Fluids, Electrolytes & Nutrition: Nutritional Assessment

Calorimetry

Direct Calorimetry (Whole-Room Calorimeter)

Direct Measurement of the Heat Generated by the Body to Determine Energy Expenditure
Gold Standard for Measuring Metabolic Rate
- Does Not Provide Any Information About the Nature of Substrates Being Oxidizes to Generate Energy
Requires Placing the Whole Body into a Large Chamber for Measurement
Not Practical in the Hospital Setting – Large, Expensive & Complex Engineering

Indirect Calorimetry (Metabolic Cart)

Measures Oxygen Consumed & Carbon Dioxide Produced to Estimate Energy Expenditure
Gold Standard for Determining In-Hospital Energy Requirements
Respiratory Quotient (RQ) = CO2 Produced / O2 Consumed
- Measure of Energy Expenditure
- Values:
  - RQ > 1.0: Overfeeding (Lipogenesis)
    - Management: Decrease Carbohydrates & Calorie Intake
  - RQ < 0.7: Starving (Ketosis)
    - Management: Increase Carbohydrates & Calorie Intake
- Values of Pure Utilization:
  - Carbohydrate/Glucose = 1.0
  - Protein = 0.8
  - Fat = 0.7
Use Has No Proven Benefit to Morbidity or Mortality

Serum Protein Half-Life

Used as Markers of Nutritional Status
*Values Can be Significantly Decreased During Inflammatory States & May Not Accurately Represent Nutritional Status

Half-Lives

Prealbumin: 2 Days
- Best Protein Indicator of Acute Nutritional Status
Transferrin: 1 Week
Albumin: 2-3 Weeks
- Deficiency (< 3.0 g/dL) is a Strong Risk for Morbidity and Mortality

Nitrogen Balance

Nitrogen Balance = Nitrogen Intake – Nitrogen Output
- Balance = (Protein/6.25) – (UUN + 4)
Nitrogen Intake = Protein (g) / 6.25
Nitrogen Output = Total Urine Nitrogen (TUN) + Insensible Loss
- Values:
  - Insensible Loss (In Feces & Sweat) = 2 g (Estimate)
  - Urinary Urea Nitrogen (UUN): Measured in Lab
  - Total Urine Nitrogen (TUN) = UUN + 2
    - 2: Estimate for Non-Urea Urinary Nitrogen Content
- Estimates:
  - Nitrogen Output = TUN + 2
  - Nitrogen Output = UUN + 4

Interpretation

Positive Balance: Anabolism
- Ex: Growth, Wound Healing, Pregnancy
Negative Balance: Catabolism
- Ex: Burns, Tissue Injury, Fever, Periods of Fasting

Limitations