Relevance of RNIs (DRVs) to Nutritional Support

Alan Shenkin

Department of Clinical Chemistry

University of Liverpool

The Glib Answer

Not much

DRVs provide the guidelines for oral

nutritional requirements in health

Of particular relevance to populations

rather than the individual.

The individual and population reference values

Relationship between requirement, intake,and likelihood of deficiency

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

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

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

Leads to excess energy provision

At best, fat synthesis

At worst fatty liver, glucose intolerance

Benefits/safety of hypocaloric feeding

• Maintains a supply of energy substrate

Benefits/safety of hypocaloric feeding

• Maintains a supply of energy substrate

• Does not overload the liver with non-oxidised substrates

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

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.

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

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.

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

0

20

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80

100

120

140

160

Zinc iron selenium vit c

RNIStandard FeedFibre Feed

mg/μg

RNIs and two typical tube feeds (1500Kcal)

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

RNIs and IVN

010

20

30

40

50

6070

80

90

100

zinc selenium iron thiamine vit C

RNIIV

mg/μg

X10

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?

Different objectives in different patients

• Maintenance in long term home EN

• Reduction in complications and optimal speed of recovery in acutely ill patients

NS and reduction in complications

• Wound healing

• Improved immune function

• Improved mobility

• Improved mental state

What is the optimal intake for

vitamins/trace elements/protein –energy

in short term and long-term NS ?

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

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