Parental Nutrition

Indications 

• intestinal failure (IF) due to disease or treatment 
• (short bowel syndrome, inflammatory bowel diseases, intestinal pseudo-obstruction, radiation enteritis), 
• high-output fistulas, 
• severe intestinal obstruction
• supplemental PN is also indicated to achieve estimated nutritional requirements.
• In post surgery patient-The ESPEN guidelines on clinical nutrition in surgery recommend that if oral and enteral intake cannot cover >50% of requirements for more than 7 days, a combination of enteral nutrition and PN is recommended 

—IF has been defined as a reduction in gut functions below the minimum necessary for the absorption of nutrients from the gastrointestinal tract to maintain health and growth.

Timing

• In well-nourished patients who are not able to achieve necessary nutritional requirements after 7 days 
• In patients at risk of malnutrition, within 3–6 days, if they are unlikely to achieve satisfactory oral nutrition or EN.

Vascular Access and Administration

• Most of the Peripheral PN formulations are between 750 and 900 mOsm/L. These formulations are based on a decreased dextrose concentration and osmolarity (by increasing final volume). Therefore, patients with fluid restriction should not be candidates for PPN due to the risk of fluid overload to achieve their energy requirements. 
• Peripheral PN is recommended for short-term therapies (≤10–14 days) because of the low reliability of peripheral VADs(Vascular Access Devices).
• peripheral PN < 900 mOsm/L for pediatric patients and <800–850 mOsm/L for adults 

• For administration of hyperosmolar PN admixtures, a central VAD is needed.
• The most common insertion sites include the subclavian, internal jugular, femoral, cephalic and basilic veins.
• Central VADs four categories: peripherally inserted central catheters (PICCs), nontunneled (inserted into jugular, subclavian or femoral vein), tunneled and implanted.

Administration

• Continuous infusion-Administration over 24h enables less manipulation and a lower infusion rate, limiting the overloading of glucose as well as fluids. 
• cyclic (discontinuous) schedule-during a portion of the day or night allows the patient freedom from the intravenous tubing and pump apparatus .Cyclic PN administration has also been used as a strategy against liver impairment associated with PN. When cyclic administration is proposed, glycemia should be monitored to avoid hypoglycemia after discontinuation, as well as hyperglycemia due to the increased rate of infusion.
• Risk of infusing particulates, recommendations to use in-line filters.
• PN admixtures should be protected from light.

Composition of PN Admixtures

• In an all-in-one system, also called total PN (TPN) or total parenteral admixture (TNA), all nutrients are mixed in a single bag and infused simultaneously. 
• To reduce osmolarity, PPN should have an increased total volume as well as reduced solutes (mainly macronutrients).
• General recommendations for PPN macronutrient content are as follows: amino acids < 4%, glucose < 10%. Consequently, a lower load of amino acids and glucose is often compensated for by an increased lipid load to achieve caloric goals due to the lower osmolarity of the lipids.

Proteins

• energy (4 kal/g) 
• 6.25 g of protein = 1 g of nitrogen
• Non-protein calories per nitrogen ratio range from 125 to 225 kcal/g N for non-stressed PN patients.if non protein calories are inadequate then protein will be used as sole source of energy 
• American Society for Parenteral and Enteral Nutrition (ASPEN) guidelines, the best non-protein calories/nitrogen ratio is from 70:1 to 100:1 for critically ill .patients, reduced to 30:1 to 50:1 for obese critically ill patients 
• the usual dose of protein is 1 g/kg of body weight for unstressed healthy patients 
• The recommended dose of protein in patients with acute renal failure is 0.6–0.8 g/kg/day 
• 0.8–1 g/kg/day in chronic renal failure. 
• renal replacement therapy is implemented (1.2–1.5 g/kg/day with hemodialysis and 1.3–2 g/kg/day with continuous renal replacement therapy).
• current European Society for Clinical Nutrition and Metabolism (ESPEN) guidelines recommend BCAA-enriched formulas in patients with hepatic encephalopathy in need of EN.

Carbohydrates

• most commonly used carbohydrate substrate is dextrose
• 4 kcal/g 
• 50–60% of total daily calories.
• minimum of 130 g of carbohydrates must be provided in healthy patients. 
• Continuous dextrose infusion rates in adult patients should be kept at ≤4–7 mg/kg/min

Lipids

• Each gram of fat provides 10kcal
• 20–30% of total daily calories
• 1 g/kg body weight/day 
• The currently available IVFEs are derived from soybean, safflower, coconut, olive or fish oil. 
• Commercially available IVFEs for PN have a 20% concentration
• Coconut oil is the source of medium-chain triglycerides (MCT) in IVFE. 

Micronutrients: Electrolytes, Vitamins and Trace Elements

• Baseline serum electrolyte measurements are recommended before ordering a PN solution and then electrolytes are added accordingly. 
• vitamins and trace elements should be administered daily, and therefore routinely added to PN solutions,

Complications and Monitoring

• Hyperglycemia -the most common complication of PN.
• Lipid overload has been associated with hypertriglyceridemia and liver dysfunction.
• In stressed patients, as well as in renal impairment, lipoprotein lipase activity is decreased leading to an accumulation of lipids in blood 
• Acceptable serum triglyceride concentrations for those receiving PN are <400 mg/dL 
• a lowering of dextrose has also been suggested if hypertriglyceridemia is thought to be associated with dextrose overfeeding. 
• Refeeding Syndrome-starting with a low caloric intake (10–20 kcal/kg/day or less in extreme cases) in patients at risk of RS, increasing slowly over 4–7 days to meet requirements
• Catheter-Related Complications
• vol-overload(if weight gain>1kg/day)

Hepatobiliary Complications

• Parenteral nutrition-associated liver disease (PNALD) is a spectrum of diseases that can range from mild liver enzyme abnormalities to steatosis to eventual fibrosis or cirrhosis. 
• There are three primary types of PNALD: steatosis, cholestasis, and gallbladder sludge/stones. Patients may have one of these disorders or a combination of the three. 
• Other terms for PNALD, intestinal failure-associated liver disease (IFALD) and parenteral nutrition-associated cholestasis (PNAC).
• occurs within 2 weeks of PN initiation.  

defined biochemically as 1.5 times the upper limit of normal elevation of two out of the following liver test: gamma-glutamyl transferase or alkaline phosphatase and/or serum conjugated bilirubin ≥2 mg/dL.

Monitoring

Rbs- 3times/daily

Na,k,Cl,Hco3,bun-daily until stable then 2/weekly

Cbs,creat,albumin,ca,mg,po4-baseline then 2/week

INR-baseline then weekly

Discontinuation of TPN

• When pt meets 75% of energy or protein requirement by enteral route
• Infusion rate halved for 1 hour, then again halved then stopped(tapered tp prevent hypoglycaemia)

Total Volume Required

• 25-35ml/kg/day add  insensible loss exp 10% increase with 1 degree celsius.