An observational study in Refeeding Syndrome, Critical Illness and Metabolic Changes During Critical Illness, sponsored by Vastra Gotaland Region. Not yet recruiting. Open to participants aged 18 Years and older. Per ClinicalTrials.gov, last updated 2026-09-02.
Sponsored by Vastra Gotaland Region · Observational
Critically ill patients often experience major changes in metabolism during the first days of intensive care. When nutrition is started or increased after a period of reduced intake, some patients may develop refeeding syndrome, a potentially serious condition associated with shifts in electrolytes such as phosphate, potassium, and magnesium.
This study will investigate whether changes in respiratory quotient (RQ), measured by indirect calorimetry, are associated with changes in serum phosphate during the first intensive care week. RQ reflects the balance between oxygen consumption and carbon dioxide production and provides information about which energy substrates are being used by the body. A rising RQ may indicate increasing carbohydrate metabolism and could potentially provide an early physiological marker of metabolic changes associated with refeeding.
Mechanically ventilated adult intensive care patients will undergo daily indirect calorimetry during the first five days of the study period, with an additional measurement on day 7 when feasible. Serum phosphate and other electrolytes, nutritional intake, insulin treatment, ventilator parameters, and relevant physiological variables will be recorded at corresponding time points.
The study will also evaluate how well established screening criteria for refeeding risk, including the NICE criteria, identify patients who subsequently develop metabolic changes consistent with refeeding. No study-specific changes to nutrition or other treatment will be made.
This accurately reflects the observational nature of the study: routine IC, laboratory and nutritional data are collected without changing treatment.
Indirect calorimetry (IC) provides measurements of oxygen consumption (VO2) and carbon dioxide production (VCO2), allowing calculation of respiratory quotient (RQ) and resting energy expenditure (REE). RQ reflects the relative contribution of carbohydrate and fat oxidation and may therefore provide information about changes in substrate metabolism during the early phase of critical illness.
Refeeding syndrome is characterized by metabolic and electrolyte disturbances following initiation or escalation of nutritional therapy after a period of insufficient intake. A decrease in serum phosphate is one of its characteristic biochemical features. However, currently used clinical risk-screening tools have limited ability to identify which critically ill patients will subsequently develop metabolic changes associated with refeeding. The present study investigates whether longitudinal changes in RQ may provide additional physiological information regarding the development of refeeding-related metabolic changes. The protocol specifically examines whether rising RQ values, including values ≥0.90, occur in association with or shortly after a clinically relevant fall in serum phosphate, and whether low RQ values may precede subsequent phosphate decreases.
This is a prospective observational study conducted in mechanically ventilated adult patients admitted to the central and neurointensive care units at Sahlgrenska University Hospital. Participants will undergo daily indirect calorimetry during the first five study days, with an additional measurement on day 7 when feasible. Measurements are planned at a standardized morning time point after a stabilization period without changes in ventilator settings, nutrition, vasoactive medication, or sedation. Only measurements fulfilling predefined steady-state and technical-quality criteria will be included in the main analyses.
Serum phosphate, magnesium, potassium, and calcium will be recorded in temporal proximity to each indirect calorimetry measurement. Nutritional intake, including total energy and macronutrient delivery, as well as insulin treatment, PaCO2, temperature, ventilator parameters, and other relevant clinical variables will also be recorded. Risk of refeeding syndrome will be assessed using established NICE criteria at initiation of nutritional therapy.
The primary objective is to evaluate the within-participant association between serum phosphate and RQ over time. Longitudinal associations will be analyzed using mixed-effects regression models accounting for repeated measurements within participants. Time-lagged analyses will explore whether changes in RQ precede changes in serum phosphate or vice versa. Analyses will account for relevant potential confounders, including energy intake, carbohydrate intake, insulin treatment, PaCO2, and body temperature.
Secondary objectives include evaluation of the relationship between other electrolyte changes and metabolic measurements, characterization of longitudinal changes in RQ and REE during the early ICU course, and assessment of the ability of NICE refeeding-risk criteria to identify patients who subsequently demonstrate metabolic and biochemical changes compatible with refeeding.
The study is observational. No study-specific changes are made to nutritional treatment, ventilator settings, or other clinical management. Indirect calorimetry, laboratory testing, and nutritional monitoring are performed within established clinical care, with research-specific activities consisting of standardized collection and analysis of these data.
24 studies on the registry are indexed under Refeeding Syndrome; 7 are open to participants now.
This study's planned enrollment of 40 is below the median of 57 across 16 observational studies indexed under Refeeding Syndrome.
Browse Refeeding Syndrome studies →Vastra Gotaland Region is the lead sponsor of 275 studies on the registry; 109 are open to participants now.
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Adult patients admitted to the central intensive care unit (CIVA) or neurointensive care unit (NIVA) at Sahlgrenska University Hospital who are receiving invasive mechanical ventilation, have an expected ICU stay of more than 72 hours, and have enteral or parenteral nutrition started or planned. Eligible patients are identified prospectively during routine daily ICU screening and included according to predefined inclusion and exclusion criteria.
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.
Exclusion Criteria:
Mechanically ventilated adult intensive care patients followed prospectively during the first intensive care week with repeated indirect calorimetry, serum phosphate and other electrolyte measurements, and nutritional data collection. No study-specific change in nutrition, ventilator settings, or other clinical treatment is made.
Other: Nutritional Exposure During Early Critical Illness
Enteral and/or parenteral nutrition is provided according to usual clinical care. Energy intake, carbohydrate intake, protein intake, fat intake, and changes in nutritional delivery are recorded prospectively to evaluate their relationship with respiratory quotient, serum phosphate, and other metabolic variables. No nutrition strategy is assigned by the study.
Within-Participant Regression Coefficient for Respiratory Quotient Versus Serum Phosphate Concentration
Respiratory quotient (RQ) will be calculated from indirect calorimetry as VCO2/VO2, and serum phosphate will be measured in mmol/L. The primary outcome will be the within-participant regression coefficient describing the change in RQ associated with a 0.1 mmol/L change in serum phosphate concentration, estimated using a linear mixed-effects model with participant as a random effect. The model will account for repeated measurements and prespecified covariates including energy intake, carbohydrate intake, insulin treatment, PaCO2, and body temperature.
Time frame: Daily on study days 1-5, with an additional measurement on day 7 when feasible
Sensitivity of NICE Refeeding Risk Criteria for Prespecified Metabolic Changes
Participants will be classified as being at risk or not at risk of refeeding syndrome according to NICE criteria at initiation of nutritional therapy. Sensitivity will be calculated as the proportion of participants who develop the prespecified metabolic pattern and who were classified as at risk according to NICE criteria at baseline.
Time frame: From initiation of nutrition through study day 5, with follow-up through day 7 when available
Specificity of NICE Refeeding Risk Criteria for Prespecified Metabolic Changes
Participants will be classified as being at risk or not at risk of refeeding syndrome according to NICE criteria at initiation of nutritional therapy. Specificity will be calculated as the proportion of participants who do not develop the prespecified metabolic pattern and who were correctly classified as not at risk according to NICE criteria at baseline. The prespecified metabolic pattern is defined as respiratory quotient (RQ) ≥0.90 together with a decrease in serum phosphate of at least 0.16 mmol/L during follow-up.
Time frame: From initiation of nutrition through study day 5, with follow-up through day 7 when available
Number of Participants With RQ ≥0.90 and Serum Phosphate Decrease ≥0.16 mmol/L
The number and proportion of participants who develop both a respiratory quotient (RQ) ≥0.90 and a decrease in serum phosphate of at least 0.16 mmol/L during follow-up will be reported. The timing of the two changes relative to each other will also be described.
Time frame: Daily during study days 1-5, with an additional assessment on day 7 when feasible
No study locations are listed for this record.
Plan to share: Undecided — The feasibility and conditions for sharing de-identified individual participant data have not yet been determined. Any future data sharing will be subject to applicable ethical approvals, data protection regulations, institutional policies, and appropriate data-sharing agreements.
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This study is not yet recruiting, as verified in Aug 2026. You cannot join it, but the record below documents what was studied.
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