Nutrition

NutritionDr James F PeerlessJuly 2013ObjectivesIntroduction to nutritionAssessment of the patientFeeding requirementsMacro- & micronutrientsEnteral vs. parenteral feedingRefeeding syndrome

IntroductionNutrition support:enteral or parenteral provision ofcaloriesproteinelectrolytesvitamins, mineralstrace elementsfluidsGoal of therapy is to supply each substrate in the right quantity necessary to meet the metabolic needs of each patient

Total energyProteinLipids (fat)CarbohydratesMicronutrientsNutritionAims of nutritional support on the ICU:Provide exogenous substrates to meet macro and micronutrient requirements in dependent patientsHelp protect vital visceral organs and attenuate breakdown of skeletal muscleReduce net protein catabolismContraindications to commencing feed (enteral or parenteral) on ICU:Able to resume full oral diet within 3 daysInappropriate for ethical reasons

Nutritional RequirementsAssessment of nutritional statusIt is estimated that 60% of patients are malnourished prior to hospital admissionMalnutrition is associated with a poor outcome increased LoS and incidence of complications in critical care.Assessment difficultAnthropometric measurements good for populationsBMI does not reflect acute changesBiochemical tests have limitationsBiochemical tests have limitationsAlbumin drops rapidly during acute phase of illnessHb affected by haemorrhage, transfusion, haemolysis

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Subjective Global AssessmentHistoryWeight change (chronic and acute)Changes in food intakeGI symptoms (N, V, D, anorexia)Functional impairment

ExaminationLoss of SC fat (chest, triceps)Muscle wasting (temporal, deltoid, gluteal)OedemaAscitesSubjective (as name suggests), but can identify patients at risk of malnutrition + refeeding syndrome7Nutritional RequirementsHarris Benedict EquationFor the calculation of BMR (kcal/day)BMR for a healthy, afebrile individual25 kcal/kg/dayAlso the Schofield Equation

MaleBMR = (13.75 wgt) + (5 hgt) (6.78 age) + 66

FemaleBMR = (9.56 wgt) + (1.85 hgt) (4.68 age) + 655BMR = metabolic rate of a subject under standardised conditions at mental and physical rest, in a comfortable environmental temperature and fasted for 12 hours. NOT necessarily the minimum metabolic rate (e.g. asleep).8Nutritional RequirementsHarris Benedict EquationFor the calculation of BMR (kcal/day)BMR for a healthy, afebrile individual25 kcal/kg/day

Fever: 10% for each 1C above 37CSepsis: 9% (irrespective of TC)Surgery: 6% if post trauma or surgeryCritical Illness and RequirementsAcute critical illnessCatabolism > anabolismCHO are preferred energy source (fat mobilisation is impaired)Aim of nutritional support to minimise muscle protein breakdownAcute initial phase of critical illness 20-25kcal/kg/day

Recovery phaseAnabolism > catabolismNutritional support provides substrates for:correction of hypoproteinaemiaReparation of muscle lossReplenishes nutritional storesRecovery/anabolic phase 25-30kcal/kg/day

Acute critical illness: muscle breakdown amino acids act as the substrates for gluconeogenesis.10

Nutritional RequirementsMacronutrientsProvide energyProtein: 5.3 kcal/gLipid: 9.3 kcal/gCarbohydrate: 3.75 kcal/g

MicronutrientsRequired in small amounts to maintain health but do not provide any energy

Protein Requirements1.5 g kg-1 day-16.25 g contains 1 g of nitrogen ~ 0.20g nitrogen/kg/day.

Nitrogen losses are large in critically ill patientsNitrogen output = urinary urea/mmol/24 hours x 0.033 + obligatory losses +extra renal lossesObligatory lossesestimated as 2-4g nitrogen/day (skin, hair, faeces etc)Extra renal losses include:PyrexiaInflammatory bowel diseaseGI fistulaeExtensive bed soresBurn exudatesThe proportion of a feed made up by protein is sometimes expressed as a calorie: nitrogen ratio. 6.25g of protein contains 1g of nitrogen. The ratio is then calories (kcal) nitrogen (g). Recommended calorie: nitrogen ratios are around 100:1. The optimal ratio for lipid: carbohydrate is not known. 12Protein Requirements in Specific ConditionsRenal failureHaemofiltration associated with increased protein losses (~10%)

Liver failureProtein requirements dependent on underlying function of the liver:Compensated cirrhosis 0.19-0.20gN/kg/dayDecompensated cirrhosis 0.25-0.30gN/kg/dayPost-transplant 0.25-0.30gN/kg/dayAcute (fulminant) liver failure 0.20-0.25gN/kg/dayLipid RequirementsLipidLimit to 40% of calorie intake

Critically ill patients require approximately 0.8-1.0g/kg/day of lipid.

NB: propofol is a lipid sourceEach ml contains of 1% propofol contains 0.9kcal and can increase the risk of both fat and total calorie overfeeding and micronutrient deficiency

Carbohydrate RequirementsCarbohydrateExcess intake above this can result in:hyperglycaemialipid synthesisincreased carbon dioxide productionCarbohydrate + O2 = water + CO2 + energy production

and of particular relevance to the critically ill ventilator dependent patient, 15Micronutrient RequirementsVitaminsOrganic molecules essential for life; not synthesised by higher organismsFat-soluble: A, D, E, KWater-soluble: C, B complexMineralsSingle elements essential to life: Ca, P, Mg, Zn, Fe, ITrace elementsEssential to life, but in minute quantities: Cu, Co, Mn, Ni, Mo, CrMicronutrient RequirementsNo set levels for micronutrient requirements for the critically illaim for the normal recommended daily allowance

Specific disease statesThiamine deficiency in alcoholicsVitamin B12 deficiency in patients post gastrectomy or total ileal resectionZinc losses from pancreatic fistulaePhosphate, magnesium and potassium deficiencies upon refeeding a malnourished patientMicronutrient supplementation in patients with renal failure needs to be undertaken cautiously due to risks of toxicity.

Enteral Feeding

FeedsStandard formulation suitable for most patientsIsotonicLactose-freeProteinMixture of simple/complex CHOLong-chain fatty acidsMicronutrientsPro-bioticsVariety of formulations available:Concentrated for fluid restrictionPre-digested for enzyme deficienciesEnteral NutritionContinuous vs bolusNo difference in mortality, infection, ITU LoS

MonitoringMeasurement of gastric residuals to minimise risk of accumulation and aspirationThis is shown to correlate poorly with aspiration, and disrupts absorption.Consensus towards only measuring residual if clinically indicated.

Clnical change: abdo pain, abdo distension deterioration.20ComplicationsAspirationBackrest elevationPost-pyloric feedingSurgical/percutaneous feedingMotility agentsDiarrhoeaDehydrationMetabolic abnormalitieshyperglycemiamicronutrient deficienciesrefeeding syndromeMechanical complications

Erythromicin, metoclopramide did not alter mortality or the incidence of nosocomial pneumonia

Metoclopramide for preventing pneumonia in critically ill patients receiving enteral tube feeding: a randomized controlled trial.AUYavagal DR, Karnad DR, Oak JLSOCrit Care Med. 2000;28(5):1408.

Backrest of 45 degrees reduces riskAverage found in study was 20 no benefit21Parenteral FeedingParenteral NutritionContains a carefully formulated mixture of macronutrients, and fluidCan be used to provide 100% of patients requirementsVarying formulations (protein/lipid ratios depending on patient requirement)Minerals and trace elements are added to the bag by the pharmacy.

Initiation of PNDeliver via central venous routeHigh osmotic load poorly tolerated by peripheral veins30d tunneled lines: Groshong, HickmanDedicated portRisk of infection

MonitoringStrict input/output measurementDaily electrolytes, until regime fully establishedLFTs, and triglycerides once a week

When to Start?Early provision (