Glycemic Variability and Mortality in Glycemic Control – Protocol or Patient?

Introduction: Glycaemic control (GC) to improve outcomes in critical care has proven difficult, yielding significant glycaemic variability and hypoglycemia. The association of glycaemic variability and mortality is hypothesised to occur because survivors are less variable metabolically and thus easier to control, with non-survivors more variable and harder. Objective: This study uses a clinically validated and patient-specific insulin sensitivity (SI) level to compare metabolic variability (difficulty to control) in survivors and non-survivors with equivalent glycaemic control. Specifically, are non-survivors more variable and thus harder to control tightly? Method: Data from Days 1-3 of N=145 patients (N=119 survivors; N=26 non-survivors) on the SPRINT GC protocol within 12 hours of ICU admission and >24hours on GC. Hourly SI was determined for each patient using a clinically-validated physiological model. SI variability was defined as hourly percentage change in SI (%DSI) and is compared for both groups over 6-hour blocks to 72 hours. Results: SPRINT provided equal GC in both groups by cohort and per-patent (p>0.50). SI variability decreased over time. Distributions of %DSI were similar (p=0.12-0.77; KS-Test) except for hours 37-42 (p=0.04). SI level was similar for the first 30 hours (p>0.14) and higher for non-survivors afterward (p<0.05). Results did not change considering only patients who stayed >72hours. Conclusions: Similar distributions of SI variability (%DSI) for survivors and non-survivors over the first 72 hours suggests equal ability to control, and that glycaemic variability in patients with glycaemic control is predominantly a function of the protocol and not patient outcome. Without effective protocols able to provide equal glycaemic variability between survivors and non-survivors, what may be witnessed is not the outcome of benefit from GC, but the outcome of harm from poor GC.