Formula Osmolality andNutritional NeedsDr. Samaa ElsoadaaAssistant Professor, Clinical NutritionDepartment, Umm Alqura University
Formula Osmolality• The osmolality of an enteral formula is animportant consideration in terms of tolerance.• Osmolality is the number of molecules andions per kilogram of a solution.• It may be easier to think of osmolality as thenumber of particles per kilogram of water.
Formula OsmolalityOsmolality of Body Fluid andFormulas• The osmolality of body fluid isaround 300 milliosmoles per liter.• The osmolality of most enteralformulas ranges from 250 to 800milliosmoles per liter.
Formula OsmolalityIsotonic Formulas• If the enteral formula has an osmolality nearthat of the body fluid it is considered anisotonic formula.• Isotonic formulas are generally well toleratedby patients.
Formula OsmolalityHypertonic Formulas• If the enteral formula has anosmolality greater than that of thebody fluid it is considered ahypertonic formula.• Hypertonic formulas create anosmotic gradient that attracts waterfrom the body into the lumen of theGI tract.
Formula OsmolalityComplications of Hypertonic FormulasMonomeric formulas tend to be the mosthypertonic. When hypertonic formulas drawwater into the lumen of the GI tract, thefollowing symptoms can occur:• Cramping• Nausea• Vomiting• Diarrhea
Formula OsmolalityTolerance of Hypertonic Formulas• It may take time for the body to adaptto a hypertonic formula; therefore,hypertonic formulas must beintroduced slowly or diluted* untiladaptation occurs. This is particularlyimportant if the patient has beenwithout feedings (NPO) for a while.
Formula OsmolalityTolerance of Hypertonic Formulas• Additionally, patients with low serum albuminconcentrations may have a lower than normalbody fluid osmolality. These patients are atparticular risk for symptoms related to hypertonicformulas.• For most patients, gradual administration of theformula is sufficient - dilution of the formula isusually not necessary and is now rarely practiced.
Nutritional Needs of Tube Fed PatientsVolume of Formula• The volume of enteral formulathat a person needs variesdepending on individualrequirements. Caloric andprotein requirements of a TFpatient are calculated thesame as for any other patient.
Nutritional Needs of Tube Fed PatientsKcaloric and Protein Needs of TF Patients• There are several methods to determine kcaloricand protein needs of tube fed patients.• When you calculate your patients requirements,remember that the mathematical equations youuse give you estimates of needs.• Individual needs vary; so you must monitor yourpatient and adjust energy intake as appropriate.
Nutritional Needs of Tube Fed PatientsCalculation of Protein Needs• Protein requirements vary with disease state.Protein needs can be estimated by multiplyingkg of body weight by a factor or by a nitrogenbalance study.• Grams protein/ kg Method• Nitrogen Balance Method• NPC:Ratio
Nutritional Needs of Tube Fed PatientsGram/kg Method to Determine Protein Needs• The simplest, but least precise, method toestimate protein needs is by multiplying IBW inkilograms by a factor appropriate for the patientscondition.• If this method is used, the patient must bemonitored for protein status to determine ifadjustment in the protein prescription isnecessary.
Nutritional Needs of Tube Fed Patients*RequirementHealth Status0.8 – 1.0Normal1.0 – 2.0Moderately stressed (infection, fracture, surgery)2.0 – 2.5Severely stressed (burns, multiple fractures)Renal Disease0.6 – 0.8Predialysis1.1 – 1.4Hemodialysis1.2 – 1.5Peritoneal dialysisAdults*values represent grams of protein per kilogram of IBW per day.
Nutritional Needs of Tube Fed PatientsStressedNormalAge (years)2.2 – 3.02.00.0 – 0.51.6 – 3.01.60.5 – 1.01.2 – 3.01.21 – 31.1 – 3.01.14 – 61.0 – 2.51.07 – 101.0 – 2.51.011 – 141.0 – 2.50.8515 – 24Pediatrics*values represent grams of protein per kilogram of IBW per day.
Nutritional Needs of Tube Fed PatientsExample Gram/kg Calculation:• IBW : 120 lb; 54.5 kg (120/2.2)Moderate stress:[factor = 1.5 (from chart)]• 54.5 x 1.5 = 81.75 (82) grams protein/day
Nutritional Needs of Tube Fed PatientsNitrogen Balance Method• A nitrogen balance study isthe comparison of nitrogenbeing consumed (orally orvia IV) compared to theamount of nitrogen beinglost from the body.• Most nitrogen is lost viathe urine, but some is lostwith feces, sweat &sloughed off skin cells.Nitrogen In Food TPN AANitrogen Out- Urine - Feces- Sweat - Skin
Nutritional Needs of Tube Fed PatientsThree Scenarios of Nitrogen Balance( 1 ) N-Equilibrium: Nitrogen in = Nitrogen OutThe person is in a state of maintenance where theirbody is neither losing or gaining body protein.( 3 ) Negative N-Balance( 2) Positive N-BalanceNitrogen in < Nitrogen OutThe person is losing bodyprotein. Negative nitrogenbalance is an undesirable statethat occurs with weight loss,traumatic injury and someillnesses.Nitrogen in > Nitrogen OutThe person is gaining bodyprotein. Positive Nitrogen balanceoccurs during periods of growth,including pregnancy, with proteinrepletion therapy, and with weightlifting exercise that builds muscle.
Nutritional Needs of Tube Fed PatientsSteps to Calculate Nitrogen Balance1. Determine nitrogen lost in urine by a 24 hoururinary urea nitrogen test.2. Add 4* to the UUN to account for non-urinary losses of nitrogen3. Determine nitrogen intake by dividing thedaily protein intake by 6.254. N-bal.= value from #3 - value from #4*a factor of 4 is used to estimate the nitrogen losses from non-urine sources (sweat,feces, etc.)
Nutritional Needs of Tube Fed Patients• If the nitrogen balance is 0, the person isconsuming the correct amount of protein formaintenance.• If the nitrogen balance is negative, increasethe protein intake by a factor determined bymultiplying the nitrogen balance figure by6.25.• If goal is repletion, increase protein intakeover what would result in nitrogenequilibrium.
Nutritional Needs of Tube Fed PatientsExample N-balance Calculation• Protein intake: 90 gm protein• 24 hr UUN : 20 gm NN intake = 90 / 6.25 = 14.4 gm N20 + 4 = 24 gm N (total output)N-balance = 14 - 24 = -10 gm N This person is losing 10 X 6.25 = 62.5 gmprotein per day
Nutritional Needs of Tube Fed PatientsCalculation of Energy Needs• ( 1 ) Basal energy expenditure x activity factor x stress factorBEE x AF x IF Method• ( 2 ) Kcals per kilogram body weight according to weight &activity classificationKcal / kg Method
Nutritional Needs of Tube Fed PatientsBEE x AF x IF Method• There are two main methods to ascertainbasal energy expenditure (BEE) - - indirectcalorimetry and via a prediction equation.• The most common of which is the HarrisBenedict Equation (HBE).• Once BEE has been determined, that figure ismultiplied by an activity factor (AF) then aninjury factor (IF) to determine total energyneeds.
Nutritional Needs of Tube Fed PatientsThe Harris-Benedict Equation• Men:BEE (kcal/d) = 66.5 + (13.8 x W) + (5.0 x H) - (6.8 x A)• Women:BEE (kcal/d) = 655.1 + (9.1 x W) + (1.8 x H) - (4.7 x A)• Where: W = weight in kg H = height in cm A = age inyears
Nutritional Needs of Tube Fed PatientsExample Calculation of BEE:• Male; W = 60kg; H = 150 cm; A = 30 yBEE (kcal/d) = 66.5 + (13.8 x 60) + (5.0 x 150) -(6.8 x 30)66.5 + 828 + 750 - 204 = 1440 kcal/day
Nutritional Needs of Tube Fed PatientsExample calculation of energy needs:Estimated energy needs (kcals) = BEE x AF X IF• BEE = 1000; AF = 1.2; IF = 1.2• Energy needs = 1000 x 1.2 x 1.2 = 1440kcal/day
Nutritional Needs of Tube Fed PatientsActivity and Injury FactorsActivity Factor (AF)1.2Bed rest1.3Ambulatory
Nutritional Needs of Tube Fed PatientsVitamins and Minerals in Formula• Most enteral formulas provide 100% of theRDA for vitamins and minerals in ml,depending on the formula.
Fluid Needs of Tube Fed Patients• Fluid needs are important to consider for TFpatients.• Specific water needs for an individual can becalculated as 1 ml/kcal or 35 ml/kg usual bodyweight (UBW).• Patients who have large water losses throughperspiration or oozing wounds may requiremore fluids.
Fluid Needs of Tube Fed PatientsSample Fluid Needs Calculation:• 80 kg patient, intake 2500 kcal• 80kg x 35ml/kg = 2800ml water/dor2500 kcal x 1ml/kcal = 2500ml water/d
Fluid Needs of Tube Fed PatientsFree water• Most enteral formulas contain 80-85% freewater, and fluid needs can be met with a smallamount of additional water.• However, calorically dense formulas contain aslittle as 60% free water, so the failure tosupplement water with the denser formulascan result in dehydration.
Fluid Needs of Tube Fed PatientsExample Free Water Calculation:• Fluid requirement for patients: 2000mlFormula intake: 2200mlFormula: 80% free water• 2200 ml formula x 0.80 = 1760 ml free water• Additional water needs:2000 ml – 1760 ml = 240 ml water
Fluid Needs of Tube Fed PatientsObligatory Fluid Output• One way to assess the appropriateness of fluidintake is to monitor the pateints urine output.• Obligatory fluid output is the minimum outputof urine necessary to remove wastes and isestimated to be 700 ml per day or 30 ml perhour.• For the tube fed patient, obligatory fluidoutput can be determined more preciselyusing the renal solute load of the formula.
Fluid Needs of Tube Fed PatientsRenal Solute Load• The renal solute load (RSL) is the sum of thematerials that must be excreted via the urine,including urea, sodium, potassium, andchloride.
Fluid Needs of Tube Fed PatientsRenal Solute Load• Each gram of protein ingested yields a RSL of5.8 mOsm in adults and 4.0 mOsm in children.• Protein yields a lower RSL in growing childrenand those in anabolic states since moredietary protein is being used to synthesizebody proteins.• On the other hand, the RSL will be higher incatabolic patients.• Each mEq of electrolyte yields a RSL of 1mOsm.
Fluid Needs of Tube Fed Patients• The renal solute load from a tube feeding canbe calculated as follows:Renal Solute Load = (gm prot x 5.8) + mEq(Na+ K+Cl)• Substitute 4.0 for 5.8 if the patient is a child.
Fluid Needs of Tube Fed PatientsObligatory Urine Output for Tube Feeding• For optimum kidneyfunction, the total urineoutput should be 1.5 - 2times the renal solute load.• Desired Urine Output = 1.5 xRSL
Fluid Needs of Tube Fed PatientsExample Desired Urine Output Calculation:• RSL: 385• Desired Urine Output• = 1.5 -2 x RSL= 1.5 -2 x 385= 510 - 770 ml or cc
Tube Feeding AdministrationMethods to administer tube feedings:( 1 ) Continuous Drip Feeding• The continuous drip method ismost commonly used. Continuousdrip is administered via gravity or apump and is usually tolerated betterthan bolus feeding
Tube Feeding Administration( 2 ) Bolus FeedingsBolus feedings allow for more mobility thancontinuous drip feedings because there arebreaks in the feedings, allowing the patient tobe free from the TF apparatus for activitiessuch as physical therapy.( 3 ) CombinationA combination of continuous drip (at night)and bolus feedings (during the day) can beused.
Tube Feeding AdministrationContinuous Drip vs. Bolus FeedingsThe rate of the continuous dripadministration can be controlledwith a pump, and the initial rateshould be slow to allow for adaptionto a hyperosmolar formula and tomonitor for tolerance.Bolus feedings should consist of 250 -300 mL given over 15 minutes,followed by 25-60 mL water whichhelps prevent dehydration andclogging of the tube. At least 3hours should elapse between eachbolus feeding.
Tube Feeding Administration• Residual VolumeBefore each bolus feeding, gastric contentsshould be suctioned out and returned to thestomach before a new feeding is administeredto ensure that minimal residue remains fromthe previous feeding.
Tube Feeding Administration• residual volume should be checked every 3-5hours when feeding is by continuous drip.Excess residual volume (>100 -150 mL) mayindicate an obstruction or some otherproblem that must be corrected beforefeeding can be continued.
Tube Feeding AdministrationPatients placed on continuousdrip TF often cannot toleratelarge volumes of hypertonicformulas with greater than 500mOsm/L. Therefore, hypertonicformulas may need to bediluted at first to 1/2 to 1/3strength*.Administering for Maximum Tolerance
Tube Feeding Administration• Formulas should be administered slowly atfirst, about 50 ml per hour, then increased by25 ml per hour every 8-12 hours as tolerateduntil the required volume of formula is met. Atypical final rate is 100-125 ml /hr.
Tube Feeding Administration• Determination of Final Rate• To determine the desired final rate of formuladelivery, divide the required volume of formulaby 24 hours. If the formula is diluted, strength canbe increased slowly after the final rate has beenachieved.• Remember, however, that recent literaturesuggests that most patients can tolerate fullstrength formulas from the start.
Tube Feeding Administration• Example Final Rate Calculation:• Required volume is 2800 ml• 2,800 ml / 24 hr = 117 mL /hr(which is close to 120 mL/hr)
Tube Feeding Administration• Hypoalbuminemia is commonly implicated inthe development of diarrhea among TFpatients. If the albumin value is less than3.5g/dl it is best to dilute the formula. If thealbumin value is less than 2.5g/dl enteralfeeding may not be tolorated at all.
Tube Feeding Administration• If the patient is not toleratingthe formula, the rate should beslowed and/or concentrationshould be diluted untiltolerance is achieved.• Signs of intolerance includediarrhea, nausea, vomiting,dehydration and cramping.Another factorwhich oftencauses diarrhea inthe TF patient isantibiotictherapy.
Tube Feeding Administration• Careful administration of TF helpsprevent bacterial contamination.Blenderized formulas should beprepared under sanitaryconditions and should be usedwithin 24 hours to reduce the riskof bacterial infection.Prevention of Bacterial Contamination
Tube Feeding Administration• Unopened cans of formula can be stored atroom temperature, but must be refrigeratedonce opened and used within 24 hours.• Fresh formula should never be added toformula remaining in the feeding bag. Thefeeding bag and tubing (except tubingconnected to the patient) should be changedevery 12 -24 hours.
Tube Feeding Administration• Body Positioning The pateintsbody position is also importantwhen administering a TF for bothcontinuous drip and bolusfeedings. The patients head shouldbe elevated at least 30 degreesduring and after the feeding toprevent regurgitation.• If the patient is receiving a tubefeeding into the intestine,positioning is not critical.
Administration of Medicine• Medications are often administered via thefeeding tube, but this should be avoided ifpossible because: pills can be crushed andmixed with water before being added to thefeeding tube, but particles may clog the tube.• Some pills cannot be crushed because theyhave time released coatings.
Administration of Medicine• The feeding tube should be flushedwith 30 ml of water or salinebefore and after administration of adrug. Liquid forms of medicationshould be used if possible.• Some medications can be added tothe TF formula, but drug-nutrientinteraction may occur. Some drugscan cause the formula to clump andclog the feeding tube.Flush the tubewith water orsaline afteradministrationof a medication.
Administration of Medicine• Placement of the feeding tube can affect drugaction. Some drugs require the acidicenvironment of the stomach to be dissolved,and therefore may not be well absorbed if thefeeding tube is placed in the intestine.
Monitoring ToleranceThe TF patient must be carefully monitored fortolerance of formula, hydration status, andadequacy of nutrition support. Tolerance offormula has been discussed previously.Symptoms to look for include: diarrhea• nausea• cramping• constipation• aspiration
Monitoring Tolerance• Hydration status can be monitored via dailyweights, hematocrit, blood urea nitrogen(BUN), and electrolytes. High values for theabove parameters indicate dehydration. Aweight change of 2.2 pounds represents 1 L offluid if the weight change is due to fluid.• Nutritional assessment indicators of proteinstatus can be used to determine adequacy ofprotein intake, and weight can be used todetermine adequacy of kcalories, unless thepatient is retaining fluid.