SHORT GUT SYNDROME


DEFINITION

A syndrome primarily characterised by diarrhoea, electrolyte imbalance and malnutrition, typically after surgical resection of an extensive portion of the intestine.

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INCIDENCE

Varies by aetiology.
Surgical resection is most common in neonates and elderly.
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AETIOLOGY

Massive surgical resection, e.g. following:

Congenital
Malrotation / malfixation of the midgut loop with volvulus.
Congenital atresia.
Hirschprung's Disease.
Intussusception.

Inflammatory
Necrotising colitis (in preterm babies).
IBD.

Tumours
Multiple tumours, e.g.  adenocarcinoma, carcinoid

Degenerative / vascular
Arterial thrombosis / midgut infarction, embolism.

Mechanical
Strangulated herniae with massive infarction

Trauma

Abdo trauma.

Idiopathic

Iatrogenic radiation enterocolitis.
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BIOLOGICAL BEHAVIOUR

Physiology

How much bowel is enough?
Can go down to 75cm, assuming intact pylorus and ileocaecal valve.
If no colon, need 150cm for independence from TPN.
Pts with e.g. crohn's require a greater length of bowel

Pathophysiology
Depends on site and extent resected.
May affect any small-bowel function:

Proximal bowel
If a significant amount resected (~50-100 cm), transit time decreases and malabsorption pertinent.
Electrolytes & water follow diarrhoea.
Protein, minerals, CHO, fat absorption.

Terminal Ileum
Bile salt losses.
Fat absorption deficit.
B12 deficit (intrinsic factor resorption).
Fat soluble vitamins absorption deficit (DEKA).

Role of Colon
Recruitment of bypassed colon has advantages and disadvantages
Better fluid, electrolyte and some nutrient absorption
But in context of ileal loss, bile acid diarrhoea may increase output causing perianal excoration.
- (may be beneficial to move to an end sigmoidoscopy when reversing ileostomy in anticipated cases of severe ileum loss so as to prevent this)

Complications
Gastric hypersecretion.
Renal calculi.
- due to hyperoxaluria due to increased oxalate absorption
- fatty acids increased in lumen, so bind Ca2+, stopping it from binding to oxalate and forming insoluble calcium oxalate to be secreted.
Gallstones (cholesterol and bile salt production increase).

Adaptation
Remaining bowel undergoes morphologic and physiologic changes
- villous hypertrophy and hyperplasia
--> increased surface area.
This reduces loss of fluids and electrolytes after a resection.
Also increased efficiency of absorption by increased number and density of amino acids and glucose transporters
However, adaptive absorption of more nutrient lags
- depends on location of remaining bowel, feeding enterally and patient's own degree of volitional intake
Mediated by gut hormone signals
- hence focus on hormonal therapies to speed up adaptation.
 
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MANIFESTATIONS

Symptoms

Local
Diarrhoea (transit time).
Steatorrhoea (fat malabsorption).
Cholerrhic diarrhoea (bile salts stimulate Na and H20 secretion).

Systemic
Growth retardation in children.
Weight loss (malabsorption).
Accompanying nutrition deficit.

Specific losses
Features of anaemia with symptoms.
Features of electrolyte imbalances (Ca2+, Na+, K+, Mg2+).
Including tetany, cramps, paraesthesia, osteoporosis / bone pain.
Vitaminosis D, E, K, A and symptoms.
Eg vision issues, osteomalacia.
Possibly oedema / clotting issues (protein losses).

Complications
Peptic ulcer & symptoms.
Renal stones & symptoms.
Gallstones & symptoms.

Signs

As appropriate to cause.
Malabsorption.
Weight, pallor, bones, etc.
Others as relevant to complications.
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INVESTIGATIONS

Bloods
FBC.

Biochemistry
Electrolytes.
Vitamin levels.
Protein (albumin, clotting time).

Imaging
Eg for complications.
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MANAGEMENT

Principles
Maximize function of remaining bowel
If that cannot be achieved, efforts to avoid TPN complications and to augment enteral feeding.

Management Strategies
      1.       Acute phase
      a.       Treat postoperative complications
      b.       Maintain full support via the parenteral route
      c.       Initiate low-rate trophic enteral feeds
      d.       Document amount and site of remaining bowel and underlying disease

      2.       Early adaptation (up to 1 year postsurgery)
      a.       Increase enteral nutrition to tolerance; supplement with glutamine
      b.       Achieve permanent parenteral access, if indicated
      c.       Maximize antiperistaltic agents
      d.       Octreotide for high output ostomy or fistula
      e.       Dietary counseling
      f.        Clinical trials of trophic growth factors

      3.       Long-term adaptation (>1 year postsurgery)
      a.       Recruit bypassed bowel
      b.       Bowel-lengthening procedure (Bianchi or STEP)
      c.       Monitor for development of TPN-associated complications, and refer for transplant prior to recurrent sepsis, thrombosis, or end-stage liver disease

1. Avoid Dehydration and Reduce Diarrhoea
Avoid Na and water depletion.
- may occur from diarrhoea, stomas, as well as third spacing
Measure all ostomy outputs and judicious parenteral fluid supplementation.
Avoid hyperosmolar foods, lactose, high fat diet.

2. Optimize Nutritiona
Close involvement of dietician
Ensure nutrient support for deficiencies.
TPN may be necessary.
- but even small amounts of enteral feeding are crucial for accelerating adaption and reducing septic complications from translocation
- use only percutaneous subclavian lines for TPN (sepsis); preferable to int jugular as difficulty in maintaining dressings next to tracheostomy sites.
Trial enteral feeding at 10ml/hr initially, increasing by 5-10ml/hr each day as tolerated.
- monitor stomal / diarrhoea losses and watch for metabolic acidosis.

3. TPN Administration
1.5 g protein / kg / day
30 kcal / kg / day
Patients may become hyperglycaemic due to sepsis or surgical stress
-->  mixed fuel substrate with reduced dextrose (15%) and 25% of calories as fat; and insulin infusions may be needed

4. Anti-motility agents
Ie loperamide, codeine, phenoxylate. 
Ocreotide may reduce fluid and electrolyte losses
- but inhibits trophic hormones, slows adaptation, and associated with hyperglycaemia
- still useful for controlling fluid and electrolyte losses, especially when stoma is poorly fitting
- short term then move to once-monthly depot prep.

5. Once acute phase is over, increase oral feeding
Appropriate diet depends.
Oral rehydration solutions are higher in electrolytes, encouraged to maintain euvolemia.
- though if colon present, that helps fluid and electrolyte absorption, soluble fibre supplementation creates short-chain fatty acids and provides additional calories.
Diets are high in protein (30% calories), limited in fat, and are 40% complex carbohydrates.
- patients with massive ileal resections should receive medium chain fatty acids

6. Glutamine
A conditionally essential amino acid, primary fuel of enterocytes and supports GI immune function.
Conventional TPN does not contain glutamine.
Supplementation either IV or orally
Improved nutrient uptake and reduced TPN dependence if combine oral glutamine, parenteral growth hormone, and specialized diet.
Oral dose is 0.5 mg/kg/day

7. Gastrin
Patients become hypersecretary with elevated gastrin.
- can reduce with H2 antagonists or PPIs
But permissive hypergastrinaemia is a tropic gut signal

8. Treat any Overgrowth
Pts with strictures or defuntionalized segments may have bacterial overgrowth, leading to diarrhoea and further fluid and electrolyte loss
Rotate nonabsorbable antibiotics (e.g. tetracyclines) may help symptoms but not necessarily absorption.

9. Role of hormone augmentation
a) Human Growth Hormone
Anabolic protein that initiates cell division and regulates nutrient metabolism
- with stimulation of protein synthesis and gluconeogensis
Anterior pituitary gland hormone
- effect mediated through IGF1
Approved by FDA for use in short gut syndrome but only in a comprehensive program of intestinal rehabilitation
- associated with fluid retention, joint pain and hyperglycaemia.

b) Epidermal Growth Factor (EGF)

Peptide from saliva and pancreas that bathes the GI tract.
Overexpression leads to massive villous hypertrophy and hyperplasia
Promising but not yet available commercially, investigational.

c) Glucagon-like Peptide 2
Most tropic hormone; released from 'L cells' in ileum and colon.
Structural adaptation of small bowel and upregulation of jejunal nutrient transport
Improves intestinal absorption of energy, weight and nitrogen.
Also slows gastric emptying.
Long-acting version teduglutinate in phase III trials.  Promising

Surgical Considerations

1. At baseline operation
Document clearly length and location of residual gut
Biopsy liver if suspect as a baseline prior to TPN
Prophylactic cholecystectomy is appropriate

2. Nipple valves, reversed segments, colonic interpositions?
Theoretic advantage of slow motility outweighed by complications (mainly obstructions)
Not advised.

3. Bowel dilation...
As bowel adapts, it also dilates
- does not necessarily improve absorption, but can be surgically used to achieve length.

Bianchi procedure

image
Mesentery divided in two
Split longitudinally and reanastomosed
Good results in expert hands but damage to mesenteric vessels can make the problem worse
So not done often

Serial Transverse Enteroplasty Procedure (STEP)
Bowel plicated intact at mesenteric and antimesenteric edges
image
2cm gaps, consistent with normal bowel calibre; can double bowel length.
TPN wean rate 60%

Intestinal Transplant
Continues to develop
Good outcomes considering critically ill nature of patients subjected
- 1yr survival 80%; 3yr survival 50%
In patients with progressive TPN liver disease, can combine with a liver transplant
Main challenge is identifying patients who fail to adapt (often with ultra-short gut <60cm) and likely to get TPN liver disease
- recurrent bouts of line sepsis and fungaemia are another indication that TPN will fail.
Living relative donation is a developing option but technically extremely difficult.
- optimal human leukocyte antigen matching.

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