Basal metabolic rate
OVERVIEW
Basal metabolic rate is the body’s caloric consumption during the following conditions:
- at rest
- horizontal position – no muscular activity
- ambient temperature in the thermoneutral zone (ie. 25-30 C)
- 12 hours after the last meal
- related to body surface area
Total daily energy expenditure
= sum of basal metabolic rate + thermogenesis (shivering) + physical activity
-> normal per day = 25kcal/kg or 100kJ/kg
MEASUREMENT OF BMR
Direct calorimetry
- amount of heat produced by body over an hour via an insulated Atwater-Benedict chamber
Indirect calorimetry
- O2 consumption measured on the assumption that it is proportional to metabolic rate
- assumed that the respiratory quotient = 0.75 in the fasting state
- respiratory quotient = ratio of CO2 produced : O2 consumed (1.0 when fuel carbohydrates, 0.8 when protein, 0.7 when fat)
- patient breaths in and out of a Benedict-Roth bell spirometer filled with O2 & with a CO2 absorber
- rate of decline of the volume of spirometer = O2 consumption
Calculation of Resting Energy Expenditure
- using the Harris-Benedict equation
REE (males) = 66.5 + (13.7 x body weight in kg) + (5.0 x height in cm) (6.8 x age in years)
REE (females) = 66.5 + (9.6 x body weight in kg) + (1.7 x height in cm) (4.7 x age in years)
- use ideal body weight
- resting energy expenditure in calories
- multiply this by a stress factor to allow for effects of disease (no exercise = 1.2, very heavy exercise twice a day = 1.9)
- more accurate to measure REE by indirect calorimetry
Critical Care
Compendium
Chris is an Intensivist and ECMO specialist at the Alfred ICU in Melbourne. He is also a Clinical Adjunct Associate Professor at Monash University. He is a co-founder of the Australia and New Zealand Clinician Educator Network (ANZCEN) and is the Lead for the ANZCEN Clinician Educator Incubator programme. He is on the Board of Directors for the Intensive Care Foundation and is a First Part Examiner for the College of Intensive Care Medicine. He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives.
After finishing his medical degree at the University of Auckland, he continued post-graduate training in New Zealand as well as Australia’s Northern Territory, Perth and Melbourne. He has completed fellowship training in both intensive care medicine and emergency medicine, as well as post-graduate training in biochemistry, clinical toxicology, clinical epidemiology, and health professional education.
He is actively involved in in using translational simulation to improve patient care and the design of processes and systems at Alfred Health. He coordinates the Alfred ICU’s education and simulation programmes and runs the unit’s education website, INTENSIVE. He created the ‘Critically Ill Airway’ course and teaches on numerous courses around the world. He is one of the founders of the FOAM movement (Free Open-Access Medical education) and is co-creator of litfl.com, the RAGE podcast, the Resuscitology course, and the SMACC conference.
His one great achievement is being the father of three amazing children.
On Twitter, he is @precordialthump.
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