Total Parenteral Nutrition (TPN)

OVERVIEW

  • Total parental nutrition is the complete provision of nutrition intravenously, bypassing the GI tract.

INDICATIONS = unable to establish enteral feeding

General

  • EN contraindicated (have low threshold to use perioperatively depending on nutritional state)
  • EN fails to meet nutritional requirements

Specific

  • prolonged bowel obstruction and ileus
  • short bowel syndrome with severe malabsorption
  • severe dysmotility
  • high output intestinal fistulae
  • anastomotic break down
  • intolerance to EN

GENERAL

  • ensure adequate central venous access (subclavian lines have lowest infection rates – aseptic insertion, 2% chlorhexidine in alcohol, permeable polyurethane dressings, antimicrobial catheters)
  • dedicated lumen for TPN (daily infusion set changes)
  • if requires TPN for > 2 months -> consider tunneled line
  • assess why patient cannot be enterally fed -> this is known to be safer
  • 12 hourly reassessment of whether patient can be enterally fed
  • requires close liaising with dietician and pharmacy

ASSESSMENT OF NUTRITIONAL STATUS (CALORIC REQUIREMENTS)

  • calculate Resting Energy Expenditure (using the Harris-Benedict equation)

REE (males) = 66.5 + (13.7 x body weight in kg) + (5.0 x height in cm) (6.8 x age in years)
REE (females) = 66.5 + (9.6 x body weight in kg) + (1.7 x height in cm) (4.7 x age in years)

  • use ideal body weight
  • resting energy expenditure in calories
  • multiply this by a stress factor to allow for effects of disease (no exercise = 1.2, very heavy exercise BD = 1.9)
  • more accurate to measure REE by indirect calorimetry
  • most hospitalized patients require 25-30 kcal/kg/day
  • mechanically ventilated are on the lower aspect of range
  • burns and trauma patient may require 45 kcal/kg/day
  • high protein hypocaloric nutrition preferred in obese patents (esp BMI >40)

NUTRITIONAL REQUIREMENTS

Protein

  • utilisation of exogenous protein = 1.5g/kg/day
  • other techniques:

-> non-protein calorie to nitrogen ratio (100-200kcal/g of nitrogen often used)
-> nitrogen balance = (protein intake (g) / 6.25) – (urinary nitrogen (g) + 4) -> 4 = empirical factor added to account for non-urinary nitrogen loss (faeces and sweat)

  • crystalline solutions of L-amino acids (varying essential amino acids)

Carbohydrates

  • daily requirement of glucose = 4-5g/kg/day in severely catabolic patients

Lipids

  • requirements 1g/kg/day
  • 1/3 of energy given as non-protein
  • advantages: prevents fatty acid deficiency and provides more concentrated calories
  • disadvantages: can cause pancreatitis, immunosuppression, overfeeding -> increase in CO2 production
  • check lipids daily and check clearance of lipids

Minerals and Micronutrients

  • Na+, K+, Ca2+, Mg2+, phosphate -> guided by serum plasma levels
  • inorganic trace elements
  • organic vitamins (thiamine, folic acid, fat soluble vitamins D, E, K, A, water soluble vitamins B and C)

H2O

  • 25-40mL/kg/day (+ losses)

MONITOR FOR COMPLICATIONS

  • catheter related sepsis
  • catheter occlusion
  • hyperglycaemia
  • hypercholesterolaemia
  • refeeding syndrome (Po43-, K+, Mg2+)
  • abnormal LFTs
  • trace elemental deficiency: > 2-4 weeks of poor nutrition
  • copper: anaemia, neutropenia
  • iodine: hypothyroidism
  • chromium: glucose intolerance
  • zinc: mental apathy, diarrhoea, rash
  • selenium: cardiomyopathy

-> treatment: supplement, follow levels (serum, tissue, white cells)

PRESCRIPTION

  • total energy: 25 kcal/kg/day
  • protein: 1.5g/kg/day
  • carbohydrate: 4g/kg/day
  • lipids: 1g/kg/day
  • H2O: 30mL/kg/day + other losses
  • electrolytes
  • organic vitamins
  • inorganic trace elements

AN APPROACH

  • exhaust all means of feeding enterally
  • dietician involvement
  • calculate requirements (caloric and nutritional)
  • start slowly
  • monitor for refeeding and complications
  • frequent reassessment about whether patient can be fed enterally

VIDEO

Roger Harris on the physical properties of TPN solution (nothing to do with sex!):

References and Links

Journal articles

  • Ziegler TR. Parenteral nutrition in the critically ill patient. N Engl J Med. 2009 Sep 10;361(11):1088-97. doi: 10.1056/NEJMct0806956. Review. PubMed PMID: 19741230; PubMed Central PMCID: PMC3064749.

FOAM and web resources

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