range (Fig. 6).

Discussion

:oj

lb Duration of retrograde

20

30

cerebral perfusion (ntn)

Fig. 6. Difference in oxygen content between the perfused blood and the blood draining from the arch vessels during continuous retrograde cerebral perfusion

Even with the advances in modern surgical technology, surgery for the aortic arch remains a technical challenge for the cardiovascular surgeon. It requires cerebral protection, as well as individualization of both operative planning and perfusion techniques. Selective perfusion of the arch vessels [lo, 181and profound hypothermic circulatory arrest [2,4 -9, 11~ 17,201 are two surgical options for the treatment of aneurysms involving the aortic arch.

40

Profound hypothermic circulatory arrest has been widely used [2,4-9, II- 17,201 and provides a dry, quiet, motionless surgical field unencumbered by multiple clamps and cannulas. Profound hypothermia protects the brain, heart, kidneys, and other organs, presumably by decreasing the metabolic activity. In 1982, Livesay and colleagues reported “open aortic anastomosis,” in which distal anastomosis was achieved from within the aorta during circulatory arrest [15]. Distal aortic clamping causes crowding and distortion of the aortic lumen, and in acute dissection often results in fragmentation of the fragile vessel wall, and further dissection when flow is resumed. Using the open aortic method, the false lumen can be safely and accurately obliterated with the distal suture line. Initially, circulatory arrest was accomplished by first clamping the arch vessels and then stopping extracorporeal bypass to prevent cerebral air embolism [I 5, 161.Grey and colleagues found it unnecessary to clamp the brachiocephalic vessels as a matter of routine, especially in aortic dissection, if the patient was placed in the Trendelenburg position to minimize the risk of air introduction into the cephalic vessels [12]. Recent reports of Crepps and co-workers [7], Luosto and colleagues [ 171, and Crawford and colleagues [6] mentioned that dissection of the aneurysm was almost unnecessary, because the arch vessels were not routinely snared, clamped or perfused. Ergin and colleagues reported the safety and efficacy of profound total body hypothermia with circulatory arrest in the treatment of enlarging aneurysms of the aortic arch and emergency treatment of acute dissection of an intimal tear located in the aortic arch [9]. They advocated this technique as simple and producing results superior to methods reported involving selective cerebral perfusion during arch replacement. They also emphasized that clamps on arch branches should be placed during circulatory arrest. Deville and co-workers also reported that the arch vessels were routinely cross-clamped just before circulatory arrest, and that they were left unclamped in cases where the clamping of these vessels appeared hazardous [8]. Manipulation of the tributaries of the aortic arch has the risk of embolization of atheromatous debris or extension of dissection. Minimized dissection and absence of clamps are major advantages of deep hypothermic circulatory arrest and allow for faster aortic arch repair or replacement within the safe limits of brain protection [4-9, 15 - 171. If a patient is placed in a deep Trendelenburg position during open aortic anastomosis under circulatory arrest without clamping of the arch vessels air may get into the descending aorta, which is the highest level and filled by low-flow femoral perfusion. Air in the descending aorta will be backflushed by femoral arterial return after re-establishment of cardiopulmonary bypass. In 1980, Mills and Ochsner reported that retrograde perfusion via the superior vena cava with hypothermia at 20°C was effective in the management of massive air embolism during cardiopulmonary bypass [19]. We initially used this retrograde perfusion method to expel air in the aortic arch and its branches after profound hypothermic circulatory arrest without dissecting or clamp-

ing any of the branches. Pressure in the internal jugular vein must be maintained at 10 to 15 mm Hg to prevent air introduction into the cephalic vessels before opening the aorta, as described in the operative technique. Patients are placed in a flat or slight Trendelenburg position [24]. Lemole and co-workers reported surgical therapy for dissection of the thoracic aorta, using an intraluminal sutureless prosthesis that requires no end-to-end anastomosis [14]. They also mentioned that they developed a technique of intermittent retrograde cerebral perfusion via the superior vena cava with a selective pump system for 2 min out of every 10 min providing cerebral oxygenation during this period. We extended their method to continuous retrograde cerebral perfusion with a simplified perfusion circuit. We use the bypass circuit connecting the arterial and venous lines of the extracorporeal circuit to reverse the flow into the superior vena cava cannula during systemic circulatory arrest instead of their selective pump system [24, 251. Hospital mortality was 20% (two patients; 70% of CL were from 7 to 41%) in this series. One patient with acute aortic dissection had liver cirrhosis preoperatively and severe haptic failure was the cause of death. The other patient died from sepsis and multiple systemic emboli produced by backflushing of the femoral arterial return. Since this case we have preferred Option 2 for patients with atherosclerotic aneurysm containing atheroma. Manipulation of the aneurysm and arch vessels should also be avoided. We do not feel that CRCP was the cause of death in our two patients and fatal complications involved extensive lesions of major organs. All eight survivors were in NYHA class I or II, and there were no late deaths. The efficacy of cerebral protection by CRCP is a major concern. The difference in oxygen content between the perfused blood and the blood draining from the arch vessels at the beginning of CRCP ranged from 1.2 to 5.8 ml/dl, and this suggested the washout of metabolites accumulated during the short period of cerebral ischemia prior to establishing the CRCP. After 10 to 30 min of CRCP, DO, tended to decrease but was still in the 1.5 to 5 ml/d1 range. This most likely reflected the steady-state metabolism of the brain during the deep hypothermic state and should provide sufficient metabolic support to the brain during deep hypothermia. CRCP also maintains the brain temperature at an optimal level by the cold blood perfusate during systemic circulatory arrest. Monitoring of intraoperative cerebral function by EEG and SEP revealed fairly good recovery in a short period of rewarming in patients with CRCP compared with those under conventional circulatory arrest [24, 261. A safe period of circulatory arrest has not been established, but is considered to be around 40- 50 min at 18 “C [3, 5-8, IO]. Although our CRCP time was less than 60 min, extension of the safe limits of hypothermic circulatory arrest is expected by CRCP. Recently, experimental transvenous retrograde perfusion of the brain for stroke has been reported by Ueda and colleagues [22, 231 and Shinha and co-workers [21]. They mentioned that the cerebral venous system and blood-brain barrier tolerated fairly high venous pressure [22] and that retrograde perfusion was effective in reducing the size of stroke [21,23].

41

Although the precise flow dynamics and metabolism in CRCP have yet to be established in humans and the number of patients in our study was small, we believe that this technique extends the safe limits of the brain still maintains the simplicity and advantages of hypothermic circulatory arrest. It also offers advantages such as obviating the need of dissecting and clamping the arch tributaries, and embolism of particulate debris from the arch is eliminated.

References 1. Coles JG, Taylor MJ, Pearce JM, Lowry NJ, Stewart DJ, Trusler GA, Williams WG (1984) Cerebral monitoring of somatosensory evoked potentials during profoundly hypothermic circulatory arrest. Circulation 70 [Suppl I]: 1-96-I-102 2. Cooley DA, Ott DA, Frazier OH, Walker WE (1981) Surgical treatment of the transverse aortic arch: experience with 25 patients using hypothermic techniques. Ann Thorac Surg 32: 260272 3. Coselli JS, Crawford ES, Beall AC Jr, Mizrahi EM, Hess KR. Pate1 VM (1988) Determination of brain temperature for safe circulatory arrest during cardiovascular operation. Ann Thorac Surg 45: 638-642 4. Crawford ES, Saleh SA (1981) Transverse aortic arch aneurysm. Improved results of treatment employing new moditications of arotic reconstruction and hypothermic cerebral circulatory arrest. Ann Surg 194: 180- 188 5. Crawford ES, Snyder DM (1983) Treatment of aneurysm of the aortic arch. A progress report. J Thorac Cardiovasc Surg 85: 237-246 6. Crawford ES, Svensson LG, Coselli JS, Sati HJ, Hess KR (1989) Surgical treatment of aneurysm and/or dissection of the ascending aorta, transverse aortic arch, and ascending aorta and transverse aortic arch. Factors influencing suvival in 717 patients. J Thorac Cardiovasc Surg 98: 659-674 7. Crepps JT Jr, Allmendinger P, Ellison L, Hanphrey C, Preissler P. Low H (1987) Hypothermic circulatory arrest in the treatment of thoracic aortic lesions. Ann Thorac Surg 43: 644647 8. Deville CL Roques X, Fernandez G, Laborde N. Baudet E, Fontan F (1988) Should circulatory arrest with deep hypothermia be revised in aortic arch surgery? Eur J Cardio-thorac Surg 2: 185-191 9. Ergin MA, O’Connor J, Guinto R, Griepp RB (1982) Experience with profound hypothermia and circulatory arrest in the treatment of aneurysms of the aortic arch. Aortic arch replacement for acute arch dissections. J Thorac Cardiovasc Surg 84: 649-655 10. Frist WH, Baldwin JC, Starnes VA, Stinson EB, Oyer PE, Miller DC, Jamieson SW, Mitchell RS, Shumway NE (1986) A reconsideration of cerebral perfusion in aortic arch replacement. Ann Thorac Surg 42:273-281 CL, Hurwitz JB, 11. Galloway AC, Colvin SB, LaMendola Baumann FG, Harris LJ, Culliford AT, Grossi EA. Spencer FC (1989) Ten-year operative experience with 165 aneurysms of the ascending aorta and aortic arch. Circulation 80 [Suppl I]: I-249 -I-256 12. Grey DP, Ott DA, Cooley DA (1983) Surgical treatment of aneurysm of the ascending aorta with aortic insufficiency. A selective approach. J Thorac Cardiovasc Surg 86: 864-877

13. Griepp RB, Stinson EB, Hollingsworth JF, Buehler D (1975) Prosthetic replacement of the aortic arch. J Thorac Cardiovasc Surg 70: 1051-1063 14. Lemole GM, Strong MD, Spagna PM, Karmilowicz NP (1982) Improved results for dissecting aneurysms. Intraluminal sutureless prosthesis. J Thorac Cardiovasc Surg 83: 249-255 15. Livesay JJ, Cooley DA, Duncan JM. Ott DA, Walker WE, Reul GJ (1982) Open aortic anastomosis: improved results in the treatment of aneurysms of the aortic arch. Circulation 66 [Suppl I]:I-122-1-127 16. Livesay JJ, Cooley DA, Reul GJ, Walker WE, Fraizier OH, Duncan JM, Ott DA (1983) Resection of aortic arch aneurysms: a comparison of hypothermic techniques in 60 patients. Ann Thorac Surg 36: 19-28 17. Luosto R, Maamies T, Peltola K, Jarvinen A, Mattila S (1987) Hypothermia and circulatory arrest in reconstruction of aortic arch. A report of nine cases. Stand J Thorac Cardiovasc Surg 21:113-117 18. Matsuda H, Nakano S, Shirakura R, Matsukawa R, Ohkubo N, Ohtani M. Hirose H, Kawashima Y (1989) Surgery for aortic arch aneurysm with selective cerebral perfusion and hypothermic cardiopulmonary bypass. Circulation 80 [Suppl I]: I-243 -1-248 19. Mills NL. Ochsner JL (1980) Massive air embolism during cardiopulmonary bypass. Causes, prevention, and management. J Thorac Cardiovasc Surg 80: 708-717 20. Ott DA, Frazier OH, Cooley DA (1978) Resection of the aortic arch using deep hypothermia and temporary circulatory arrest. Circulation 58 [Suppl I]: I-227-1-231 21. Sinha UK, Hinton DR, Frazee JG. Jordan SE, Dion JE, Kar S, Norel EJ, Vinela F, Corday E (1990) Pathology of retroperfusion in experimental cerebral ischemia. Abstract from International Congress of Neuropathology in Kyoto 22. Ueda T, Yamamoto YL, Takara E, Diksic M (1989) Tolerance of the cerebral venous system to retrograde perfusion pressure in focal cerebral ischemia in rats. Stroke 20: 3788385 23. Ueda T, Yamamoto YL, Diksic M (1989) Transvenous perfusion of the brain with verapamil during focal cerebral ischemia in rats. Stroke 20: 501-506 24. Ueda Y, Miki S, Kusuhara K, Okita Y, Tahata T. Yamanaka K (1990) Surgical treatment of aneurysm or dissection involving the ascending aorta and aortic arch, utilizing circulatory arrest and retrograde cerebral perfusion. J Cardiovasc Surg 31: 553558 25. Ueda Y, Miki S. Kusuhara K, Okita Y, Tahata T, Yamdnaka K (1991) Surgery for aortic arch aneurysm using deep hypothermic circulatory arrest and retrograde cerebral perfusion. J Jpn Assoc Thorac Surg 39: 704-706 26. Wilson GJ, Rebeyka IM, Coles JG, Desrosiers AJ, Dasmahapatra HK, Adler S, Feitler DA, Sherret H, Kielmanowicz S, lkonomidis J. Gatley RAA, Taylor M (1988) Loss of the somatosensory evoked response as an indicator of reversible cerebral ischemia during hypothermic, low-flow cardiopulmonary bypass. Ann Thorac Surg 45: 2066209

Yuichi Ueda, MD Department of Cardiovascular Tenri Hospital 200 Mishima-cho Tenri, Nara 632 Japan

Surgery

42

Discussion Dr. J. Bachet (Suresnes, France). I would like to compliment Dr. Ueda and his coworkers for bringing to our attention an elegant method of assessing cerebral protection. However, the method described here deserves a few comments and raises some questions. In my opinion, and I suppose in the opinion of most colleagues, a new technique to be adopted must prove to be either simpler or more efficient than the currently used methods. This method is obviously elegant and astute. But, the flow of 300 to 500 ml/min, permanently running from the arch vessels at the very site of the distal anastomosis, must be rather cumbersome, as is the double femoral and aortic cannulation described in “Option 2,” in order to avoid back-flushing of debris and thrombus. My main criticism is linked to the fact that this method uses profound hypothermia associated with circulatory arrest. On the one hand, it has been widely demonstrated by Griepp and many others that profound hypothermia alone is efficient in protecting the central nervous system when the circulatory arrest lasts less than 45 min. On the other hand it has been recently demonstrated by Swain and coworkers that high-energy phosphates disappear while major cellular acidosis is observed. At very low temperatures (less than ISC) only low flow (10 ml/kg per min) perfusion maintains the autoregulation system of the cerebral flow and preserves the high-energy phosphates and cellular pH. The idea of enhancing the cerebral protection provided by profound hypothermia with low-flow perfusion seems then logical. But, as in your series, the average time of circulatory arrest was rather short (35 min), it is not quite clear whether the brain has been protected by profound hypothermia or by retrograde perfusion or, as I would guess, by both techniques. The fact that SEP monitoring and EEG recording demonstrated a complete recovery in all patients but one only proves that the brain was protected. It does not show which technique provided the protection. Incidentally, you infer that the patient who experienced severe neurologic disorders had multiple cerebral emboli, but you give neither clinical nor pathoanatomic proof, and you do not indicate the duration of ciculatory arrest and retrograde perfusion in this case. You also infer that the difference in oxygen content between the perfused blood and the blood draining from the arch tributaries provides sufficient metabolic support to the nervous cells. Considering that at low temperatures oxygen is mainly transported in the dissolved form, I am not sure that the difference in oxygen content is a good indicator of the metabolic activity. However, the use of hypothermic cerebral perfusion is certainly beneficial, as we have recently demonstrated in our experience with the so-called “cold blood cerebroplegia” in more than 70 patients over a 6-year period. In our series, cerebral activity reappeared at a mean of 12 min after rewarming and was completely restored after a mean of 66 min. By comparison, it would have been of interest to know the average time for complete recovery of cerebral activity in

your patients. As we know, profound hypothermia has been held responsible for severe complications and is associated, at least in our experience, with a high rate of neurologic morbidity, especially in the elderly. Although these complications did not occur in your series, the number of patients is too limited to conclude that you will not face the drawbacks of profound hypothermia. Thus, it is a pity that the use of cerebral retrograde perfusion did not allow you to do without deep-core hypothermia or to reduce the amount of time it was used. Thus, I would like to ask a few questions. Have you any anatomic or experimental proof that retrograde perfusion provides the brain with a total, regular, constant flow as does antegrade perfusion? Have you any experimental evidence that retrograde perfusion per se could provide sufficient metabolic support to the brain? If so, and in order to reduce or eliminate the disadvantages of profound core hypothermia, why don’t you use topical hypothermic retrograde cerebral perfusion through a separate heat exchanger placed on the bypass line, maintaining the patient at moderate core hypothermia? Again, I congratulate Dr. Ueda and thank him for forwarding his manuscript in advance.

Dr. Ueda: I would like to thank Dr. Bachet for his comments. Dr. are really to the point. Regarding anatomical and experimental proof that retrograde perfusion provides the brain with constant flow, we have conducted experiments in six mongrel dogs with the continuous retrograde cerebral perfusion technique. But we had problems in that internal jugular veins are quite small and rudimentary. On the other hand, the external jugular veins are the main drainage channel from the head of the dog. The external jugular veins contain many functioning valves that obstruct retrograde perfusion. However, infusion of microparticles of the carbon black pigment into the peripheral end of the jugular veins revealed that the pigment was distributed in venulae all over the brain. The cerebral venous system has rich collaterals and contains no valves. We strongly feel that retrograde cerebral perfusion in human will be more effective because the internal jugular veins are the major drainage route from the brain. I think it will be possible to answer this question. Regarding experiment evidence of metabolic support, we have not conducted any elegant experiments such as magnetic resonance spectrograms, but we hope to get into the very area you mentioned. Thirdly, regarding the optimal level of hypothermia, I agree with your comments. We initially used deep hypothermia because we did not have much experience. There are several good results for moderate hypothermia and circulatory arrest, but in our opinion circulatory arrest alone is somehow limited and should be reserved for experienced surgeons. Thus, I would agree with your comment. We would try moderate hypothermia with cold retrograde cerebral perfusion in patients with aortic arch reconstruction. Bachet’s questions