Endogenous Energy Production in Critically Ill Patients

The aim of this study is to investigate when critically ill patients transition from a non-suppressible catabolism to a normal response to feeding. Endogenous production of glucose, fat and protein will be studied on a minimum of two occasions in mechanically ventilated ICU patients, in a fasted state and during parenteral nutrition. Substrate kinetics are estimated by a tracer dilution method using infusions of isotopically labeled glucose, glycerol and phenylalanine. Blood sampling for metabolomics analysis will be performed to elucidate potential biomarkers indicating an anabolic response to nutrition.

Inclusion Criteria: For the ICU group: 1. ≥18 years old and admitted to the ICU 2. Invasive mechanical ventilation 3. Arterial and central line in situ 4. Expected to remain in ICU \>72 hours For the control group: 1\. ≥18 years old Exclusion Criteria: 1. Lack of informed consent by patient/next of kin 2. Liver transplant 3. Acute or acute on chronic liver failure 4. Cirrhosis 5. Known diabetes mellitus 6. Pancreatic surgery 7. Acute or chronic pancreatitis 8. Pregnancy 9. Intubated only for airway protection or neurologic deficit 10. Mitochondrial disease 11. Disorder of amino acid metabolism 12. Familial hypertriglyceridemia 13. Severe acquired hypertriglyceridemia (≥10 mmol/L) 14. Requiring treatment of hypoglycemia in the last 72 hours before inclusion. 15. Requiring ongoing large volume resuscitation of crystalloids or blood products 16. \>72 hours in ICU before enrollment 17. Readmission to ICU within 1 week of ICU discharge. 18. Morbidly obese (BMI ≥35) 19. Limitations of treatment to best supportive care 20. Ongoing treatment with insulin/glucose related to hyperkalemia