relevance of rnis (drvs) to nutritional support alan shenkin department of clinical chemistry...
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Relevance of RNIs (DRVs) to Nutritional Support
Alan Shenkin
Department of Clinical Chemistry
University of Liverpool
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The Glib Answer
Not much
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DRVs provide the guidelines for oral
nutritional requirements in health
Of particular relevance to populations
rather than the individual.
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The individual and population reference values
Relationship between requirement, intake,and likelihood of deficiency
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Different requirements at different stages of disease
• Stabilise - rehydrate/electrolytes- vitamins/trace elements- antibiotics/disease control
• Repair -slow correction of deficiencies
-concern about refeeding syndrome
• Replete - increased requirements
Chronic depletion
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Different requirements at different stages of disease
Acute disease
If hypermetabolic, minimise extent of negative nitrogen balance
How much energy/protein?
EAR for energy based on health, activity and age
? REE plus a stress factor
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Predicting energy requirements
• Schofield/Harrison Benedict BMR+ 10% - 50% Stress+ Fever (10%/degree C)
+ 10% Thermic effect of feeding
• Activity-10% ventilated+10% lying in bed+20% Bed to chair+40% up around ward
• +20% for anabolism
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Leads to excess energy provision
At best, fat synthesis
At worst fatty liver, glucose intolerance
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Benefits/safety of hypocaloric feeding
• Maintains a supply of energy substrate
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Benefits/safety of hypocaloric feeding
• Maintains a supply of energy substrate
• Does not overload the liver with non-oxidised substrates
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Benefits/safety of hypocaloric feeding
• Maintains a supply of energy substrate
• Does not overload the liver with non-oxidised substrates
• Does not overload the lungs
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Benefits/safety of hypocaloric feeding
• Maintains a supply of energy substrate
• Does not overload the liver with non-oxidised substrates
• Does not overload the lungs
• More likely to be balanced to micronutrient supply.
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Different requirements at different stages of disease
Acute disease
If hypermetabolic, minimise extent of negative nitrogen balance
How much energy/protein?
As hypermetabolism settles, meet requirements, with extra for anabolism
Benefits/safety of hypocaloric feeding
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Protein requirements
Protein RNIs- male- 55g/d i.e 0.75 g/kg/d
female- 45g/d i.e 0.75g/kg/d
‘It is prudent for adults to avoid protein intakes of more than twice the RNI’ (DoH)
In catabolic disease, net protein catabolism is lowest when 1.5-2g/kg/d protein is supplied with adequate energy.
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RNIs and ETF
• Comparable in some patients- especially long-term NS• Depends on status on starting ETF- ?depletion ??
general/specific nutrients• On going requirements - ?catabolic/anabolic
- losses
- digestion/absorption
- bioavailability
- proportion from EN/IVN
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0
20
40
60
80
100
120
140
160
Zinc iron selenium vit c
RNIStandard FeedFibre Feed
mg/μg
RNIs and two typical tube feeds (1500Kcal)
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RNIs and TPN
• Bypass the regulating role of the gut
• Generally, lower requirement by IVN than
by EN
• Continuous intake rather than bolus
• Probably only relevant for home IVN
• Effects of disease- lower/higher requirements
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RNIs and IVN
010
20
30
40
50
6070
80
90
100
zinc selenium iron thiamine vit C
RNIIV
mg/μg
X10
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RNI approach to supply in Nutrition Support-the underlying problem
What outcome are you trying to achieve ?
Maintenance of body composition?
Positive nitrogen balance?
Optimal tissue function?
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Different objectives in different patients
• Maintenance in long term home EN
• Reduction in complications and optimal speed of recovery in acutely ill patients
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NS and reduction in complications
• Wound healing
• Improved immune function
• Improved mobility
• Improved mental state
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What is the optimal intake for
vitamins/trace elements/protein –energy
in short term and long-term NS ?
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The challenge for PENG in the next 21 years
To become seriously research active
To undertake studies that matter in terms of patient outcome
To characterise optimal intakes in disease
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Conclusions• DRVs/RNIs are of little value in deciding the nutritional
requirement of individual patients
• Requirements vary with disease type/severity/ phase/duration/complications, and the balance of EN to IVN
• The skill of the nutritionist is to apply knowledge, clinical assessment, and understanding of nutrition and metabolism to the individual patient
• More research is needed on optimal intakes in relation to
outcome