End‐tidal Carbon Dioxide Predicts the Presence and Severity of Acidosis in Children with Diabetes

Abstract

Background: Patients with diabetic ketoacidosis (DKA) hyperventilate, lowering their alveolar (PACO 2 ) and arterial carbon dioxide (PaCO 2 ). This ventilatory response lessens the severity of their acidemia in a predictable way. Because end‐tidal CO 2 (ETCO 2 ) closely approximates PaCO 2 , measured ETCO 2 levels should allow for predictions about the presence and severity of acidosis in diabetic patients. Objectives: 1) To evaluate the relationship between measured serum bicarbonate (HCO 3 ) and ETCO 2 measured via nasal capnography in children with suspected DKA; and 2) to assess the ability of capnography to predict DKA. Methods: Children being evaluated in a pediatric emergency department for suspected DKA (known or suspected diabetes presenting with hyperglycemia with or without ketonuria) were enrolled in a cross‐sectional, prospective, observational study. Prior to the availability of venous HCO 3 results, ETCO 2 values were measured using a Nellcor NPB‐70 Handheld Capnograph. Results: Forty‐two patients were enrolled. Linear regression analysis revealed a significant relationship between HCO 3 and ETCO 2 (R 2 = 0.80, p < 0.0001). Mean ETCO 2 was 37 torr (95% CI = 35.5 to 37.9 torr) in the children without DKA and 22 torr (95% CI = 17.4 to 26.9 torr) in the children with DKA (p < 0.0001). An ETCO 2 cut‐point of <29 torr correctly classified the most patients (95%), with a sensitivity of 0.83 (95% CI = 0.52 to 0.98) and a specificity of 1.0 (95% CI = 0.88 to 1.0). No patient with an ETCO 2 of ≥36 torr had DKA, for a sensitivity of 1.0 (95% CI = 0.74 to 1.0). Conclusions: End‐tidal CO 2 is linearly related to HCO 3 and is significantly lower in children with DKA. If confirmed by larger trials, cut‐points of 29 torr and 36 torr, in conjunction with clinical assessment, may help discriminate between patients with and without DKA, respectively.