An interventional study of Stable isotope tracers and Parenteral nutrition in Critical Illness and Metabolism and Nutrition Disorder, sponsored by Karolinska University Hospital. Recruiting at 1 site in Sweden. Open to participants aged 18 Years and older, including healthy volunteers. Per ClinicalTrials.gov, last updated 2026-08-20.
Sponsored by Karolinska University Hospital · Not applicable, Interventional, and Diagnostic
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.
Background and aims
Critical illness is characterized by several metabolic alterations, including an upregulation of catabolic pathways promoting endogenous energy substrate production. In contrast to starvation catabolism, this endogenous energy supply cannot be suppressed by feeding in the early acute phase of critical illness. This observation is one of the reasons that current guidelines recommend hypocaloric nutrition during the first week in ICU [1]. However, it is not known when this anabolic resistance subsides and a transition towards a normal response to feeding occurs.
The aims of this study are two-fold: 1) to investigate the temporal changes in non-suppressible endogenous energy production during critical illness, and 2) identify potential biomarkers indicating a normalized response to exogenous nutrients.
Protocol
For ICU patients, the protocol is first performed within 24-72 hours (early acute phase) from ICU admission. The protocol will be repeated if an enrolled patient is still in the ICU 120-168 hours (late acute phase) and 240-288 hours (late phase) after the first study session.
Infusions of intravenous (i.v.) glucose, enteral/parenteral nutrition (EN/PN) and insulin are stopped at 02:00 hours. Blood glucose concentrations will be monitored at least hourly during the fasting period. The protocol will be terminated in case of hypoglycaemia (\<4 mmol/L), and the patient will be excluded from the trial. The infusion rate of propofol will remain unchanged from 04:00 unless a change is clinically indicated, determined by the nurse or physician. Healthy controls will be asked to fast from midnight. In the control group, a peripheral i.v. line and a radial arterial line will be placed under local anaesthesia.
Baseline blood samples will be drawn from the arterial catheter, whereafter primed i.v. infusions of ring-2H5-phenylalanine, 2H2-glucose, and 2H5-glycerol will be started at 07:00. Measured resting energy expenditure (mREE) is then determined by 20-minute indirect calorimetry (IC) using the Q-NRG device (Cosmed, Rome, Italy) in ventilator or canopy mode. After 165 minutes, four blood samples will be drawn at 5-minute intervals from the arterial catheter to determine glucose, glycerol, and amino acid kinetics in a fasted state. Additional blood samples are drawn to analyze circulating hormones, cytokines, metabolites, and markers of autophagy.
PN (Olimel perifer N4E, Baxter) is then started at a rate that, including calories from propofol and other non-nutritional energy sources, corresponds to 100% of mREE. Repeated blood samples (same as above) are drawn at 45-60, 105-120 and 165-180 minutes after the start of PN. An additional IC is performed during the final 30 minutes of the PN. If hyperglycemia occurs during the PN administration, an insulin infusion will be started to keep blood glucose levels \<14 mmol/L.
After the final blood samples, all tracer infusions and PN are stopped. In ICU patients, nutritional therapy will be restarted as prescribed by the care team. In healthy controls, all catheters are removed.
Patients
Adult patients with an estimated ICU length of stay (LOS) >72 hours will be recruited from the intensive care unit (ICU) at Karolinska University Hospital Huddinge, a tertiary university hospital with approximately 800 annual ICU admissions. Exclusion criteria include liver disease (liver transplant, acute or acute-on-chronic liver failure, cirrhosis), diabetes, pancreatic surgery or pancreatitis, pregnancy, intubation for airway protection only, mitochondrial disease, amino acid metabolism disorder, familial hypertriglyceridemia, severe hypertriglyceridaemia (≥ 10 mmol/L), hypoglycemia within the last 72 h, requiring ongoing large-volume resuscitation and/or blood transfusions, readmission within one week of ICU discharge, BMI ≥35, limitations to best supportive care or ongoing insulin/glucose treatment related to hyperkalemia.
Control group
Healthy, age- and sex-matched controls.
Statistical analysis and sample size considerations
Normal distribution will be assumed a priori. Primary and secondary outcomes will be analyzed using Student's T-test for paired or independent samples or one-way ANOVA as appropriate. The level of statistical significance is p ≤ 0.05. Correction for multiple comparisons will not be applied.
Based on previous data describing endogenous glucose production in a fasted and fed state in critically ill patients, 10 subjects in each group are required to detect a 20% difference in change in glucose rate of appearance with 80% power. No similar studies describing glycerol or amino acid kinetics are available for sample size calculations. Due to missing data, dropouts and inter-/intraparticipant variability, 10 patients with measurements of substrate kinetics in both the early acute and late acute phases are required to answer the primary and secondary outcome measures. To identify potential biomarkers of attenuated catabolism, 30 patients who complete the protocol in both the early acute and late acute phases will be included, i.e. two measurements per patient. Ten volunteers will be recruited to an age-matched control group.
233 studies on the registry are indexed under Nutrition Disorders; 26 are open to participants now.
This study's planned enrollment of 40 is below the median of 105 across 169 interventional studies indexed under Nutrition Disorders.
Browse Nutrition Disorders studies →Karolinska University Hospital is the lead sponsor of 279 studies on the registry; 55 are open to participants now.
Compared within Nutrition Disorders, this study's primary condition as ClinicalTrials.gg classifies it; the registry's first condition term is Critical Illness. The counts are of registry records indexed under each term, refreshed daily. How we classify →
Go through the criteria one by one — yes, no or not sure — and take the list to your doctor or the study team. Kept in this browser only.
For the ICU group:
For the control group:
1. ≥18 years old
Exclusion Criteria:
Underlined terms in the criteria open these too. Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Before you join, the study team explains what taking part involves — its purpose, what happens, the risks and possible benefits — and answers your questions, so you can decide freely. Consent is usually recorded on a form (the informed consent form, ICF) signed by you or, where the law allows, by someone legally authorised to decide for you.
You can keep asking questions during the study, you are told of new information that matters, and you can choose to leave at any time.
Weight in kilograms divided by height in metres squared. Example: 70 kg and 1.75 m gives 70 ÷ (1.75 × 1.75) ≈ 22.9.
What counts as overweight or obesity differs between countries (some use lower cut-offs), so go by the range the study states.
Informed consent
Before you join, the study team explains what taking part involves — its purpose, what happens, the risks and possible benefits — and answers your questions, so you can decide freely. Consent is usually recorded on a form (the informed consent form, ICF) signed by you or, where the law allows, by someone legally authorised to decide for you.
You can keep asking questions during the study, you are told of new information that matters, and you can choose to leave at any time.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
BMI (body mass index)
Weight in kilograms divided by height in metres squared. Example: 70 kg and 1.75 m gives 70 ÷ (1.75 × 1.75) ≈ 22.9.
What counts as overweight or obesity differs between countries (some use lower cut-offs), so go by the range the study states.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Mechanically ventilated patients admitted to the study site ICU.
Other: Stable isotope tracers · Dietary Supplement: Parenteral nutrition
Non-hospitalized study subjects recruited through public advertising at the study site, age-matched on group level.
Other: Stable isotope tracers · Dietary Supplement: Parenteral nutrition
Deuterium-labelled non-radioactive stable isotopes of glucose, phenylalanine and glycerol.
Parenteral nutrition infused a rate corresponding to 100% of measured energy expenditure, started after blood sampling during a baseline fasting period.
Attenuation of glucose production in response to nutrition in early acute phase in ICU.
Difference in endogenous rate of appearance of glucose, calculated from enrichment of labelled substrates in plasma of glucose between the fasted and fed state in the early acute phase in ICU.
Time frame: Early acute phase of critical illness, i.e., 24-72 hours after ICU admission. The difference between substrate kinetics at 165-180 min and 345-360 min after the start of the tracer infusion will be calculated.
Attenuation of phenylalanine production in response to nutrition in early acute phase in ICU.
Difference in endogenous rate of appearance of phenylalanine, calculated from enrichment of labelled substrates in plasma of phenylalanine, between the fasted and fed states in the early acute phase in ICU.
Time frame: Early acute phase of critical illness, i.e., 24-72 hours after ICU admission. The difference between substrate kinetics at 165-180 min and 345-360 min after the start of the tracer infusion will be calculated.
Attenuation of glycerol production in response to nutrition in early acute phase in ICU.
Difference in endogenous rate of appearance of glycerol, calculated from enrichment of labelled substrates in plasma of glycerol, between the fasted and fed states in the early acute phase in ICU.
Time frame: Early acute phase of critical illness, i.e., 24-72 hours after ICU admission. The difference between substrate kinetics at 165-180 min and 345-360 min after the start of the tracer infusion will be calculated.
Attenuation of glucose production in response to nutrition in the late acute phase compared to the early acute phase in the ICU.
Difference in endogenous rate of appearance, calculated from enrichment of labelled substrates in plasma glucose, between the fasted and fed state in the early acute phase, compared to the late acute phase in the ICU.
Time frame: The early acute phase is between 24 and 72 hours after ICU admission, and the late acute phase between 120 and 148 hours, i.e., 5-7 days after ICU admission.
Attenuation of glycerol production in response to nutrition in the late acute phase compared to the early acute phase in the ICU.
Difference in endogenous rate of appearance, calculated from enrichment of labelled substrates in plasma glycerol, between the fasted and fed state in the early acute phase, compared to the late acute phase in the ICU.
Time frame: The early acute phase is between 24 and 72 hours after ICU admission, and the late acute phase between 120 and 148 hours, i.e., 5-7 days after ICU admission.
Attenuation of phenylalanine production in response to nutrition in the late acute phase compared to the early acute phase in the ICU.
Difference in endogenous rate of appearance, calculated from enrichment of labelled substrates in plasma phenylalanine, between the fasted and fed state in the early acute phase, compared to the late acute phase in the ICU.
Time frame: The early acute phase is between 24 and 72 hours after ICU admission, and the late acute phase between 120 and 148 hours, i.e., 5-7 days after ICU admission.
Attenuation of glucose production in response to nutrition in the early acute phase in the ICU compared to healthy controls.
Difference in endogenous rate of appearance, calculated from enrichment of labeled substrates in plasma of glucose between fasted and fed state in the early acute phase, compared to healthy controls.
Time frame: Early acute phase of critical illness, i.e., 24-72 hours after ICU admission. The difference between substrate kinetics at 165-180 min and 345-360 min after the start of the tracer infusion will be calculated.
Attenuation of glycerol production in response to nutrition in the early acute phase in the ICU compared to healthy controls.
Difference in endogenous rate of appearance, calculated from enrichment of labelled substrates in plasma of glycerol between fasted and fed state in the early acute phase, compared to healthy controls.
Time frame: Early acute phase of critical illness, i.e., 24-72 hours after ICU admission. The difference between substrate kinetics at 165-180 min and 345-360 min after the start of the tracer infusion will be calculated.
Attenuation of phenylalanine production in response to nutrition in the early acute phase in the ICU compared to healthy controls.
Difference in endogenous rate of appearance, calculated from enrichment of labelled substrates in plasma of phenylalanine between fasted and fed state in the early acute phase, compared to healthy controls.
Time frame: Early acute phase of critical illness, i.e., 24-72 hours after ICU admission. The difference between substrate kinetics at 165-180 min and 345-360 min after the start of the tracer infusion will be calculated.
Difference in non-suppressible glucose production in the fed state between ICU patients.
Mean change in endogenous rate of appearance, calculated from enrichment of labelled substrates in plasma of glucose between the fasted and fed state in the early acute phase compared to the late acute phase.
Time frame: The early acute phase is between 24 and 72 hours after ICU admission, and the late acute phase between 120 and 148 hours, i.e., 5-7 days after ICU admission.
Difference in non-suppressible glycerol production in the fed state between ICU patients.
Mean change in endogenous rate of appearance, calculated from enrichment of labelled substrates in plasma of glycerol between the fasted and fed state in the early acute phase compared to the late acute phase.
Time frame: The early acute phase is between 24 and 72 hours after ICU admission, and the late acute phase between 120 and 148 hours, i.e., 5-7 days after ICU admission.
Difference in non-suppressible phenylalanine production in the fed state between ICU patients.
Mean change in endogenous rate of appearance, calculated from enrichment of labelled substrates in plasma of phenylalanine between the fasted and fed state in the early acute phase compared to the late acute phase.
Time frame: The early acute phase is between 24 and 72 hours after ICU admission, and the late acute phase between 120 and 148 hours, i.e., 5-7 days after ICU admission.
Metabolomics
Within-group changes in ICU patients between the fasted and fed states of metabolomics. This will be compared between the early acute and the late acute phase.
Time frame: The early acute phase is between 24 and 72 hours after ICU admission, and the late acute phase is between 120 and 148 hours, i.e., 5-7 days after ICU admission.
Attenuation of glucose production in response to nutrition in the late phase compared to the early acute phase in the ICU.
Difference in endogenous rate of appearance, calculated from enrichment of labelled substrates in plasma of glucose between fasted and fed states in the early acute phase, compared to the late phase in the ICU.
Time frame: The early acute phase is between 24 and 72 hours after ICU admission, and the late acute phase is more than 240 hours, i.e., 10 days after ICU admission.
Attenuation of glycerol production in response to nutrition in the late phase compared to the early acute phase in the ICU.
Difference in endogenous rate of appearance, calculated from enrichment of labelled substrates in plasma of glycerol between fasted and fed states in the early acute phase, compared to the late phase in the ICU.
Time frame: The early acute phase is between 24 and 72 hours after ICU admission, and the late acute phase is more than 240 hours, i.e., 10 days after ICU admission.
Attenuation of phenylalanine production in response to nutrition in the late phase compared to the early acute phase in the ICU.
Difference in endogenous rate of appearance, calculated from enrichment of labelled substrates in plasma of phanylalanine between fasted and fed states in the early acute phase, compared to the late phase in the ICU.
Time frame: The early acute phase is between 24 and 72 hours after ICU admission, and the late acute phase is more than 240 hours, i.e., 10 days after ICU admission.
Changes in insulin levels
Within-group changes in ICU patients between the fasted and fed states of insulin. This will be compared between the early acute and the late acute phase.
Time frame: The early acute phase is between 24 and 72 hours after ICU admission, and the late acute phase is between 120 and 148 hours, i.e., 5-7 days after ICU admission.
Changes in C-peptide levels
Within-group changes in ICU patients between the fasted and fed states of C-peptide. This will be compared between the early acute and the late acute phase.
Time frame: The early acute phase is between 24 and 72 hours after ICU admission, and the late acute phase is between 120 and 148 hours, i.e., 5-7 days after ICU admission.
Changes in glucagon levels
Within-group changes in ICU patients between the fasted and fed states of glucagon. This will be compared between the early acute and the late acute phase.
Time frame: The early acute phase is between 24 and 72 hours after ICU admission, and the late acute phase is between 120 and 148 hours, i.e., 5-7 days after ICU admission.
Changes in C-reactive protein levels.
Within-group changes in ICU patients between the fasted and fed states of C-reactive protein. This will be compared between the early acute and the late acute phase.
Time frame: The early acute phase is between 24 and 72 hours after ICU admission, and the late acute phase is between 120 and 148 hours, i.e., 5-7 days after ICU admission.
Changes in cytokine levels.
Within-group changes in ICU patients between the fasted and fed states of cytokines. This will be compared between the early acute and the late acute phase.
Time frame: The early acute phase is between 24 and 72 hours after ICU admission, and the late acute phase is between 120 and 148 hours, i.e., 5-7 days after ICU admission.
Changes in urea levels.
Within-group changes in ICU patients between the fasted and fed states of urea. This will be compared between the early acute and the late acute phase.
Time frame: The early acute phase is between 24 and 72 hours after ICU admission, and the late acute phase is between 120 and 148 hours, i.e., 5-7 days after ICU admission.
Changes in free amino acids levels.
Within-group changes in ICU patients between the fasted and fed states of free amino acids. This will be compared between the early acute and the late acute phase.
Time frame: The early acute phase is between 24 and 72 hours after ICU admission, and the late acute phase is between 120 and 148 hours, i.e., 5-7 days after ICU admission.
Changes in triglyceride levels.
Within-group changes in ICU patients between the fasted and fed states of triglycerides. This will be compared between the early acute and the late acute phase.
Time frame: The early acute phase is between 24 and 72 hours after ICU admission, and the late acute phase is between 120 and 148 hours, i.e., 5-7 days after ICU admission.
Changes in free fatty acid levels.
Within-group changes in ICU patients between the fasted and fed states of free fatty acids. This will be compared between the early acute and the late acute phase.
Time frame: The early acute phase is between 24 and 72 hours after ICU admission, and the late acute phase is between 120 and 148 hours, i.e., 5-7 days after ICU admission.
Plan to share: Undecided — IPD will not be routinely shared due to patient confidentiality. Anonymized parts of the data set may be shared on reasonable request.
No publications or documents are linked to this record.
Started Jul 2025 (actual). Primary completion is estimated for Dec 2027, 29 months after the start.
Of 54 non-industry interventional studies with no phase under Nutrition Disorders, half reached primary completion within 23 months of starting (the median), counting those still running; a quarter within 10 and three quarters within 57. This study's planned 29 months is above that.
Counting every sponsor, half of 56 studies reached it within 22 months; a quarter within 10 and three quarters within 48.
How these figures are worked out, and which studies are left out of them.
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