Nutrient Uptake During Continuous Enteral Feeding

Continuous enteral nutrition is used to feed patients in intensive care who are unable to eat normally. The goal of this observational study is to learn about the uptake of nutrients from feeding formula. The study method will first be applied in healthy persons to establish workability and normal values, then in patients in the intensive care unit to learn how nutrient uptake is affected by critical illness.The main questions this study aims to answer are:what is the time course of uptake of phenylalanine (an amino acid) and glucose (a sugar) from enteral feeding formula given continuously over several hourswhat is the time course of the filling volume of the stomach during continuous enteral feedingParticipants receive feeding formula through a nasogastric feeding tube and blood samples are taken at short intervals to analyse uptake of nutrients into blood. Simultaneously, the filling volume of the stomach is measured by gastric ultrasound.

Inclusion Criteria (ICU patients):- stable enteral nutrition of >80% of measured or calculated energy expenditure by nasogastric feeding tube or gastrostomyExclusion Criteria (ICU patients):enteral nutrition by postpyloric route such as jejunostomy or postpyloric tuberemaining ICU stay expected < 12 hrsongoing bleeding that requires surgery/intervention or transfusion of > 2 units red cells/24 hrsinability to use feeding tube or arterial lineInclusion Criteria (healthy subjects):- healthy volunteerExclusion Criteria (healthy subjects)- any condition or medication affecting nutrition or metabolism