Is acid base determination an accurate predictor of pyloric stenosis?

OBJECTIVE

To determine if acid base status predicts which vomiting patients have pyloric stenosis.

DESIGN

Retrospective chart review.

SETTING

Tertiary paediatric hospital.

METHODOLOGY: We compared the clinical and biochemical parameters of 100 patients with a discharge diagnosis of pyloric stenosis and 84 patients of a similar 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, and sodium.

RESULTS

Independent variables of significance were pH, BE, chloride, bicarbonate, potassium, weight loss (all of which had a P value < 0.0001), and sex (P = 0.006). Each variable was placed in a logistic regression equation with 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 for 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 considering pyloric stenosis. This model now needs to be validated on a prospective series of patients with vomiting.