Transcutaneous carbon dioxide monitoring during diabetic ketoacidosis in children and adolescents

Objective: Our aim was to evaluate the utility of transcutaneous CO ₂ (TC-CO₂) monitoring in following the response to therapy in children and adolescents in diabetic ketoacidosis (DKA) requiring ICU admission. Methods: During therapy for DKA, TC-CO₂ was monitored and compared with the serum bicarbonate values (HCO₃^-). As clinically indicated, serum electrolytes including serum HCO₃ ^- were drawn and at the same time, the TC-CO₂ value was recorded. Using the TC-CO₂ value and the equation (PaCO₂ = 1.5 x HCO₃^- + 8), a calculated HCO₃ ^- value was determined. The measured serum HCO₃ ^- value was subtracted from the calculated HCO₃ ^- value and the absolute difference was recorded. The difference between the measured serum HCO₃^- and the calculated HCO₃^- was analysed using analysis of variance after stratification for serum HCO₃^- values and patient age ranges. Calculated to serum HCO₃^- values were compared using linear regression analysis. In addition, serum HCO₃ ^- values were plotted against TC-CO₂ values to derive an equation from these data which would relate the TC-CO₂ values to the measured serum HCO₃^-. Results: The cohort included 28 patients ranging in age from 1.6 to 21 years (9.4 ± 4.7 years) and in weight from 13 to 96 kg (35.6 ± 18.2 kg). Two additional patients were not included as the initial TC-CO₂ values were inaccurate because of tissue hypoperfusion. In the remaining 28 patients, the absolute difference between the calculated bicarbonate and serum bicarbonate values was 1.5 ± 1.2 mmol·l^-1. The difference was ≤2 mol·l in 74.4% of samples and ≤5 mmol·l^-1 in 99.2%. No difference in the value between the calculated and measured serum HCO ₃^- was present according to serum HCO₃ ^- value or patient's age. Linear regression analysis of calculated HCO₃^- against serum HCO₃^- revealed a slope of 0.95 and an r² value of 0.88. Linear regression analysis using serum HCO₃^- against TC-CO₂ resulted in the following equations: TC-CO₂ = (1.64 × HCO₃ ^-) + 3.9 or HCO₃^- = 0.61 × (TC-CO ₂ - 3.9). Conclusions: TC-CO₂ correlates with serum HCO₃^- and can be used to follow therapy in children and adolescents in DKA.