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N u t r i t i o n t

Amult id iscipl inaryapproach to themanagement oftients receiving TPNis recom me nded toreduce complications,writes DeirdreMcCormack

TOTAL parenteral nutrition is the asepticdelivery of nutrients into the circulatorysystem via a central venous catheter or theperiphera l veins.TPN is used wh en the gu tis not functioning and there are severalindications that may suggest its use fseeTable 1).Access routes and dur at ion

Establishing and maintaining suitableaccess to th e c irculation is essential for th esuccessful managem ent of TPN. The routeused is dependent on the anticipatedduration of feeding and the osmolarity ofthe solution.

Central vein cannulation is the mostcom monly used route, however peripheralfeeding is an acceptable alternative forshort - term fee ding. A single dedicatedTable 1

lumen should be used for adm inistrationofTPN.Nutr i t ion al assessment

Prior to commencement of TPN thepatient 's nutrit ional requirements areassessed. Energy and nitr og en requ ire-ments can vary, dep endin g on age, sexbody composit ion, clinical status andactivity.

A baseline biochemical assessmenshould identify any abnormal plasmaelectrolyte levels, liver functio n tests, renafunc tion tests, glucose levels or l ipi dscreen.Nutritional requirementsFluid

TPN may be the sole source of fluid orused in combination with other sources

Indications for totai parenteral nutritionI Inadequate absorption resulting from short bowel syndromeI Gastrointestinal fistulaI Bowel obstructionI Prolonged bowel rest

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N u t r i t i o n

Table 2 Monitor ing pat ients rece iv ing TPNI Fluid balance - Monitor dailyI Glucose tolerance - Initially levels checked every 4-6 h ours; daily w hen stahleI Weight - Daily weights can show fluid changes

- Long term trends determine changes in tissue massI Venous access - Venous access site regularly checked for signs of infection, phlehitisI Routine biochem istry - Serum Na, K, urea and creatinine checked daily initially

- Ca, Mg and P checked at least twice a week initially- Trace elements - zinc, copper, selenium checked monthly- Vitamins - B12, Folate. Vitamin A, V itamin E checked monthly

I Urinaiysis - Urinary levels of electrolytes useful when determining clinicalsignificance of plasma levels

such as iv f lu ids , Jv an t ib io t ics and b loodproducts . The f lu id ba lance ch ar t i s ani n f o r m a t i v e s u m m a r y o f d e t e r m i n i n gadequacy of input versus output.

Acu te changes in f lu id can a l so bedetermined by m on i to r ing acu te changesin b ioche m ica l pa rame ters such asa lbum in , hae m og lob in , mean ce l l vo lume,urea and sodium.To m aintain f lu id levels ,the fo l lowing is required; 18-60 years old - 35m l/kg/da y > 60 years old - 30m l/kg/da y

P lus rep lacement o f ongo ing f lu idlosses, eg . py rexia, ur ine, dra ins, excesswound exudates , s tomas and h igh G llosses.Energy

Energy requirements are m ost comm onlyes t imated us ing pred ic t i ve equat ions . 'These are based on p opula t ion data, tak-ing into ac count act ivity and stress fac tors.

It is im pe rative tha t these equations arenot used in isolat ion and tha t m onitoringof the pat ient occurs to assess ef f icacy.Ind i rec t ca lo r imet ry may be used .However, this is not practical in the acutesett ing.

Nutr i t ional requirements are alsoaf fected by m edica l condit ions, thus a l ter-nate evidence based pred ict ive equat ionsexist for certa in condit ions such as l iverdisease, renal fa i lure and the cr i t ica l ly i l lobese.Nitrogen

Pat ients d o not have a requirem ent forn i t rogen pe r se , but for am ino acids, wh ichare the subs t ra tes needed fo r p ro te insynthesis ( lg nitrogen = 6.25g protein).

in parentera l nutr i t ion is provided In theform of an am ino acid so lut ion.Electrolytes

The norma l da i l y e lec t ro l y te requ i re -me nts are:o Sodium 1 -1.5 m m ol/kgo Potassium l -1.5mmol/kg Calcium 0.1 -0 .15mmol/kg Magnesium 0.1-0.2 m m o l / k g Phosph ate 0.5-0.7mm ol/kg.Vitatriins an d trace elements Wa ter so luble (Pabr inex), fat so luble

(V i t l ip id ) and combined prepara t ions(Ce rnevit Mul t ib ionta ) o f v i tam ins areavailable.

Ad d i t race con ta ins trace e leme n ts , eg .iron, zinc, m anganese, coppe r,chromium,s e l e n i u m , m o l y b d e n u m , f l u o r i d e a n diodine.

M o n i t o r i n gReg ular m onitor ing is esse nt ia l to

d e t e c t a n d m i ni m i s e c o m p l i c a ti o ns a n ddetermine response to nu t r i t iona lsupport .

Patients receiving TPN should have theirnu t r it iona l requ ireme n ts rev iewe d regu-lar ly, taking into account cl inical c ondit ion,t rea tme n ts (eg . d ia l ys is ) , d rug therapy ,nutr i t ional s tatus, response to TPN andsupp orting laboratory data.

C l in ica l assessment o f the pa t ien t ca nrevea l asc ites , oedem a, imp a i red w oundheal ing or loss o f muscle mass that mayn o t b e e v i d e n t fr o m m o n i t or i n g w e i g h tand b iochem ical indices fseerab/e2J.C o m p l i c a t i o n s

M ech an ica l , in fec t ious and nu t r i tiona lcomplicat ions can arise, including:

- f lu id over load/dehy drat ion- electrolyte imbalance- hyperg lycaemia/hypoglycaemia- o v e r f e e d i n g- re-feeding syndrome- nutrient deficiency- hepatobil iary dysfunction.

S t a n d a r d v e r s us t a i lo r e d r e g i me n sTPN can be p rov ide d by a s tandard o

patient specif ic prescript ion. Many factorin f luence th is dec is ion such as f requencyof use, pa t ien t t ypes , loca l c om pound ingfacil ities a nd cost.

Pa t ients on TPN t ha t a re metabo l ica l l ystable can to lerate s l ight under or oveprovision of nutrients, f luid or elec trolytew ith no compl icat ions.

I t is the carefu l assessment that wi lidentify those p atients wh o are l ikely to besubstrate in to lera nt and require f requenmanipulat ions or specif ical ly tai lored regimens.Albumin

A low p lasma a lbumin leve l i soccasional ly used as a reason for nutrit ionsuppor t . A lbumin is a negat ive acu tephase p ro te in , l eve ls d ropp ing w i th in s ixhours of an acute injury, decreasing by upto 50% in severe case s.This is due to th eincreased transcapil lary escape rate and areduced re tu rn v ia the l ymp hat ic sys temAlbumin is not a usefu l indicator onutr i t iona l s tatus, but is a use fuprognost ic marker .Novel substrates

The pr inc ipa l nove l subs t ra te w i th themost c l in ica l ev idence is g lu tamine . tshould be reserved for cr i t ica l ly i l l andsurg ica l pa t ien ts w i th an t ic ipa tedpro longed length o f s tay.Af ter in jury/hypercatabo l ic condit ionspro found in t race l lu la r g lu taminede p le t ion has been found , t hus isregarde d as a ' cond i t iona l l y ' essen t iaa m i n o ac id . Stud ies have shownimp rovem ents in the c l inica l ou tcom e ohypermetabo l ic pat ients.O p t i m a l m a n a g e m e n t

Parenteral nutrition is t he m ost comp lexand expensive form of ar t i f ic ia l nutr i t ions u p p o r t . A mui t id isc ip l inary approach tot h e m a n a g e m e n t o f t h e s e p a t i e n t s c a nopt im ise th is therapy and reduce com p l i

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