Surgical therapy for aortic arch disease involves partial or complete replacement of the arch with great vessel reimplantation during a period of time when native cerebral blood flow is temporarily interrupted. In its original description, this interval of suspended cerebral perfusion required the cessation of blood flow to the entire body and was labeled hypothermic circulatory arrest (HCA). HCA employs the use of systemic hypothermia to protect the brain and visceral organs during the ischemic period, and provides a bloodless operative field to facilitate arch reconstruction. Since the initial report of the use of HCA for aortic arch replacement, cerebral protection, and circulation management techniques have evolved to enable safe, reproducible arch reconstruction with excellent neurologic outcomes.1
HCA traces its beginnings to the work of Bigelow who demonstrated a role for hypothermia in cardiac surgery in a canine model.2 John Lewis used systemic hypothermia at 28°C combined with venous inflow occlusion to perform the first successful atrial septal defect repair. He subsequently described the use of profound systemic hypothermia (9°C) with one hour of circulatory arrest without any evidence of central nervous system injury to treat an adult with ovarian carcinoma.3,4 Systemic hypothermia was temporarily abandoned with the arrival of the cardiopulmonary bypass machine, but was rediscovered and used in isolated reports of arch replacement in the 1960s.5,6 However, it was the translational research of Dr. Randall Griepp, who applied lessons learned from his canine laboratory models to successfully repair aortic arch aneurysms using HCA, that ushered in the modern era of aortic arch surgery.1
For the purposes of clarity throughout this chapter, the use of HCA without adjunctive cerebral perfusion will be termed as “HCA alone”. The classification system in Table 15-1 will be used to describe varying degrees of hypothermia used for HCA Table 15-1. Deep hypothermic circulatory arrest (DHCA) and moderate hypothermic circulatory arrest (MHCA) are the two levels of HCA that will be primarily focused upon throughout the subsequent text.
TABLE 15-1:Consensus on Hypothermia Classifications in Aortic Arch Surgery ||Download (.pdf) TABLE 15-1: Consensus on Hypothermia Classifications in Aortic Arch Surgery
|Category ||Nasopharyngeal temperature |
|Profound hypothermia ||≤14°C |
|Deep hypothermia ||14.1-20°C |
|Moderate hypothermia ||20.1-28°C |
|Mild hypothermia ||28.1-34°C |
Cerebral Metabolism and Blood Flow
Comprehension of HCA mandates a fundamental understanding of cerebral metabolism and blood flow. The metabolic rate and energy requirements of the brain are approximately 7.5 times the metabolism of non-nervous system tissues. The brain depends upon the aerobic process of glycolysis for energy and is estimated to have only a 2-minute supply of glucose stored as glycogen in neurons ...