Ch 2: Energy Flashcards
Penn State equation has been validated as one of the most accurate ways of calculating energy expenditure up to a BMI of:
80
Use of glucose, fat, protein in metabolism
- Glucose used after meals
- Fat stored for later oxidation
- Protein used for structural and funtional (not oxidative) purposes
TEE
- Basal metabolic rate (BMR)
- Energy required for thermogenic effect of digestion
- Energy expenditure associted with physical activity
Difference between BMR and RMR?
BMR = basal metabolic rate
RMR = resting metabolic rate
BMR = fasted state; immediately upon waking up and before any physical activity
RMR = fasted state, but some movement allowed (dressing, walking) before testing
RMR is determined by
body size and composition
Sex and age also play a part to a lesser degree
Thermogenic effect of digestion
Increase in metabolic rate s/p PO intake
5-10% increase in TEE
Is the thermogenic effect of digestion induced in TF patients on continuous feeds?
No
** Healthy patients
Where is hypermetabolism noted?
People who are chronically or acutely ill
Why are RMR equations for healthy people (Mifflin, Harris-Benedict) routinely found to be inaccurate in critically ill patients?
Critically ill patients are hypermetabolic
What determines the RMR?
inflammatory response or the actual illness?
Inflammatory response
Direct calorimetry
Measures heat and chemical energy release from the body
Requires patient in a chamber that is thermally isolated from the outside - this measures the heat released into the air of the chamber the patient is in
Where is direct calorimetry most appropriately used?
Study of healthy subjects in research and academic environments
Indirect Calorimetry
measures respiratory gas exchange to estimate energy metabolism
Why is the energy loss from urea excretion in urine usually ignored during IC measurements?
Not found to significantly alter the accuracy of IC measurement
Respiratory quotient values
Metabolic range of RQ is 0.67 to 1.3
- Fat = 0.7
- Protein = 0.8
- CHO = 1.0
- RQ of >1.0 = net fat synthesis, taken as an indicator of overfeeding
– Suggest excessive CHO or calorie provision that can result in increased CO2 production and cause difficulty weaning from mechanical ventilation. - A RQ of <0.7 might suggest underfeeding and use of ketones as a fuel source.
Indications for IC
- BMI <20.5
- BMI > 80
- Concern about overfeeding a pt with unexplained high vent req/who can’t be liberated from vent
- Unwanted weight loss over time not explained by volume status and pt receiving ~100% EEN
- Massive tissue loss from amputation
- Preadmission fluid overload (ascites, volume resuscitation, third spacing) without reliable BW
Contraindications for IC
- Air leak (chest tube, cuff leak, any other leak in vent circuit, leak around face masks/canopies)
- ECMO
- HD (during and several hours later)
- FIO2 >60%
- SBT patients:
1) reliant on supplemental O2
2) inability to cooperate with measurement
3) Claustrophobia or anxiety about the measurement
What should be done prior to IC measurement?
- check for recent vent changes x30 minutes before reading
- recent nursing care (movement/pain) within last 30 minutes
PO/TF and IC
- PO: test after 7 hour fast
- Bolus feeds: test 4 hours after feed
How long are IC results useful for in critically ill patients?
3-4 days
Weekly IC studies are no more accurate over time vs predictive equations
Mifflin St Jeor
& OBESITY
Accuracy of equation falls when applied to obese people
kcal/kg ratio
not an accurate way to predict RMR in critically ill patients
This is because it does not consider age, sex, altered physiology
Penn State
Accurate in:
* Morbidly obese pts (80% accuracy up to 80 BMI)
* Brain injuries
* Barbituate coma
Lower accuracy in:
* Low BMI (<20.5)
* Cystic fibrosis (most of these pts have a low BMI which is likely the underlying reason)
