EE: Introduction (2013)
Energy Expenditure (2013) Measuring RMR in the Critically Ill Evidence-Based Nutrition Practice Guideline
Guideline Narrative Overview
The focus of this guideline is on the appropriate preparation of critically ill patients for a measurement of resting metabolic rate (RMR) using indirect calorimetry, as well as the interpretation and application of the result. The goal of incorporating indirect calorimetry into the nutrition care plan of critically ill patients is to minimize physiologic decline (Heidegger et al, 2011) and promote recovery. Clinical judgment is crucial in the application of this guideline.
Rationale for Focusing on Measurement of Resting Metabolic Rate
The purpose of this guideline is to provide instruction on the appropriate method of achieving resting conditions and measuring RMR in critically ill people. Resting metabolic rate is only one component of total energy expenditure (TEE) [i.e., total metabolic rate (TMR)]. The other components include the thermic effect of feeding (TEF) and the energy expended during movement. These components must be estimated and added to the measured RMR to determine the TEE. In this guideline, we focus on RMR for four reasons:
- 1) RMR is the largest component of TEE;
- 2) RMR is the most reproducible of the components of TEE;
- 3) RMR is comparable to a reference standard; and
- 4) RMR is the most feasible component of TEE to measure.
Share of the Total Energy Expenditure. In critically ill patients RMR usually accounts for 90-95% of the TEE (Frankenfield et al, 1994; Weissman et al, 1986). Individual acts of nursing care can raise the metabolic rate by 30%, but these are short lived and therefore contribute only 5-10% of the daily TEE. Patients who are shivering, posturing, or who are fully conscious will have much larger components of their TEE as physical activity.
Reproducible. Resting metabolic rate is the most reproducible component of TEE. The state of rest is clearly defined, with specific conditions of environment and subject preparation, if followed, produce a near minimum level of metabolic rate. This state can then be reproduced over time within an individual and across populations. Total energy expenditure is more difficult to reproduce because the environment and personal attributes, such as diet, movement and sedation level, are highly variable.
Comparison to a Reference Standard. From a nutrition diagnosis perspective, measurement of the RMR allows the RDN to diagnose alterations in energy expenditure as compared to a healthy reference standard. For example, a PES statement may be written as: Increased nutrient needs (energy) related to inflammatory response as evidenced by measured RMR 30% above healthy RMR calculated by the Mifflin-St. Jeor equation. There are no reference standards for activity level or TEF because of high variability in these components of TEE.
Feasibility. If conditions are controlled as outlined in this guideline, a measurement of RMR can be accomplished within 30 minutes. However, measurement of TEE may require considerably more time, and this time requirement severely limits the number of patients that can be measured (Zijlstra et al, 2007). RMR is therefore the more feasible of the two parameters to measure.
Frankenfield DC, Wiles CE, Bagley S, Siegel JH. Relationships between resting and total energy expenditure in injuryed and septic patients. Crit Care Med 1994; 22: 1, 796-1, 804.
Heidegger CP, Graf S, Thibault R, Darmon P, Berger M, Pichard C. Supplemental parenteral nutrition (SPN) in intensive care unit (ICU) patients for optimal energy coverage: improved clinical outcome. Clin Nutr 2011; 1(S): 2-3.
Weissman C, Kemper M, Damask MC, Askanazi J, Hyman AI, Kinney JM. Effect of routine intensive care interactions on metabolic rate. Chest. 1984 Dec; 86(6): 815-818.
Zijlstra N, ten Dam SM, Hulshof PJ, Ram C, Hiemstra G, de Roos NM. 24-hour indirect calorimetry in mechanically ventilated critically ill patients. Nutr Clin Pract 2007; 22: 250-255.
Extrapolation from Resting Metabolic Rate to Total Energy Expenditure
Conversion of the measured RMR to an estimation of TEE is an important step in determining the energy goal for the patient’s nutrition support, but there are few data to guide the process. Two studies exist in which the TEE measured was 5 or 10% above RMR, but these percentages were means and therefore do not represent most patients, and the measurements were largely conducted in sedated patients. The percentages likely do not translate to non-sedated patients. Clinical judgment must be applied to the multiplication factor used in converting RMR to TEE. Part of that judgment should include the recognition that non-sedated patients who are moving typically move intermittently, rather than continuously, therefore limiting the overall multiplier to the RMR.
Medical Nutrition Therapy and Critical Illness
Scientific evidence supports the importance of the RDN as a member of the interdisciplinary team caring for critically ill patients. In many acute care settings, it is the RDN who carries out indirect calorimetry measurements as an important component of the nutrition care process.
The RDN plays an integral role on the interdisciplinary care team by determining the optimal nutrition prescription and developing the nutrition care plan for critically ill patients in all phases of illness. Based on the patient’s clinical status, plan for treatment, and comorbidities, the RDN monitors and evaluates the effectiveness of the nutrition care plan in promoting the patient’s nutritional health and quality of life. The dietitian adjusts the nutrition care plan as necessary to achieve desired outcomes.
Clinical judgment is needed to determine when the RMR will be a critical element of the nutrition care plan and likely to significantly impact important patient/client outcomes. Regardless of the method to determine RMR (i.e., estimated or measured), careful clinical judgment is essential to evaluate the RMR value and its application in an individual’s nutrition care and outcomes.
Guideline Development and Contributors
This guideline outlines the most current information on measurement of RMR in the critically ill patient. The recommendations developed in this guideline were based upon a systematic review of the literature in multiple practice areas. To view the guideline development and review process, click here. A summary of the evidence analysis is below:
- EE: Thermic Effect of Feeding (TEF)
- EE: Diurnal (Time of Day) Variation
- EE: Gas Collection Devices
- EE: Room Conditions
- EE: Body Positions
- EE: Duration of Rest Period
- EE: Duration of Measurement (Steady State)
- EE: Application of Respiratory Quotient (RQ)
The number of supporting documents for these topics is below:
- Recommendations: 13
- Conclusion Statements: 12
- Evidence Summaries: 8
- Article Worksheets: 21
All Academy guidelines are revised every five years. The literature search will begin for each guideline topic three years after publication to identify new research that has been published since the previous search was completed. An expert work group will convene to determine the need for new and revised recommendations. The updated guideline will be developed using the Academy of Nutrition and Dietetics Evidence Analysis Process (see Academy Evidence Analysis Manual from the Methodology tab).
New research may warrant a revision to a specific question or recommendation prior to the full project or guideline revision. Once identified, information is gathered and the EAL oversight committee will make a decision on the appropriate action.
Other Guideline Overview Material
For more details on the guideline components, click an item below:
- Scope of Guideline
- Statement of Intent and Patient Preference
- Guideline Methods
- Implementation of the Guideline
- Benefits and Harms of Implementing the Recommendations.