24-hour indirect calorimetry in mechanically ventilated critically ill patients

Two-hour indirect calorimetry measurement as a predictor of 24-hour energy expenditure in critically ill surgical patients: A longitudinal study

BACKGROUND

Measuring energy expenditure (EE) by indirect calorimetry (IC) has become the gold standard tool for critically ill patients to define energy targets and tailor nutrition. Debate remains as to the optimal duration of measurements or the optimal time of day in which to perform IC.

METHODS

In this retrospective longitudinal study, we analyzed results of daily continuous IC in 270 mechanically ventilated, critically ill patients admitted to the surgical intensive care unit in a tertiary medical center and compared measurements performed at different hours of the day.

RESULTS

A total of 51,448 IC hours was recorded, with an average 24-h EE of 1523 ± 443 kcal/day. Night shift (00:00-8:00) was found to have significantly lower EE measurements (mean, 1499 ± 439 kcal/day) than afternoon (16:00-00:00; mean, 1526 ± 435 kcal/day) and morning (8:00-16:00; mean, 1539 ± 462 kcal/day) measurements (P < 0.001 for all). The bi-hourly time frame that most closely resembled the daily mean was 18:00-19:59, with a mean of 1521 ± 433 kcal/day. Daily EE measurements of the continuous IC at days 3-7 of admission showed a trend toward a daily increase in 24-h EE, but the difference was not statistically significant (P = 0.081).

CONCLUSIONS

Periodic measurements of EE can differ slightly when performed at various hours of the day, but the error range is small and may not necessarily have a clinical impact. When continuous IC is not available, a 2-h EE measurement between 18:00 and 19:59 can serve as a reasonable alternative.

Doubly labelled water for determining total energy expenditure in adult critically ill and acute care hospitalized inpatients: A scoping review

BACKGROUND & AIMS

Doubly labelled water (DLW) is considered the reference standard method of measuring total energy expenditure (TEE), but there is limited information on its use in the Intensive Care Unit (ICU) and acute care setting. This scoping review aims to systematically summarize the available literature on TEE measured using DLW in these contexts.

METHODS

Four online databases (MEDLINE, Embase, Emcare and CINAHL) were searched up to Dec 12, 2020. Studies in English were included if they measured TEE using DLW in adults in the ICU and/or acute care setting. Key considerations, concerns and practical recommendations were identified and qualitatively synthesized.

RESULTS

The search retrieved 7582 studies and nine studies were included; one in the ICU and eight in the acute care setting. TEE was measured over 7-15-days, in predominantly clinically stable patients. DLW measurements were not commenced until four days post admission or surgery in one study and following a 10-14-day stabilization period on parenteral nutrition (PN) in three studies. Variable dosages of isotopes were administered, and several equations used to calculate TEE. Four main considerations were identified with the use of DLW in these settings: variation in background isotopic abundance; excess isotopes leaving body water as carbon dioxide or water; fluctuations in rates of isotope elimination and costs.

CONCLUSION

A stabilization period on intravenous fluid and PN regimens is recommended prior to DLW measurement. The DLW technique can be utilized in medically stable ICU and acute care patients, with careful considerations given to protocol design.

Continuous Indirect Calorimetry in Critically Injured Patients Reveals Significant Daily Variability and Delayed, Sustained Hypermetabolism

BACKGROUND

Previous studies have used using Indirect Calorimetry (IC) with solitary or sparse measurements of resting energy expenditure (REE). This "snapshot" may not capture the dynamic nature of metabolic requirements. Using continuous IC, we describe the variation of REE during the first days in the intensive care unit.

METHODS

Injured adults (≥18 years) requiring mechanical ventilation from March 2018 to September 2018 were enrolled. IC was initiated within 4 days of admission and continuous REE recorded until 14 days, extubation, or death. Multiple 10-minute periods collected during steady state were used to calculate daily REE maximum, minimum, average, and variability [(REEmax - REEmin/2)/average REE].

RESULTS

We included 55 patients. Median age was 38 [27-58] years, 38 (69%) were male, body mass index was 28 [25-33] kg/m² , and Acute Physiology and Chronic Health Evaluation II was 17 [14-24]. Mechanism of injury was: blunt (n = 38, 69%), penetrating (n = 9, 16%), and burn (n = 8, 15%). Average REE increased gradually from 1,663 kcal [1,435-2,143] to a maximum of 2,080 [1,701-2,336] on day 7, a relative 25% increase, which was sustained through day 14. REE variability ranged 8%-13% and was not reliably predicted by fever, tachycardia, elevated intracranial pressures, hypertension, or hypotension.

CONCLUSION

In critically injured patients, steady-state REE measurements display fluctuations over a 24-hour period and demonstrate a gradual rise over the first few days after injury. Continuous REE, if available, is recommended for more precise matching of energy delivery to metabolic requirements.

Systematic review of factors associated with energy expenditure in the critically ill

BACKGROUND AND AIMS

Indirect calorimetry is the reference standard for energy expenditure measurement. Predictive formulae that replace it are inaccurate. Our aim was to review the patient and clinical factors associated with energy expenditure in critically ill patients.

METHODS

We conducted a systematic review of the literature. Eligible studies were those reporting an evaluation of factors and energy expenditure. Energy expenditure and factor associations with p-values were extracted from each study, and each factor was classified as either significantly, indeterminantly, or not associated with energy expenditure. Regression coefficients were summarized as measures of central tendency and spread. Metanalysis was performed on correlations.

RESULTS

The search strategy yielded 8521 unique articles, 307 underwent full text review, and 103 articles were included. Most studies were in adults. There were 95 factors with 352 evaluations. Minute volume, weight, age, % body surface area burn, sedation, post burn day, and caloric intake were significantly associated with energy expenditure. Heart rate, fraction of inspired oxygen, respiratory rate, respiratory disease diagnosis, positive end expiratory pressure, intensive care unit days, C- reactive protein, and size were not associated with energy expenditure. Multiple factors (n = 37) were identified with an unclear relationship with energy expenditure and require further evaluation.

CONCLUSIONS

An important interval step in the development of accurate formulae for energy expenditure estimation is a better understanding of relationships between patient and clinical factors and energy expenditure. The review highlights the limitations of currently available data, and identifies important factors that are not included in current prediction formulae of the critically ill.

Energy estimation and measurement in critically ill patients

The estimation of caloric needs of critically ill patients is usually based on energy expenditure (EE), while current recommendations for caloric intake most often rely on a fixed amount of calories. In fact, during the early phase of critical illness, caloric needs are probably lower than EE, as a substantial proportion of EE is covered by the non-inhibitable endogenous glucose production. Hence, the risk of overfeeding is higher during the early phase than the late phase, while the risk of underfeeding is higher during the late phase of critical illness. Therefore, an accurate measurement of EE can be helpful to prevent early overfeeding and late underfeeding. Available techniques to assess EE include predictive equations, calorimetry, and doubly labeled water, the reference method. The available predictive equations are often inaccurate, while indirect calorimetry is difficult to perform for several reasons, including a shortage of reliable devices and technical limitations. In this review, the authors intend to discuss the different techniques and the influence of the method used on the interpretation of the results of clinical studies.

Indirect calorimetry measurements in the ventilated critically ill patient: facts and controversies--the heat is on

The provision of nutrition to critically ill patients in the ICU often receives lower priority compared with hemodynamic and ventilation control. This frequently results in a significant calorie deficit. Overestimation of daily energy expenditure may also result in adverse outcomes. In many centers, nutritional decision making is based on predictive formulas, which have been shown to underestimate true energy requirements. Such estimations are ideally performed using indirect calorimetry. Nevertheless, the use of indirect calorimetry has been limited owing to costs and technical difficulties. Controversies about its actual clinical benefits are the focus of recent clinical studies and recommendations. The aim of this review was to describe the advantages of measuring indirect calorimetry within the concept of energy-protein goal-oriented therapy.