Variability of serum AST and ALT measurements in infants with moderate to severe post-asphyxial hypoxic-ischemic encephalopathy (PA-HIE) suggests variable efficiency of the Diving Reflex 1112

Background: The diving reflex directs blood away from organs which are not easily or irreparably damaged by hypoxemia to preserve vital organ function. Hypothesis: AST/ALT measurements reflect severity of PA-HIE and risk of adverse outcome. Methods: 121 babies with PA-HIE in whom serum enzymes were measured as part of their care, and whose outcomes were known, were studied retrospectively. For methods/ definitions see Ekert P et al. J Pediatr 1997;131:613-7. Results: The Figure show ALT and AST values (y axis) by age in hours at sampling (x axis). The interrupted line represents the mean values of infants with death/severe neurological impairment by 12 months of age (adverse outcome) and the solid line, good outcome. There was no apparent difference in the distribution of AST values for the two outcome groups. The risk of adverse outcome was inversely related to ALT values. 16/18 babies with ALT values above 600mmol/l had good outcomes. Enzyme values rise in the first 18 to 36hrs, and fall after 60hrs to the normal range. Conclusion: ALT results were consistent with the existence of the diving reflex, however many individuals may have an inefficient reflex. Extrapolation backwards of the rise of enzymes may time the insult.

Figure 1