Extran du Bulletin de la Société Internationale de Chirurgte, T. XV, Nv 3. mai 1956. pp. 206 4 215. Hypothermia in the Surgical Treatment of Aortic Aneurysms (**) Denton A. Coorry, M.D., and Michael E. Dr Baxey, M.D. (*). (Houston) During recent years the treatment of aortic aneurysms by sur- gical excision has been established as the method of choice wherever conditions permit its satisfactory application (1, 5, 10). However, a number of factors primarily concerned with the nature and location ot the lesion determines the operative method to be employed. In gene- ral, two types of procedures may be used for this purpose depending upon whether the aneurysm is fusiform or sacciform in type. In the treatment of sacciform lesions, for example, the procedure consists in tangential excision with repair by lateral aortorrhaphy. This is accom- plished by isolating and clamping the neck of the aneurysm with a large minimal trauma clamp, excising the sac and repairing the wall of the aorta with multiple mattress sutures. This method is particu- Jarly well suited to syphilitic aneurysms of the ascending thoracic aorta and aortic arch. In these cases the aortic wall adjacent to the neck of the aneurvsm jis usually of leathery consistency and holds sutures well. Furthermore tangential clamping of the aneurysm does not interrupt circulation through the aorta itself. a factor of considerable importance at this high level. For fusiform aneurysms involving the entire aortic circumference temporary cross clamping of the aorta is necessary in order to excise the lesion and replace the diseased segment of aorta with an aortic homograft or plastic prosthesis. During the period of occlusion ische- mic damage to tissues located distally may occur and prevent a success- (*) From the Department of Surgery, Baylor University College of Medicine, ind the Jefferson Davis, Methodist, and Veterans Administration Hospitals, Houston, Texas. (**) Supported in part by a grant from the Houston Heart Association, and the Cora and Webb Mading Fund for Surgical Research. BULLETIN DE LA SOCIETE INTERNATIONALE DE CHIRURGIE, N° 3, 1956 ful outcome. The level and duration of occlusion and length of the segment to be excised are important factors influencing the success of this method of treatment. Thus, in our experience with 140 consecu- tive cases of aneurysms of the abdominal aorta in which the aorta was clamped below the Jevel of the renal arteries for as long as 126 minutes there has not been a single instance of serious ischemic effect upon tissues below the point of occlusion. Above this level the tissue most vulnerable to periods of temporary ischemia is the central nervous system. Based upon our experience with abdominal and the- racic aneurysms damage to other organs has not occurred following occlusion distal to the left common carotid artery. On the other hand. occlusion of the descending thoracic aorta at this level for 20 to 30 minutes will produce significant and often fatal spinal cord damage in a high percentage of cases. Thus in the removal of lesions involving the distal aortic arch and proximal descending aorta the prevention ot this complication constitutes the principal problem. To overcome this difficulty a number of approaches may be used including the use of temporary shunts around the excluded segment of aorta, general body hypothermia, and certain steps in the operation designed to minimize the period of circulatory occlusion. We have employed all of these methods and believe that each is of vital import: ance. This presentation, however, is concerned primarily with a consi- deration of the uscfulness of hypothermia in the surgical treatment of aortic aneurysms. At reduced body temperature oxygen demand of the tissues may be significantly diminished (3, 4). Experimental studies have demon- strated that hypothermia provides a definite protective influence upon the spinal cord during periods of high aortic occlusion (2.11). ‘Thus, in our own experiments there was a striking reduction in the incidence of paraplegia after 60 minute periods of thoracic aortic occlusion just distal to the left subclavian artery. Tor example, 65 per cent of nor- mothermic animals. but none of the hypothermic animals, developed paraplegia (11). These observations have been confirmed by our clint- cal experience. Among 5 cases of aortic aneurysm which involved the proximal descending thoracic aorta where the operation consisting of excision with homograft replacement was performed at normal body temperature, there were 3 survivors and all had manifestations of spinal cord injurv although the symptoms were transient. Moreover. in one of the patients who died soon atter operation there was evidence = at autopsy of ischemic necrosis of the spinal cord. Thus spinal cord damage occurred in 4 of the 5 cases operated upon at normothermic levels (Table 1). On the other hand, among 10 patients who underwent nh resection of anecurvsms of the proximal thoracic aorta under hypother- inic conditions, none developed neurologic sequelae after operation (Table 1}. Moreover, in those who succumbed in the postoperative period there was ¢vidence of normal motor function in the lower extre- : Date of Period of Location Case | Etiology | Operation | Occlusion | and Technic Result | OJ. vr: “lt. Transient 50 dC. Syphilis | 6-11-53] 48min. | paraplegia 2. LS TM. | syphitis | 11-9-53 | 77 mi Cente Ay YpNiis -J- min. later 58 dW. Shock ? 3. MW 7 Died-30min. 48dC Syphilis | Il-23-54| 88min. later : Heart failure 4. ME ‘ . tte , Transient 402 W Dissection} 1!-11-55 | 34min. : paresthesias 5. M.H. i -?}- i Partial 289 W Traumatic] 1-21-55} 4i min. | paraplegia TABLE I. Patients undergoing excision of aneurysms of proximal descending thoracic aorta without hypothermia. mities before death. In 4 patients in whom the aneurysm was located in the terminal thoracic aorta operation was performed under normo- thermic conditions and in none were neurologic sequelae encountered (Table Hl). From this experience it appears that hypothermia provides significant protection to the spinal cord during temporary occlusion 2 vf the proximal thoracic aorta and_ that hypothermia may not he necessary in instances of temporary occlusion of the terminal thoracic aorta. Fusiform aneurysms which involve the ascending and proximal : Date of Period of Location Case | Etiology Operation | Occlusion | and Technic Result L DJ Died - | week ‘6 w |Congenital | [-!-54[ S3min. later 182 Ww 9 Septicemia 2. MM. |Traumatic] 2-5-54} 62 mi Recovered 31 dw | praumatic min. 3. JB Died- 8hrs. a Syphilis | 3-4-54] 54min. later 66 dC. Secondary hemorrhage 4. FV. | syphilis | 7-5-54} 58mi R d 52 dw | Syphilis min. ecovere 5. FM. |Dissection| 7-7-54 | 54mi R d 58 dW issection min, ecovere TABLE II. Patients undergoing excision of aneurysms of proximal descending thoracic aorta with hypothernia. portion of the aortic arch provide an even more difficult problem. Obviously clamping the ascending aorta would be instantly fatal unless the strain on the left ventricle were relieved by means of a shunt to conduct the flow of blood around the occluded point. If both the pro- ximal and distal portions of the aortic arch are occluded, an extravascu- 4 lar shunt from the ascending to descending thoracic aorta might pro- vide adequate circulation to the spinal cord and lower part of tl ye body. Prevention of cerebral damage under such circumstances could then be achieved by placing additional shunts into the carotid vessels. . Date of Period of Location Case | Etiology Operation | Occlusion | and Technic Result 6. AM | syphilis | 7-29-54) 31 mi R d 639C yphilis min. ecovere 7 GC. | syphilis | 10-11-54] 65 mi Recovered 43d w | Syphilis min. covere 8. we Died-/8 hrs. ee Dissection | 11-23-54 | 65 min. later 460 W Ventricular fibrillation 9. C.B. a 4 5 mi 550W. Syphilis -B8-55/ 35min. Recovered 10. i Died-3days MB. Arterio- . . . 6-28-55 | 40min. later 59 2W isclerotic Cardiac foilure TaBLe II (continuation). Cerebral tissue is much more sensitive to ischemic damage than is the spinal cord and irreparable damage may occur within four to. six minutes of circulatory arrest. With general hypothermia, however, this period of temporary arrest of circulation to the brain mav be increased. This is indicated by our experiments upon animals with complete tem- porary interruption ot cerebral flow for periods of one hour. Thus, On among the control group of normothermic animals the incidence of fatal brain damage was approximately 50 per cent, whereas among the hypothermic group this figure was zero (12). It may be advisable. therefore, to employ both hypothermia and temporary shunts in the excision of aneurvsms involving the aortic arch in order to provide the widest margin of safety possible in preventing cerebral damage. ‘ Date of Period of Location Case | Etiology Operation | Occlusion | and Technic Result t a7 dw Syphilis 1-5-53 | 45min. Recovered 2 509 C. Syphilis H-19-53 ; 38min. Recovered 3 G.B. Syphili 57 oC. | Syphilis 8-9-54} 24min. Recovered 4 GW. 7 Died-8days 63dC. Syphilis | 10-21-54; 7Ornin. later Hemorrhage TABLE IIT. Patients undergoing excision of aneurysms of lower descending thoracic aorta without hypothermia. We have used combined general body hypothermia and external shunts ia one case of aneurysm involving the entire aortic arch { ) (Fig. 1). Unfortunately, a thrombus formed in one of the carotid “hunts during replacement of the arch with a Polyvinyl sponge (Ivalon) prosthesis and cerebral damage occurred which led to the patient's death one week later. Nevertheless. the patient tolerated clamping of the ascending aorta for 53 minutes. Although hypothermia may not have been vital in this case it probally limited the extent of cerebral damage that 6 resulted from the period of temporary carotid occlusion. During the period while the proximal aorta was occluded and the shunt was deli- vering blood to the descending thoracic aorta. the systolic blood pres- sure in the legs dropped only 10 mm. Hg. and the pulses were easily palpable. This case illustrates the advantage of combining the various methods of preventing central nervous system damage during operation on the upper reaches of the aorta. Fic. 1. Drawing showing method of resection of entire aortic arch for aneurysm with the use of temporary by-pass shunts. The optimum hypothermic level for such operative procedures has not been established but for most cases a rectal temperature between 58-92 degrees seems to be satisfactory. These levels of hypothermia mav be readily obtained by means of a refrigerating blanket or ice water alcohol baths. General anesthesia is first induced with intravenous bar- biturates following which one or two intravenous injections of Chlor- promazine 25 mg each are made to promote smooth induction of hvypo- thermia. When the patient's rectal temperature is g2 degrees F.. the hypothermic procedure is discontinued. and the operation is begun. During the operative procedure the body temperature may decrease o another 4 to 8 degrees and remain at this level throughout. After com- ~~ pletion of the operation rewarming is accomplished in a Hubbard hydrotherapy tank with warm water circulating at 110 degrees F. and usually normal body temperature is restored in Jess than 1 hour, Complications related to the hypothermic state have been largely eliminated recently by rapid rewarming. Previously where rewarming was done over a prolonged period of several hours secondary hemor. rhage was noted jn several patients. but this has not occurred follow- ing the present technique. Another patient develo: - ventricular fibrill- ation secondary to a tension pneumothorax during vradual rwarming and although cardiac resuscitation was temporarily successful he died 18 hours after operation. Cardiac irregularities under hypothermia are relatively frequent and disappear upon return to normothermic levels. Ordinarily, however, at the mild levels of hypothermia emploved in aortic Operations in contrast to those used for open cardiac procedures, arrhythmias are not serious. BIBLIOGRAPHY, 1. BAHNSON, H. T. — Definitive Treatment of Saccular Aneurysms of the Aorta with Excision of the Sac and Aortic Suture. Surg. Gynec. and Obst., 96 : 383, 1953. 2. BEATTIE, E. J., Jr., ADOVASIO, D., KESHISHIAN, J. M., BLADES, B, — Refrige- ration in Experimental Surgery of the Aorta, Surg. Gynec. and Obst., 96 : 711, 1953. 3. BIGELOW, w, G., CALLAGHAN, J. C., HOPPS, J. a, — Genera] Hypothermia for Experimental Intracardiac Surgery. Ann. Surg., 132 : 531, 1950. 4. BIGELOW, W. G., LINDSAY, w. K., HARRISON, R. C., GORDON, R. A., GREEN- WOOD, W. F, — Oxygen Transport and Utilization in Dogs at Low Body Tempe- ratures. Am. J. Physiol., 160 - 125, 1950. 5. COOLEY, D. A, DE BAKEY, M. E, — Surgical Considerations of Intrathoracic Aneurysms of the Aorta and Great Vessels. Ann. Surg.. 135 : 650, 1952. 6. COOLEY, D. A, DE BAKEY, M. E, — Resection of the Thoracic Aorta with Repla- cement by Homograft for Aneurysms and Constrictive Lesions. J, Thor, Surg... 29 : 66, 1955. 7. COOLEY, D. A. MAHAFFEY, p. E.. DE BAKEY, M. E. — Total Excision of the Aortic Arch. surg. Gynec, & Obst.. 101 : 667, Dec, 1955, 8. DE BAKEY, M. E., COOLEY, bp, A. — Surgical Treatment of Aneurysm of the Abdominal Aorta by Resection and Restoration of Continuity with Homogratft, Surg. Gynec. and Obst.. 97 : 257, 1953. 9. DE BAKEY, Michael E., COOLEY, Denton A. — Successful Resection of Aneurysm of Distal Aortic Arch and Replacement by Graft. J.A.M.A,, 155 : 1398, 1954. 10. DE BAKEY, M. E,, COOLEY, D. A., CREECH, Oscar, Jr. — Treatment of Aneu- rySms and Occlusive Disease of the Aorta by Resection : Anal. 87 Cases, JAMA. 157 :; 203-208, Jan. 15, 1955. 1l. PONTIUS, R. G., BROCKMAN, H. L., HARDY, E. G,, COOLEY, D. A., DE BAKEY, M. E. — The Use of Hypothermia in the Prevention of Paraplegia Following Tem- porary Aortic Occlusion, Experimental Observations, Surgery, 36 : 33, 1954. 12. PONTIUS, R. G., BLOODWELL, R. D., COOLEY, D. A., DE BAKEY, M. E. — The Use of Hypothernia in the Prevention of Brain Damage Following Temporary Arrest of Cerebral Circulation : Experimental Observations, Surgical Forum or the Amer, College of Surgeons, 1954. w. B. Saunders, Co, H SUMMARIES, Depending upon the jevel and extent of the lesicn, temporary occlusion of the descending thoracic aorta during resection of ancurysms may result in spinal cord damage from ischemia and paraplegia. In order to prevent this complication hypothermia was used in ten cases with no neurologic sequelae. Among five other cases with aneurysms of the proximal descending aorta. manifestations of cord damage occurred in four and one was fatal. In one patient the entire aortic arch was resected and replaced with an Ivalon prosthesis using hypothermia and temporary by-pass shunts. Hvpothermia is unnecessary in excisional therapy of abdominal aneurvsms and aneurvems of the terminal thoracic aorta. Abhaingend vom Grad und c