[Anion gap in perinatal asphyxia]

The aim of this study was to assess the usefulness of the anion gap (AG) for the diagnosis of Perinatal Asphyxia (PA), as well ass to evaluate the relation of AG with umbilical artery cord pH and the outcome of the newborn. We studied 62 infants in whom umbilical artery blood gases were obtained within the first 15 minutes of life. Serum sodium, chloride and potassium were simultaneously measured. AG was calculated according to the following formula: (Na + K) - (Cl + HCO3). Patients were divided in two groups depending on their pH values. Infants with a pH of 7.10 or less, were assigned to the PA group (n = 22); infants with a cord pH higher than this value, were taken as a control group. Additionally, the total group of patients was divided in survivors and non-survivors. Statistical analysis was done with mean comparation tests. Pearson's correlation index, and the sensibility, specificity and predictive values, positive and negative were calculated for a diagnosis test. Both groups were similar in gestational age, birthweight and serum electrolytes. There was significative difference in the Apgar score at one (4 vs 5.5 for PA and control group respectively) and five minutes (6 vs 7.5 respectively), as well as in the pH (6.89 +/- 0.20 vs 7.25 +/- 0.06) and the anion gap (23.4 +/- 8.1 for PA group vs 13.9 +/- 3.1 in control group). 20 mEq/L was considered as the cut-off point for AG normality. The sensibility of the test for diagnosis PA was 0.81, specificity 0.52, positive predictive value 0.48 and negative predictive value 0.84. From 37 infant newborns with a higher value than 20 mEq/L, were 11 nonsurvivors, than from 25 with a lowest measurement was 4 nonsurvivors, without statistically difference between these groups. From the total of 62 patients, were 47 survivors and 15 nonsurvivors, without difference between them in their AG, Apgar score, gestational age or serum ions. We did find statistically significant differences regarding birthweight (p < 0.05), pH (p < 0.05), and bicarbonate (p < 0.001), all these values were higher in the survivors infants. No significant correlation was found between AG and pH, however was positive correlation between AG and HCO3 (r = 0.33, p < 0.01), sodium (r = 0.22, p < 0.01) and chloride (r = 0.33, p < 0.001).