Background: Changes and increases in blood glucose and lactate during and after cardiac surgery in the intensive care unit (ICU) can be associated with complications. Recognizing these changes during and after surgery can be significant.Methods: The present prospective observational case-series study assessed 163 children aged between 1 and 170 months undergoing open-heart surgery on cardiopulmonary bypass (CPB) over a 3-month period. Blood glucose and lactate were assessed using arterial blood samples before surgery, during surgery (at 15 and 45 minutes on CPB, after warm-up, and after sternum closure), and at 1, 6, 12, 24, and 48 hours after admission to the ICU.Results: In the first hour following ICU admission, a significant number of patients needed inotropes. Also at this time point, the percentage of patients with lactate levels > 2.5 mmol/L was higher than that at the other time points. Further, most changes in blood glucose and lactate occurred in the first 6 hours following ICU admission. A significant relationship existed between changes in blood sugar and serum lactate in the first 6 hours post-ICU admission (P < 0.001).Conclusions: The results demonstrated a significant relationship between changes in blood glucose and serum lactate in the first 6 hours following ICU admission.