key: cord-0968158-btxgw21i authors: De Waele, Elisabeth; van Zanten, Arthur R. H. title: Routine use of indirect calorimetry in critically ill patients: pros and cons date: 2022-05-05 journal: Crit Care DOI: 10.1186/s13054-022-04000-5 sha: 08aba45c42e602cb06f64bfc7ad23577de9c32a2 doc_id: 968158 cord_uid: btxgw21i nan IC measuring O 2 consumption (VO 2 ) and CO 2 production (VCO 2 ) represents real-time energy metabolism [1] . REE assessment by IC to guide nutrition therapy is recommended by international nutrition guidelines for adult ICU patients, although the level of evidence is still low (grade B recommendation) [2] . Indirect calorimetry is not lifesaving but a monitoring tool providing factual information on metabolism. Retrospective data revealed a U-shaped association between 60-day mortality and calorie intake in early critical illness, underlining the importance of targeting individual energy demands and preventing both overfeeding and underfeeding [3] . In a systematic review and meta-analysis in 2020, no improved outcomes were found when IC was used, although prescribed energy targets were more closely met when IC informed energy delivery compared with predictive equations [4] . The more precise intake observed suggests that IC feedback improves feeding performance, compared with equations, and may prevent underfeeding and overfeeding in individual patients. In 2021, another meta-analysis showed a 23% reduction in short-term mortality when energy targets were based on IC [5] . In another meta-analysis, lower 28-day mortality was found when isocaloric IC-guided nutrition was compared with (hypocaloric) feeding protocols using predictive equations, however, without effect on nosocomial infections and 90-day mortality [6] . All meta-analyses did not find a shorter length of stay (LOS) or mechanical ventilation duration, possibly due to higher calorie intake leading to higher CO 2 production, potentially prolonging mechanical ventilation duration and LOS. Personalised nutrition should be based on individual energy targets. However, predictive equations are highly inaccurate, potentially leading to 500-1000 kcal/ day nutrition targets higher or lower than individual demands, conferring marked risks of underfeeding and overfeeding [7] . Using only the VCO 2 from mechanical ventilators to estimate REE is inferior to IC and barely better than predictive equations [8] . Responding to varying needs during the patient journey is recommended. IC using a canopy can be expanded to the post-ICU phase [9] . The ICALIC research group helped to develop moderate-cost highly efficient technology to measure REE in ventilated and spontaneous breathing patients [10] . *Correspondence: zantena@zgv.nl In ventilated patients with FiO 2 > 0.7 and PEEP > 12 cmH 2 O, no reliable measurements of VO 2 and VCO 2 are possible. Furthermore, any air leak excludes the use of IC as not all exhaled gas will meet the device's sensors. Typical examples are pneumothorax, subcutaneous emphysema, or tracheal-oesophageal fistula. High-flow nasal oxygen therapy or non-invasive ventilation precludes IC use. As moisture affects the performance of sensors, nebulisation during measurement is not recommended. In non-ventilated patients, measurements can only be taken when oxygen therapy has been stopped [1] . As these limitations are present in many patients, equations are still needed then. You should give nutritional energy to meet the REE in all patients-no, you shouldn't REE can be used to set energy targets until a new measurement has been taken. However, endogenous energy production can be marked in the early phase of critical illness (> 1000 kcal/day). Adding full nutrition to this non-inhibitable energy production may induce overfeeding [1] . Gradually advancing to target is recommended. IC should not be followed during this phase. However, over 3-4 days, this effect dissipates in most patients. Then, IC can be used to set targets. Another reason not to follow IC REE is administering non-nutritional calories (propofol, glucose, and citrate). Although not intended as nutrition, these calories contribute to energy intake and are substantial in individual patients [1] . When after commencement of nutrition, plasma phosphate drops below 0.65 mmol/l, known as refeeding hypophosphatemia (RFH), caloric restriction (< 500 kcal/ day) is warranted. Studies have demonstrated increased mortality with high-calorie intake during RFH [1] . Therefore, then REE should not be the target. Large tidal volume variations during spontaneous mechanical ventilation can affect reliable measurements. Devices with a mixing chamber have better performance [10] . Early COVID-19 guidelines recommended against IC to reduce infection transmission as ventilator circuit disconnections may enhance aerosol production [11] . However, later studies using strict hygiene protocols show that safe application is feasible and provide crucial insights into metabolic changes of (hyper)metabolism over time [12] . Measuring REE during extracorporeal treatments (like CRRT and ECMO) poses significant challenges. Techniques may disturb REE by impacting temperature and stress levels. Moreover, techniques can also affect metabolism (adding bicarbonate and/or citrate) or nonpulmonary gas exchange. The effects of these techniques on REE are probably limited but also variable. Performing IC among these patients remains challenging [13] . Using complex equations to adjust for metabolic and gas exchange disturbances is possible but seems less feasible in daily practice [14] . Costs of IC comprise device investment costs, consumables, calibration gas, and service. Additionally, staff time should be added. Typically, a procedure to measure takes 5-10 min. Modern interfaces are intuitive, and training during IC implementation can be limited to 1-2 h. Formal health economic evaluations are not available. Modern devices have acceptable costs per measurement (personal communication: EdW, AvZ). The business case is positive when improved outcomes reported in metaanalyses (mortality) translate into daily practice. Optimising nutritional performance may impact readmission rates, long-term functional outcomes (recovery from ICU-acquired weakness), and quality of life. Unfortunately, these endpoints have not been studied yet. Indirect calorimetry is the gold standard for measuring energy expenditure to set nutrition therapy goals during critical illness. Although recommended, the evidence underlying recommendations is limited. We have summarised when not to follow the REE from IC. Also, technical and patient-related limitations have been addressed. Future developments of IC to monitor REE continuously and during oxygen therapy and non-invasive ventilation are warranted to further enhance its application in daily practice. Energy expenditure and indirect calorimetry in critical illness and convalescence: current evidence and practical considerations ESPEN guideline on clinical nutrition in the intensive care unit Resting energy expenditure, calorie and protein consumption in critically ill patients: a retrospective cohort study Is energy delivery guided by indirect calorimetry associated with improved clinical outcomes in critically ill patients? A systematic review and meta-analysis Energy delivery guided by indirect calorimetry in critically ill patients: a systematic review and meta-analysis The effect of indirect calorimetry guided isocaloric nutrition on mortality in critically ill patients-a systematic review and meta-analysis Measured versus calculated resting energy expenditure in critically ill adult patients. Do mathematics match the gold standard? Resting energy expenditure by indirect calorimetry versus the ventilator-VCO2 derived method in critically ill patients: the DREAM-VCO2 prospective comparative study Nutrition therapy and critical illness: practical guidance for the ICU, post-ICU, and long-term convalescence phases • fast, convenient online submission • thorough peer review by experienced researchers in your field • rapid publication on acceptance • support for research data, including large and complex data types • gold Open Access which fosters wider collaboration and increased citations maximum visibility for your research: over 100M website views per year • At BMC, research is always in progress. Learn more biomedcentral.com/submissions Ready to submit your research Ready to submit your research ? 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