Indirect Calorimetry

Definiton

• A method of assessing a patient’s metabolic and nutritional status

• Measurement of the number of calories that is used by the body during metabolism

Purpose

• To estimate resting energy expenditure (REE) over usually a 24-hour period (kcal/day), VO2 and VCO2

• Indicated when the nutritional status of the patient is in question

• For patients at risk for ventilatory failure

• Determine the utilization of substrates

(when reviewed with urinary nitrogen (UN)

Equipment

• Spirometer

• Metabolic cart

• Unidirectional valve with mouthpiece and nose clips or

• A ventilated hood or canopy or connector for adaptation to a

ventilator

Techniques

open circuit or closed circuit

• OPEN CIRCUIT MOST USED TECHNIQUE

Open Circuit

• Uses a mixing chamber, or breath by breath measurements (like exercise tests).

• Pt. connected to system by a standard directional valve with mouthpiece and nose clips, or a ventilated hood/canopy

• Technique of choice for ventilated patients:

– Usually, breath by breath analysis of inspired

and expired gas

• Canopy/hood allows long term measurements

Close Circuit

• The patient rebreathes from a volume type spirometer with carbon dioxide absorbers

• Two types of closed-circuit techniques, oxygen depletion and oxygen replacement

• Needs an added CO2 analyzer to measure CO2 production

• With ventilated patients, spirometer system is connected between the patient and ventilator

• Ventilator ventilates the spirometer which then ventilates the patient. (usually need bellows type spirometer in a fixed volume container)

Preparation for Testing

• Patient must be recumbent or supine for 20 –30 minutes prior to testing and stay quiet during the test

• Must fast for 2 – 4 hours prior or be on continuous feedings not bolus feeding

• Must have a normal temperature (1 degree could change REE by 13%)

• Medications that alter metabolism should be avoided

Preparation for testing con’t

• Collection must continue long enough for steady state conditions to occur (usually 10 -15 min but may be as short as 5 minutes)

– Steady state is: Vo2 and Vco2 should not vary more than 5% from mean & RQ should be 0.67 – 1.30

• Patients on ventilators:

– No change in vent settings for 1-2 hours prior or during

– FiO2 > 0.60 may cause errors in Vo2

– Watch for leaks (Circuit, chest tubes or ETT)

– Valves needed if using continous flow mode

• Calibrated at least daily, preferably before each test

• Gas analyzers should be calibrated at FiO2 likely to

be used

Significance of Testing

• Estimates resting energy expenditure(REE), reported in kilocalories(kcal)

• REE is normally 2/3 of your daily caloric requirements

• Measurement of exhaled volume and exhaled gases, VO2 , VCO2, VE, allows for calculation of the respiratory quotient

• Respiratory quotient indicates how the calories are being consumed

What’s the respiratory quotient (RQ) varies from

from 0.71 to 1.0 depending on the substrates being

metabolized

– Carbohydrates 1.0

– Lipids 0.71

– Proteins 0.82

• Detects undernourishment, overnourishment, or

use of inappropriate substrate

Ketosis cause by extreme fasting or diebtic ketoacidosis results in RQ of —

< 0.7

Most commonly, low RQ is due to calibration
error of CO2 & O2 analyzers

REE values

• REE < predicted = hypometabolic state or technical error

• REE > last 24-hour intake = underfed or febrile

• REE < last 24-hour intake = overfed

Undernourishment

• Negative energy balance = caloric expenditure in excess of caloric intake

• Fat stores and protein from muscle breakdown to contribute to metabolism (not good!)

Overnurishment

• Any substrate supplied in excess of energy requirements

• Excess lipid or carbohydrate calories are stored as fat

pulmonary disease

• Excess carbohydrates results in increased CO2 levels

• Causing increased ventilatory load on the patient

• There may also be atrophy of ventilatory muscles measured

by the protein portion of calorimetry

Technical Considerations

• Accuracy of gas analysis

• Accurate measurement of expired volumes

• Achieving steady state*

what technical consideration need to be made for supplemental oxygen and Positive pressure

• Supplemental oxygen may cause problems especially on ventilated patients as the blenders/proportional solenoids may not deliver accurate concentrations

• Positive pressure changes on the ventilators also must be taken into consideration during calculations as pressure affects analyzer function

Patient factors to considered before implementation of Rehab

• Effect of the disease on the quality of life

• Is physical activity reduced

• Changes in occupational performance

• Dependence vs. Independence in daily living

• Psychosocial status

• Use of medical resources

• Other medical conditions

• Pulmonary function assessment

• Smoking history

• Patient motivation

• Commitment and active participation

• Patient transportation needs

• Financial resources

Type of breathing Retraining used for rehab

• Pursed lip

• Diaphragmatic

• Cough techniques

Role of Exercise

• Improved appetite

• Better sleep

• Enhance tolerance to dyspnea

• Ability to achieve a higher work level

Role of Metabolic Assessment

• Assess the nutritional status of the patient

• A good nutritional state improves muscle function in COPD

patients