The Blood-Interstitial Glucose Gap

Metabolic monitoring is fundamental to guiding nutritional therapy in critically ill patients. Although indirect calorimetry is the established gold standard for measuring resting energy expenditure, its routine clinical use is constrained by practical challenges, including procedural complexity, time-intensive nature, significant cost, and limited feasibility in patients on advanced life support, such as extracorporeal membrane oxygenation (ECMO). Dysregulation of glucose metabolism is common in this population, characterized not only by absolute dysglycemia but also-and perhaps more critically-by impairments in the efficiency of glucose transport and utilization across the microcirculatory continuum (from arterial blood, through the interstitial space, to venous return). This study seeks to examine the relationship between novel dynamic metrics-such as the arterio-interstitial glucose gradient-and key clinical parameters, including energy expenditure, organ function, and patient outcomes. Our objective is to assess the utility of these measures as minimally invasive, real-time biomarkers of metabolic state in critical illness.