Is acid base determination an accurate predictor of pyloric stenosis?

Objective: To determine if acid base status predicts which vomiting patient s have pyloric stenosis Design: Retrospective chart review. Setting: Tertiary paediatric hospital. Methodology: We compared the clinical and biochemical parameters of 100 pat ients with a discharge diagnosis of pyloric stenosis and 84 patients of a s imilar age who presented to the emergency department with vomiting and who had an acid base determination. Patients were included from January 1995 to January 1997. Clinical correlates consisted of age, duration of vomiting, weight loss, gestation, and family history of pyloric stenosis. Biochemical correlates were pH, bicarbonate, base excess (BE), chloride, potassium, an d sodium. Results: Independent variables of significance were pH, BE, chloride, bicar bonate, potassium, weight loss (all of which had a P value <0.0001), and se x (P = 0.006). Each variable was placed in a logistic regression equation w ith pyloric stenosis being the dominant variable. Variables of significance were pH (P = 0.0001), BE (P = 0.0001), and chloride (P = 0.009). A model f or predicting pyloric stenosis using these variables was then created with pH > 7.45, chloride < 98, and BE > +3, with a positive predictive value of 88%. Conclusion: Acid base determination is a useful screening tool when conside ring pyloric stenosis. This model now needs to be validated on a prospectiv e series of patients with vomiting.