Artificial nutrition

Indications:

5-7 days of expected inadequate intake
5-7 days of sustained inadequate intake

Enteral feeding

Delivery of nutrients into the GIT

Routes:

Oral, including supplements
- Patients who can drink but have impaired appetite or intake for other reasons
Tube-feeding (NGT/NJT/PEG/PEJ)
- Route selection
  - Standard NGT is ok, but use a fine-bore feeding tube if planning to do it for more than a week - causes fewer gastric and oesophageal erosions
  - If planning for more than 4-6 weeks, use a PEG to minimise risk of complications from long-term NGT
  - In most patients, it is appropriate to start with gastric feeding and then progress to jejunal feeding if required
  - Jejunal feeding may be preferable in pancreatitis or if there is another reason to want to bypass the stomach
- Techniques
  - Fine-bored NGT insertion
    - See 'NGT insertion'
  - PEG insertion
    - See description under 'gastroscopy procedures'
- Regime
  - Should have regime by dietician
    - Boluses of 200-500mL pushed by syringe several times per day - the most physiologic and easiest method - only for gastric feeding
    - Intermittent infusions over 20-30 mins - generally tolerated well in gastric/small bowel feeding tubes
    - Continuous - common in ICU - can be run overnight to increase appetite for eating during the day
  - Aim to reach goal rate at 2 or 3 days
  - Start at 20-30mL/hr
  - Discontinue feeding for 4-5 hours overnight to allow gastric pH to return to normal
  - Aspirates on a regular basis, and if they exceed 200mL over a two hour period, then feeding temporarily discontinued

Types of feeds:

Polymeric - contain intact protein, so require digestion
Elemental/monomeric - contain nitrogen in the form either free amino acids or peptides
- Much less palatable, rarely used
Other newer options may contain glutamine or fibre or arginine or fish oil, but generally seen as controversial and unproven

Advantages of enteral feeding as opposed to TPN:

Risks:

Resulting from intubation of GIT
- Malposition
- Blockage
  - Tube blockage is common, especially with fine-bore NGT
    - Prevention - flush twice daily
    - Treatment - flush with chymotrypsin or papain. Don't use guidewire as this may perforate the tube and/or patient.
- Displacement
  - Insert Foley if it comes out
  - If suspicious of displaced enterostomy, need contrast imaging
- Breakage/leakage
- Pressure necrosis of nasal mucosa
- Aspiration pneumonia
  - Keep head up while feeding
  - Use of PPI/H2 antagonist increases pH, which reduces risk of harm
  - Prokinetics if delayed emptying suspected
  - Consider more distal tube
Resulting from nutrient delivery
- Diarrhoea
  - Occurs in >30%, especially critically ill
  - Usually multifactorial, including antibiotic treatment
  - Villous atrophy due to prior periods without enteral feeding
  - Infections
  - Reducing feed rates or using loperamide/codeine to slow transit time can help
- Bloating
- Vomiting
  - Elevate head of bed
  - Continuous feeding
  - Assess sedation + analgaesia requirements
  - Oropharyngeal decontamination
  - Distal feeding
  - Prokinetics
Metabolic complications are uncommon
Enteric infections are rare if feeds are stored properly

Intolerance

Try more distal access
Prokinetics
Look for institutional protocols

Parenteral nutrition

Indications for TPN

1. Cannot or will not eat pre-op in elective surgery
2. GIT obstructed/prolonged ileus post-op (expected 10-14 days without adequate enteral nutrition, or earlier if malnutrition at baseline or complicated course)
3. 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
4. Short bowel syndrome
5. Enterocutaneous fistula from small bowel, esp high-output (about a third of these will spontaneously heal without operation)
6. IBD flare
7. 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