The thermodilution technique for measuring resting energy expenditure does not agree with indirect calorimetry for the critically ill patient

Methods for Estimating Energy Expenditure in Critically Ill Adults

Energy expenditure (EE) is the sum of metabolic activity within the body at a given time and comprises basal EE, diet-induced thermogenesis, and physical activity. In the intensive care unit, EE is most often assessed to determine a patient's caloric requirements. Energy expenditure also may be useful to understand disease states and the metabolic impact of interventions. Several methods for estimating EE are relevant for clinical use, including indirect calorimetry, predictive equations, exhaled carbon dioxide volume, and the Fick method. Indirect calorimetry is the preferred method for evaluating EE and is considered the gold standard for estimating EE in hospitalized patients. However, use of indirect calorimetry is not always practical or possible. Therefore, other methods of estimating EE must be considered. In this review, methods of evaluating EE in critically ill adults are examined and the benefits and limitations of each method are discussed, with practical considerations for use.

Indirect Calorimetry in Clinical Practice

Indirect calorimetry (IC) is considered as the gold standard to determine energy expenditure, by measuring pulmonary gas exchanges. It is a non-invasive technique that allows clinicians to personalize the prescription of nutrition support to the metabolic needs and promote a better clinical outcome. Recent technical developments allow accurate and easy IC measurements in spontaneously breathing patients as well as in those on mechanical ventilation. The implementation of IC in clinical routine should be promoted in order to optimize the cost–benefit balance of nutrition therapy. This review aims at summarizing the latest innovations of IC as well as the clinical indications, benefits, and limitations.

Strategies for optimal calorie administration in critically ill patients

Nutritional therapy is one of the important treatments in critically ill patients. How to estimate calorie consumption and how to determine an optimal calorie dose are clinical questions of great importance. Although indirect calorimetry is the gold standard for assessing energy expenditure, many intensivists are unable to use this technique. Therefore, the use of formulas, such as the Harris-Benedict equation, or the simple predictive value of 25 kcal/kg/day is reasonable. Several studies and guidelines have shown that the strategies for nutritional therapy depend on the nutritional risk of patients. If patients have low nutritional risks, these estimated values should not be adopted in the acute phase. Until the patient’s condition improves, less than 18 kcal/kg/day might be an optimal calorie target. Contrastingly, cumulative negative energy balance can also be harmful to critically ill patients. Thus, it is important to accurately determine the energy requirement and to make the required changes in the administered calorie dose to go from a strategy of “defense” to that of “offense” in a timely manner. In this article, the concepts of optimal calorie administration in critically ill patients were reviewed.

Monitoring Energy Metabolism with Indirect Calorimetry: Instruments, Interpretation, and Clinical Application

Indirect calorimetry is the best measure to guide calorie administration during nutrition support. This article presents an update of the types of currently available indirect calorimeters and reviews the recent advances that guide the clinical application of indirect calorimetry. The emphasis of this report is placed on issues that the practicing clinician can use to evaluate, interpret, and apply measurements of energy expenditure.

Nutritional support of the obese and critically ill obese patient

With the dramatic increase in the prevalence of obesity worldwide and in the United States, it is virtually certain that clinicians will be caring for bariatric and obese nonbariatric patients in increasing numbers. This patient population presents several difficulties from the medical and surgical management perspectives. In particular, nutrition of the bariatric patient and critically ill obese patient is challenging. A clear understanding of the nutritional assessment and unique management strategies available for the bariatric and the critically ill obese patient is essential to provide them with the safest and most effective care.

History of right heart catheterization: 100 years of experimentation and methodology development

The development of right heart catheterization has provided the clinician the ability to diagnose patients with congenital and acquired right heart disease, and to monitor patients in the intensive care unit with significant cardiovascular illnesses. The development of bedside pulmonary artery catheterization has become a standard of care for the critically ill patient since its introduction into the intensive care unit almost 40 years ago. However, adoption of this procedure into the mainstream of clinical practice occurred without prior evaluation or demonstration of its clinical or cost-effectiveness. Moreover, current randomized, controlled trials provide little evidence in support of the clinical utility of pulmonary artery catheterization in the management of critically ill patients. Nevertheless, the right heart catheter is an important diagnostic tool to assist the clinician in the diagnosis of congenital heart disease and acquired right heart disease, and moreover, when catheter placement is proximal to the right auricle (atria), this catheter provides an important and safe route for administration of fluids, medications, and parenteral nutrition. The purpose of this manuscript is to review the development of right heart catheterization that led to the ability to conduct physiologic studies in cardiovascular dynamics in normal individuals and in patients with cardiovascular diseases, and to review current controversies of the extension of the right heart catheter, the pulmonary artery catheter.

Prediction of resting metabolic rate in critically ill adult patients: results of a systematic review of the evidence

Metabolic rate is generally assessed by use of equations in critically ill patients, but evidence pertaining to the validity of these equations in this population has not been systematically evaluated. This paper represents the first such systematic analysis in adult patients. A work group created by the American Dietetic Association identified pertinent peer-reviewed articles. The work group systematically evaluated these articles and formulated conclusion statements and grades based on the available evidence. Seven equations plus the Fick method were found to have validation work that met criteria for inclusion in this analysis. The Harris-Benedict equation with and without modifiers had the most validation work behind it (n=13), followed by Ireton-Jones (1992 and 1997) (n=9), Penn State (1998, 2003) (n=2), and Swinamer (n=1). Five studies pertaining to the Fick method met acceptance criteria. Based on these validation studies, the Harris-Benedict, Ireton-Jones 1997, and Fick methods can be confidently eliminated from use in assessment of energy expenditure in critically ill patients. The Penn State 2003, Swinamer, and Ireton-Jones 1992 equations may be useful in critically ill nonobese patients, whereas the Ireton-Jones 1992 and Penn State 1998 equations seem to be useful in obese patients. The strength of these conclusions is moderated because of limited and sometimes inconsistent data. More validation work is needed to confirm and increase the strength of these conclusions.

Basal energy expenditure and diet- induced modifications to thermogenesis in short bowel syndrome

BACKGROUND & AIM

The influence of food intake on diet-induced thermogenesis, in the absence of parenteral nutrition, has not been assessed in short bowel syndrome (SBS) patients. We studied basal energy expenditure (BEE) and diet-induced thermogenesis in SBS patients (n=8) and paired healthy adult volunteer controls (n=8).

METHODS

Energy expenditure was measured by indirect calorimetry (IC) before and after control diet intake. All study participants received oral control diet randomly given in 3 doses (A=1.0, B=1.5 and C=2.0)x1/6 of BEE calories. Bioelectric impedance was assessed. Pairing criteria for controls were: age, sex, body mass index.

RESULTS

No significant differences were found between SBS and paired healthy control groups in relation to absolute BEE (P=0.146) and when it was adjusted for body mass index, lean and fat body mass (P=0.861, 0.208 and 0.574, respectively). All diets promoted thermogenesis in both groups. The interaction between the control diet (A, B and C) and SBS and healthy control groups for diet induced thermogenesis presented a significant difference (P=0.026). When comparing groups (SBS vs healthy controls) in relation to the control diet (B and C) we observed: P=0.030 and 0.004, respectively.

CONCLUSION

In patients with SBS it was observed that: (1) BEE measured by IC in absolute values or adjusted by lean body mass is similar to healthy control group; (2) Diet-induced thermogenesis was lower than the healthy control group for higher caloric diets (B and C).

Assessment of resting energy expenditure in mechanically ventilated patients

BACKGROUND

Usual equations for predicting resting energy expenditure (REE) are not appropriate for critically ill patients, and indirect calorimetry criteria render its routine use difficult.

OBJECTIVE

Variables that might influence the REE of mechanically ventilated patients were evaluated to establish a predictive relation between these variables and REE.

DESIGN

The REE of 70 metabolically stable, mechanically ventilated patients was prospectively measured by indirect calorimetry and calculated with the use of standard predictive models (Harris and Benedict's equations corrected for hypermetabolism factors). Patient data that might influence REE were assessed, and multivariate analysis was conducted to determine the relations between measured REE and these data. Measured and calculated REE were compared by using the Bland-Altman method.

RESULTS

Multivariate analysis retained 4 independent variables defining REE: body weight (r(2) = 0.14, P < 0.0001), height (r(2) = 0.11, P = 0.0002), minute ventilation (r(2) = 0.04, P = 0.01), and body temperature (r(2) = 0.07, P = 0.002): REE (kcal/d) = 8 x body weight + 14 x height + 32 x minute ventilation + 94 x body temperature - 4834. REE calculated with this equation was well correlated with measured REE (r(2) = 0.61, P < 0.0001). Bland-Altman plots showed a mean bias approaching zero, and the limits of agreement between measured and predicted REE were clinically acceptable.

CONCLUSION

Our results suggest that REE estimated on the basis of body weight, height, minute ventilation, and body temperature is clinically more relevant than are the usual predictive equations for metabolically stable, mechanically ventilated patients.

Indirect calorimetry: a trend toward continuous metabolic assessment

Physiologic monitoring of the patient's metabolic response to illness and nutritional needs has been available for many decades. Traditional methods for estimating and intermittently assessing the patient's metabolic status provide incomplete and often misleading information. The measurement oxygen consumption (VO2) and carbon dioxide production (VCO2) for assessment of the critically ill patient's metabolic status has been underutilized partly because of the limitations of available technologies. Recent advances in gas exchange technologies have made VO2 and VCO2 assessment readily available at the bedside on a continuous basis. This article provides a clinical review of specific current literature related to indirect calorimetry. A synthesis of the data supports the use of gas exchange measurements of VO2 and VCO2 for serial assessment of metabolic changes and for monitoring of the patient's nutritional status. Furthermore, a multidisciplinary approach to metabolic monitoring and nutritional assessment provides a cost-efficient means of patient care, which, when properly implemented, improves patient outcomes.

Evaluation of accuracy and reliability of indirect calorimetry for the measurement of resting energy expenditure in healthy dogs

OBJECTIVE

To assess accuracy and reliability of open-flow indirect calorimetry in dogs.

ANIMALS

13 clinically normal dogs.

PROCEDURE

In phase 1, oxygen consumption per kilogram of body weight (VO2/kg) was determined in 6 anesthetized dogs by use of open-flow indirect calorimetry before and after determination of VO2/kg by use of closed-circuit spirometry. In phase 2, four serial measurements of VO2 and carbon dioxide production (VCO2) were obtained in 7 awake dogs by use of indirect calorimetry on 2 consecutive days. Resting energy expenditure (REE) was calculated.

RESULTS

Level of clinical agreement was acceptable between results of indirect calorimetry and spirometry. Mean VO2/kg determined by use of calorimetry before spirometry was significantly greater than that obtained after spirometry. In phase 2, intraclass correlation coefficients (ICC) for REE and VO2 were 0.779 and 0.786, respectively, when data from all 4 series were combined. When the first series was discounted, ICC increased to 0.904 and 0.894 for REE and VO2, respectively. The most reliable and least variable measures of REE and VO2 were obtained when the first 2 series were discounted.

CONCLUSIONS AND CLINICAL RELEVANCE

Open-flow indirect calorimetry may be used clinically to obtain a measure of VO2 and an estimate of REE in dogs. Serial measurements of REE and VO2 in clinically normal dogs are reliable, but a 10-minute adaption period should be allowed, the first series of observations should be discounted, multiple serial measurements should be obtained, and REE.

Estimating energy expenditure in critically ill adults and children

Designing effective nutrition support regimens for critically ill patients requires an understanding of the energy needs of each patient. Many disease processes result in elevated caloric requirements, whereas some clinical procedures and medications may diminish the metabolic response. Experienced clinicians are unable to predict the extent to which trauma or injury will affect energy requirements for an individual. Both under- and overfeeding a critically ill patient may prolong hospitalization and increase morbidity and mortality. Applying equations that were originally developed for healthy nonhospitalized individuals to predict the energy requirements of critically ill patients will often result in significant errors and may lead to provision of inappropriate nutritional support. The measurement of resting energy expenditure by indirect calorimetry is a valuable tool and can be used to predict energy requirements for most spontaneously breathing critically ill patients, but may lead to spurious results in mechanically ventilated pediatric patients. In the complex and rapidly changing context of critical illness, individualized assessment of energy requirements is crucial. Whichever technique is used initially to assess energy requirements, sequential monitoring and constant reassessment of each patient is essential to provide the appropriate nutritional care regimen. The purpose of this article is to review the equations for estimating and the techniques, practical aspects, and interpretation of measuring energy expenditure in critically ill patients.