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

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 > or =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.