Editing Artificial nutrition (section)

== '''Parenteral nutrition''' ==

=== '''Indications for TPN''' ===

*# Cannot or will not eat pre-op in elective surgery
*# GIT obstructed/prolonged ileus post-op (expected 10-14 days without adequate enteral nutrition, or earlier if malnutrition at baseline or complicated course)
*# Short-term TPN is permissible in patients with obstructive GIT malignancy, but ONLY if there is a prospect of either resolution (e.g. on chemo) or as a bridge to surgery
*# Short bowel syndrome
*# Enterocutaneous fistula from small bowel, esp high-output (about a third of these will spontaneously heal without operation)
*# IBD flare
*# Gut not usable due to major intra-abdo sepsis

=== '''Contraindications to TPN''' ===

** Any patients not meeting above criteria

=== '''Post-op''' ===

** '''Indications'''
*** Anastomotic leak
*** Gastrointestinal fistula
*** SBO/ileus
*** Post-op delayed gastric emptying
*** Chyle leak
*** Inadequate absorptive capacity
*** Feeding tube complications
*** Pre-existing malnutrition
** '''Absolute contraindications'''
*** Able to receive enteral feeding
*** Anticipated duration of fasting less than 5 days
*** Terminal illness with short life expectancy
*** Refusal/advance directive
** '''Relative contraindications'''
*** Shock - can worsen their condition
*** Catheter-related infection
*** Acid-base disturbance
*** Severe electrolyte disturbance
*** Refeeding syndrome
*** Volume overload
*** Lack of central venous access
** '''Timing'''
*** Risks outweigh benefits for first five days post-op in most patients
*** Can start earlier than five days in patients with chronic malnutrition and anticipated prolonged fasting
*** Should certainly be given at 14 days of starvation in otherwise healthy patients

=== '''Formulation''' ===

** Macronutrients
*** '''Carbohydrates''' - about 75% of calories supplied as glucose - aim about 2g/kg body weight/day
**** The dextrose content is expressed as weight per volume: 5% dextrose means 5g dextrose per 100mL water
*** '''Lipid''' emulsion is a soluble form of fat which allows it to be infused. Consists of an oil stabilised in an emulsion with egg yolk lecithin. No clinical benefit to giving fat in amounts greater than 30% of total energy.
**** Rate of lipid clearance from blood does not reflect rate of oxidation - normal triglyceride levels doesn't guarantee the infusion rate is appropriate
**** Lipid content usually expressed as a percentage of weight per volume, i.e. 10%, 20% or 30% are commonly used.
*** '''Protein''' supplied as free amino acids - concentration expressed in terms of nitrogen content. Relatively low amounts of protein, about 1g/kg body weight/day. No evidence for using specific amino acids.
** Micronutrients
*** Must be added separately, starting from the first day, since most patients getting TPN will also be deficient in micronutrients to start with
*** Water-soluble vitamins
**** B1 thiamine
**** B2 riboflavin
**** B3 niacin
**** B5 pantothenic acid
**** B6 pyridoxine
**** B7 biotin
**** B9 folic acid
**** B12 cobalamin
**** C ascorbic acid
*** Fat-soluble vitamins
**** A
**** D
**** E
**** K
*** Trace elements
**** Chromium
**** Copper
**** Iodide
**** Iron
**** Manganese
**** Molybdenum
**** Selenium
**** Zinc
*** Electrolytes
**** Sodium
**** Magnesium
**** Calcium
**** Potassium
**** Phosphorus
** '''Situations where formula is likely to need altering:'''
*** Increased GIT losses - often needs more zinc, copper and selenium
*** Biliary losses - need more copper and manganese
*** Burns - more zinc, copper and selenium, as these are lost in burn exudate
*** Pregnancy - no set recommendations
*** Renal failure - caution - excretion of some trace elements is altered, so can overdose
*** Liver disease - likely to be low in folate, vitamin C, thiamine, B group vitamins
*** Refeeding syndrome - monitor for it

=== '''Route of administration''' ===

** Peripheral
*** Appropriate for short-term feeding (up to two weeks)
*** Can be given via a conventional canula (need to re-site it every 12 hours to avoid permanently destroying veins via thrombophlebitis) or a PICC
*** Mandates the use of isotonic solutions to avoid thrombophlebitis
*** No point in doing it if central access already exists
** Central
*** Can be given via a PICC or central line. Small risk of thrombophlebitis through a PICC.
**

=== '''Regime''' ===

** Main consideration when setting rate is not to overfeed patient. It's usually safe to start at goal rate, with close monitoring of BSLs. The exception is patients at risk of refeeding.
** Prescribing (as per Austin guideline 2021)
*** Day 1: TPN 1000mL over 24 hours
*** Day 2: TPN 2000mL over 24 hours
*** From this point on, need advice on target rate from dietician

=== '''Monitoring (in initial, acute setting)''' ===

** Baseline FBE, UEC, CMP, LFT, INR, triglycerides
** Check electrolytes six hours after starting, if high refeeding risk
** Daily weight
** Daily bloods: FBE, UEC, CMP, LFT, INR
** Can step down to second-daily after a week or two if everything is stable
** Long-term micronutrient screen:
*** Vitamins A, D, E, K, B12, folate
*** Copper
*** Selenium
*** Zinc
*** Manganese
*** Chromium
*** Molybdenum
*** Calcium
*** Iodine
*** Aluminium
*** Carnitine
*** Choline

=== '''Stopping TPN''' ===

** Stop once patient is able to consume about 75% of their energy requirements orally/enterally 
** Continue monitoring for rebound hypoglycaemia, especially if no other nutrition yet or patient is taking insulin (peripheral infusions, which are low in glucose, rarely cause problems)
** Consider a tapering regime if BSLs are a bit labile or other factors, but often can be just stopped
** Can be continued through surgery, but it's a bit annoying for nurses, so is usually just stopped

=== '''Complications''' ===

** Related to nutrient deficiency
*** Refeeding syndrome
**** Severe fluid and electrolyte shifts in malnourished patients undergoing refeeding
**** Results in low phosphate, magnesium and calcium
**** Need to replace phosphate and magnesium and increase TPN rate slowly
****
*** Chronic deficiency syndromes
** Related to overfeeding
*** Excess glucose: hyperglycaemia (may need insulin infusion), hyperosomolar dehydration, hepatic steatosis, hypercapnia, increased sympathetic activity, electrolyte abnormalities
*** Excess fat: hypercholesterolaemia/hypertriglyceridaemia
**** Consider whether propofol is being used - also has a high lipid content - reducing it can help with triglyceride levels
**** Alternatively, some lipid-free emulsions are available
*** Excess amino acids
** Fluid overload
** Deranged LFTs
*** Intra-hepatic cholestasis
*** Hepatic steatosis
*** Hepatomegaly 
*** Sometimes need to reduce fat content of TPN in this setting
*** For more discussion on what to do about LFT derangements with TPN, see the 'LFTs' page under Periop medicine
** Catheter-related blood-stream infection
*** Prevent by choosing the right site (avoid femoral), hand hygiene, alcohol-based chlorhex skin prep, maximum barrier precautions, catheter-care guidelines
*** Suspect CLABSI with low-grade fever for a few days, then spiking fever and rigors. Take cultures from the line and also somewhere else. Culture tip when removing CVC. Will need 24-48 hours of adequate Abx coverage before reinserting central line.
*** Ideally, whenever line infection is suspected, you would remove the line and culture the tip. However if this is going to create problems, a compromise would be to just culture the line.
** Blocked line
*** Flush with saline
*** Occasionally alteplase/urokinase are used
** Central venous thrombosis
*** As per topic under 'vascular'

=== '''Long-term complications''' ===

** Osteoporosis
** Liver dysfunction
** Gut atrophy
** Renal dysfunction
** Hyper-manganesaemia

[[Category:Nutrition]]