Monday, January 23, 2012

Indirect Calorimetry for Nutrition Assessment

By: Angela Farris, MA

I've spent 12 weeks of my dietetic internship in my clinical rotation. I was lucky enough to spend a few hours of my last day at the hospital in the Pulmonary Function Lab learning about indirect calorimetry. By definition, indirect calorimetry is the amount of heat generated in an oxidation reaction by determining the intake of oxygen consumed (breathing in) and the amount of carbon dioxide out (breathing out). Using the correct equipment and computer program, a range of calculations will be formed revealing useful information for dietitians.

I entered the room and was told to sit down in a chair and relax; any movement can alter the results. I answered provided simple questions like my age, height, weight, and sex. Next I was fitted with a mask and my nose was plugged. The machine was turned on and for the next 5-7 minutes I took normal breaths. This simple test revealed some interesting information!

Here are the results from my indirect calorimetry:

REE (Kcal/day): 1672 *REE=Resting Energy Expenditure, or predicted amount of calories my body burns each day.

RQ: 1.35 *RQ=Respiratory Quotient, or the ratio of carbon dioxide I released to the oxygen I consumed. Goal should be between 0.85-1. (I was told my 1.35 could be related to my carb-loaded breakfast of cream of wheat & fruit)

VCO2 (mL/min): 289 *VCo2=average rate of elimination of carbon dioxide
VO2 (mL/min): 213 *VO2=average rate of elimination of oxygen

Dietitians can utilize indirect calorimetry to get an educated estimate of their patient's exact caloric needs using REE. In Critical Care it is a golden rule to not 'overfeed' the patient. Using indirect calorimetry in conjunction with professional judgement can possibly lower the time a patient is critically ill. Just another reason nutrition matters! :)

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