The purpose of the study is to determine the comparative effectiveness of tight glycemic control to a target range of 80-110 mg/dL (TGC-1, 4.4-6.1 mmol/L) vs. a target range of 150-180 mg/dL (TGC-2, 8.3-10.0 mmol/L) on hospital mortality and intensive care unit (ICU) length of stay (LOS) in hyperglycemic critically ill children with cardiovascular and/or respiratory failure. This will be accomplished using an explicit insulin titration algorithm and continuous glucose monitoring to safely achieve these glucose targets. Both groups will receive identical standardized intravenous glucose at an age-appropriate rate in order to provide basal calories and mitigate hypoglycemia. Insulin infusions will be titrated with an explicit algorithm combined with continuous glucose monitoring using a protocol that has been safely implemented in 490 critically ill infants and children.