Parenteral Nutrition Formula Calculations and Monitoring Protocols

Macronutrient Concentrations in PN Solutions Macronutrient concentrations (%) = the grams of solute/100 ml of fluid D70 has 70 grams of dextrose per 100 ml. 10% amino acid solution has 10 grams amino acids/100 ml of solution 20% lipids has 20 grams of lipid/100 ml of solution

Protein Content Calculations To calculate the grams of protein supplied by a TPN solution, multiply the total volume of amino acid solution (in ml*) supplied in a day by the amino acid concentration. Example Protein Calculation 1000 ml of 8% amino acids: 1000 ml x 8 g/100 ml = 80g Or 1000 x .08 = 80 g

Calculation of Dextrose Calories Calculate grams of dextrose: Multiply the total volume of dextrose soln (in ml) supplied in a day by the dextrose concentration. This gives you grams of dextrose supplied in a day. Multiply the grams of dextrose by 3.4 (there are 3.4 kcal/g dextrose) to determine kcalories supplied by dextrose in a day.

Sample Dextrose Calculation 1000 ml of D50W (50% dextrose) 1000 ml x 50g / 100 ml = 500g dextrose OR 1000 ml x .50 = 500g dextrose 500g dextrose x 3.4 kcal/g = 1700 kcal

Calculation of Lipid Content To determine kcalories supplied by lipid*, multiply the volume of 10% lipid (in ml) by 1.1; multiply the volume of 20% lipid (in ml) by 2.0. If lipids are not given daily, divide total kcalories supplied by fat in one week by 7 to get an estimate of the average fat kcalories per day. *|Lipid emulsions contain glycerol, so lipid emulsion does not have 9 kcal per gram as it would if it were pure fat. Some use 10 kcal/gm for lipid emulsions. Source: http://www.csun.edu/~cjh78264/parenteral/calculation/calc07.html

Example Lipid Calculation for 2-in-1 500 ml of 10% lipid 500 ml x 1.1 kcal/ml = 550 kcal 500 ml 20% lipid 500 ml x 2.0 kcal/ml = 1000 kcal Or, alternatively, 500 ml of 10% lipid = 50 grams lipid x 10 kcal/g or 500 kcal Source: http://www.csun.edu/~cjh78264/parenteral/calculation/calc07.html

Calculation of Dextrose/AA with Piggyback Lipids (2-in-1) Determine patient's kcalorie, protein, and fluid needs. Determine lipid volume and rate for "piggy back" administration. Determine kcals to be supplied from lipid. (Usually 30% of total kcals). Divide lipid kcals by 1.1 kcal/cc if you are using 10% lipids; divide lipid kcals by 2 kcal/cc if you are using 20% lipids. This is the total volume. Divide total volume of lipid by 24 hr to determine rate in cc/hr. Source: http://www.csun.edu/~cjh78264/parenteral/calculation/calc07.html

Determine protein concentration Subtract volume of lipid from total fluid requirement to determine remaining fluid needs. Divide protein requirement (in grams) by remaining fluid requirement and multiply by 100. This gives you the amino acid concentration in %. Multiply protein requirement in grams x 4 to determine calories from protein Source: http://www.csun.edu/~cjh78264/parenteral/calculation/calc07.html

Determine dextrose concentration. Subtract kcals of lipid + calories from protein from total kcals to determine remaining kcal needs. Divide "remaining kcals" by 3.4 kcal/g to determine grams of dextrose. Divide dextrose grams by remaining fluid needs (in protein calculations) and multiply by 100 to determine dextrose concentration. Determine rate of AA/dex solution by dividing "remaining fluid needs” by 24 hr. Source: http://www.csun.edu/~cjh78264/parenteral/calculation/calc07.html

Example Calculation Nutrient Needs: Kcals: 1800. Protein: 88 g. Fluid: 2000 cc   1800 kcal x 30% = 540 kcal from lipid Lipid (10%): 540 kcal/1.1 (kcal/cc) = 491 cc/24 hr = 20 cc/hr 10% lipid (round to 480 ml) Remaining fluid needs: 2000cc - 480cc = 1520cc

Protein Calculations Protein: 88 g / 1520 cc x 100 = 5.8% amino acid solution 88 g. x 4 kcal/gm =352 kcals from protein Remaining kcal needs: 1800 – (528 + 352) = 920 kcal

Dextrose Concentration 920 kcal/3.4 kcal/g = 270 g dextrose 270 g / 1520 cc x 100 = 17.7% dextrose solution Rate of Amino Acid / Dextrose: 1520 cc / 24hr = 63 cc/hr TPN recommendation: Suggest two-in-one PN 17.7% dextrose, 5.8% a.a. @ 63 cc/hr with 10% lipids piggyback @ 20 cc/hr

Re-check calculations TPN recommendation: Suggest two-in-one PN 17.7% dextrose, 5.8% a.a. @ 63 cc/hr with 10% lipids piggyback @ 20 cc/hr 63 cc/hr x 24 = 1512 ml 1512 * (.177) = 268 g D X 3.4 kcals= 911 kcals 1512 * (.058) = 88 g a.a. x 4 kcals = 352 20 cc/hr lipids*24 = 480*1.1 kcals/cc = 528 1791

3 in 1 TNA Solutions | Determine patient's kcalorie, protein, and fluid needs. Divide daily fluid need by 24 to determine rate of administration. Determine lipid concentration. Determine kcals to be supplied from lipid. (Usually 30% of total kcals). Determine grams of lipid by dividing kcal lipid by 10. * Divide lipid grams by total daily volume (= fluid needs or final rate x 24) and multiply by 100 to determine % lipid.

3-in-1 TNA Solutions Determine protein concentration by dividing protein needs (grams) by total daily volume and multiply by 100. Multiply protein needs in grams x 4 kcal/gm = kcals from protein Determine dextrose grams. Subtract kcals of lipid and kcals from protein from total kcals to determine remaining kcal needs. Divide "remaining kcals" by 3.4 kcal/g to determine grams of dextrose. Determine dextrose concentration by dividing dextrose grams by total daily volume and multiply by 100

Sample Calculation 3-in-1 Nutrient Needs: Kcals: 1800 Protein: 88 g Fluid: 2000 cc   Lipid : 1800 kcal x 30% = 540 kcal 540 kcal / 10 kcal per gram = 54 g 54 g / 2000 cc x 100 = 2.7% lipid Protein: 88 g / 2000 cc x 100 = 4.4% amino acids 88 g x 4 = 352 kcals from protein

Sample Calculation 3-in-1(cont) Dextrose: 908 kcal (1800 – 540 - 352) 908/3.4 kcal/g = 267 g dextrose 267 g / 2000 cc x 100 = 13.4% dextrose solution Rate of Amino Acid / Dextrose/Lipid: 2000 cc / 24hr = 83 cc/hr TPN prescription: Suggest TNA 13.4% dextrose, 4.4% amino acids, 2.7% lipids at 83 cc/hour provides 88 g. protein, 1800 kcals, 2000 ml. fluid

Evaluation of a TNA Order PN 15% dextrose, 4.5% a.a., 3% lipid @ 100 cc/hour

Evaluation of a PN Order PN 15% dextrose, 4.5% a.a., 3% lipid @ 100 cc/hour Total volume = 2400 Dextrose: 15g/100 ml * 2400 ml = 360 g 360 g x 3.4 kcal/gram = 1224 kcals Lipids 3 g/100 ml x 2400 ml = 72 g lipids 72 x 10 kcals/gram = 720 kcals

Evaluation of a PN Order Amino acids: 4.5 grams/100 ml * 2400 ml = 108 grams protein 108 x 4 = 432 kcals 1224 + 720 + 432 = 2376 total kcals Lipid is 30% of total calories Dextrose is 51.5% of total calories Protein is 18% of total calories

Calculation of Nonprotein Calories Some clinicians discriminate between protein and nonprotein calories although this is falling out of favor This is more commonly used in critically ill patients

Calculation of Non-Protein Calories To determine the nonprotein kcalories (NPC) in a TPN prescription, add the dextrose calories to the lipid calories In the last example, 1224 kcals (dextrose) + 720 kcals (lipid) = 1944 non-protein kcals Dextrose is 63% of nonprotein kcals (1224/1944) Lipid is 37% of nonprotein calories In critically ill patients, some clinicians restrict lipid to 30% of nonprotein kcals

Calculation of NPC:N Ratio | Calculate grams of nitrogen supplied per day (1 g N = 6.25g protein) Divide total nonprotein calories by grams of nitrogen Desirable NPC:N Ratios: 80:1 the most severely stressed patients 100:1 severely stressed patients 150:1 unstressed patient Source: http://www.csun.edu/~cjh78264/parenteral/calculation/calc07.html

Example NPC:N Calculation 80 grams protein 2250 nonprotein kcalories per day 80g protein/ 6.25 = 12.8 2250/12.8 = 176 NPC:N = 176:1 Source: http://www.csun.edu/~cjh78264/parenteral/calculation/calc07.html

Example %NPC Fat Calculation* 2250 nonprotein kcal 550 lipid kcal 550/2250 x 100 = 24% fat kcals *Limit is 60% NPC

Osmolarity in PPN When a hypertonic solution is introduced into a small vein with a low blood flow, fluid from the surrounding tissue moves into the vein due to osmosis. The area can become inflamed, and thrombosis can occur.

IV-Related Phlebitis

Calculating the Osmolarity of a Parenteral Nutrition Solution Multiply the grams of dextrose per liter by 5. Example: 100 g of dextrose x 5 = 500 mOsm/L Multiply the grams of protein per liter by 10. Example: 30 g of protein x 10 = 300 mOsm/L Multiply the grams of lipid per liter by 1.5. Example: 40 g lipid x 1.5 = 60. Multiply the (mEq per L sodium + potassium + calcium + magnesium) X 2 Example: 80 X 2 = 160 Total osmolarity = 500 + 300 + 60 + 160 = 1020 mOsm/L Source: K&M and PN Nutrition in ADA, Nutrition in Clinical Practice. P 626

Osmolarity Quick Calculation To calculate solution osmolarity: multiply grams of dextrose per liter by 5 multiply grams of protein per liter by 10 add a & b add 300 to 400 to the answer from "c". (Vitamins and minerals contribute about 300 to 400 mOsm/L.) Source: http://www.csun.edu/~cjh78264/parenteral/calculation/calc07.html

Is the solution compoundable? TPN is compounded using 10% or 15% amino acids, 70% dextrose, and 20% lipids The TPN prescription must be compoundable using standard base solutions This becomes an issue if the patient is on a fluid restriction

Is the Solution Compoundable? What is the minimum volume to compound the PN prescription? Example: 75 g AA 350 g dextrose 50 g lipid 2000 ml fluid restriction AA: 10 g = 75 g = 750 ml using 10% AA 100 ml X ml OR divide 75 grams by the % base solution, 75 g/ .10

Is the solution compoundable? Dextrose: 70 g = 350 g x = 500 ml 100 ml X ml Lipid: 20 g = 50g X = 250 ml 100 ml x ml Total volume = 750 ml AA + 500 ml D + 250 ml lipid + 100 ml (for electrolytes/trace) = 1600 ml (minimum volume to compound solution) Tip: Substrates should easily fit in 1 kcal/ml solutions

Is this solution compoundable? PN prescription: AA 125 g D 350 g Lipid 50 g Fluid restriction 1800 ml/day

Is this solution compoundable? AA: 10 g = 125 g = 1250 ml 10% AA 100 ml X ml Dextrose: 70 g = 350 g x = 500 ml (350/.70) 100 ml X ml Lipid: 20 g = 50g X = 250 ml (50/.20) 100 ml x ml Total volume = 1250 ml AA + 500 ml D + 250 ml lipid + 100 ml (for electrolytes/trace) = 2100 ml (minimum volume to compound solution) Verdict: not compoundable in 1800 ml. Action: reduce dextrose content or use 15% AA base solution if available (could deliver protein in 833 ml of 15%)

Parenteral Nutrition Monitoring

Monitoring for Complications Malnourished patients at risk for refeeding syndrome should have serum phosphorus, magnesium, potassium, and glucose levels monitored closely at initiation of SNS. (B) In patients with diabetes or risk factors for glucose intolerance, SNS should be initiated with a low dextrose infusion rate and blood and urine glucose monitored closely. (C) Blood glucose should be monitored frequently upon initiation of SNS, upon any change in insulin dose, and until measurements are stable. (B) ASPEN BOD. Guidelines for the use of enteral and parenteral nutrition in adult and pediatric patients. JPEN 26;41SA, 2002

Monitoring for Complications Serum electrolytes (sodium, potassium, chloride, and bicarbonate) should be monitored frequently upon initiation of SNS until measurements are stable. (B) Patients receiving intravenous fat emulsions should have serum triglyceride levels monitored until stable and when changes are made in the amount of fat administered. (C) Liver function tests should be monitored periodically in patients receiving PN. (A) ASPEN BOD. Guidelines for the use of enteral and parenteral nutrition in adult and pediatric patients. JPEN 26;41SA, 2002

Acute Inpatient PN Monitoring Parameter Daily Frequency 3x/week Weekly Glucose Initially √ Electrolytes Phos, Mg, BUN, Cr, Ca TG Fluid/Is & Os Temperature T. Bili, LFTs Adapted from K&M, p. 549

Inpatient Monitoring PN Parameter Daily Frequency Weekly PRN Body Weight Initially √ Nitrogen Balance HGB, HCT Catheter Site Lymphocyte Count Clinical Status

Monitor—cont’d Urine: Glucose and ketones (4-6/day) Specific gravity or osmolarity (2-4/day) Urinary urea nitrogen (weekly) Other: Volume infusate (daily) Oral intake (daily) if applicable Urinary output (daily) Activity, temperature, respiration (daily) WBC and differential (as needed) Cultures (as needed)

Monitoring: Nutrition Serum Hepatic Proteins Parameter t ½ Albumin 19 days Transferrin 9 days Prealbumin 2 – 3 days Retinol Binding Protein ~12 hours

Complications of PN Refeeding syndrome Hyperglycemia Acid-base disorders Hypertriglyceridemia Hepatobiliary complications (fatty liver, cholestasis) Metabolic bone disease Vascular access sepsis

Refeeding Syndrome Patients at risk are malnourished, particularly marasmic patients Can occur with enteral or parenteral nutrition Results from intracellular electrolyte shift

Refeeding Syndrome Symptoms Reduced serum levels of magnesium, potassium, and phosphorus Hyperglycemia and hyperinsulinemia Interstitial fluid retention Cardiac decompensation and arrest

Refeeding Syndrome Prevention/Treatment Monitor and supplement electrolytes, vitamins and minerals prior to and during infusion of PN until levels remain stable Initiate feedings with 15-20 kcal/kg or 1000 kcals/day and 1.2-1.5 g protein/kg/day Limit fluid to 800 ml + insensible losses (adjust per patient fluid tolerance and status) Fuhrman MP. Defensive strategies for avoiding and managing parenteral nutrition complications. P. 102. In Sharpening your skills as a nutrition support dietitian. DNS, 2003.

Glycemic Control in Critical Care Until recently, BG<200 mg/dl was tolerated in critically ill patients. Now greater attention is given to glycemic control due to evidence that glucose is associated with morbidity/mortality and risk of infection New recommendation is to keep BG<150 mg/dl or as close to normal as possible Van den Berghe et al. NEJM, 2001

Glycemic Control in PN In critically ill patients, recommendation is to keep dextrose infusion <5 mg/kg/minute or <60% of total kcals. ASPEN Nutrition Support Practice Manual, 2005, p. 267

Glycemic Control in PN For Patients Not Previously on Insulin Monitor blood glucose levels prior to initiating PN When therapy is initiated, monitor BG q 4-6 hours and use sliding scale or insulin drip as needed Add a portion of the previous day’s insulin to TPN to maintain blood glucose levels Charney P. A Spoonful of Sugar: Glycemic Control in the ICU. In Sharpening your skills as a nutrition support dietitian. DNS, 2003.

Glycemic Control in PN For Patients Previously on Insulin Determine amount of insulin needed prior to illness Determine amount of feedings to be given Provide a portion of daily insulin needs in first PN along with sliding scale or insulin drip to maintain glucose levels (generally insulin needs will increase while on PN) Charney P. A Spoonful of Sugar: Glycemic Control in the ICU. In Sharpening your skills as a nutrition support dietitian. DNS, 2003.

Regular Insulin in PN Availability in TPN : 53 – 100% Short half-life Delivery coincides with nutrient infusion

Fluid Excess Critically ill pts and those with cardiac, renal, hepatic failure may require fluid restriction May need to restrict total calories to reduce total volume Use most concentrated source of PN components (70% dextrose = 2.38 kcal/ml; 20% lipid = 2 kcal/ml) PPN may be contraindicated due to fluid volume of 2-4 liters

Fluid Deficit Patients with excessive losses may require sterile water added to the PN Provide consistently required fluid volume in PN Monitor I/O, weight, serum sodium, BUN, HCT, skin turgor, pulse rate, BP, urine specific gravity

Electrolytes Electrolytes in PN should be given at a stable dose with intermittent requirements for supplementation given outside the PN Sodium levels often reflect fluid distribution versus sodium status Hypokalemia may be due to excessive GI losses, metabolic alkalosis, and refeeding Hyperkalemia may be due to renal failure, metabolic acidosis, potassium administration, or hyperglycemia

Acid-Base Balance Balance chloride and acetate to maintain/achieve equilibrium The standard acetate/chloride ratio is 1:1 Increase proportion of chloride with metabolic alkalosis; increase proportion of acetate with metabolic acidosis Consider chloride and acetate content of amino acids

Metabolic Acidosis Etiology Increased renal or GI loss of bicarbonate Addition of strong acid or underexcretion of H+ ion Ketoacidosis Renal failure Lactic acidosis Excessive Cl- administration

Metabolic Acidosis Treatment Determine and treat underlying cause Prove acetate forms of electrolytes with HCO3- losses Decrease chloride concentration in TNA Consider chloride concentration in other IV fluids

Metabolic Alkalosis Etiology loss of H+ ion from increased gastric losses Excessive base administration Contraction alkalosis

Metabolic Alkalosis Treatment Determine and treat underlying cause Increase Cl- when alkalosis is due to diuretics or NG losses

Transitional Feeding Maintain full PN support until pt is tolerating 1/3 of needs via enteral route Decrease TPN by 50% and continue to taper as the enteral feeding is advanced to total TPN can reduce appetite if >25% of calorie needs are met via PN TPN can be tapered when pt is consuming greater than 500 calories/d and d-c’d when meeting 60% of goal TPN can be rapidly d-c’d if pt is receiving enteral feeding in amount great enough to maintain blood glucose levels

Cessation of TPN Rebound hypoglycemia is a potential complication Decrease the volume by 50% for 1-2 hours before discontinuing the solution to minimize risk PPN can be stopped without concern for hypoglycemia

Defense Against PN Complications Select appropriate patients to receive PN Aseptic technique for insertion and site care of IV catheters Do not overfeed Maintain glycemic control <150-170 mg/dl Limit lipids to 1 gm/kg and monitor TG levels Adjust protein based on metabolic demand and organ function Monitor fluid/electrolyte/mineral status Provide standard vitamin and trace element preps daily