Methods for improving neurological recovery after hypothermic circulatory arrest:fructose-1,6-bisphosphate and hypertonic saline dextran in a surviving porcine model

Abstract During surgery of the aortic arch and pediatric heart surgery, the blood flow to the brain has to be interrupted at times to allow a bloodless operation field and adequate conditions for surgical repair. During this no-flow period the brain is exposed to a high risk of ischaemic injury, as it will become irreversibly damaged after 5 minutes of circulatory arrest at 37°C. Additional time can be gained by cooling the patient with an extracorporeal heart-lung machine, as hypothermia reduces the cerebral metabolic rate and allows longer safe periods of circulatory standstill. This method of cerebral protection, called hypothermic circulatory arrest (HCA), is widely used in clinical practice. Thus the brain becomes susceptible to ischaemic injury after 30 minutes of HCA at 15°C. Lower temperatures than this are not practicable, however, as they require longer periods of cardiopulmonary bypass, which may further aggravate cerebral injury. To ensure a better outcome for patients undergoing these operations, additional ways of protecting the brain are required. The present work focuses on neuroprotective biochemical and fluid therapy methods for use during HCA, employing a surviving porcine model. Fructose-1,6-bisphosphate (FDP), a high-energy intermediate of glycolysis, was examined for potential neuroprotective properties in two cerebral injury settings associated with HCA. First, FDP was administered before and after a 75-minute period of HCA at a brain temperature of 18°C. This led to better survival, neurological recovery and brain histopathological findings and had supportive effects on brain metabolism (I). Second, a 25-minute period of HCA along with an iatrogenic embolic load produced by microsphere injection was used to generate a massive ischaemic injury to the brain. In this setting FDP did not affect the neurological outcome but had a clear supportive impact on cerebral metabolism (II). In addition, cerebral histopathological samples taken during the first study were analysed by electron microscopy, which revealed significant preservation of the ultrastructure in the FDP-treated animals (III). Hypertonic saline dextran (HSD) is a novel fluid therapy method which has been shown to enhance the outcome after hypovolaemic shock with or without head injury and is potentially very effective in reducing ischaemia-reperfusion injury. Its administration led to a decrease in intracranial pressure, improved brain metabolism, faster and better recovery and less histopathologically observable morphological damage (IV). The findings indicate that both FDP and HSD have significant neuroprotective properties and should be assessed in humans as well