Postmortem human brain pH and lactate in sudden infant death syndrome

Lactate and pH were measured in frontal and temporal cortex, cingulate gyrus, and caudate nucleus in brains from sudden infant death syndrome (SIDS) cases, control infants, and control adults. Both the lactate levels and the pH values were significantly correlated (p less than 0.001) between the four brain areas, whereas lactate and pH values were significantly correlated within each brain area (p less than 0.001) with a value of pH 7.2 for zero lactate. The lactate concentration in heart blood was significantly correlated with brain lactate (p less than 0.001). Adult sudden death cases (heart attacks) had low lactate and high pH values, whereas agonal state cases had high lactate and low pH values. Control infants who had died because of accidents also had low lactate and high pH values, but infants who might have been exposed to hypoxia before death had high lactate and low pH values. SIDS cases fell into two groups: the first, consisting of all victims over 30 weeks of age and about one-half to two-thirds of those aged less than 30 weeks, had low lactate and high pH values; the second group, consisting of about one-third to one-half of those less than 30 weeks old, had high lactate and low pH values. The changes in lactate levels and pH values indicate that the majority of SIDS cases had died suddenly, but that a sizeable minority had been exposed to hypoxia prior to death.