Nutrition – EN/PN

Master answer

Overview of parental nutrition

• Parental nutrition is the delivery of nutrients into venous circulation (peripherally or centrally) instead of the enteral route → it can be used to supplement nutrient delivery via enteral route, or supplement nutrient delivery in its entirety (total parental nutrition)
• It is prepared by sterile technique → typically a 3L bag of hyperosmolar solution (containing glucose, amino acids, lipids, H2O, electrolytes, vitamins and trace elements)
• It can only be administered by CVC due to its ↑ tonicity (Nb. issues with irritation and thrombosis if given via PIVC) → infused over 24 hrs
• It also requires multidisciplinary team involvement

Indications for parental nutrition

• Indicated for those unable to ingest or digest nutrients or to absorb them from GI tract for a prolonged period of time (> 3-4 days) → includes those who have:
• A failed trial of enteral feeding
• Contraindications to enteral nutrition:
  • GI obstruction
  • Upper GI strictures and fistulae (Eg. enterocutaneous fistulae)
  • Severe pancreatitis
  • Prolonged ileus (Eg. major abdominal surgery where feeding not anticipated for days, paralytic ileus)
  • Inflammatory conditions (Eg. IBD or mucositis due to chemotherapy)
  • Short gut syndromes (Eg. major SB resection)

Daily nutritional requirements for parental nutrition

BUT these vary according to:

• Physiological factors:
  • Age, gender, body size
  • Pregnancy
  • Activity level
  • Hydration status
• Pathological factors
  • Burns and sepsis → ↑ protein and caloric intake
  • Renal failure → ↓ volume, protein and electrolyte (esp K+) content
  • CCF → fluid reduction
  • Hepatic failure → ↓ a.a/protein content to prevent encephalopathy
  • Respiratory failure → ↓ glucose to minimise CO2 production

Components of parental nutrition

• (1) Energy source → glucose:lipid mixture (60:40 or 50:50)
  • Glucose (as 50% dextrose)
    • Used as an energy substrate → provides 50% of daily caloric needs
    • Glucose has ↓ energy density → 3.4 kcal/g only (cf. 4 kcal/g for carbohydrates) → 50% dextrose needs to be given (1 L = 940 kcal) → BUT this is hypertonic (1900 mosm/L) and requires delivery via CVC
    • Insulin can be given to aid glucose utilisation (esp in stressed patients)
    • Need to avoid excess glucose delivery → risk of ↑ BGL, lipogenesis (liver disease), ↑ MR and ↑ CO2 production (delayed ventilatory wean)
  • Lipid (as 10% or 20% intralipid)
    • Used as (i) an energy substrate (provides 30-40% daily caloric needs), and (ii) provision of essential FAs (vital for cell membranes and PG synthesis)
    • ↑ energy density cf. glucose → 1.1 kcal/mL (10%) and 2 kcal/mL (20%) → thus 1000 kcal can be achieved by 500 mL of 20% or 1L of 10%
    • Can be infused separately (Ie. not mixed with glucose/a.a. solution) → can be given 1x/week BUT usually given daily to aid caloric delivery in the smallest volume of solution –
• Nitrogen-source (as symthamin 17)
  • Used for (i) tissue protein synthesis (Eg. enzymes) and (ii) caloric needs
  • Includes > 50% essential a.a.’s (isoleucine, leucine, valine, lysine, methionine, phenylalanine, threonine, tryptophane) and > 25% branched chain a.a
  • Nb. A.a. are all L-isomers (as the body cannot use D-isomers)
• H2O → to maintain body H2O balance and replace losses (Eg. dehydration, bleeding)
• Electrolytes (Na+ /K+ /Cl- /PO4 3-/Mg2+, Ca2+) → to maintain and replace losses
• Vitamin/trace elements → vital to enzyme systems and metabolic pathways in body
  • Vitamin solutions – both H2O and fat-soluble vitamins (esp folic, thiamine, vitamin K)
  • Trace elements (Zn, Fe, Cu, Mn, Co, Se, I, Cr, Mb)

Monitoring of parental nutrition

• Needed to assess for (i) progress of nutritional state and (ii) complications of therapy
• Involves:
  • Clinical r/v (Eg. fluid balance, weight, nutritional assessment, infections)
  • Frequent ward glucose testing (until BGL stabilises)
  • Investigations → daily EUC, CMP, BGL; weekly FBC, LFT (incl albumin), Coags, Lipid studies, and plasma/urine osmolality

Complications of parental nutrition

• Catheter-related (MOST common) → PTX, chylothorax, embolism (air/thrombus), infection, Etc.
• Fluid/electrolyte disturbances
  • Fluid overload or hyperosmolar dehydration
  • Electrolyte disturbances
  • Normal AG metabolic acidosis (due to ↑ Cl- content)
• Metabolic disturbances
  • Hyperglycaemia (initially) → delay in ↑ endogenous insulin (thus supplemental insulin required)
  • Rebound hypoglycaemia (with abrupt cessation of TPN) → due to ↑ levels of endogenous insulin
  • Metabolic bone disease
• Others:
  • Immune suppression (due to fat component)
  • Liver disease → initially deranged LFTs → later fatty liver/steatohepatitis
  • ↑ PaCO2 (due to excessive glucose metabolism)

Bianca