Measured and predicted caloric expenditure in the acutely ill

A prospective randomised study comparing oral 13C-bicarbonate tracer technique versus indirect calorimetry for measurement of energy expenditure in adults

“…Indeed were it sufficiently accurate to use an estimated RQ; then EE could be calculated in a simpler way by obtaining VCO 2 readings from the ventilators used on intensive care units. Systematic error may also have resulted from IRIS®-calculations using an estimated 13 C fractional recovery value of 0.7. Although we did not measure fractional recovery of 13 C, a previous study of similar design albeit utilising a smaller number of older subjects 17 , reported this to vary between 63.8% to 68.7%.…”

“…The latter uses measurements of VCO 2 together with an estimated respiratory quotient (RQ) value of 0.85 and an estimated 13 C fractional recovery value of 0.7 to calculate energy expenditure via the Weir equation as previously described 18,19 . In order to validate IRIS® measurements, a 10 ml sample from each breath bag was aspirated (using a 3-way tap and syringe) into 12 ml Exetainer® vials (Labco Ltd, Buckinghamshire, UK) which were measured using continuous flow isotope ratio mass spectrometry (IRMS, AP2003, Analytical Precision Ltd, Northwich, Cheshire, UK) against a calibrated reference gas, and the results expressed as % relative to Pee Dee Belemnite, an international standard of known 13 C composition. Statistical analyses were performed using IBM SPSS Statistics® for Windows™ v19 software (IBM SPSS Statistics, Feltham, UK).…”

“…Bland-Altman plots 22 were used to assess agreement and bias between BT-IRIS® and IC. Three comparisons were undertaken in this study: 1) VCO 2 and EE at rest derived using BT-IRIS® versus IC, 2) VCO 2 and EE during mild exercise derived using BT-IRIS® versus IC, and 3) IRIS®-derived 13 C delta over base (dob) measurements versus those derived from IRMS.…”

“…Although the Harris-Benedict formula 9 is widely utilised to estimate energy requirements in routine clinical practice, it does not allow for inter-individual variations in energy requirements associated with critical illness [10][11][12] . Indeed previous studies have demonstrated both overestimates of up to 50% in calculated EE 13 and underestimates 14 when compared to indirect calorimetry (IC). Furthermore, EE calculated using predictive equations that apply an average weight adjustment, to allow for obese patients, correlates poorly with data from IC 15 .…”

Limitations of nutrient intake. The effect of stressors: trauma, sepsis and multiple organ failure

“…Although it is the simplest solution, no manufacturer so far appears to have taken it up, despite the fact that at present the standard method of measuring energy expenditure in the free living individual is to measure carbon dioxide production and assume an RQ, or derive one from the food intake (Coward, 1988). Measurements of energy expenditure in ventilated patients with MOF have consistently shown a very wide range of values from 50 ± 200% of the basal value, predicted from age, height and weight, with an average of around 120 ± 140% Mann et al, 1985;Weissman et al, 1986;Swinamer et al, 1987). It has to be borne in mind that such measurements are markedly affected by the varying degrees of sedation and muscle relaxation required to facilitate arti®cial ventilation.…”