[Surgical replacement of the aortic arch]

Abstract

Deep hypothermia with circulatory arrest is the usual method of cerebral protection during replacement of the aortic arch. However, this technique only gives the surgeon a limited period of time to carry out aortic repair. It also requires that cardiopulmonary bypass be prolonged to rewarm the patient which may cause many complications. Selective carotid artery perfusion may also be used. When this perfusion is derived from the principal arterial line the aorta must be clamped to perform the repair. In addition, there is some uncertainly as to what constitutes adequate cerebral perfusion at normal temperature or during moderate hypothermia. In order to reconcile the advantages of both methods whilst avoiding the disadvantages, the authors described a new technique of cerebral protection in 1984. The principle was to selectively perfuse the carotid arteries with blood cooled to 6 to 12 degrees C via a separate heat exchanger while maintaining the central temperature in moderate hypothermia (25 to 28 degrees C rectal). In order to carry out an "open" distal anastomosis, the main cardiopulmonary bypass is stopped whilst carotid perfusion is maintained (350 to 500 ml/min). When the distal anastomosis has been completed, general cardiopulmonary bypass is restarted and the patient rewarmed. Using this technique. 158 patients aged 25 to 83 (average 55 years) were operated between January 1984 and July 1997. The operative indications were for different anatomic situations (114 patients had chronic lesions and had planned operation and 50 patients were operated as an emergency for acute dissection of the ascending aorta requiring replacement of the aortic arch). The average duration of cardiopulmonary bypass was 121 minutes and the duration of circulatory arrest was 31 minutes. The electroencephalogram recorded continuously during these operations showed return of cerebral activity after an average of 12 minutes and perfectly normal activity after an average of 66 minutes. The hospital mortality was 17% (27 deaths). Death was directly related to a neurological accident in 6 patients. All the others recovered within a normal period and were perfectly conscious at the 24th hour. Twenty non-lethal neurological complications were observed. The type of lesion, age and gender had non significant influence on the outcome of the patients: neither did the duration of circulatory arrest and of cerebral perfusion. No correlations could be established between the duration of cerebral perfusion and the frequency of neurological complications. In the authors' experience, the technique of selective anterograde perfusion of the brain with cooled blood during surgery of the aortic arch has shown its value. It does not require prolonged cardiopulmonary bypass and does not limit the time available to repair of the aorta. It should therefore be considered to be the method of choice for cerebral protection during this type of surgery.