Point‐Counterpoint: Indirect Calorimetry Is not Necessary for Optimal Nutrition Therapy in Critical Illness

Abstract

Clinicians have widely recognized that indirect calorimetry (IC) is the "gold standard" for measuring energy expenditure (EE) and thus would intuitively anticipate that its use would be needed to provide optimal nutrition support in critical illness. Recent studies in the literature as well as dramatic changes in clinical practice over the past decade, though, would suggest that such a precise measure by IC to set energy goals is not required to maximize clinical benefit from early feeding in the intensive care unit (ICU). Results from randomized controlled trials evaluating permissive underfeeding, use of supplemental parenteral nutrition to achieve tight calorie control, and caloric density of formulas to increase energy delivery have provided an important perspective on 3 pertinent issues.First, a simple weight-based predictive equation (25 kcal/kg/day) provides a clinically useful approximation of EE. Second, a precise measure of EE by IC does not appear to improve outcomes compared with use of this less accurate estimation of energy requirements. And third, providing some percentage of requirements (50%-80%), achieves similar clinical benefit to full feeding (100%) in the early phases of critical illness. The value from IC use lies in the determination of caloric requirements in conditions for which weight-based equations are rendered inaccurate (anasarca, amputation, severe obesity) or the clinical state is markedly altered (such as the prolonged hyperinflammatory state of coronavirus disease 2019 ). In most other circumstances, routine use of IC would not be expected to change clinical outcomes from early nutrition therapy in the ICU.

Nutrition Therapy in Non-intubated Patients with Acute Respiratory Failure

“…There is a contentious debate as to whether indirect calorimetry should be routinely implemented in clinical practice [ 14 , 15 ]. While some experts advocate for the routine use of indirect calorimetry in critically ill patients [ 14 ], others suggest its use for situations in which weight-based formulas are likely to be inaccurate such as anasarca, severe obesity, or the recovery phase of critical illness [ 16 ]. There is, however, consensus that indirect calorimetry remains the gold standard for measuring energy expenditure and it allows for a better understanding of metabolic processes taking place in patients in acute respiratory failure.…”

“…The intensive provision of full caloric requirements in the initial phase of critical illness has been replaced by a strategy consisting of initial trophic feeding and slow advancement to caloric goals. Early initiation of nutrition and high protein feeding remain important, but the caloric goal is set at 70 to 80% of the estimated caloric requirement in the initial 5 to 7 days of hospital admission [ 16 ]. The bases for this new approach were randomized, multicenter clinical trials in critically ill patients that showed that underfeeding, as compared to full feeding, did not worsen outcomes [ 24 , 25 ] and could improve gastrointestinal tolerance [ 24 ].…”

Indirect calorimetry: should it be part of routine care or only used in specific situations?

“…The technique has been in use for over 40 years as a method to assess mREE and substrate oxidation in hospitalized patients [ 3 ]. However, routine application of indirect calorimetry remains far from ubiquitous in the modern ICU, and there is still debate over the clinical utility of indirect calorimetry [ 4 ].…”

Indirect Calorimetry Measurements Compared to Guideline Weight‐Based Caloric Calculations in Critically III Stroke Patients: One Clinician's Perspective

“…McClave and colleagues make an argument for evaluating how much of an effect accuracy in energy expenditure estimation has in overall outcome. 12 Given the availability and application of precise tools for the care of critically ill patients, such as mechanically ventilated stroke patients, should not measurement of energy expenditure be the standard of care? 13 One final thought, from one nutrition support clinician to another: feed the patient and do no harm.…”

“…Is this nuance of energy discrepancy going to alter the outcome? McClave and colleagues make an argument for evaluating how much of an effect accuracy in energy expenditure estimation has in overall outcome 12 …”