The spectrum of serum electrolytes in hypertrophic pyloric stenosis.

Metabolic alkalosis is regarded as the "classical" electrolyte abnormality occurring with hypertrophic pyloric stenosis (HPS) but recent experience suggests that atypical electrolyte findings frequently occur and delay establishing the correct diagnosis. The records of 65 infants with HPS treated by pyloromyotomy during the past 4 years were reviewed to determine the serum electrolytes at the initial presentation. The four study groups formed included 8 (12.3%) patients in group A with serum bicarbonate (HCO3) below 18 mEq/L (mean 15.7 +/- 0.5 mEq/L); 19 (29%) in group B with HCO3 between 18 and 25 (22.9 +/- 0.3); 22 (33.8%) in group C with HCO3 between 25 and 30 (27.0 +/- 0.3) and 16 (24.6%) in group D with HCO3 over 30 (34.0 +/- 0.9). Established values for normal HCO3 in neonates is 20.1 +/- 2.5 (mean +/- SD). The mean values in group D for HCO3, potassium (4.0 +/- 0.18 mEq/L), and chloride (88.75 +/- 2.15 mEq/L) were each significantly different (p less than 0.001) from determinations of similar electrolytes in other groups. The duration of vomiting in group D of 10.5 +/- 1.3 days is almost double the time (p less than 0.001) in group A, and was associated with more severe dehydration, predominantly acid urine (pH less than 6), and ketonuria as compared to other groups. No significant difference in other demographic characteristics including the age at presentation, the gestational age, sex distribution, or types of formula used was observed. The results of the study emphasize that serum electrolytes in early HPS may be normal, that HCO3 is significantly lower than established normals for older children, and that the effects of hydrogen-ion loss elevating the serum HCO3 precedes alterations in other serum electrolytes.