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Citation:
 
Study Design:
Class:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:
  • Define energy expenditure and describe how chemical energy is changed to mechanical energy for muscle contractions, thermal energy for regulation of body temperature, and electrical energy for brain and nerve activity.
  • RQ: The ratio of carbon dioxide expired to the amount of oxygen inspired.
Inclusion Criteria:
  • None specified.
Exclusion Criteria:
  • None specified.
Description of Study Protocol:
  • None specified.
Data Collection Summary:

Outcome(s) and other measures

  1. Defining RQ and physiological range
  2. IC equipment types and how they operate
  3. How to complete a measure
  4. Troubleshooting and interpreting measures.
Description of Actual Data Sample:

28 references

  • Number of articles identified not specified
  • There were ~15 primary research articles dating from 1949 (Weir JB article) to article by Makk, et al, in 1990. The latter had 26 in study. Sample sizes ranged from 8 to 61 individuals.
  • Participants in the studies reflected critically ill patients. Two studies reported studies completed using children.
  • Four narrative reviews were cited (Foster G, Knox LS, Depmsey DT, Mullen JL, 1987; Feurer ID, Fullen JL, 1986; Peronnet I, Massicotte D, 1991; Branson JD, 1990). There were two animal studies cited.
Summary of Results:

REE, BEE, & TEE

REE accounts for 75% to 90% of total energy expenditure; the remainder is accounted for by thermogenesis of foodstuffs, shivering, and physical activity. (Elwyn DH, Kinney JM< Askanazi J. Energy expenditure in surgical patients, Surg Clin North Am, 1981; Feurer ID, Mullen JL. Bedside measurement of resting energy expenditure and respiratory quotient via indirect calorimetry, Nutr Clin Pract, 1986.)

INTERPRETING THE RESPIRATORY QUOTIENT

  • The RQ should be in physiologic range and consistent with the patient’s history and feeding.
  • If RQ:
    >1, then the total caloric load should be decreased
    =1, then decrease CHO and/or increase lipid
    >0.82, then, increase total energy intake.

PHYSIOLOGICAL CAUSES (I.E., OXIDATION) FOR RQ <0.71

  • Oxidation of ethanol and ketones
  • Lipolysis
  • Underfeeding
  • Diabetes mellitus
  • Ketoacidosis
  • High rates of urinary glucose excretion.

NON-SUBSTRATE UTILIZATION CAUSES FOR RQ<0.71

  • Hypoventilation and technical difficulties associated with actual measurement.

PHYSIOLOGICAL CAUSES (I.E., OXIDATION) FOR RQ>1.0

  • Excess CO2 production
  • Hydrogen-ion buffering by bicarbonate-generating CO2
  • Lipogenesis
  • Overfeeding.

NON-SUBSTRATE UTILIZATION CAUSES FOR RQ>1.0

  • Hyperventilation
  • Metabolic alkalosis
  • Postoperative period 6-8 hr after general anesthesia
  • Adaptation to ventilator settings.
  • Immediately following a meal, RQ is 1.0; during starvation it is 0.83; and in diabetes mellitus it is 0.71
    [Sources for this statement: Two animal models, 1 book; and primary studies of:
    Schultz Y, Ravussin E. Respiratory quotients lower than 0.70 in ketogenic diets. Am J Clin Nutr. 1980;33:131C.
    Frayn KN. Calculation of substrate oxidation rates in vivo from gaseous exchange. J Appl Physiol. 1983;55:628-634; Weissman C, Kemper M, Askanazi J, Hymen AL, Kinney JM. Resting metabolic rate of the critically ill patient: measured versus predicted. J Anesthesiol. 1986;64:673-679.; Anderson CF, Loosbrock LM, Moxness KE. Nutrient intake in critically ill patients: too many or too few calories?, Mayo Clin Proc, 1986)]

CLOSED CIRCUIT SYSTEMS

The major advantage of the closed system is that inspired minute ventilation can be measured rather than calculated using the Haldane equation. In ventilated patients with high forces inspiratory oxygen (FIO2), the Haldane equation becomes less accurate as the denominator (1-FIO2) approaches zero. Therefore, there is no FIO2 upper limit with a closed system. O2 analyzers are not required.

Breathing resistance increased; and inspiratory time is prolonged and may increase work of breathing by 10% Branson RD, Hurst JM, Davis K, Bower R. Comparison of open-circuit and closed-circuit methods for measuring oxygen consumption. J Parenter Enter Nutr, 1989; Borwoning JA, Linberg SE, Turney S, Chodoff P. The effects of fluctuating FIO2 on metabolic measuremtns in mechanically ventilated patients. Crit Care Med, 1982)

Closed-circuit systems are affected by changes in lung volume or leaks in the system. Since O2 consumption is interpreted as a volume loss per unit time, any leak will be interpreted as a change in VO2.

OPEN CIRCUIT SYSTEMS

  • These should not be used for patients receiving FIO2>60% because the Haldane transformation is used in the calculation.
  • Since oxygen analyzers are used, open-circuit systems are susceptible to fluctuations in FIO2. Many systems provide a display of oxygen, CO2 and flow to permit direct monitoring of leak detection, FIO2 stability, and system functioning. Breath-by-breath systems that measure for FIO2 each breath minimize changes caused by fluctuating FIO2 because of the frequent sampling.

OTHER CONSDERATIONS

  • Patients with incompetent endotracheal tube cuffs, leaking chest tubes, bronchopleural fistulas should be be measured because complete gas collection cannot be guaranteed.
  • Water vapor must be eliminated from the gas before it reaches the analyzers, which may be accomplished by heating or cooling the sample or using desiccants, water traps, or special tubing.

PERFORMING INDIRECT CALORIMETRY, Test validity

  • The overall RQ physiologic range is 0.67 to 1.3 (Source: Branson JD. The measurement of energy expenditure: instrumentation, practical considerations, and clinical application. Respir Care. 1990; 640-659).
  • The physiologic range of VO2 is 1.7 to 3.4 mL/min?kg, and the range of VCO2 is 1.4 to 3.1 mL/min/kg (Source: Bursztein S, Elwyn DH, Askanazi J, Kinney JM. Energy metabolism, Indirect Calorimetry, and Nutrition. Baltimore, MD: Williams & Wilkerns; 1989;64-65,219-220).
  • The measurement should be clinically evaluated. For example, an RQ>1.0 in a fasting patients or a minute ventilation that is<5 L or >10 L probably signifies an invalid test.

INTERPRETING IDC MEASRUEMENTS

  • RQ should be in the physiologic range and consistent with the patient’s history and feeding. IF RQ is? 1.0, decrease total caloric intake and adjust carbohydrate-to-lipid ratio. If RQ is <0.812, increase total caloric intake.
  • RQ can be used as a clinical guide where weight gain is desirable.
Author Conclusion:
  • IDC can be a useful tool in the provision of nutrition support;
  • The measurement must be obtained using good technique to ensure an accurate test. The dietetics professional must understand the methodology to evaluate the validity of the test.
Funding Source:
University/Hospital: Cleveland Clinic Foundation
Reviewer Comments:
  • Good overview on RQ definition, how it is established and interpreting.
  • Findings generalizable to hospitalized critically ill patients.
  • Weakness includes a publication year of 1997 and most current cited literature was 1990.
Quality Criteria Checklist: Review Articles
Relevance Questions
  1. Will the answer if true, have a direct bearing on the health of patients? Yes
  2. Is the outcome or topic something that patients/clients/population groups would care about? Yes
  3. Is the problem addressed in the review one that is relevant to dietetics practice? Yes
  4. Will the information, if true, require a change in practice? N/A
 
Validity Questions
  1. Was the question for the review clearly focused and appropriate? No
  2. Was the search strategy used to locate relevant studies comprehensive? Were the databases searched and the search termsused described? No
  3. Were explicit methods used to select studies to include in the review? Were inclusion/exclusion criteria specified andappropriate? Wereselectionmethods unbiased? No
  4. Was there an appraisal of the quality and validity of studies included in the review? Were appraisal methodsspecified,appropriate, andreproducible? No
  5. Were specific treatments/interventions/exposures described? Were treatments similar enough to be combined? Yes
  6. Was the outcome of interest clearly indicated? Were other potential harms and benefits considered? No
  7. Were processes for data abstraction, synthesis, and analysis described? Were they applied consistently acrossstudies and groups? Was thereappropriate use of qualitative and/or quantitative synthesis? Was variation in findings among studies analyzed? Were heterogeneity issued considered? If data from studies were aggregated for meta-analysis, was the procedure described? No
  8. Are the results clearly presented in narrative and/or quantitative terms? If summary statistics are used, are levels ofsignificance and/or confidence intervals included? No
  9. Are conclusions supported by results with biases and limitations taken into consideration? Are limitations ofthe review identified anddiscussed? No
  10. Was bias due to the review's funding or sponsorship unlikely? Yes