- Click here for explanation of classification scheme.

fTo address metabolic measurement during mechanical ventilation

Population studied

Mechanically ventilated patients in the hospital or extended care facility settings.

No criteria mentioned.

No criteria mentioned.

There were four members on the Mechanical Ventilation Guidelines Committee. All members were Registered Respiratory Therapists (RRT) and one has attained a PhD.

 

Outcome(s) and other measures

IC Outcomes reported:

1. (9.2) Interpretation and confirmation/manipulation of patient nutritional support regimen by physician or nutritionist based on measurement results
2. (9.3) Successful manipulation of the mechanical ventilator settings and/or hemodynamic management based on the measurement of the VO₂

Articles were summarized in the following categories: patient characteristics of whom would benefit from IC, contraindications, hazards/complications, procedural accuracy, types of IC, monitoring (and frequency) and infection control. Literature citations were listed where relevant. No analytic methods were used.

56 articles were cited

(Note: Elia citation listed as reference #2 and #34)

There were 31 primary research articles, 11 reviews, 2 textbook references, and 2 abstract proceeding citations. There were 8 in-vitro validation studies and one Centers for Disease Control guidelines describing Universal Precautions for prevention of transmission of human immunodeficiency virus, hepatitis B and other bloodborne pathogens.

• Sample sizes ranged from n=2 “young” patients (Dark DS Pingleton SK, Kerby GR. Hypercapnia during weaning: a complication of nutritional support. Chest. 1985;88:141-143) to the largest sample size of 100
• (Foster GD, Knox LS, Dempsey DT, Mullen JL. Caloric requirements in total parenteral nutrition. J Am Coll Nutr. 1987;6:231-253). Using abstracts, there were 5 studies where the sample size wasn’t available.

6 articles were published before 1980; 16 were published 1980-1985, 32 published between the years 1986-1990; and 1 was published between 1991-1994.

Diseases studied included neurologic trauma (8 citations), paralysis (citation), COPD (4 citations), acute pancreatitis (1 citation), cancer with residual tumor burden (1 citation), multiple trauma (3 citations), amputations (1 citation), patients in whom height and weight cannot be accurately obtained (1 citation), and patients who fail to respond adequately to estimated nutritional needs (1 citation); new patients on home TPN (1 citation); patients who are unable to eat and who require mechanical ventilation for >5 days (1 citations), transplant patients (1 citation), and severely hypermetalolic or hypometabolic patients (no citation).

Calculation of RQ and REE

[VO₂ (3.941)+VCO₂ (1.11)] 1440 min/day

No quantitative analysis or effect sizes reported

QUALITATIVE RECOMMENDATIONS

Risk of patient harm
6.1&2: Closed circuit calorimeters may reduce alveolar ventilation due to increased compressible volume of breathing cirucuit (4 citations representing 1 review, 2 equipment validation and 1 primary research article with n=21 patients), trigger sensitivity of the ventilator and result in increased patient breathing work (same 4 citations).

6.3: Short-term disconnect may result in hypoxemia, bradycardia, and pt discomfort (2 citations)

6.4: Inappropriate calibration or system setup results in incorrect patient management (3 citations where 2 are review articles and 1 is a book chapter)

Procedural Limitations

Inaccurate due to
7.1: Patient condition or bedside procedures/activities (3 references w/two by same researcher)

7.2: Gas leaks from the patient, ventilator circuit, tracheal tube cuffs or uncuffed tubes, chest tubes or bronchopleural fistula (2 review articles and one primary research article with 9 subjects)

7.3: Peritoneal and hemodialysis (2 review articles, 1 textbook article and one primary study n=15)

7.4: REE and RQ related to pen circuit measurement error caused by

• .1) Unstable oxygen concentration delivered w/breath or breath to breath d/t changes in gas pressure and ventilator blender/mixing characteristics (1 primary research article, 1 equipment validation study)
• .2) Flow of delivered O₂>0.60 (same as 0.1)
• .3) Inability to separate inspired and expired gases due to ventilation system (2 studies)
• .4) Presence of anesthetic gases
• .5) Water vapor
• .6) Inappropriate calibration (1 article published 1979)
• .7) Connect to IC to certain ventilators interferes with triggering mechanism, pressure measurement or ventilator maintenance (Review article)
• .8) Total circuit flow exceeds IC internal gas flow with dilutional principle (peds study)

7.5: Close circuit measurements caused by:

• .1) Short measurement period not allowing for CO₂absorber life and VCO₂
• .2) Functional residual capacity resulting in spirometer volume changes not associated with VO₂ (1 review, 2 validation studies, 1 primary research article)
• .3) Gas leaks during spontaneious breathing measurements that add to system volume and cause erroneously low VO₂readings (same as 0.2)
• .4) Increased compressible volume that prevents adequate tidal volume resulting in alveolar hypoventilation changes in VCO₂VO₂ (same citations as 0.2)
• .5) Increased compressible volume and resistance results in difficulty triggering the ventilator and increased the work of breathing (same citations as 0.2)

9.0: Test Quality Assessments

• .1) Compare to nutrition intake (1 textbook, 4 reviews)
• .2) Normal physiologic range 0.67-1.3 (same as 0.1)
• .3) Measured VO₂±10% mean value and measured VCO₂±6% mean value (1 review)
• .4) Environment during measurement w/patient lying in bed, aware of his/her surroundings (1 primary research article; n=17 patients)

10.0: Calibration Procedures

10.1: Open or closed-circuit IC:

• .1) Gas mixture = Gas concentration measured clinically (same as 9.1 references)
• .2) Calibrate on measurement day
• .3) If IC measurements suspect or instable repeated measurement, an in-vitro test or measuring healthy volunteer is appropriate

10.2: Open-circuit methods need to stabilize flow delivered O₂10.3 Isolation valve, double-piloted exhalation valve or other device that separates inspiratory aand expiratory flow should be used when continuous flow in the ventilator circuit is used (1 citation)

10.4: Personnel training needs to include documented ability to:

• .1) Calibrate, operate, and maintain an indirect calorimeter
• .2) Operate mechanical ventilator, including air-oxygen blending system, spontaneous breathing mechanisms, and alarm/monitoring functions
• .3) Recognize metabolic measurement values withing the normal physiologic range and evaluate the results in light of the patient’s current nutritional/clinical status
• .4) Assess patient hemodynamic and ventilatory status and make recommendations on appropriate corrective/therapeutic maneuvers to improve or reverse pt’s clinical course

RRT, CRTT, RN, or RPFT is desirable

(No references for personnel training)

11.0: Monitoring

11.1: Monitoring during test:

• .1)Clinical observation of resting state
• .2)Values correspond to clinical situation
• .4)Equipment function
• .5)Measured VO₂±10% of the mean value and measured VCO₂±6% of the mean value

12.0: Monitoring frequency

1.0-1.2 (and 12.2) Rapidly changing clinical course due to hemodynamic instability, spiking fevers, immediate postoperative period or those being weaned from mechanical ventilation (1 primary research article, n=17)

13.0: Infection Control Guidelines (CDC Universal precautions):

13.1: Equipment is contaminated with blood or other body fluids

13.2: Appropriate use of barriers and handwashing

13.3: Tube used in direct expiratory gas from the ventilator to the IC should be disposed or cleaned between patients

13.4: Inspiratory limb connections of the circuit proximal to the humidifier should be subjected to high-level disinfection b/t pt

13.5: Bacteria filters may be used to protect equipment in inspired and expired lines, but caution is used to prevent moisture from increasing filter resistance resulting in poor gas sampling flow or increased resistance to exhalation.

“The measurement of REE in mechanically ventilated patients has been shown to be more accurate than published formulas used to predict REE, to reduce the incidence of overfeeding and underfeeding, and to decrease costs associated with total parenteral nutrition (TPN). Measurement of REE and RQ has been shown to be helpful in designing nutritional regimens to reduce VCO₂in patients with chronic obstructive pulmonary disease and patients requiring mechanical ventilation. Studies demonstrating improved outcome, improved weaning success, or shorter ICU/hospital stays are lacking.”

The strength of these guidelines is that the Committee members are experienced researchers whom have completed many Indirect Calorimeter measurements. The cited references reflect small sample sizes and the patient populations studied represent clinical settings between 1980-1990. There are few nutrition guidelines recommended (e.g., compare to what patient intake is) cited. The patient population on total parenteral nutrition has the most IC citations but needs updated primary research articles. The process described by experienced RPT is also generalizable with some caution as updated studies and nutrition assessment, intervention and outcomes are needed. Of note, Weir equation does NOT match project definition.