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.

This prospective observational study aims to investigate the association between blood-interstitial fluid glucose concentration differences and resting energy expenditure, organ function, and clinical outcomes in critically ill patients, while also exploring potential factors influencing these glucose concentration differences.

Inclusion Criteria:

• Age≥ 18 years and < 80 years
• ICU stay ≤48 hours
• Expected ICU stay > 24 hours
• APACHE II score≥ 8

Exclusion Criteria:

• local infection within the sensor placement area
• Laparotomy within lower abdomen
• Participated in this study before
• In other clinical trails

critically ill patient