Carbon Dioxide and Hemoglobin at Presentation with Hypertrophic Pyloric Stenosis—Are They Relevant? Cohort Study and Current Opinions

Background: Recurrent vomiting in infantile hypertrophic pyloric stenosis (IHPS) leads to metabolic alkalosis and a respiratory driven compensatory hypercapnia. Alkalosis has been identified as the main causal factor for respiratory depression on admission. The value of contribution of hemoglobin and carbon dioxide partial pressure to this phenomenon will be evaluated. Materials and methods: A retrospective cohort study was conducted on 105 infants with IHPS. The acid-base status, including levels of hemoglobin, sodium and lactate, were recorded. The U-test, correlation analysis, linear regression and multivariate regression analysis was applied. Results: Twelve (11.4%) infants had hypercapnia, and six (5.7%) low hemoglobin. Hypercapnia was associated with increased sodium (p = 0.033) and mean corpuscular hemoglobin concentration (p = 0.029). A positive correlation was found between pCO2 and hemoglobin (p = 0.042). The multivariate linear regression analysis showed that pCO₂ is dependent on the pH (p < 0.001) and on hemoglobin (p = 0.002), among other factors. Increased pCO2 was found in infants with low hemoglobin (p = 0.056). Conclusion: Increased carbon dioxide levels directly stimulate- respiratory drive, but in higher concentrations, elicid a depressant effect on respiratory drive. The extent to which low levels of hemoglobin and strongly increased pCO2 contribute to respiratory depression needs to be further investigated.