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

PURPOSE OF REVIEW: Indirect calorimetry (IC) is increasingly recommended to guide energy delivery in the ICU. This review aims to provide a critical overview of current literature in support of these recommendations. RECENT FINDINGS: There is insufficient evidence to ascertain a mortality benefit from IC-guided energy delivery. However, large variations in energy expenditure during critical illness pose a risk for significant under- and overfeeding if IC is not routinely used. SUMMARY: Even in the absence of demonstrable clinical benefits, there is a strong physiological rationale in favor of performing IC. Measurements can be prioritized in complex patients and should be repeated during prolonged ICU stay.

Whole-body protein kinetics in critically ill patients during 50 or 100% energy provision by enteral nutrition: A randomized cross-over study.

BACKGROUND: Enteral nutrition (EN) is a ubiquitous intervention in ICU patients but there is uncertainty regarding the optimal dose, timing and importance for patient-centered outcomes during critical illness. Our research group has previously found an improved protein balance during normocaloric versus hypocaloric parenteral nutrition in neurosurgical ICU patients. We now wanted to investigate if this could be demonstrated in a general ICU population with established enteral feeding, including patients on renal replacement therapy. METHODS: Patients with EN >80% of energy target as determined by indirect calorimetry were randomized to or 50% or 100% of current EN rate. After 24 hours, whole-body protein kinetics were determined by enteral and parenteral stable isotope tracer infusions. Treatment allocation was then switched, and tracer investigations repeated 24 hours later in a crossover design with patients serving as their own controls. RESULTS: Six patients completed the full protocol. During feeding with 100% EN all patients received >1.2 g/kg/day of protein. Mean whole-body protein balance increased from -6.07 to 2.93 µmol phenylalanine/kg/h during 100% EN as compared to 50% (p = 0.044). The oxidation rate of phenylalanine was unaltered (p = 0.78). CONCLUSIONS: It is possible to assess whole-body protein turnover using a stable isotope technique in critically ill patients during enteral feeding and renal replacement therapy. Our results also suggest a better whole-body protein balance during full dose as compared to half dose EN. As the sample size was smaller than anticipated, this finding should be confirmed in larger studies.

Can exercise and nutrition stimulate muscle protein gain in the ICU patient?

PURPOSE OF REVIEW: The intended purpose of nutritional and exercise interventions during ICU stay is often to limit the muscle loss associated with critical illness. Unfortunately, direct measurements of muscle protein turnover or potential surrogates have often been neglected in clinical trials. RECENT FINDINGS: We discuss the potential advantages and drawbacks of common outcome measures for assessing changes in muscle structure and function over time, and how temporal changes in patient physiology require consideration. There is an increasing awareness of emphasizing functional outcomes in recent clinical trials. We here summarize the latest research on therapies attempting to limit muscle loss in ICU patients, with a focus on muscle protein metabolism. No recent or older studies show any effect of nutritional interventions on muscle protein gain, although some smaller studies show a promising positive effect on muscle thickness and function. Some studies show a positive effect of increased physical activity in the ICU on muscle mass and function but heterogeneity of the interventions and outcome measures make any general conclusions impossible. SUMMARY: Several knowledge gaps remain regarding the importance of muscle protein regulation as a driver of improved physical function following ICU discharge. In our opinion, physiological investigations are needed to guide the design and interpretation of future clinical trials.

An attenuated rate of leg muscle protein depletion and leg free amino acid efflux over time is seen in ICU long-stayers.

BACKGROUND: There is extensive documentation on skeletal muscle protein depletion during the initial phase of critical illness. However, for intensive care unit (ICU) long-stayers, objective data are very limited. In this study, we examined skeletal muscle protein and amino acid turnover in patients with a prolonged ICU stay. METHODS: Patients (n = 20) were studied serially every 8-12 days between days 10 and 40 of their ICU stay as long as patients stayed in the ICU. Leg muscle protein turnover was assessed by measurements of phenylalanine kinetics, for which we employed a stable isotope-labeled phenylalanine together with two-pool and three-pool models for calculations, and results were expressed per 100 ml of leg volume. In addition, leg muscle amino acid flux was studied. RESULTS: The negative leg muscle protein net balance seen on days 10-20 of the ICU stay disappeared by days 30-40 (p = 0.012). This was attributable mainly to an increase in the de novo protein synthesis rate (p = 0.007). It was accompanied by an attenuated efflux of free amino acids from the leg. Leg muscle protein breakdown rates stayed unaltered (p = 0.48), as did the efflux of 3-methylhistidine. The arterial plasma concentrations of free amino acids did not change over the course of the study. CONCLUSIONS: In critically ill patients with sustained organ failure and in need of a prolonged ICU stay, the initial high rate of skeletal muscle protein depletion was attenuated over time. The distinction between the acute phase and a more prolonged and more stable phase concerning skeletal muscle protein turnover must be considered in study protocols as well as in clinical practice. TRIAL REGISTRATION: Australian New Zealand Trial Registry, ACTRN12616001012460 . Retrospectively registered on 1 August 2016.

A supplemental intravenous amino acid infusion sustains a positive protein balance for 24 hours in critically ill patients.

BACKGROUND: Providing supplemental amino acids to ICU patients during a 3-h period results in improved whole-body net protein balance, without an increase in amino acid oxidation. The primary objective was to investigate if a 24-h intravenous amino acid infusion in critically ill patients has a sustained effect on whole-body protein balance as was seen after 3 h. Secondary objectives were monitoring of amino acid oxidation rate, urea and free amino acid plasma concentrations. METHODS: An infusion of [1-13C]-phenylalanine was added to ongoing enteral nutrition to quantify the enteral uptake of amino acids. Primed intravenous infusions of [ring-2H5]-phenylalanine and [3,3-2H2]-tyrosine were used to assess whole-body protein synthesis and breakdown, to calculate net protein balance and to assess amino acid oxidation at baseline and at 3 and 24 hours. An intravenous amino acid infusion was added to nutrition at a rate of 1 g/kg/day and continued for 24 h. RESULTS: Eight patients were studied. The amino acid infusion resulted in improved net protein balance over time, from -1.6 ± 7.9 µmol phe/kg/h at 0 h to 6.0 ± 8.8 at 3 h and 7.5 ± 5.1 at 24 h (p = 0.0016). The sum of free amino acids in plasma increased from 3.1 ± 0.6 mmol/L at 0 h to 3.2 ± 0.3 at 3 h and 3.6 ± 0.5 at 24 h (p = 0.038). Amino acid oxidation and plasma urea were not altered significantly. CONCLUSION: We demonstrated that the improvement in whole-body net protein balance from a supplemental intravenous amino acid infusion seen after 3 h was sustained after 24 h in critically ill patients. TRIAL REGISTRATION: This trial was prospectively registered at Australian New Zealand Clinical Trials Registry. ACTRN, 12615001314516 . Registered on 1 December 2015.

High protein intake without concerns?

The high fashion in nutrition for the critically ill is to recommend a high protein intake. Several opinion leaders are surfing on this wave, expanding the suggested protein allowance upwards. At the same time, there is no new evidence supporting this change in recommendations. Observational data show that in clinical practice protein intake is most often far below current ESPEN recommendations of 1.2-1.5 g/kg/day. Therefore, it may be in the best interests of our patients just to adhere to that guideline, and not to stretch them upwards for protein intake? Here we give arguments to stay conservative.

Nutritional needs for the critically ill in relation to inflammation.

PURPOSE OF REVIEW: This review focuses on nutritional needs in critically ill patients. The inflammation corresponding to acute stress is highlighted. Simultaneously, we try to avoid limiting the perspective to only the acute phase. RECENT FINDINGS: During the last year, a number of important studies on nutritional needs in the critically ill have been published, including large randomized controlled trials. In particular studies addressing the needs for energy and proteins in the critically ill have imparted new knowledge in this field. However, there are few studies concerning the rehabilitation phase after critical illness. SUMMARY: Although the recent findings and publications contribute to a more nuanced understanding of nutrition during critical illness, the implications for clinical practice are not in discord with the current recommendations of guidelines.