Ch 2: Energy

Question 1

Penn State equation has been validated as one of the most accurate ways of calculating energy expenditure up to a BMI of:

Answer 1

80

Question 2

Use of glucose, fat, protein in metabolism

Answer 2

• Glucose used after meals
• Fat stored for later oxidation
• Protein used for structural and funtional (not oxidative) purposes

Question 3

TEE

Answer 3

1. Basal metabolic rate (BMR)
2. Energy required for thermogenic effect of digestion
3. Energy expenditure associted with physical activity

Question 4

Difference between BMR and RMR?

BMR = basal metabolic rate
RMR = resting metabolic rate

Answer 4

BMR = fasted state; immediately upon waking up and before any physical activity

RMR = fasted state, but some movement allowed (dressing, walking) before testing

Question 5

RMR is determined by

Answer 5

body size and composition

Sex and age also play a part to a lesser degree

Question 6

Thermogenic effect of digestion

Answer 6

Increase in metabolic rate s/p PO intake

5-10% increase in TEE

Question 7

Is the thermogenic effect of digestion induced in TF patients on continuous feeds?

Answer 7

No

** Healthy patients

Question 8

Where is hypermetabolism noted?

Answer 8

People who are chronically or acutely ill

Question 9

Why are RMR equations for healthy people (Mifflin, Harris-Benedict) routinely found to be inaccurate in critically ill patients?

Answer 9

Critically ill patients are hypermetabolic

Question 10

What determines the RMR?
inflammatory response or the actual illness?

Answer 10

Inflammatory response

Question 11

Direct calorimetry

Answer 11

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

Question 12

Where is direct calorimetry most appropriately used?

Answer 12

Study of healthy subjects in research and academic environments

Question 13

Indirect Calorimetry

Answer 13

measures respiratory gas exchange to estimate energy metabolism

Question 14

Why is the energy loss from urea excretion in urine usually ignored during IC measurements?

Answer 14

Not found to significantly alter the accuracy of IC measurement

Question 15

Respiratory quotient values

Answer 15

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.

Question 16

Indications for IC

Answer 16

• 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

Question 17

Contraindications for IC

Answer 17

• 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

Question 18

What should be done prior to IC measurement?

Answer 18

• check for recent vent changes x30 minutes before reading
• recent nursing care (movement/pain) within last 30 minutes

Question 19

PO/TF and IC

Answer 19

• PO: test after 7 hour fast
• Bolus feeds: test 4 hours after feed

Question 20

How long are IC results useful for in critically ill patients?

Answer 20

3-4 days

Weekly IC studies are no more accurate over time vs predictive equations

Question 21

Mifflin St Jeor

& OBESITY

Answer 21

Accuracy of equation falls when applied to obese people

Question 22

kcal/kg ratio

Answer 22

not an accurate way to predict RMR in critically ill patients

This is because it does not consider age, sex, altered physiology

Question 23

Penn State

Answer 23

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)