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Literature Review

Indirect Calorimetry Literature Summary

Read the importance of Indirect Calorimetry on different care areas and with special populations, such as COVID-19 patients.

Please scroll to the bottom of the page to download the PDF version of this Indirect Calorimetry Literature Summary

Table of contents


  • Articles on research conducted with GE Healthcare respiratory modules
  • Articles involving use of GE Healthcare Technology
  • Articles on research conducted with Deltatrac monitor
  • Articles on research conducted with non-GE technology
  • Special Patient Population
    •  Pediatrics
    • COVID-19
    • Sepsis
    • Burns
    • Obesity
    • Weaning
    • Perioperative Care
  •     General Review and Editorial Articles
    • Pediatrics



The views expressed in the articles listed herein are those of the respective authors of the articles and may not reflect the opinion of GE Healthcare.

Articles on research conducted with GE Healthcare respiratory modules

Ang, D., R. Chari, A. Garcia, J. Clark, J. Farrah, J. Hagan, C. Watson, W. Richards, H. Liu, D. Donaldson, J. Barde and T. Alderman (2019). “Optimizing energy expenditure and oxygenation toward ventilator tolerance is associated with lower ventilator and intensive care unit days.” J Trauma Acute Care Surg 87(3): 559-565.

Summary: IC: CARESCAPE R860 ventilator with E-sCOVX respiratory module (GE Healthcare): The hypothesis of this study was that if both EE and oxygenation are optimized toward ventilator tolerance (RQ = 0.7 to 1.0); this would provide patients with the best condition to be liberated from the ventilator. In this single-center prospective study of trauma patients requiring mechanical ventilation, 1,090 patients were included in a primary analysis of ventilator days between the intervention arm and historical controls. The primary outcome favored the intervention arm by approximately three days. In this study, all patients achieved the RQ goal (between 0.7-1.0) and over 95% met their REE nutritional goal.


Bae, E., et al. (2018). “Increased energy expenditure using indirect calorimetry among acute phase patinets in neurosurgical intensive care unit.” 37: S52.

Summary: This study evaluated IC measured using the CARESCAPE B650 compared to predictive equations in neurosurgial criticaly ill patients. Predictive equations were found to underestimate EE in both acute (<14 day LOS) neurosurgical patients, and to a lesser extent, in chronically ill (>14 day LOS) patients. IC should be used to assess EE in neurosurgical patients, notably during the acute phase of disease.


Chen, Y. H., et al. Comparison of the Metabolic Load in Patient Ventilated with Pressure Support Ventilation and Adaptive Support Ventilation Mode with the Same Minute Ventilation. A104. CRITICAL CARE: INVASIVE, NON-INVASIVE, CONVENTIONAL, AND NON- CONVENTIONAL VENTILATION IN ACUTE RESPIRATORY FAILURE: A2550-A2550.

Summary: The Engström CareStation was used to evaluate VO2 and VCO2 during pressure-support ventilation (PSV) and adaptive support ventilation (ASV). Metabolic load was significantly lower during ASV versus PSV, as were VO2 and VCO2. It is suggested that this lower metabolic load is the result of reduced work of breathing.


Ferreruela, M., et al. (2017). “Effect of FiO2 in the measurement of VO2 and VCO2 using the E-COXV metabolic monitor.” Med Intensiva 41(8): 461-467.

Summary: This study demonstrated good precision for VO2 and VCO2 with the GE Healthcare E-COVX module with FiO2 up to 0.40. There was no clinically significant bias observed with FiO2 0.40-0.80. Precision was vulnerable to increased FiO2, with clinically inadequate VO2 observed when FiO2 exceeded 0.6. Measurement of VCO2 was not affected by changes in FiO2.


Lee, I. H., Y.-W. Kuo, F.-C. Lin, C.-W. Wu, J.-S. Jerng, P.-H. Kuo, J.-C. Cheng, Y.-C. Chien, C.-K. Huang and H.-D. Wu (2020). “Kinetics of oxygen uptake during unassisted breathing trials in prolonged mechanical ventilation: a prospective pilot study.” Scientific Reports 10(1): 14301.

Summary: GE Healthcare CARESCAPE Monitor B650 and Engström Carestation: This pilot study investigated the kinetics of VO2 during unassisted breathing trials (UBT) in patients with prolonged mechanical ventilation. 49 patients were evaluated in a prospective observational trial. The median VO2 increased significantly (from 235.8 to 298.2 ml/min; P = 0.025) in the failure group, but there was no significant change in the success group (from 223.1 to 221.6 ml/min; P = 0.505). In multivariate logistic regression analysis, an increase in VO2 > 17% from the beginning period and a peak inspiratory pressure greater than −30 cm H2O were significantly associated with the success of 120-minute UBT. The authors concluded, “Our findings show the potential of monitoring VO2 in the final phase of weaning in tracheostomized patients with prolonged mechanical ventilation.


Panitchote, A., et al. (2017). “Energy expenditure in severe sepsis or septic shock in a Thai Medical Intensive Care Unit.” Asia Pac J Clin Nutr 26(5): 794-797.

Summary: This study aimed to measure energy expenditure in severe sepsis/septic shock patients by indirect calorimetry and to assess the correlation of energy expenditures between indirect calorimetry and predictive equations. IC was measured using an Engström Carestation mechanical ventilator. There was poor agreement and correlation between EE using predictive equations versus EE using IC. The Bland-Altman analysis showed a mean difference (limits of agreement) of -757 kcal/day between EE using IC and EE using predictive equations.


Satoh, D., et al. (2018). “Effects of intraoperative nutrients administration on energy expenditure during general anesthesia.” Nutrition 45: 37-40.

Summary: This study explored the physiological benefits of the administration of exogenous nutrients during general anesthesia. Recent reports have indicated that intraoperative infusions of glucose and amino acids exert anticatabolic effects. IC was measured with the GE Healthcare E-COVX module. The number of days of intubation and the length of the ICU stay did not differ among the three patient groups studied. The lengths of hospital stay were shorter in the groups receiving intraoperative glucose and amino acids, compared to the control group. Additionally, these results indicate that the infusion of glucose and amino acids during general anesthesia increases REE and exerts a thermogenic effect.


Smallwood, C. D. and N. M. Mehta (2013). “Gas exchange measurement during pediatric mechanical ventilation--agreement between gas sampling at the airway and the ventilator exhaust.” Clin Nutr 32(6): 988-992.

Summary: This investigation compared oxygen consumption (VO2), carbon dioxide elimination (VCO2), Resting Energy Expenditure (REE) and respiratory quotient (RQ) in mechanically ventilated children, obtained by two devices using distinct gas sampling methods. Despite strong correlations and small mean biases for VO2, VCO2 and REE obtained by the Viasys Healthcare Vmax® and GE Healthcare E-COVX®, the limits of agreement were beyond the clinically acceptable range. These devices should not be used interchangeably for gas exchange measurements in mechanically ventilated children.


Smallwood, C. D., et al. (2017). “Accuracy of Oxygen Consumption and Carbon Dioxide Elimination Measurements in 2 Breath-by- Breath Devices.” Respir Care 62(4): 475-480.

Summary: This study assessed the accuracy and agreement of two devices used to quantify oxygen consumption (VO2) and carbon dioxide elimination (VCO2) in children, using a pediatric in vitro model of gas exchange. Of the two devices tested, only the newest module demonstrated a bias and limits of agreement that were within an a priori determined clinically acceptable range of ±20% for VO2 and VCO2 (E-sCAiOVX). The limits of agreement were clinically acceptable from 40 to 100 mL/min. This range corresponds to approximate patient weights of 5-16 kg. The older device (E-COVX) did not demonstrate agreement with the simulated values and therefore is not clinically acceptable for use in pediatric patients.


Stapel, S. N., et al. (2018). “Indirect calorimetry in critically ill mechanically ventilated patients: Comparison of E-sCOVX with the deltatrac.” Clin Nutr.

Summary: In this prospective study with Deltatrac and E-sCOVX, measurements of energy expenditure (EE) in critically ill, mechanically ventilated patients were performed simultaneously. Mean EE-E-sCOVX was higher than EE-Deltatrac, with a bias of 235 ± 149 kcal/day, corresponding to a percentage error of 12.1% of the reference method. EE, VCO2 and VO2 measured by E-sCOVX and Deltatrac were significantly correlated. RQ was not. The authors concluded –that the E-sCOVX is not accurate and its use is therefore not recommended in critically ill patients. Because maintenance of the Deltatrac is no longer supported, there is a need for a new and reliable device.


Sundström Rehal, M., et al. (2016). “Measuring energy expenditure in the intensive care unit: a comparison of indirect calorimetry by E-sCOVX and Quark RMR with Deltatrac II in mechanically ventilated critically ill patients.” 20(1): 54.

Summary: The aim of this study was to determine the level of agreement in gas exchange measurements between the E-sCOVX, Quark RMR and the Deltatrac II in mechanically ventilated ICU patients. There was a significant bias toward higher VO2 and VCO2 values with both E-sCOVX and Quark RMR as compared to Deltatrac; that corresponded to 10% overestimation of REE.


Tan, J., et al. (2018). “Pilot experience with use of continuous indirect calorimetry in ICU.” 37: S53.

Summary: This pilot study evaluated the GE Healthcare R860 ventilator for determining REE. The technology was easy to use by staff. REE was not affected by time of day and therefore measurement can be obtained daily.


Uber, A., et al. (2018). “Preliminary observations in systemic oxygen consumption during targeted temperature management after cardiac arrest.” 127: 89-94.

Summary: Cardiac arrest patients receiving targeted temperature management were evaluated. Continuous VO2 and VCO2 measurements were obtained with the GE Healthcare CARESCAPE™ B650 monitor and the CARESCAPE E-sCOVX respiratory module. In a post-hoc analysis of the first 12 hours after return of spontaneous circulation, VO2 was associated with survival (median VO2 in survivors 3.35 mL/kg/min [2.98, 3.88] vs. non-survivors 2.61 mL/kg/min p=0.039). There was no cut-off value for VO2 that differentiated survivors and non-survivors. There was no association between VCO2 and survival. The RQ was higher in survivors -- patients whose first measured RQ was <0.7 had a survival rate of 17%, compared to 64% in patients whose initial RQ was ≥0.7. Venous hyperoxia may offer future prognostic benefit in this population - venous hyperoxia as a state in which central venous oxygen saturation remains elevated despite low-to-normal cardiac output suggests a cellular inability to utilize oxygen and portends a poor prognosis.


Vasileiou, G., M. B. Mulder, S. Qian, R. Iyengar, L. M. Gass, J. Parks, E. Lineen, P. Byers and D. D. Yeh (2020). “Continuous Indirect Calorimetry in Critically Injured Patients Reveals Significant Daily Variability and Delayed, Sustained Hypermetabolism.” JPEN J Parenter Enteral Nutr 44(5): 889-894.

Summary: IC: E-sCOVX or E-COVX (GE Healthcare): This study evaluated the use of continuous indirect calorimetry over a two-week period among trauma patients in the ICU. Data from multiple 10-minute periods was collected daily during steady state and was used to calculate REE daily maximum, REE daily minimum, REE daily average and REE variability. 55 patients comprised the final analysis, the majority with blunt injuries (69%). A 25% increase in average REE was noted on Day 7 that was sustained through Day 14. The authors concluded: “Isolated REE measurements may not accurately reflect the true metabolic requirements (especially during early hospitalization), and continuous REE measurements, if available, are recommended for capturing the variations of metabolism as they occur on a day-to-day basis.”


Articles involving use of GE Healthcare Technology

Diehl, J. L., N. Peron, R. Chocron, B. Debuc, E. Guerot, C. Hauw-Berlemont, B. Hermann, J. L. Augy, R. Younan, A. Novara, J. Langlais, L. Khider, N. Gendron, G. Goudot, J. F. Fagon, T. Mirault and D. M. Smadja (2020). “Respiratory mechanics and gas exchanges in the early course of COVID-19 ARDS: a hypothesis-generating study.” Ann Intensive Care 10(1): 95.

Summary: IC: CARESCAPE R860 ventilator with E-sCOVX respiratory module (GE Healthcare): This study evaluated the respiratory mechanics and gas exchange associated with COVID-19 infected patients with ARDS. A total of 22 patients were evaluated, and gas exchange was characterized by hypercapnia and high physiological dead space. The ventilatory ratio was 2.9.


Fabiano Alves, V. G., E. E. M. da Rocha, M. C. Gonzalez, R. B. Vieira da Fonseca and M. H. do Nascimento Silva (2019). “Resting Energy Expenditure Measured by Indirect Calorimetry in Obese Patients: Variation Within Different BMI Ranges.” Journal of Parenteral and Enteral Nutrition 44(1): 129-137.

Summary (IC: Deltatrac II): This study aimed to determine if there was an appreciable difference in REE in obese patients between the fasted and fed state. In total, 97 IC measurements were obtained from 63 patients during 2009 - 2012 with a BMI range of 27.3 to 53.4 kg/m2. There was no difference in measured REE between fasted and fed states across three BMI groups (overweight, obese, morbidly obese). Additionally, there was a negative correlation between REE and progression of BMI from overweight through morbidly obese (r=-0.35, p=0.04). The authors concluded that no method can be recommended to estimate REE in extremely obese patients given the risk of underestimating energy requirements.


Lee, S. J., H.-J. Lee, Y.-J. Jung, M. Han, S.-G. Lee and S.-K. Hong (2020). “Comparison of Measured Energy Expenditure Using Indirect Calorimetry vs Predictive Equations for Liver Transplant Recipients.” Journal of Parenteral and Enteral Nutrition n/a(n/a).

Summary (IC: GE Healthcare, specific device not specified): In this study, commonly used predictive equations were compared to EE measured via IC in patients undergoing liver transplantation. The four predictive methods evaluated were the simple weight-based equation (25 kcal/kg/day, rule of thumb) and Harris-Benedict, Ireton-Jones (for ventilated patients), and Penn State 1988 equations. In total, 46 patients were evaluated. The predicted REE calculated using the Penn State 1988 method agreed with the measured REE. All four predictive equations showed a fixed bias and appeared to be inaccurate for predicting REE in this cohort of liver transplant recipients. The authors concluded that precise measurements using IC may be helpful when treating critically ill patients to avoid underestimating or overestimating their metabolic needs.


Pereira-da-Silva, L., S. Barradas, A. C. Moreira, M. Alves, A. L. Papoila, D. Virella and G. Cordeiro-Ferreira (2020). “Evolution of Resting Energy Expenditure, Respiratory Quotient, and Adiposity in Infants Recovering from Corrective Surgery of Major Congenital Gastrointestinal Tract Anomalies: A Cohort Study.” Nutrients 12(10): 1-17.

Summary (IC: Deltatrac II): This study aimed at quantifying the evolution of REE, RQ, and adiposity of infants during the late anabolic phase after corrective surgery of major congenital gastrointestinal tract anomalies and to explore the determinants associated with these components of energy balance. 29 neonates were included for analysis, which included 15 pre-term infants. In total, 317 longitudinal calorimetry measurements were performed. In infants born pre- term, the median REE varied between 55.7 and 67.4 kcal/kg/day, and median RQ changed from 0.70 to 0.86-0.92 between 34 and 42 weeks. In infants born at term, the median REE varied between 57.3 and 67.9 kcal/kg/day while the median RQ increased from 0.63 to 0.84-0.88 from 38 to 44 weeks PMA (post-menopausal age).


Poulsen, M. K., L. P. Thomsen, S. Kjærgaard, S. E. Rees and D. S. Karbing (2019). “Reliability of, and Agreement Between, two Breath‐ by‐Breath Indirect Calorimeters at Varying Levels of Inspiratory Oxygen.” Nutrition in Clinical Practice 34(5): 767-774.

Summary: IC: Beacon 3 (Mermaid Care, device 2) and ECOVX (GE Healthcare, device 1), reference method): Thisstudy investigated whether measurements of EE, VO2, and VCO2 by breath-by-breath IC devices 1 and 2 were within-day reliable under conditions of varying FiO2,and whether the two systems measured in agreement. (Device 2 does not use the Haldane transformation). The study was conducted in 20 healthy male subjects and IC was measured while breathing through a ventilator facemask, conscious and sitting. Both systems measured EE, VO2, and VCO2 at 21%–85% FiO2 reliably, but with bias at 85% FiO2. The devices were in agreement at 21% and 50% FiO2, but further studies need to confirm accuracy at high FiO2.


Singer, P., E. De Waele, C. Sanchez, S. Ruiz Santana, J. C. Montejo, P. F. Laterre, A. Soroksky, E. Moscovici and I. Kagan (2021). “TICACOS international: A multi-center, randomized, prospective controlled study comparing tight calorie control versus Liberal calorie administration study.” Clinical nutrition (Edinburgh, Scotland) 40(2): 380-387.

Summary: IC: Deltatrac II, COVX (both GE Healthcare) and Quark (Cosmed): This follow-on to the compendium of TICACOS studies completed to date evaluated the impact of measuring daily REE and the impact on infection rates in critically ill patients. In total 332 patients were allocated into a control or study intervention arm; but the study failed to achieve the targeted enrollment numbers. The primary outcome of infection was not significantly decreased between the study and control groups. There was a trend for decreased hospital mortality in the study arm that did not reach statistical significance. The authors concluded, “these results together with other prospective randomized studies using indirect calorimetry might give a signal toward improved survival when patients’ medical nutritional therapy is guided by indirect calorimetry.”


Smetana, K. S., Y. Hannawi and C. C. May (2020). “Indirect Calorimetry Measurements Compared With Guideline Weight-Based Energy Calculations in Critically Ill Stroke Patients.” JPEN. Journal of parenteral and enteral nutrition.

Summary: CARESCAPE R860 ventilator with E-sCOVX respiratory module (GE Healthcare): The energy requirements of neuro-critical care patients are largely unknown. This study in critically ill stroke patients evaluated the energy requirements during the acute disease process. In this single-center, retrospective, observational study, IC was obtained at the baseline of the critical-care journey and low-weight and high-weight-based energy estimates were compared. The low-weight-based group was significantly lower than the REE target measured by IC, while high-weight-based group was similar to IC REE targets. Linear regression analysis showed that weight, height, and hemorrhagic stroke subtype were associated with IC.


Sungurtekin, H., S. Karakuzu and S. Serin (2019). “Energy Expenditure in Mechanically Ventilated Patients: Indirect Calorimetry vs Predictive Equations.” Dahili ve Cerrahi Bilimler Yoğun Bakım Dergisi 10(1): 7-12.

Summary: IC: M-CAiOVX (GE Healthcare): This prospective study evaluated multiple predictive equations compared to indirect calorimetry measurements in mechanically ventilated critically ill patients. In total, 114 patients were evaluated. All of the predictive equations showed moderate correlation among themselves (P<0.05). The Harris- Benedict and Penn State equations showed the better agreement with IC, compared to other equations. The authors concluded: “Predictive equations are not reliable in determining EE; the confidence intervals are very high and can lead to inadequate feeding or overfeeding.”


Tamura, T., T. Yatabe and M. Yokoyama (2019). “Energy expenditure measured using indirect calorimetry after elective cardiac surgery in ventilated postoperative patients: A prospective observational study.” Clinical Nutrition Experimental 24: 15-23.

Summary: IC: CARESTATION Engstrom ventilator (GE Healthcare): This study evaluated REE in patients undergoing cardiac surgery during the post-operative period. This prospective observational study enrolled 47 patients. Bland-Altman analysis was conducted. The mean difference was 116.6 kcal/day between REE measured and REE estimated by Harris-Benedict. Secondary analysis determined no significant difference in REE between on-pump and off-pump groups.


Vasileiou, G., S. Qian, R. Iyengar, M. B. Mulder, L. M. Gass, J. Parks, G. D. Pust, R. Rattan, E. Lineen, P. Byers and D. D. Yeh (2019). “Use of Predictive Equations for Energy Prescription Results in Inaccurate Estimation in Trauma Patients.” Nutrition in Clinical Practice 35(5): 927-932.

Summary: CARESCAPE R860 with integrated IC: This study of 55 mechanically ventilated trauma ICU patients showed that predictive equations (e.g. Harris-Benedict) overestimated REE compared to IC. On the first day of REE measurement, overestimation was 26%; over seven days, the overestimation was 13%, and at 14 days, the overestimation remained greater than IC at 7%. The study concluded that “The use of weight-based equations and formulas fails to account for the continuous metabolic changes that occur in this population during the first days after injury.”


Articles on research conducted with Deltatrac monitor

Kagan, I., et al. (2018). “Validation of carbon dioxide production (VCO2) as a tool to calculate resting energy expenditure (REE) in mechanically ventilated critically ill patients: a retrospective observational study.” Crit Care 22(1): 186.

Summary: A retrospective observational study involving ventilated patients compared the REE derived from VCO2 (REE- VCO2) with the REE derived from IC (REE-IC). REE and RQ were calculated using the Weir equation. 497 measurements were conducted with a median of three measurements per patient. Results showed that there was wide variability without a consistent bias, suggesting that the VCO2 measurement could widely under- and over-estimate REE. Therefore, REE via IC remains the best tool to estimate caloric needs.


Weintraub, V., F. B. Mimouni and S. Dollberg (2007). “Changes in energy expenditure in preterm infants during weaning: a randomized comparison of two weaning methods from an incubator.” Pediatr Res 61(3): 341-344.

Summary: IC: Deltatrac II (GE Healthcare): In this study, 42 preterm infants were assessed in an RCT with one of two weaning methods to assess the impact on REE. REE increased significantly at the time an infant was weaned from the incubator, regardless of weaning method. A comparison of the six infants who failed weaning with the 36 that had a successful weaning from the incubator revealed that mode of weaning was not significantly influential( two failures/19 infants (10.5%) in the warming bassinet group versus 4/23 (17.4%) in the incubator group, p =0.67). Baseline REE was almost significantly lower (p = 0.06) in the failed group (219 ± 11 kJ/kg/d) than in the successful group (236 ±7 kJ/kg/d).


Zusman, O., et al. (2016). “Resting energy expenditure, calorie and protein consumption in critically ill patients: a retrospective cohort study.” Crit Care 20(1): 367.

Summary: This study, the largest retrospective study (n=6994) completed using indirect calorimetry as opposed to predictive equations to determine energy requirements in mechanically ventilated, critically ill patients, demonstrated a non-linear, significant association between the percent Administered Calories/REE and mortality by 60 days. The findings suggest that both underfeeding and overfeeding appear to be harmful to mechanically ventilated, critically ill patients. Intuitively, achieving a goal of 100 % calories administered would be optimal; in fact, the ideal goal for calories administered with the most favorable survival was achieved at 70%.


Zusman, O., et al. (2018). “Predictive equations versus measured energy expenditure by indirect calorimetry: A retrospective validation.” Clin Nutr.

Summary: A retrospective study in ICU patients evaluating REE estimates compared to IC (Deltatrac) was conducted on 1,565 patients, for a total of 5,847 measurements. This is the largest study evaluating REE versus predictive equations. The results confirm what has been observed in many smaller studies as well as a systematic review, showing a large variability and poor accuracy of predictive equations. The level of accuracy never exceeded 50%.

For the remaining articles, please download the attached pdf.

  • Respiratory
  • Nutrition
  • Intensive care
  • Operational
  • Neonatal care
  • Operational
  • Economic
  • Perioperative care
  • Operational