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Cerebral effects of low-flow cardiopulmonary bypass and hypothermic circulatory arrest
C K Mezrow1, A M Sadeghi, A Gandsas
1Department of Cardiothoracic Surgery, Mount Sinai Medical Center, New York, New York 10029.
Insights
Hypothermic circulatory arrest (HCA) and low-flow cardiopulmonary bypass (CPB) present risks for neurologic complications. HCA creates a vulnerable period post-surgery, increasing cerebral injury risk if stressed.
Area of Science:
- Cardiovascular Surgery
- Neurology
- Pediatric Cardiology
Background:
- Hypothermic circulatory arrest (HCA) and low-flow cardiopulmonary bypass (CPB) are established methods for complex cardiovascular surgeries.
- Concerns persist regarding potential neurologic sequelae following these procedures.
Purpose of the Study:
- To compare the safety of HCA versus low-flow CPB by evaluating cerebral hemodynamics and clinical outcomes in a puppy model.
- To identify potential vulnerable periods after these interventions that could lead to cerebral injury.
Main Methods:
- Sixteen puppies underwent 45 minutes of either HCA or low-flow CPB after cooling to 13°C.
- Cerebral blood flow, oxygen and glucose consumption, and cerebrovascular resistance were measured using radioactive microspheres and other techniques at various temperature points and post-procedure intervals (2, 4, 8 hours).
Main Results:
- No significant neurologic deficits were observed in the 15 surviving puppies.
- Both HCA and low-flow CPB maintained cerebral metabolic rate of oxygen postoperatively.
- Cerebrovascular resistance increased markedly after HCA, necessitating higher oxygen extraction, while low-flow CPB showed only a slight increase.
- Glucose metabolism mirrored oxygen metabolism trends in both groups.
Conclusions:
- Hypothermic circulatory arrest (HCA) leads to a prolonged postoperative vulnerable period (up to 8 hours) characterized by high cerebrovascular resistance.
- Cerebral metabolism during this HCA-induced vulnerable interval is maintained by increased oxygen and glucose extraction.
- Additional stressors during this period could precipitate cerebral injury, highlighting the importance of careful management after HCA.
Abstract:
Although both hypothermic circulatory arrest (HCA) and low-flow cardiopulmonary bypass (CPB) are accepted techniques for the operative management of complex cardiovascular pathology, the potential for neurologic sequelae is still a concern. To assess the relative safety of these techniques, we compared cerebral hemodynamics and clinical outcome in two groups of puppies. Sixteen puppies underwent 45 minutes of either HCA or low-flow CPB (25 mL.kg-1.min-1) after cooling to 13 degrees C. Methodology included radioactive microsphere determination of cerebral blood flow; calculation of cerebral oxygen extraction (arteriovenous oxygen content difference) and consumption; measurement of glucose consumption, and determination of cerebrovascular resistance. Measurements were obtained at baseline (37 degrees C), 13 degrees C, and 30 degrees C and at 2, 4, and 8 hours after HCA or low-flow CPB. No neurologic deficits were observed in any of the survivors (15/16). In both groups, cerebral metabolic rate of oxygen was maintained at baseline or greater levels postoperatively. Cerebrovascular resistance rose slightly in the low-flow CPB group postoperatively in contrast to a marked elevation in the HCA group. During the period of high cerebrovascular resistance after HCA, cerebral metabolic rate of oxygen was maintained by increased oxygen extraction. After low-flow CPB, oxygen extraction was not significantly different from baseline, presumably because of less severe changes in cerebrovascular resistance. Glucose metabolism followed the same trends as oxygen metabolism in both groups. These data suggest that after HCA there is a vulnerable interval, lasting as late as 8 hours postoperatively, in which cerebrovascular resistance remains high and cerebral metabolism is maintained primarily by high oxygen and glucose extraction. Any additional stress during this interval (a decrease in arterial oxygen content or perfusion pressure) could result in cerebral injury.