Study Design:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:
  • What is the overall effect of indirect calorimetry (IC) in critically ill patients when the IC test is consistently performed (due to adherence to a strict protocol by team members and using appropriate equipment) and metabolic measurements accurately interpreted and translated into an appropriate nutrition management?
  1. Identify the factors that affect the measurement of resting energy expenditure and respiratory quotient from indirect calorimetry
  2. Identify the potential sources of error that may occur when performing indirect calorimetry
  3. Describe how measurement errors may be avoided
  4. Describe the conditions necessary to obtain optimal results when performing metabolic tests
  5. Describe the clinical effect indirect calorimetry has had in the nutritional management of critically ill patients.
Inclusion Criteria:
  1. None discussed.
Exclusion Criteria:
  1. None discussed.
Description of Study Protocol:
Terminology Defined
  • Adequate nutritional support: Provision of nutrients in such a manner that optimal patient outcome is achieved
  • Adequate enteral tubefeeding: Provision of 2.5L in 72 hours (Atkinson S, Sieffert E, Bihari, 1998)
  • Indirect calorimetry: Weir equation
    Energy expenditure = (3.94 x VO2)+(1.11 x VCO2) such that 80% O2 consumption accounts for energy expenditure and 20% due to CO2 production (Weir JB, 1949)
  • Steady state or metabolic equilibrium: A five-minute interval during which VO2 and VCO2 change by less than 10% or the coefficient of variation for these two values is <5% (Feurer ID, Crosby LO, Mullen JL, 1984; Feurer ID, Mullen JL, 1986)
  • Respiratory quotient: Ratio of VCO2 to VO2; an associated physiologic range is from 0.67 to 1.3; hence, values outside this range are generated though error and beneficially used to validate IC measurement accuracy (Branson RD, 1990).
Data Collection Summary:
Outcome(s) and other measures
  • Why type of information was abstracted from articles  
  • How was it combined?
  • What analytic methods were used, if any?
Description of Actual Data Sample:
  • 36 included in publication
  • 10 of the 36 (28%) cited articles were written by the primary author
  • Eight (22%) are narrative reviews citations
  • Two (6%) each are abstracts and textbook citations
  • Approximately 17 (47%) are primary research citations  
  • The number of articles identified in search strategy or for consideration is not stated
  • Characteristics of the study participants include critically-ill, mechanically-ventilated suffering head injury, TPN and enteral nutrition patients and severely burned patients.
Summary of Results:
What Are the Main Results of the Review?

Factors that decrease value of IC
  1. Inadequate Enteral Tube Feeding (ETF) rates and strengths
  2. Underprescribing, slow startups, frequent cessations of feeds
    1. Physicians underorder ETF, prescribing only 65-78% of required caloric requirements, while 76-78% of prescribed calories are actually delivered [Adam S, Batson S, 1997 (UK study); Heyland D, Cook DJ, Winder B et al, 1995)
    2. Discontinuation r/t nursing care.
  3. Unknown percentage of goal calories required to maintain gut integrity and prevent bacterial translocation
  4. Ability to define “attenuation of stress response” and “reduce overall disease severity”
    1. Critically ill: Decrease in percentage of goal kcals infused; decrease in alb levels, P=0.042, 0.13 [Confounding variable: Worsening of disease?] (McClave SA, Sexton LK, Spain DA et al, 1999)
    2. Critically ill with mechanical ventilation: 0% on ETF had UGI BLDG, compared to 78% on acid-reducing TX alone [Pingleton SK, Hadzima SK, 1983 (retrospective)]
    3. Trauma: Patients receiving 59.2% of goal calories than controls (36.8%) (P=0.004) had a significant shift in the ratio of C-reactive protein to alb levels in first two-week hospitalization; decrease in fxn, decreased hospital stay,decreased rapid return to cognitive function (Taylor SJ, Fettes SB, Jewkes C et al, 1999)
    4. Burn patients: Incidence GI BLDG 8.3% without ETF vs. 3.3% in patients on ETF (P<0.05) (retrospective, multi-center) (Raff T, Germann G, Hartmann B, 1997)
    5. Critically ill: Overt GI bleed was 6% in controls vs. 5% in sucralfate and 5% in histamine2 blockers (i.e., no difference)
    6. Confounding possibility: 72% of controls maintained on ETF vs. 57% on ETF in histamine2 blockers. ETF had an RR of 0.35 (95% CI=0.16-0.76%; P=0.002) (Cook DH, Heyland DK, Griffith L et al, 1999)
    7. Adult respiratory distress SYN on ventilator: No difference if receiving some or adequate ETF. In 101 patients receiving adequate ETF, a significant difference was observed in patients receiving a sufficient volume of immune formula vs. controls given the standard formula (P<0.05) (Atkinson S, Sieffert E, Bihari, 1998).
Factors that increase IC accuracy
  1. Bedrest for 30 mins in thermo-neutral environment
  2. NPO after overnight fast for pt on oral diets and those on ETF or TPN should be placed on a continuous rate before and up through time of testing
  3. Pts on mech vent should have stable control settings for 90 mins prior to testing
  4. Analgesics should be given to control pain and sedatives to control anxiety
  5. Avoid interruptions
Factors that decrease IC accuracy
  1. Loosening steady state criteria
  2. If Coefficient of variation exceeds 9.0
  3. Adding 10% to the REE measured by IC for activity related to nursing care
  4. Adding adjustments for wound healing, growth, anabolism or diet-induced thermogenesis (McClave SA, Spain DA, Skolnick J et al, 1999).
Efficacy of nutritional support (i.e., expected results under ideal conditions)
  1. Ideal goal is to achieve 60-70% of the goal calories to maintain gut integrity, attenuate the stress response, stress prophylaxis and promote an effect from the immune-stimulating diet
  2. Measuring excesses
    1. Critically ill: Provided 110% of calories required; RQ exceeded 1.0 in 47.1% in parenteral nutrition patients (Guenst JM, Nelson LD, 1994); but 16.0% in EFT (McClave SA, Lowen CC, Kleber JM et al, 1998)
    2. An appropriate upper range of less than 150% of calories provided or required is suggested for goal settings. Patient with RQ of 1.0 increased significantly from 10% to 50% only when the degree of overfeeding exceeded 150% of calories required (McClave SA, Lowen CC, Kleber MJ et al, 1998).
  3. Maximize delivery via enteral route: FS formula, 25cc per hour and increasing 25cc per hour Q 8 H; Residual volume of 200 is the limit. Feeding should be continuted up to four hours per test or diagnositic procedure. Ordering a volume of feeding over 18 hours (allowing an off period to make U deficits) may further enhance delivery of ETF
  4. Maximize delivery via TPN: Identify goal, fat calories 15-30% of overall calories, feeding advance only if glucose is controllable <200mg/dL.
Abstract results including quantitative data and statistics, especially effect sizes, are not reported.
Author Conclusion:
  • "Efforts made to measure caloric requirements by IC are meaningless unless an equal effort is made to actually provide enough calories to match requirements through nutritional support"
  • "IC helps to “train” clinicians in accurate nutrition assessment and direct nutritional care"
  • "Focusing on goal calories and cumulative caloric balance is a valuable practice to assure therapeutic endpoints of ETF are obtained"
Funding Source:
University/Hospital: University of Louisville
Reviewer Comments:
  • Identifies theoretical consequences of inappropriate feeding.
  • Almost 30% of reference citations were by primary author; 30 references cited.
  • Uses many narrative reviews to make the case without descriptions of strengths or weaknesses of each review
  • Critical info regarding RQ (i.e., low sensitivity and limited efficacy) is based on a poster abstract.
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? ???
  4. Will the information, if true, require a change in practice? ???
Validity Questions
  1. Was the question for the review clearly focused and appropriate? ???
  2. Was the search strategy used to locate relevant studies comprehensive? Were the databases searched and the search termsused described? ???
  3. Were explicit methods used to select studies to include in the review? Were inclusion/exclusion criteria specified andappropriate? Wereselectionmethods unbiased? ???
  4. Was there an appraisal of the quality and validity of studies included in the review? Were appraisal methodsspecified,appropriate, andreproducible? ???
  5. Were specific treatments/interventions/exposures described? Were treatments similar enough to be combined? ???
  6. Was the outcome of interest clearly indicated? Were other potential harms and benefits considered? ???
  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? ???
  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? Yes
  9. Are conclusions supported by results with biases and limitations taken into consideration? Are limitations ofthe review identified anddiscussed? ???
  10. Was bias due to the review's funding or sponsorship unlikely? ???