EE: Application of RQ (2005)

Citation:

Brandi LS, Bertolini R, Calafa M. Indirect calorimetry in critically ill patients: Clinical applications and practical advice. Nutrition. 1997;13(4):349-358

 
Study Design:
Narrative Review
Class:
R - Click here for explanation of classification scheme.
Quality Rating:
Neutral NEUTRAL: See Quality Criteria Checklist below.
Research Purpose:
[Interpret and apply how] indirect calorimetry can provide information that is essential to modulating and guiding energy intake and nutritional support.
Inclusion Criteria:
Criteria for article inclusion not specified.
Exclusion Criteria:
Criteria for article exclusion not specified.
Description of Study Protocol:

No searching procedures identified nor study quality assessed.

Types of critical care interventions and outcomes investigated were nutrition interventions that used indirect calorimetry to interpret feeding regimens in critically ill populations (including burn patients) with/without sepsis Intervening factors included mechanical ventilation settings and accuracy of IC measurement.

Data Collection Summary:

Outcome(s) and other measures

Information reported on from articles was: VO2, VCO2, RQ.

Equations to derive energy expenditure, and the effect of various nutrient substrates (CHO, pro, lipids) on RMR.

No data were combined and no analytic methods used.

Description of Actual Data Sample:

# articles included

# of articles identified: 71 articles

Forty-six out of 71 (64.7%) were primary research references; 5/71 (7%) were indirect calorimeter validation studies using varies research validation (i.e., computer modeling vs. comparison to other standards of measure). 6/71 was book citations and narrative reviews each were reported. One animal study on dogs was cited.

Studies represent acutely ill adults. Sample size ranges from n=7 (Bracco, 1995) to n=164 (Swinamer, 1990). Publication year range was a 1955 article by Farhi LE, Rahn H on “Gas store of body and unsteady state” in J Appl Physiol. 1955 to Brandi’s publication titled, Energy metabolism of thoracic surgical patients in the early postoperative period: effect of posture, in Chest. 1996.

Summary of Results:

CLINICAL APPLICATIONS

Although critically ill patients may be at rest on a bed, their metabolic rate is biased by the injury, condition of clinical care (e.g., fluid and nutritional therapy; use of sedatives and muscle relaxants, and medications that modulate intermediary metabolism.

[Source: Bursztein S, Elwyn DH, Askanazi J, Kinnery JM. Energy metabolism, indirect calorimetry and nutrition. Baltimore, 1989]

IC is the only method that provides accurate continuous measurement of energy expenditure.

Indirect Calorimetry & Hypermetobolic State

Most critically ill patients are sedated, artificially ventilated, and expending energy at a rate determined by their response to the acute illness, complications, and therapeutic procedures.

Vo NM, Waycaster M, et al evaluated the effect of caloric overfeeding with high carbohydrates (based on RQ values measured by IC) on morbidity and mortality in 24 postoperative critically ill pt who received parenteral nutrition for a total of 1088 d. This high calorie group (with RQ values >0.95) received 1.5 of measured RMR, while the normal caloric group (with RQ values <0.95) received 1.0. Septic episodes and mortality were greater in the overfed group vs. the group receiving calories are equal to measured energy expenditure.

[Source: Vo NM, Waycaster M, Acuff RV, et al. Effect of postoperative carbohydrate overfeeding. Am Surg. 1987;53:632. Poster presentation: sample size of n=24]

Indirect Calorimetry & Hypometabolic State

Hypometabolism could be due to technical errors in the application of IC, e.g., leaks in the connections, around endotracheal tubes, and chest tubes which can produce loss of volume.

Findings from three studies observed a different pattern of energy expenditure between patients with and patients without organ dysfunction: significantly lower energy expenditure and a tendency toward a condition of hypometabolism with multi organ dysfunction.

Identifying a hypometabolic response may be a predictor of the clinical outcome.

Acute Respiratory Failure

5 studies identify that the common element of the critically ill patient requiring mechanical ventilation for acute respiratory failure is a persistent hypermetabolism.

[Sources: Bartlett RH, Dechert RE et al., 1982; Swinamer DL, Predictive equation for assessing energy expenditure in mechanically ventilated critically ill patients, 1990; Vermeij CG, Feenstra et al. Day-to-day variability of energy expenditure in critically ill surgical patients, 1989; Weissman C, Kemper M, Day-to-day variation in the resting metabolic rate of mechanically ventilated critically ill patients, 1986; Forsberg E, Soop M et al. Energy expenditure and outcome in patients with multiple organ failure following abdominal surgery., 1991]

Malnutrition is a common complication in patients undergoing prolonged mechanical ventilation and can produce muscle fatigue and negative effects on the respiratory drive and integrity of pulmonary tissue.

[Sources: Doekel RC, Zwillich CH et al. clinical semisstarvation: depression of hypoxic ventilatory response. 1976; Kelly SM Rosa A et al. Inspiratory muscle strength and body composition in patients receiving total parenteral nutrition therapy., 1984]

From a clinical view, acute respiratory failure is characterized by hypermetabolism which is the major determinant of ventilatory demand; the degree of hypermetabolism is not predictable. In this category of patients, therefore, it is appropriate to perform multiple IC measures; maintaining RQ between 0.8-0.9.

Practical Advice

To obtain valid and clinically useful results, it is essential to:

  1. Gas exchange measurements should be avoided in patients under mechanical ventilation with high FIO2 (>60%). Ultman J, Bursztein S. Analysis of error in the determination of respiratory gas exchange at varying FIO2, 1981)
  2. Maintain a stable FIO2 and avoid fluctuations during the inspiratory and expiratory phases of mechanical ventilation
  3. No gas leaks from ventilatory circuit around tracheal or through the chest tubes.
  4. One study shows that 20-120 min is required to reach a new condition of stable CO2 store after a perturbation of the patient-ventilator system (e.g., bronchoaspiration, minute ventilation variation). An unpublished study (by Brandi LS) measured RQ changes for 0-120 mins before and after an abrupt change in minute ventilation (minute ventilation + 40%); Prior to the iperventilation RQ was 0.85 to 0.9. Ten minutes following the iperventilation, the RQ rose to 1.1 and gradually declined to 1.0 at 120 mins after but did not return to pre-iperventilation RQ levels. Authors suggest pt maintains a 60 min period of awareness & body temperature, and ventilatory variables should not be changed during the 90 min period prior to the measurement.
  5. Gas exchange measure must be avoided during acute changes of acid-base status since VCO2 does not reflect the metabolic cellular events; metabolic alkalosis are associated with an increase in VO2 [Source: Brandi, 1996].
  6. IC measures must be taken or must be carefully interpreted during procedure involving extracorporeal removal of CO2 (e.g. dialytic procedure, ultra filtration). [Source: vanLanshot et al in 1987 book by same author].
  7. Gas exchange measures must be sufficiently long to ensure a correct interpretation of the results obtained and to avoid periods of non-steady-state conditions.
  8. Measures must be avoided in critically ill patients during and after procedures with inhalation anesthetics; exhaled anesthetic gas renders the nitrogen method almost useless. [Aukburg, 1985 with use of computer modeling]
  9. All metabolic carts must be correctly calibrated and periodically tested in vitro.
  10. Gas exchange measures in spontaneously breathing patients must always be taken with a ventilated canopy. Use of masks, mouthpieces, and nose clips can modify the ventilatory response and induce errors in measure between 7-10% [Source: Forse, 1993]

Abstract results including quantitative data and statistics, especially effect sizes

Author Conclusion:

As stated by the author in body of report

  • “In critically ill patients, indirect calorimetry represents the most suitable, noninvasive method for the measurements of gas exchange and energy expenditure.
  • Several conclusions can be made to perform IC measures:
    1. In critically ill pt w/ prolonged ICU care to establish energy demand and avoid over-or underfeeding.
    2. Several indirect calorimetric measures to adequately establish a pattern of responses during acute phases of illnesses
    3. Of energy expenditure in critically ill patients who do not respond to nutritional treatments formulated on a fixed amount
    4. Of energy expenditure and RQ to avoid overfeeding particularly during periods of acute injury-related metabolic stress and periods of weaning.
    5. Maintain caloric balance at 1.0 times the measured RMR.
    6. To identify the true hypometabolic response that may be a predictor of pt outcome.
Funding Source:
Government: Italian Ministry of Public Education and Scientific Research
Reviewer Comments:
Note strengths and limitations of the review. Identify concerns that affect the validity of the review. How generalizable are the findings?
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? Yes
 
Validity Questions
  1. Was the question for the review clearly focused and appropriate? Yes
  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? Yes
  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? Yes
  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