DeBakeyⅠ型主动脉夹层术中双侧脑灌注脑保护的体会

目的 总结DeBakeyⅠ型主动脉夹层在深低温停循环选择性脑保护下行全弓置换＋支架象鼻术的体外循环及双侧脑保护经验.方法 350例DeBakeyⅠ型主动脉夹层患者,当鼻温降至20℃,肛温〈23℃时暂停下半身体外循环,经头臂动脉、左颈总动脉插入Y形双侧脑灌注管行脑灌注.然后完成支架象鼻、弓部置换术.恢复下半身体外循环,缓慢复温,复温至鼻咽温32℃以上,心脏复跳,辅助循环至停机.结果 体外循环时间（156.24±42.25）min;心肌阻断时间（90.82±17.73）min;脑灌注时间（35.78±10.49）min,停循环时间（19.22±9.56）min;死亡11例,死亡率3.13%.结论 DeBakeyⅠ型主动脉夹层在深低温停循环手术,行双侧顺性脑灌注,能提供满意的脑保护效果,安全、可靠、有效,术后并发症少.     

改良双侧脑灌注在DeBakey Ⅰ型急性主动脉夹层手术中的应用

目的 研究改良双侧脑灌注在DeBakeyⅠ型急性主动脉夹层手术中应用的价值.方法 14例DeBakeyⅠ型急性主动脉夹层患者在深低温停循环下行手术治疗.术中采用主动脉弓腔内直视下行头臂干和左颈总动脉插管的改良双侧脑灌注技术进行脑保护.结果 全组体外循环190～325min,平均(241.78±31.74)min,心肌阻断时间71～133min,平均(104.36±17.07)min,脑灌注时间32～70min,平均(53.50±9.25)min.全组患者仅1例出现短暂性脑神经功能异常,无脑梗塞,脑出血等其他中枢神经系统损伤.结论 DeBakeyⅠ型急性主动脉夹层手术中,采用经主动脉弓腔内直视下行头臂干和左颈总动脉插管的改良双侧脑灌注技术进行脑保护,其方法 简便、安全、有效.     

支架"象鼻"术治疗DeBakey Ⅰ型主动脉夹层动脉瘤

目的 探讨支架"象鼻"手术治疗DeBakey Ⅰ型主动脉夹层动脉瘤(AD)的方法和效果.方法 12例DeBakey Ⅰ型AD患者,平均年龄48.1岁.采用深低温停循环(DHCA),右腋动脉顺行灌注(SCP)脑保护,实施支架"象鼻"手术(即升主动脉和全弓置换及降主动脉腔内支架植入).结果 术后死亡1例,手术死亡率8.3%.术中体外循环时间(163.2±17.7)min,停循环时间(41.6±12.3)min.随访3～6个月,无死亡病例.结论 支架"象鼻"手术简单,停循环时间短,治疗DeBakey I型夹层主动脉瘤安全、有效.     

单纯无名动脉灌注的主动脉弓置换术21例

目的 探讨主动脉弓置换术中使用单纯无名动脉灌注进行脑保护的安全性和有效性.方法 2004年1月至2007年7月,2l例主动脉弓置换者使用单纯无名动脉灌注技术进行脑保护,男19例,女2例;年龄29-72岁,平均(46.5±11.4)岁.A型(Stanford分型)主动脉夹层19例,其中7例合并主动脉瓣关闭不全;升主动脉及主动脉弓真性动脉瘤伴降主动脉受累2例.所有病例均在深低温、使用单纯无名动脉选择性脑灌注下进行升主动脉、主动脉弓置换+降主动脉覆膜支架置入术.同时行Benlall手术6例,David手术1例.结果 升主动脉阻断(109.6.4-29.6)min;体外循环(186.7±56.2)min;最低鼻咽温(19.O±3.3)℃;选择性脑灌注时间(38.3.4-11.5)Ⅲ.m,流量每分钟(6.8±2.6)ml,l‘g.术后无中枢神经系统并发症.呼吸机辅助(38.6±29.O)h.1例因低心排输出量综合征于术后第5 d死亡.术后随访2-45个月,平均(24.0±12.5)个月,无死亡及心脑血管意外发生.结论 深低温、单纯无名动脉选择性脑灌注下行主动脉弓置换是安全、有效的.     

改良全弓置换术治疗A型主动脉夹层38例

目的通过对全弓置换术式进行改进、优化手术程序,以获得更好的早期临床效果。方法回顾性分析2014年9~12月期间在我院行改良全弓置换术式38例A型主动脉夹层患者的临床资料,其中男26例、女12例,年龄52.5(21~76)岁。本术式采用3根动脉泵管,动脉泵管分别连接右锁骨下动脉插管、股动脉插管后进行体外循环,并经由人工血管与左颈总动脉吻合提供同步灌注;待鼻咽温降至26℃,停循环行低流量双侧脑灌注;于降主动脉置入象鼻支架并与四分叉人工血管以及动脉壁吻合,吻合完毕即恢复全身灌注;接着行主动脉根部与人工血管的吻合完成升主动脉重建,最后在心脏跳动后行左锁骨下动脉-人工血管、无名动脉-人工血管吻合。结果38例患者均手术成功,全组停循环低流量脑灌注时间(18.8±4.2)min,升主动脉阻闭时间(86.1±14.2)min,体外循环时间(178.4±71.4)min,术后清醒时间(4.7±2.0)(最短2 h),呼吸机辅助时间(38.7±19.9)h,1例患者因术后并发多脏器功能衰竭死亡;3例术前有肾功损害,术后行血液透析治疗;6例出现一过性神经系统并发症;1例出现双下肢运动功能障碍。随访1~3个月,患者均恢复良好。结论此改良全弓置换术式缩短了停循环时间、主动脉阻闭时间和体外循环灌注时间,提供充分的内脏灌注,有效地降低脑部并发症和内脏器官损伤。     

经腋动脉右锁骨下动脉插管和选择性脑灌注技术的应用

目的　介绍经腋动脉右锁骨下动脉插管技术及其体外循环要点。　方法　经腋动脉右锁骨下动脉插管和在深低温停循环下行持续选择性脑灌注技术治疗累及主动脉弓的心血管疾病患者７０ 例。　结果　应用该技术手术治疗累及主动脉弓的心血管疾病７０ 例中,脑部低流量灌注时间最长达８１ 分钟,平均２８ ．０６ ±２１ ．０７ 分钟,术后患者６ 小时内全部清醒,无神经系统并发症。　结论　经腋动脉右锁骨下动脉插管在停循环期间持续选择性脑灌注方法对脑保护简便、安全、有效。     

猪主动脉手术选择性脑灌注期间脑血流的变化

目的 观察猪主动脉手术不同阶段脑血流流量、血流分布,以及氧代谢变化状况.方法 18～22 kg雌性小型猪8只,通过右房静脉引流,右侧颈动脉和升主动脉插入动脉灌注管建立单泵双管灌注模型,降温至20℃时停止升主动脉灌注,实施右侧选择性脑灌注,60 min后恢复循环,静脉氧饱和度达到95％以上时开始复温,膀胱温度达到36C停止体外循环转流.整个过程中使用TRANSONIC超声血流仪监测动脉插管内灌注流量,记录灌注压力,使用近红外分光光度仪监测脑氧饱和度( rSO2)动态变化,不同时间点监测血气分析和生化检查.结果 观察期间右侧股动脉压力维持(60±20) mmHg.总的血液灌注流量(85.30±6.81) ml·kg-1·min-1,其中右侧脑灌注流量( 14.42±1.76) ml·kg-1·min-1,占全部灌注流量(16.72±2.77)％.停循环选择性脑灌注期间,脑灌注流量(15.11±0.44) ml·kg-1 · min-1.实验不同阶段静脉氧饱和度波动于0.40 ～0.99(0.83 ±0.13),rSO2 0.56～0.79(0.67±0.06).停循环后血糖[(8.18±3.34) mmol/L]和乳酸浓度[(9.30±2.31) mmol/L]较停循环前明显升高(P＜0.05).结论 可以连续性观测主动脉手术体外循环转流以及停循环期间的全身以及脑部血流分布、氧代谢的小型猪动物模型,是进行主动脉弓部心血管外科研究的良好模型.     

改良全主动脉弓置换治疗老年Stanford A型主动脉夹层

目的总结改良全主动脉弓置换治疗老年Stanford A型主动脉夹层的临床经验,并探讨其疗效。方法 39例老年Stanford A型主动脉夹层患者在深低温停循环、双侧顺行脑灌注下行外科手术。根部处理根据不同病变情况,选择不同术式,包括单纯升主动脉置换、Bentall、Wheat手术。主动脉弓部采用四分支血管行全主动脉弓置换,降主动脉内置入硬象鼻支架,并行支架开窗,完成左锁骨下动脉重建。结果全组平均体外循环时间为(180.49±30.46)min,平均停循环时间(27.22±10.58)min,平均脑灌注时间(32.42±12.36)min,平均心肌阻断时间(94.84±24.83)min。升主动脉置换17例,Wheat手术10例,Bentall手术12例。全组无术中死亡,术后住院死亡2例,脑梗塞1例,短暂性神经功能障碍3例,行肾脏透析治疗3例。全组无出血再次开胸、声音嘶哑、左上肢感觉运动功能障碍等情况。术后复查主动脉CTA弓部分支血管血流通畅,象鼻支架无内漏。无术后死亡及二次手术者。结论选择合适的手术时机及手术方式,老年Stanford A型主动脉夹层患者仍能获得满意的外科手术效果。     

主动脉全弓置换加硬"象鼻"术治疗DeBakey Ⅰ型主动脉夹层

目的 总结主动脉全弓置换加硬"象鼻"术治疗DeBakey I型主动脉夹层的临床经验.方法 2005年6月至2008年3月,手术治疗41例DeBakey I型主动脉夹层病人,其中男32例、女9例;年龄27～76岁,平均57岁;急性主动脉夹层31例,慢性夹层10例.均在深低温停循环、低流量脑灌注下行主动脉全弓置换加硬"象鼻"手术.其中Bentall+全弓+硬象鼻术(术中支架系统直视下置入)24例,Wheat+全弓+象鼻术6例,升主动脉及全弓置换+硬象鼻术11例.结果 平均体外循环(168±32)min,平均主动脉阻断(109±24)min,选择性脑灌注(31±11)min.术后并发症14例(34.1%),12例治愈(85.8%),2例死亡.出院前均复查CT示升主动脉、主动脉弓部人工血管,术中支架系统血流通畅,位置良好,降主动脉真腔较术前明显扩大,未闭的降主动脉假腔血栓形成,无不良事件发生.随访1～12个月,死亡1例,无再次手术者.结论 主动脉全弓置换加硬"象鼻"术是治疗DeBakey I型主动脉夹层安全、有效的方法.     

急性复杂型Stanford A型主动脉夹层的外科治疗

目的：评价急性复杂型Stanford A 型主动脉夹层手术中改良双侧选择性顺行脑保护的效果及升主动脉插管、左锁骨下动脉（LSA）“开窗”技术对手术风险的影响。方法122例急性复杂型Stanford A 型主动脉夹层患者行改良全主动脉弓置换加降主动脉内支架象鼻植入术,按照脑保护及动脉供血管插管方式分为单侧脑保护组与改良双侧脑保护组及右锁骨下动脉（RSA）插管组与主动脉插管组,比较各组的手术方式、死亡率及并发症率。部分患者采用左锁骨下动脉“开窗”技术重建血运。结果单侧脑保护组与改良双侧脑保护组总的院内死亡率分别为5．77％、2．86％,差异无统计学意义（P值为0．650）;神经系统总并发症率分别为26．92％、10．00％,差异有统计学意义（P值为0．014）。右锁骨下动脉插管组与升主动脉插管组总的院内死亡率均为4．55％,总并发症率分别为15．9％、15．2％,差异均无统计学意义（P值分别为1、0．914）。左锁骨下动脉“开窗”者术后多次复查CTA左锁骨下动脉均通畅,无左锁骨下盗血综合征发生,1例出现无需处理的少量内漏。结论改良双侧选择性顺行脑保护安全、可行、可靠;选择升主动脉插管符合生理、操作简捷,不增加手术风险;左锁骨下动脉“开窗术”简化了手术,缩短了深低温停循环时间,增加了手术安全性。     

Axillary cerebral perfusion for arch surgery in acute type A dissection under moderate hypothermia

Backgound: Aortic arch surgery is still associated with increased mortality and morbidity especially in acute type A aortic dissection. Adequate brain protection is essential and commonly performed by either antegrade selective perfusion of the brachiocephalic arteries or an interval of profound hypothermic circulatory arrest. We present our experience for open aortic arch repair with continuous antegrade brain perfusion by means of direct cannulation of the right axillary artery, under moderate hypothermia in patients with acute type A aortic dissection. Methods: In, 25 consecutive patients (17 men) with a mean age of 62.6 ± 14.8 years, aortic repair extended to the arch, for acute type A aortic dissection, was performed through a midline sternotomy. The right axillary artery was used for arterial systemic and brain perfusion at a rectal temperature of 25–27 °C. Results: Mean duration of CPB and aortic cross-clamping was 241 ± 55 and 155 ± 72 min, respectively. The mean duration of circulatory arrest of the lower body and brain perfusion was 39.7 (range, 24–55 min). All the patients survived the procedure and all but one were discharged from hospital. One patient had left arm paralysis which he recovered the first postoperative month. There were no other transient or permanent neurologic deficits. A CT scan was performed at discharge for routine postoperative evaluation. There were no local neurovascular complications related to the cannulation site except for one local re-exploration for bleeding. Conclusions: The absence of any major permanent neurologic deficit or any visceral damages in our patients suggests that continuous moderate hypothermic cerebral perfusion, with an interval of circulatory arrest of the lower body, is adequate for acute type A aortic dissection surgery, allowing safe open repair of the distal aortic arch.     

选择性脑灌注在小儿主动脉弓手术中的应用

目的为了减轻手术中的脑损伤,探讨选择性脑灌注（SCP）技术在小儿主动脉弓手术中应用的有效性和安全性。方法2007年4月至2008年5月上海儿童医学中心对32例小儿先天性心脏病患者施行主动脉弓手术中应用SCP技术;年龄8d～103个月（14．4±25．4个月）,体重2．7～22．0kg（6．7±4．4kg）,其中主动脉缩窄伴心内畸形22例,主动脉弓中断伴心内畸形10例。采用弹簧动脉插管,在升主动脉靠近无名动脉根部处插管,转流降温至肛温18～20℃,然后将动脉灌注管向上延伸插入无名动脉内进行SCP。结果SCP时间为17～121min（39．6±19．4min）,流量维持在15～40ml／（kg·min）[29．7±6．1ml／（kg·min）]。术后死亡4例,死亡原因为低心排血量或心律失常,均无脑损伤证据。生存28例患者在临床中均无明显神经系统并发症,术后25例患者做脑电图检查均无异常,5例新生儿患者做头颅B超和脑磁共振成像（MRI）检查未见异常。结论SCP是小儿主动脉弓手术中一种简单可行和安全有效的脑保护方法。     

Stanford A 型主动脉夹层手术中的主动脉根部处理

目的 总结Stanford A型主动脉夹层手术中主动脉根部处理的临床经验.方法 根据主动脉夹层累及主动脉根部的程度及主动脉根部基础病变,对59例Stanford A型主动脉夹层病人进行主动脉根部处理.Bentall手术31例,Wheat手术15例,David手术13例.结果 手术死亡1例(1.72%).术后一过性精神状态异常17例;术后感染2例,1例死亡;胸骨哆开1例;单侧下肢血供障碍1例,二期行股股分流术后恢复正常.出院前复查心脏彩超、主动脉CT血管成像及心电图,均正常.随访2～54个月,4例死于非心源性疾病,余者正常.结论 根据主动脉夹层累及主动脉根部的程度及主动脉根部基础病变,制定相应处理方案,可显著提高手安全性并改善预后.

Abstract：

Objective To summarize the experience of aortic root surgery in Stanford A aortic dissection operations.Methods From January 2005 to September 2010, the clinical data of 59 patients with Stanford A aortic dissection was analyzed. There were 43 men and 16 women , ranging in age from 21 to 74 years old, duration of disease varied from 16 hours to 27 days. Among the group, 31 complicated by aortic valve incompetence, 12 Marfan syndrome, 9 single lower limb blood supply dysfunction, 6 right coronary artery involvement. All cases received aortic root surgery under deep hypothermic circulatory arrest. Bentall procedure was performed in 31 patients, Wheat procedure in 15 patients and David procedure in 13 patients.Results The time of cardiopulmonary bypass in the group was 149 to 204 min with an average of ( 171 ± 19) min,and the cross clamp time was 81 to 122 min with an average of (104 ±13) min, and the arrest time was 30 to 47 min with an average of (39 ±7) min. There was 1 case of operative death, which was treated on an emergency basis. Postoperative complications occurred in 20 cases. 17 cases experienced temporary mental dysfunction, 2 cases were infected with MRS A, 1 of which died from MODS, 1 case of single lower limb blood supply dysfunction remained after the first operation and recovered by reoperation (bilateral femoral bypass operation) . All cases were reexamined before discharge, postoperative mean LVEF was (56. 3 ±3.4)% (ranged 51% -62%), aortic annular diameter varied from 22 mm to 27 mm, aortic sinus diameter range from 23 mm to 31mm. 51 patients were followed up, with a mean follow-up time of (24.9 ± 17.2) months (ranged 2-54 months). 54 patients of Stanford A aortic dissection survived well with normal lives and activities. Four non cardiac deaths, one was chronic renal failure, the others were brain hemorrhage. Conclusion Prognosis and operative security of Stanford A aortic dissection patients can be significantly improved by individualized aortic root surgery.     

不同深低温停循环方法对脑组织S-100蛋白表达的影响

目的观察不同深低温停循环方法对脑组织S—100蛋白表达及组织结构的影响。方法将18只实验犬随机分为3组，深低温停循环（deep hypothermic circulatory arrest，DHCA组）组，深低温停循环结合逆行脑灌注（retrograde cerebral perfusion，RCP，DHCA＋RCP组）组，深低温停循环结合顺行性间断脑灌注（intermittent antegrade cerebral perfusion，IACP，DHCA＋IACP组）组。3组犬体外循环开始后将鼻咽温降至18℃，随后停循环90min，开放循环后复温至36℃，随后停机。在停循环前、停循环后45min、90min及开放循环后15min和30min由颈静脉插管留取血液标本进行S-100蛋白含量测定。手术结束时取脑海马组织作透射电子显微镜检查，观察脑组织及神经细胞超微结构的变化。结果3组犬在停循环前颈静脉血S-100蛋白含量差异无统计学意义（P〉0．05），停循环后DHCA组和DHCA＋RCP组S-100蛋白含量较停循环前显著升高（P〈0．01），DHCA＋IACP组S-100蛋白含量停循环前后无显著变化。结论DHCA时间较长时，脑组织会发生缺血缺氧性损伤；RCP对脑组织有一定的保护作用，但易发生脑组织及神经细胞水肿；IACP的脑保护效果较为理想。     

The methodologies of hypothermic circulatory arrest and of antegrade and retrograde cerebral perfusion for aortic arch surgery

In spite of recent advances in thoracic aortic surgery, postoperative neurological injury still remains the main cause of mortality and morbidity after aortic arch operation. The use of cardiopulmonary bypass (CPB) and hypothermic circulatory arrest, temporary interruption of brain circulation, transient cerebral hypoperfusion, and manipulations on the frequently atheromatic aorta all produce neurological damages. The basic established techniques and perfusion strategies during aortic arch replacement number three: hypothermic circulatory arrest (HCA), antegrade cerebral perfusion (ACP), and retrograde cerebral perfusion (RCP). During the past decade and after several experimental studies, RCP lost its previous place in the armamentarium of brain protection, giving it up to ACP as a major method of brain perfusion during HCA. HCA should be applied at a temperature of asymptotically equal to 20 degrees C with long-lasting cooling and rewarming and should not exceed by itself the time of 20-25 min. RCP does not seem to prolong safe brain-ischemia time beyond 30 min, but it appears to enhance cerebral hypothermia by its massive concentration inside the brain vein sinuses. HCA combined with ACP, however, could prolong safe brain-ischemia time up to 80 min. Cold ACP at 10 degrees -13 degrees C should be initially applied through the right subclavian or axillary artery and continued bihemispherically through the left common carotid artery at first and later the anastomosed graft, with a mean perfusion pressure of 40-70 mm Hg. The safety of temporary perfusion is being confirmed by the meticulous monitoring of brain perfusion through internal jugular bulb O2 saturation, electroencephalogram, and transcranial comparative Doppler velocity of the middle cerebral arteries.     

Two different techniques of retrograde cerebral perfusion for thoracic aortic surgery through a left thoracotomy

The authors used profound hypothermic circulatory arrest and continuous retrograde cerebral perfusion for aortic surgery that involved the distal arch through a left thoracotomy. For the first seven patients, oxygenated blood from cardiopulmonary bypass was perfused retrogradely through a venous cannula positioned into the right atrium. In the last 11 cases, venous blood, provided by a perfusion from the lower body, was circulated passively in the brain with the descending aorta clamped. The period of profound hypothermic circulatory arrest was 34.6 +/- 11.1 min, and continuous retrograde cerebral perfusion was 31.3 +/- 11.1 min. Seventeen patients survived, but there was one early death. Two patients with a severely atherosclerotic aneurysm developed permanent neurological dysfunction. The combination of profound hypothermic circulatory arrest, continuous retrograde cerebral perfusion and open aortic anastomosis through a left thoracotomy protects the brain adequately, and facilitates evacuation of debris and air in the aortic arch. It produces satisfactory results for aortic surgery that involves the distal arch.     

Outcomes after ascending aorta and proximal aortic arch repair using deep hypothermic circulatory arrest with retrograde cerebral perfusion: analysis of 207 patients

OBJECTIVES Correction of ascending aorta and proximal aortic arch pathology with numerous surgical techniques having been proposed over the years remains a surgical challenge. This study was undertaken to identify risk factors influencing outcome after aortic arch operations, requiring deep hypothermic circulatory arrest (DHCA). METHODS Between 1993 and 2010, 207 consecutive patients were operated for ascending aorta and proximal arch correction with the use of deep hypothermic circulatory arrest with retrograde cerebral perfusion. All patients were followed up with regular out-patient clinics, transthoracic echocardiography and, when required, chest computed tomography. RESULTS There were 102 (49.3%) emergencies (acute type A dissection) and 105 (50.7%) elective cases. Mean age: 63.5?±?12?years. Mean circulatory arrest time was 25.4?±?13?min. Unadjusted analysis of factors associated with 30-day mortality revealed emergency status, preoperative hemodynamic instability, acute dissection, reoperation, increased circulatory arrest time, postoperative bleeding, postoperative creatinine levels and presence of neurological dysfunction. Multi-adjusted analysis revealed duration of circulatory arrest as the only and main factor related to death. Thirty-day mortality was 2.4% for the elective and 7.2% for emergencies cases. Survival during long-term follow-up was 93, 82 and 53% at 1, 5 and 10?years, respectively. CONCLUSIONS Ascending aorta and proximal aortic arch replacement with brief duration of deep hypothermic circulatory arrest combined with retrograde cerebral perfusion is a safe method with acceptable short- and long-tem results.     

Total aortic arch replacement with a branched graft and limited circulatory arrest of the brain

BACKGROUND: Total replacement of the aortic arch is commonly performed with either antegrade perfusion of the brachiocephalic arteries by means of direct cannulation or with an interval of hypothermic circulatory arrest of at least 30 to 40 minutes. We present a technique with a branched graft that uses antegrade brain perfusion without the need for direct cannulation of the brachiocephalic arteries or a separate perfusion circuit, with only a brief period of circulatory arrest of the brain. METHODS: Twelve patients underwent resection of the aortic arch through either a midline sternotomy (4 patients) or a bilateral anterior thoracotomy (8 patients). The right axillary artery was used for arterial return and for brain perfusion. After establishing hypothermic circulatory arrest, the brachiocephalic arteries were detached from the aorta, flushed, and occluded with clamps. Hypothermic perfusion of the brain was established through the right axillary artery, and the brachiocephalic arteries were sequentially attached to the limbs of a branched aortic graft. Flow to the brain was then established in the antegrade direction through the axillary artery. RESULTS: The mean duration of circulatory arrest of the brain at a mean nasopharyngeal temperature of 16 degrees C was 8.8 minutes (range, 6-13 minutes). The subsequent period of hypothermic (20 degrees C-22 degrees C) brain perfusion, during which the 3 branches of the graft were attached to the brachiocephalic arteries, averaged 35 minutes (range, 23-44 minutes). All the patients survived the procedure and were discharged from the hospital. No patient sustained a permanent neurologic deficit. One patient had lethargy for 2 days, with full recovery. Nine of the 12 patients were extubated within 72 hours. CONCLUSIONS: This technique obviates the need for direct cannulation of the brachiocephalic arteries and for a separate perfusion circuit and requires only a brief period of circulatory arrest of the brain.