Indirect calorimetry--a review of recent clinical applications

Combined enteral and parenteral nutrition

PURPOSE OF REVIEW

To review and discuss the evidence and arguments to combine enteral nutrition and parenteral nutrition in the ICU, in particular with reference to the Early Parenteral Nutrition Completing Enteral Nutrition in Adult Critically Ill Patients (EPaNIC) study.

RECENT FINDINGS

The EPaNIC study shows an advantage in terms of discharges alive from the ICU when parenteral nutrition is delayed to day 8 as compared with combining enteral nutrition and parenteral nutrition from day 3 of ICU stay.

SUMMARY

The difference between the guidelines from the European Society of Enteral and Parenteral Nutrition in Europe and American Society for Parenteral and Enteral Nutrition/Society of Critical Care Medicine in North America concerning the combination of enteral nutrition and parenteral nutrition during the initial week of ICU stay was reviewed. The EPaNIC study clearly demonstrates that early parenteral nutrition in the ICU is not in the best interests of most patients. Exactly at what time point the combination of enteral nutrition and parenteral nutrition should be considered is still an open question.

Novel portable device measures preoperative patient metabolic gas exchange

BACKGROUND

Indirect calorimetry (IC), the measurement of airway CO2 elimination (VCO2), O2 [corrected] uptake (VO2) [corrected], and respiratory exchange ratio (RER = VCO2/VO2), is a noninvasive modality for the assessment of body metabolism. In anesthesia, IC can signal critical events and onset of acute metabolic derangements. We have previously demonstrated the accuracy and precision of a new IC measurement system designed for mechanically ventilated patients, comprised of a new clinical bymixer, fast response humidity and temperature sensor, and a flowmeter. However, measurement of IC during spontaneous breathing is challenging because of unstable tidal volume, frequency, and functional residual capacity (FRC).

METHODS

A new device for IC measurements, designed specifically for spontaneous breathing, was validated against a metabolic lung simulator bench setup. In a second study, the same device was used to conduct preoperative measurements of VCO2 and VO2 in 15 patients.

RESULTS

Our measurements showed excellent correlation and agreement with metabolic lung simulator values: The average (+/-SD) percent error for airway VCO2 was -4.7% +/- 3.31%; the average (+/-SD) percent error for airway VO2 was -0.30% +/- 5.25%. Average values of VCO2 and VO2 in the patient study (3.01 +/- 0.56 and 3.44 +/- 0.69 mL x kg(-1) x min(-1), respectively) were in agreement with previously reported values.

CONCLUSION

We have shown that the new, portable bymixer-flow device, using a bymixer and a fast response humidity sensor, provided accurate and convenient bedside measurement of VCO2 and VO2. We believe that it can contribute in the future to preoperative assessment and baseline reference value for perioperative management.

Determining the least time required for measuring energy expenditure in premature neonates

OBJECTIVE

To compare O2 consumption, CO2 production, respiratory quotient and resting metabolic rate in premature neonates measured for 5 and 10 min steady-state periods and 15 and 20 min non-steady-state periods versus a 2-h measurement period.

METHODS

A prospective study with neonates evaluated by indirect calorimetry. The measurements from the 5, 10, 15, and 20 min periods were taken based on the printout data from the IC monitor at an interval of 1 h before the beginning feeding and were contained in the 2-h measurement. The 5- and 10-min measurements followed the steady-state criterion.

RESULTS

We evaluated 35 premature neonates appropriate for gestational age (born at 28-34 weeks' gestation). Mean age was 20 days+/-9 (median 14 days) and mean weight was 1530+/-270 g (median 1510 g). There was no statistically significant difference between mean VO2, VCO2, respiratory quotient and energy expenditure at 5, 10, 15, and 20 min and 2 h.

CONCLUSIONS

The 5 and 10 min steady-state measurements or a measurement of more than 15 min without reaching steady state produce results similar to those of 2 h measurements.

Can measured resting energy expenditure be estimated by formulae in daily clinical nutrition practice?

PURPOSE OF REVIEW

To recognize the fundamental factors that alter energy expenditure on a daily basis and the impact they have on the measurement of caloric consumption by the human body, through respiratory indirect calorimetry, and thus to try to determine which predictive equation best correlates with total energy expenditure generated from energy measurements.

RECENT FINDINGS

The most important compartment of the body, for its metabolic activity and influence upon resting metabolic rate, is fat-free mass. Other variables affecting energy expenditure are sex, weight, height, age, body surface area, fat mass and ethnicity. Metabolic and activity factors such as the thermic effect of nutrients, facultative thermogenesis, anabolism/growth and physical activity, also contribute, comprising total daily energy expenditure. Following the pioneering work of Harris and Benedict for the estimation of energy expenditure, several authors turned their experimental interest to this area, and various recent predictive formulae were derived. These are useful and easy to apply in daily clinical nutrition practice. However, because of the cited variables upon energy expenditure, the final daily caloric estimates show inherent errors ranging from -23.5 to +22.5% upon measured caloric expenditure. These are particularly remarkable in critically ill patients who are exposed to medical and surgical interventions.

SUMMARY

One has to be careful in choosing, understanding and clinically applying the results from predictive equations, bearing in mind that the original population from which the equation was derived does not always correspond to that currently being evaluated.