ORIGINAL ARTICLE
An algorithm for balanced protein/energy provision in critically ill mechanically ventilated patients

https://doi.org/10.1016/j.eclnm.2007.05.001Get rights and content

Summary

Background & aims

Optimal nutritional therapy for energy and protein in critically ill, mechanically ventilated patients can be defined as: providing calories matched with the measured energy expenditure and delivery of protein in an amount of 1.2–1.5 g/kg pre-admission weight/day. Several enteral nutritional products are available with different energy/protein proportions. We developed an algorithm to choose the nutritional formula that combines optimal energy and protein supply for individual patients.

Methods

The energy and protein values of three nutritional formulas were used together with an aimed provision of 1.2–1.5 g protein/kg/day to construct a nomogram. From that, an algorithm followed, which was tested retrospectively in 203 mechanically ventilated patients with a normal BMI and known values for energy expenditure and weight.

Results

In the nomogram cut-off points for energy/weight ratios were: 19.0–23.8 for a normal energy/high protein formula, 23.8–29.8 for a high energy/high protein formula and 30–37.5 for the normal energy/normal protein formula. The algorithm uses energy expenditure/body weight ratio of the patients to choose one of the three formulas. This resulted in an adequate provision of protein in 93% of the patients.

Conclusion

The algorithm leads to provision of adequate amounts of protein and energy in the majority of critically ill, mechanically ventilated patients.

Introduction

The goal of nutritional therapy is to conserve or restore the normal body composition. To achieve this goal, adequate amounts of energy, protein, minerals and trace elements must be provided, tailored towards the individual needs of our patients. For patients who are fully dependent on artificial nutrition, the composition of the nutritional formula is important as it determines the relationship between energy and protein that is provided. Nutritional formulas have a fixed energy/protein ratio, e.g. 1000 calories and 40 g protein/L. Thus, the patient who is fed according to his caloric needs, will have a protein provision that results from the composition of the formula used. As argued below, nutritional goals must be defined for energy and protein separately. As a consequence, the use of nutritional formulas with different energy/protein ratio's are necessary to meet the individual patients’ needs. In this article we report a mathematical model that clarifies the characteristics of different nutritional formulas with regard to energy and protein per kg body weight delivery. As energy expenditure varies widely between patients and also the weights of the patients differ considerably, we tested the mathematical model in a group of 203 critically ill, mechanically ventilated patients of whom weight and energy expenditure by indirect calorimetric measurements were available. With this validated model we offer the reader an algorithm for choosing a formula providing optimal nutritional treatment.

In a foreword to one of the handbooks in clinical nutrition1 Sir David P. Cuthbertson stressed the responsibility of the therapist as follows: “It is obvious that the power of the therapist is so complete in enteral and parenteral nutrition that it is extremely important to be well informed and to exercise it to the best available criteria. One of the most important criteria for establishing the appropriate amounts of carbohydrate, fat, and protein that should be given is the quantitative effect of each of these nutrients on maintenance of the body's cell mass, usually as measured by N balance.”

In this article, we focus only on energy and protein delivery. The specific sort of protein provided and the supply of minerals, vitamins and trace elements is beyond the scope of our discussion.

In the first part of this article we will try to determine how optimal energy and protein nutrition is defined. In the second part a model is presented which leads to cut-off points in energy/weight ratio for choosing an enteral nutritional formula that meets the energetic and protein needs of an individual patient.

The gold standard for determining resting energy expenditure (REE) in critically ill, mechanically ventilated patients is indirect calorimetry. Measurement of oxygen consumption (VO2) and carbon dioxide production (VCO2) allows for an accurate, bedside method to calculate the energetic needs of our patients. To establish total energy expenditure (TEE), 10% is added to the REE value.2

REE measurements allow prescribing nutritional regimens tailored to patients’ energy needs; in addition the measurements allow determination of substrate utilization when urinary nitrogen values are concomitantly measured.3

Although in nutritional terms the word protein delivery is used, actually the gut breaks down protein into amino acids or very short amino peptides that are absorbed. In the body these are re-synthesized and become proteins again. The capacity to synthesize protein is limited. The maximum capacity of the human body to synthesize protein is reached when 1.5–1.7 g protein/kg/day is administered, indicating that supply of amino acids above this value is useless.4, 5 In addition to data on stimulation of protein synthesis, data on changes in whole body protein mass should be considered too. The gold standard for measurement of whole body protein is in vivo neutron activation analysis. At this moment we are aware of only two studies that have used this technique. One study was done in surgical patients after major abdominal surgery. The chosen amount of protein was either 0.8 or 1.9 g protein/kg/day.6 In those patients, provision of 0.8 g protein/kg/day proved to be insufficient to maintain body protein mass, whereas body protein mass was conserved if 1.9 kg protein/kg/day was given. The other study was carried out in probably mechanically ventilated and fully immobilized intensive care patients, given, respectively, 1.1, 1.5 and 1.9 g of protein/kg fat free mass/day during 14 days.7 Provision of 1.5 g protein/kg fat free mass/day proved the optimal amount to preserve protein mass; 1.5 g per kilogram FFM/day equals 1.2 g protein/kg pre-admission weight/day.

Optimal support in terms of energy and protein in critically ill, mechanically ventilated patients in the ICU can therefore be defined as: energy delivery of measured REE+10% (=TEE) and provision of 1.2–1.5 g protein/kg pre-admission body weight/day (for extensive discussion see Sauerwein et al.8).

Section snippets

Development of the nomogram to define characteristics of nutritional formulas

Three types of enteral nutrition, that we also use in daily clinical practice, were included in the analysis. We used a normal energy/normal protein solution (Nutrison standard; Nutricia, Zoetermeer, the Netherlands), containing 1000 kcal and 40 g protein/L, a high-energy/high-protein solution (Nutrison protein plus; Nutricia, Zoetermeer, the Netherlands), containing 1250 kcal and 63 g protein/L, and a normal energy/high-protein solution (Promote; Abbott Nutrition, Hoofddorp, the Netherlands),

Results

Table 1 shows the calculated cut-off points for energy/weight ratios: 19.0–23.8 for the normal energy/high protein formula, 23.8–29.8 for the high-energy/high protein formula and 30.0–37.5 for the normal energy/normal protein solution. For the three formulas that we used, the cut-off points are corresponding: the upper limit of two enteral formulas are equal or very close to the lower limits of another formula. Therefore, the three chosen nutritional formulas offer a continuous spectrum without

Discussion

This study shows that the use of an algorithm that uses energy expenditure/weight ratios of patients combined with a nomogram that contains energy/protein ratios of three different nutritional formulas with upper and lower targets for protein provision per kilogram results in optimal provision of both energy and protein in critically ill, mechanically ventilated patients in 92.6% of cases, when the BMI is between 18.5 and 30 kg/m2.

For products that have a different composition from the ones we

Acknowledgements

The authors wish to thank Marnelle de Groot, Emilie van de Meerendonk and Rixt Koopmans for their work on the database that was used for the simulation. Ronald Driessen and Jan Peppink deserve the credits for implementing the algorithm in our patient data management system.

RS: thought of the concept to link nutritional formulas’ characteristics to patients energy/weight ratios; has done part of the indirect calorimetric measurements; has prepared the manuscript.

PW: developed Table 1; was

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