Refeeding SyndromeIC-REFEEDNCT07800143
Respiratory Quotient and Phosphate Changes During Early Critical Illness
An observational study of Refeeding Syndrome and Critical Illness, run by Vastra Gotaland Region.
Trial summary
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… Read more about this study
- Who is it for?
- Ages 18 years and older
- Conditions the study is for
- Refeeding Syndrome, Critical Illness, Metabolic Changes During Critical Illness
- What is being tested?
- Nutritional Exposure During Early Critical Illness
- How many people
- 40 participants
- Where
- No sites listed yet
- Study dates
- 1 Nov 2026to 31 Dec 2028
- Phase
- Observational
- Are there results?
- Not yet: the study is under way
Key requirements
Who can take part, as listed by the sponsor. Only the study team can confirm whether you are eligible, so take this list to your doctor.
- Ages 18 years and older
- All sexes
- No healthy volunteers
- Adult, Older adult
Study population: 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.
Who may be able to join
- Age 18 years or older.
- Admitted to the central intensive care unit (CIVA) or neurointensive care unit (NIVA) at Sahlgrenska University Hospital.
- Receiving invasive mechanical ventilation.
- Expected intensive care stay longer than 72 hours.
- Enteral or parenteral nutritional therapy started or planned.
- Arterial catheter in place for clinically indicated blood sampling.
- Participation considered clinically safe by the responsible physician and research nurse.
Who cannot join
- Ongoing or planned continuous renal replacement therapy or intermittent - hemodialysis (CRRT/iHD).
- Extracorporeal membrane oxygenation (ECMO).
- Fraction of inspired oxygen (FiO2) >0.70.
- Severe renal failure or rapidly increasing creatinine without dialysis, where phosphate levels may not adequately reflect metabolic changes.
- Terminal illness or decision for end-of-life care.
- Previous participation in the study during the same ICU admission.
Trial locations and contacts
No sites are listed yet. Contact the study team or a site near you to ask about taking part.
About this study
Official title: Association Between Serum Phosphate and Respiratory Quotient During Early Critical Illness: A Prospective Observational Study Using Indirect Calorimetry
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.
Read more
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.
Read the detailed description
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.
- Being tested
- Nutritional Exposure During Early Critical Illness
- Keywords
- Refeeding syndrome, respiratory quotient, serum phosphate, hypophosphatemia, indirect calorimetry, critical illness, nutrition, energy expenditure, NICE criteria, metabolic monitoring
- Medical subject headings
- Refeeding Syndrome, Critical Illness, Hypophosphatemia
What participants receive
What participants receive. In a randomised study each person is assigned to one group by chance.
Nutritional Exposure During Early Critical IllnessOther
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.
| Study group | Role | What they receive |
|---|---|---|
| Prospective ICU Cohort | 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. Receives: Other: Nutritional Exposure During Early Critical Illness |
What is being measured
The primary outcome is the main question the study is designed to answer.
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.
Measured: Daily on study days 1-5, with an additional measurement on day 7 when feasible
Secondary outcomes (3)
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.
Measured: 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.
Measured: 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.
Measured: Daily during study days 1-5, with an additional assessment on day 7 when feasible
Timeline
From the start of the study to its completion; the mark is today. Estimated dates are the sponsor’s plan.
- First posted2 Sep 2026
- Study start1 Nov 2026 (estimated)
- Primary completion1 Dec 2028 (estimated)
- Study completion31 Dec 2028 (estimated)
Resources
- Official record on ClinicalTrials.govThe registry entry this page is built from, with its full change history.
- Other trials for Refeeding SyndromeStudies of the same condition, open and under way.
- More trials run by Vastra Gotaland RegionThe sponsor's other registered studies.
- What the trial phases meanHow a treatment moves from first tests in people to approval.
More details
For doctors and researchers: how the study is designed, who runs it, and its registry IDs.
Study design
- Study type
- Observational
- Observational model
- Cohort
- Time perspective
- Prospective
- Enrolment
- 40 participants (estimated)
Sponsor and investigators
- Lead sponsor
- Vastra Gotaland Region
- Sponsor type
- Other government
- Responsible party
- Principal investigator, Carl Sjödin, Vastra Gotaland Region
IDs, dates and publications
- ClinicalTrials.gov ID
- NCT07800143
- Sponsor's protocol ID
- IC-RQ-REFEED-01
- Acronym
- IC-REFEED
- Status last verified
- Aug 2026
- First submitted
- 25 Aug 2026
- Last updated
- 2 Sep 2026
- Results posted
- No
- Data monitoring committee
- No
- FDA-regulated drug
- No
- FDA-regulated device
- No
- Individual data sharing
- 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.
Study at a glance
From the registry record, last updated by the sponsor on 2 Sep 2026. Recruitment status is as the sponsor reported it: confirm with the study team.
- Official title
- Association Between Serum Phosphate and Respiratory Quotient During Early Critical Illness: A Prospective Observational Study Using Indirect Calorimetry
- ClinicalTrials.gov ID
- NCT07800143
- Acronym / sponsor ID
- IC-REFEED / IC-RQ-REFEED-01
- Keywords
- Refeeding syndrome, respiratory quotient, serum phosphate, hypophosphatemia, indirect calorimetry, critical illness, nutrition, energy expenditure
- Study type
- Observational
- Recruitment status
- Not yet recruiting
- Enrolment
- 40 participants (estimated)
- Lead sponsor
- Vastra Gotaland RegionOther government
- Study start
- 1 Nov 2026 (estimated)
- Primary completion
- 1 Dec 2028 (estimated)
- Study completion
- 31 Dec 2028 (estimated)
- First posted
- 2 Sep 2026 (actual)
- Results
- Not posted in the source record
Clinical summary
The research question as the sponsor registered it. This describes what the study plans to test, not what it found.
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.
Detailed description
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.
Study design
- Observational model
- Cohort
- Time perspective
- Prospective
- Number of arms
- 1
| Arm | Type | Receives |
|---|---|---|
| Prospective ICU Cohort | – | Other: Nutritional Exposure During Early Critical IllnessMechanically 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. |
Who may qualify
- Ages
- 18 years and older
- Sex
- All
- Healthy volunteers
- Not accepted
- Age groups
- Adult, Older adult
- Study population
- 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.
Key inclusion criteria (7 listed)
- Age 18 years or older.
- Admitted to the central intensive care unit (CIVA) or neurointensive care unit (NIVA) at Sahlgrenska University Hospital.
- Receiving invasive mechanical ventilation.
- Expected intensive care stay longer than 72 hours.
- Enteral or parenteral nutritional therapy started or planned.
Key exclusion criteria (6 listed)
- Ongoing or planned continuous renal replacement therapy or intermittent - hemodialysis (CRRT/iHD).
- Extracorporeal membrane oxygenation (ECMO).
- Fraction of inspired oxygen (FiO2) >0.70.
- Severe renal failure or rapidly increasing creatinine without dialysis, where phosphate levels may not adequately reflect metabolic changes.
- Terminal illness or decision for end-of-life care.
Eligibility is decided by the study team after screening; this overview does not establish that a patient qualifies. Full inclusion and exclusion criteria.
Interventions
| Intervention | Type | Arms |
|---|---|---|
| Nutritional Exposure During Early Critical IllnessEnteral 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. | Other | Prospective ICU Cohort |
Primary outcome
Within-Participant Regression Coefficient for Respiratory Quotient Versus Serum Phosphate Concentration
Time frame: Daily on study days 1-5, with an additional measurement on day 7 when feasible
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.
3 secondary outcomes
Sensitivity of NICE Refeeding Risk Criteria for Prespecified Metabolic Changes
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
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
Time frame: Daily during study days 1-5, with an additional assessment on day 7 when feasible
Results and safety
This study is still under way. Results are not available in the source record yet.
Research links
- Official record on ClinicalTrials.govLast updated by the sponsor 2 Sep 2026.
- Individual participant dataSharing planned: 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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Referral and contact
AzTrials does not enrol participants or take referrals. Contact the study team or a site listed below; they decide who can take part.
Questions about this trial
What is this clinical trial studying?
An observational study of Refeeding Syndrome and Critical Illness, run by Vastra Gotaland Region.
The full registered description is in the About this study section and the official record.
Who may be eligible to take part?
The sponsor lists 7 inclusion and 6 exclusion criteria. Eligibility is decided by the study team after screening, so read the full criteria and contact a listed site.
Is this clinical trial currently recruiting?
The record says: opening soon, as of the sponsor's last update on 2 Sep 2026. Status can change between updates, so confirm with the study contact before making plans.
What are the possible benefits and risks?
They depend on the study and the treatment, and no study can promise a benefit. The study team explains the known risks during informed consent, before anyone joins; the record itself does not list them.
Are results available for this study?
This study is still under way. Results are not available in the source record yet.
How can a doctor refer a patient or contact the research team?
Contact Carl Sjödin, PhD student (0707163277, carl.sjodin@vgregion.se), or a site near the patient. AzTrials does not enrol participants or take referrals.
What does the primary outcome measure?
Within-Participant Regression Coefficient for Respiratory Quotient Versus Serum Phosphate Concentration (time frame: Daily on study days 1-5, with an additional measurement on day 7 when feasible). It is what the study was designed to measure, not a finding.
Where can I read the original study information?
Does a listing mean the treatment is approved or proven to work?
No. A listing means the study is registered. It does not show that the treatment is safe, works, or is approved by a regulator.
How often is this information updated?
AzTrials copies changed records from ClinicalTrials.gov every night and reloads the whole registry every week. The sponsor last updated this record on 2 Sep 2026.