Current Evidence for Estimating Energy Requirements

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Current Evidence for Estimating Energy
Requirements
Clare Soulsby, Research Dietitian
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Main components of energy expenditure

• basal metabolic rate (BMR)
• alteration in BMR due to disease process (stress
  factors)
• activity
• diet induced thermogenesis (DIT)

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Estimating BMR controversies

• basal metabolic rate (BMR) vs. resting energy
  expenditure (REE)
• prediction equations vs. measured energy
  expenditure (MEE)

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Conditions essential for measuring BMR

• post-absorptive (12 hour fast)
• lying still at physical and mental rest
• thermo-neutral environment (27 29oC)
• no tea/coffee/nicotine in previous 12 hours
• no heavy physical activity previous day
• gases must be calibrated
• establish steady-state ( 30 minutes)
• if any of the above conditions are not met REE

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Estimating BMR controversies

• basal metabolic rate (BMR) vs. resting energy
  expenditure (REE)
• prediction equations vs. measured energy
  expenditure (MEE)

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Estimating BMR prediction equations

• may over or under-estimate (compared with MEE)
• inadequately validated
• poor predictive value for individuals
• open to misinterpretation
• (Cortes Nelson, 1989 Malone, 2002 Reeves
  Capra, 2003)

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Estimating BMRwhich equation?

• Harris-Benedict
• Schofield Equations
• disease specific eg Ireton Jones
• Kcal/kg

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Estimating BMR Harris Benedict Equations

• Developed in 1919
• From data collected between 1909 and 1917 (Harris
  Benedict 1919)
• Study population
• 136 men mean age 27 9 yrs, mean BMI 21.4 2.8
• 103 women mean age 31 14 yrs, mean BMI 21.5
  4.1
• Tends to overestimate in healthy individuals
  (Daly 1985, Owen 1986, Owen 1987)

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Estimating BMR Schofield Equations

• developed in 1985 (Schofield 1985)
• meta analysis of 100 studies of 3500men and 1200
  women
• studies conducted between 1914 and 1980
  (including Harris Benedict data)
• 2200 (46) subjects were military Italian adults
• 88 (1.2) subjects were gt60 years
• SE 153-164kcal/d (women) 108 -119kcal/d (men)
  (Schofield 1985)

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Estimating BMR disease specific equations

• developed for specific patient groups (Ireton
  Jones 1992, Ireton Jones 2002)
• advantage over Schofield/ HB equations
• Schofield /HB estimate BMR of a healthy
  individual then necessary to adjust for disease
  using a stress factors
• disease specific equations include patients in
  their database so aim to more accurately reflect
  BMR of hospitalised patients

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Estimating BMR Ireton-Jones energy equations

• ventilated and breathing ICU patients
• 3 x 1 minute measurements 200 patients
• unclear whether measurements took place during
  feed infusion/ after treatment etc
• 52 burns, 31 trauma
• validation studies, IJEE had a better agreement
  with MEE
• HBx1.2, HBx1.3, 21kcal/kg

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Estimating BMR

• Schofield equation derived using meta analysis
• greater power than small/ local studies
• compiled from unstructured data set obtained for
  diverse reasons
• problems with sampling assumptions
• accuracy approx 15
• disease specific equations useful in some
  circumstances

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Estimating BMR

• what about
• the elderly?
• the obese?

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Estimating BMR the elderly

• Original Schofield equations
• only 88 (1.2) of subjects gt60 years
• particularly unsuitable for gt75yr
• included data on subjects from the tropics
• Revised equations for the elderly
• published in the 1991 COMA (DH 1991)
• include additional data from 2 studies 101
  Glaswegian men (60-70yr) 170 Italian men and 180
  Italian women
• excluded data collected in the tropics

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Estimating BMR Obesity

• equations (such as Schofield) are linear
• weight increases linearly with estimated BMR
• may overestimate in obese

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Estimating BMR obesity
BMI of Schofield database of UK population (DOH 1999)
gt 25 14.6 40.8
gt 30 4.5 9.7
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Estimating BMR Obesity

• obese data primarily obtained from 2 groups
• Burmese hill dwellers
• retired Italian military
• there were significant differences in weight/ BMR
  association between groups, Italian group showed
  greatest difference
• obese subjects in Schofield data may not be a
  statistically representative sample of the
  population is general

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Estimating BMR Obesity

• recent (Horgan 2003) reassessed validity of the
  Schofield data to predict BMR in obese
• conclusions
• BMR increases more slowly at heavier weights
• to ignore this is to over predict energy
  requirements
• any general equation for predicting BMR may be
  biased for some groups or populations.

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Estimating BMR adjusted body weight (ADJ)

• estimate of how much of the extra body weight is
  lean and thus metabolically active
• 2 methods
• 25 adjusted weight
• (actual body weight x 0.25) ideal body weight
• adjusted average weight
• (actual body weight ideal body weight) x 0.5

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Estimating BMR adjusted body weight (ADJ)

• first reported in newsletter QA format
• not validated
• studies suggest adjusted average weight has
  better predictive value than 25 adjusted weight
  (Glynn 1998, Barak 2002)
• no longer included in ASPEN guidelines (2002)

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Estimating BMR Obesity

• predicting BMR is very difficult (without
  measuring lean body mass)
• adequacy of specific equations? (Ireton-Jones et
  al., 1992 Glynn et al., 1998)
• actual body weight stress activity
  overestimate
• access to indirect calorimetry is limited

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Determining energy requirements in obesity

• non stressed patients
• calculate as normal and - 400-1000kcal for
  decrease in energy stores
• mild to moderately stress
• calculate as normal
• omission of stress and activity avoids the
  adverse effects of overfeeding
• severe stress
• might be necessary to add a stress factor to BMR
• monitoring essential eg blood glucose

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Estimating energy requirements

• The main components of energy expenditure are
  estimated
• BMR
• Alteration in BMR due to disease process (stress
  factors)
• Activity
• DIT

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Levels of evidence

• 1. a) Meta-analyses
• b) Systematic reviews of randomised controlled
  trials (RCTs)
• c) RCTs
• 2. a) Systematic reviews of case-control or
  cohort studies
• b) Case-control or cohort studies
• 3. Non-analytic studies e.g. case studies
• 4. Expert opinion
• (adapted from Draft NICE Guidelines for
  Nutrition Support in Adults, 2005)

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Stress factors

• timing of measurements
• over (hyperalimentation) vs. under-feeding
• changes in therapeutic interventions
• e.g. improved wound care, anti-pyretics,
  sedation, control of ambient room temperature
• ? err towards lower end of the range and monitor

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Stress factors

• unable to include a stress factor for every
  disease or condition
• many measured in far from ideal circumstances
• limited by data available
• may choose to underfeed in certain circumstances
• necessary to refer back to the literature
• included a checklist of factors to look for when
  reviewing papers

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Adverse effect of over-feeding

• excess carbohydrate
• difficulties controlling blood glucose
• increased CO2 production
• respiratory problems in vulnerable patients (eg
  COPD/ ventilated)
• swings in blood glucose increase mortality in
  critically ill
• aim not to exceed the glucose oxidation rate (4-7
  mg glucose/ kg/ min)
• long term excess carbohydrate can lead to
  steatohepatosis or fatty liver (Elwyn DH, 1987).

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Estimating energy requirements

• The main components of energy expenditure are
  estimated
• BMR
• Alteration in BMR due to disease process
• Activity
• DIT

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Total energy expenditure
Activity DIT
Activity DIT
BMR
BMR
Health
Disease
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Activity factor

• energy expended during active movement of
  skeletal muscle
• approximately 20-40 of energy expenditure in
  free living individuals
• depends on duration and intensity of the exercise
  
• activity is less than 20 of the energy
  expenditure in hospitalised or institutionalised
• NB assumes normal muscle function

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Activity factor for activity institutionalised
patients combined with DIT
Activity level Males and females
Bedbound immobile Bedbound mobile/ sitting Mobile on ward 10 15 20 25
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Activity factorabnormal muscle function

• hospital patients likely to have higher activity
  levels
• abnormal neuro-muscular function e.g. brain
  injury, Parkinsons, cerebral palsy, motor
  neurone disease, and Huntingtons chorea
• prolonged active physiotherapy
• effort involved in moving injured or painful
  limbs

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Community patients

• free living individuals have higher energy
  expenditure due to physical activity
• nursing home and house bound patients ? similar
  activity levels to hospital patients
• for active patients in the community a PAL should
  be added

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Physical activity level (PAL) of adults
Non-occupational activity occupational activity light M F occupational activity moderate M F occupational activity mod/ heavy M F
non active m. active very active 1.4 1.4 1.5 1.5 1.6 1.6 1.6 1.5 1.7 1.6 1.8 1.7 1.7 1.5 1.8 1.6 1.9 1.7
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Estimating energy requirements

• The main components of energy expenditure are
  estimated
• BMR
• Alteration in BMR due to disease process
• Activity
• DIT

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Diet-induced thermogenesis

• Continuous infusion of enteral feed and
  parenteral nutrition do not significantly
  increase REE
• Bolus feeding increases REE by 5
• Mixed meal increases REE 10
• PALs include DIT (COMA, 1991)
• ? guidelines include combined factor for activity
  and DIT

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Estimating requirements sources of error

• prediction equation for BMR
• stress factor
• degree of stress inaccurately assessed
• poor evidence to support stress factor used
• activity level inaccurately assessed or poorly
  understood
• DIT varies by 10 depending on feeding method

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Sources of error inaccurate weight

• Inaccurately measured weight
• estimated weight
• inaccurate scales
• patient had their feet on the floor (chair
  scales)
• patient was fluid overloaded (? 20 of hospital
  patients)
• amputees

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Conclusions

• Estimated requirements are only a starting point
• - set realistic goals of treatment for each
  patient
• - monitor and amend as patients condition
  changes
• Review and criticise the literature regularly
• - be aware of gaps in the evidence
• - understand the limitations of guidelines
• - check applicability to your patients
• Contribute to research and audit projects