Stomach
Indications:
- CKD patients who would not be able to tolerate metabolic acidosis
- Patients with little small bowel length
- Radiated small bowel
Pros:
- Less mucus
- Less permeable to urinary solutes
- Maybe less bacteriuria
- Generally minimal adhesions at stomach
Technical considerations:
- Blood supply is entirely from coeliac artery
- Left gastric artery – runs along lesser curvature of stomach
- Splenic artery – gives off short gastrics, and left gastroepiploic artery which runs in greater omentum
- Common hepatic artery – gives off right gastric and right gastroepiploic (from gastroduodenal artery)
- Typically a segment of the greater curvature is used, based off the more reliable right gastroepiploic
Complications:
- Hypochloraemic metabolic alkalosis
- Haematuria-dysuria syndrome – perhaps mediated by HCl secretion – consider PPI or H2 antagonists
- Dumping syndrome
Jejunum
Jejunum is generally not used due to the significance of metabolic and electrolyte complications.
Severe hyperkalemic, hypochloraemic, hyponatraemic metabolic acidosis.
In general, diseases that make the ileum unsuitable also make the jejunum unsuitable.
Ileum
Pros:
- Mobile and relatively easy to harvest
- Constant blood supply
- Well tested
Technical points:
- Arterial supply of small bowel is from the left side of the SMA, through a series of arcades
- Shorter vasa recta (straight vessels) and larger series of arcades which lie closer to the bowel wall (cf. jejunum)
- Terminal 15 cm of ileus should be spared
- Up to 8 cm of small bowel can potentially survival on a single straight vessel
- 2 parts of the small bowel may lie within the pelvis (important if has had pelvic radiation) – last 2 inches of terminal ileum, and 5 feet of bowel distal to Treitz which is on longest mesentery
- Those with neobladders will have more risk of metabolic complications cf. conduits due to larger amount of bowel harvested and longer urine dwell time
Complications:
- Hyperchloraemic hypokalaemic metabolic acidosis
- Reabsorption of ammonium -> ammonia and hydrogen
- Ammonia and chloride reabsorbed in exchange for excreted HCO3
- May cause generalised symptoms, lethargy, nausea
- Treat with sodium bicarbonate and potassium replacement
- Bone issues
- Buffering of acidosis results in bone loss (releasing calcium carbonate as buffer) and potentially hypocalcaemia
- This can also lead to hyperphosphataemia and stones, as well as bone disorders like osteomalacia
- Stones
- Systemic metabolic acidosis -> hypercalciuria and hypocitraturia
- Chronic UTIs and urea splitting organisms
- Foreign bodies such as suture and staple lines
- Hepatic encephalopathy
- The reabsorption of ammonium can lead to liver toxicity in those with poor liver function. Urea splitting organisms also increase ammonia load.
- B12 deficiency and bile salt malabsorption
- If large parts of the ileum, specifically the terminal ileum are used
Colon
Pros:
- Less stomal retraction and issues especially with exenteration
- Larger diameter and usually quite mobile
- Transverse colon, and parts of left and right can be used confidently in those with pelvic XRT
- Less post-operative bowel obstruction cf. ileum
- Anti-reflux techniques may be easier
Technical points:
- Large bowel is supplied by SMA (ileocolic, right colic, middle colic), IMA (left colic, sigmoid arteries, superior rectal) and internal iliac (middle rectal, inferior rectal from internal pudendal)
- Marginal artery of Drummond provides anastomotic link between middle colic and left colic – watershed area at 2/3 of transverse colon and splenic flexure
- Sudeck’s point is another watershed point – junction of last sigmoid artery and superior rectal
- Caecum is generally fixed in right lower quadrant
- Two peritoneal bands generally fix caecum and terminal ileum to posterolateral wall
- Right colon also fixed at level of liver – hepatocolic ligament
- Transverse colon generally free intraperitoneally within abdomen, fixed at splenic flexure by phrenocolic ligament and attached to stomach by greater omentum which hangs over the top from stomach
- Divide gastrocolic omentum close to colon – avascular plane here
- Descending left colon generally fixed to lateral wall, and sigmoid usually freely intraperitoneal
Complications:
- Hyperchloraemic hypokalaemic metabolic acidosis
- Severity and frequency of metabolic disturbances higher with ureterosigmoidostomies
- Bone issues
- Same as per ileum – buffering of acidosis leads to bone loss and potential hypocalcaemia
- Hepatic issues
- Reabsorption of ammonia sorted out by liver – an issue if liver not well functioning
- Urea splitting organisms also increase ammonia load
- Diarrhoea, malabsorbtion common if ileocaecal valve is used
Other issues with diversions
Abnormal drug kinetics
- Some drugs can be excreted in urine, and reabsorbed by bowel segments – phenytoin, lithium, methotrexate
Malignancy
- Combination of urothelium, colonic mucosa, urine and faeces may predispose to malignancy
- Average latent period of 20 + years
- Highest risk of ureterosigmoidostomies, ileocaecal pouch
- Potential mechanisms – ?bacteriuria with reduction of urinary nitrates to nitrites by gut bacteria, which react with urinary amines to form N-nitrosamines, implicated in carcinogenesis
Renal failure over time
- Multi-factorial: strictures, UTIs, stones, ?reflux
- Up to 6 % of patients with conduits die of renal failure
Factors influencing the type and severity of metabolic complications:
- Segment of bowel used
- Surface area / length of bowel
- Contact time with urine
- Urine composition – solutes, pH
- Renal function