Effect of critical illness on blood flow to the gastrointestinal tract during feeding and the absorption of sugar in older patients

When people are critically ill in the intensive care unit (ICU), it is sometimes hard to know how well their gut (gastrointestinal tract) is absorbing nutrients from tube feeding. This study is looking at how the blood flow to the gut and sugar absorption are affected by critical illness in older patients. Understanding this could help doctors decide the best time and method to start feeding very ill patients, in order to reduce malnutrition and improve recovery. You may be eligible if: - You are 65 years or older - You are either a critically ill patient in ICU who is on a ventilator (breathing machine) and needs or is already receiving tube feeding, OR you are a healthy volunteer aged 65 or older You may NOT be eligible if: - You have had surgery on your esophagus, stomach, or duodenum (upper digestive tract) - You have had any gastrointestinal surgery during your current hospital admission - You have known diabetes mellitus - You are taking blood pressure medications (antihypertensives) - You are receiving high doses of adrenaline or noradrenaline (vasopressors) - Your BMI is above 32 kg/m² - You need very high blood pressure support Talk to your doctor about whether this trial might be right for you.