Intestinal obstruction Flashcards
What is the pathophysiology of bowel obstruction?
- Bowel segment gets occluded
- Gross dilatation of proximal bowel occurs
- Increase in peristalsis causes secretion of large amounts of fluid rich in electrolytes
- This is third spacing
- So urgent fluid resuscitation is needed
- If obstruction is not relieved there is risk of bowel perforation and peritonitis
Name 3 causes of bowel obstruction.
- Colonic carcinoma
- Diverticular disease
- Sigmoid volvulus
What are the two main causes of large bowel vs small bowel obstruction?
Large - malignancy, volvulus, diverticular disease
Small - adhesions or hernia
What 4 categories do causes of intestinal obstruction fall into?
LIFE categories:
L uminal discontinuity (e.g., atresias)
I nspissated (thickened) luminal contents (as seen in meconium ileus)
F ailure of normal intestinal peristalsis (as seen in Hirschsprung disease)
E xternal compression of the bowel (as seen in volvulus or more rarely, abdominal masses)
How can you split up the mechanical causes of intestinal obstruction?
Describe the onset of small bowel obstruction vs large bowel obstruction.
Small bowel - manifests within hours of onset as the large volume of gastric and pancreaticobiliary secretions builds up
Large bowel - more insidious in onset and delayed by as much as a week
What are the clinical features of intestinal obstruction?
Vomiting - early in proximal obstruction
- e.g. semidigested food eaten a day or two earlier = gastric outlet obstruction
- e.g. bile-stained fluid = upper small bowel obstruction
- If vomitus becomes thicker and foul-smelling (i.e. faeculent - misnomer as still small bowel content ) = more distal obstruction
Absolute constipation - early in distal obstruction, late in proximal obstruction
Abdominal pain - colicky, mild in uncomplicated obstruction; upper, middle or lower abdominal pain originates in foregut, midgut or hindgut, respectively
Focal tenderness/ guarding/ rebound tenderness - although this should not develop unless there is ischaemia developing
Tympanic sound on percussion - gas rises, flanks will be dull
Auscultation with tinkling bowel sounds - loud and frequent
Dehydration - due to third spacing
Visible peristalsis - only in very thin patients
+/- Hernia - visible in groin with or without strangulation
What are the effects of competence of ileocaecal valve on intestinal obstruction?
Competency has an effect on LARGE BOWEL obstruction
Competent ileocaecal valve → no retrograde flow → caecum distends and eventually ruptures (when it reaches 10 cm, it is in imminent danger of rupture)
What might visible peristalsis signify?
It is a hallmark of incomplete obstruction
What investigations should you do in bowel obstruction?
FBC
Monitor U&Es
VBG - lactate checks for end organ function
Group & save
CT contrast abdo pelvis - 1st line for diagnosis and treatment guidance
NB: AXR still used in some settings.
Summarise the radiological findings in obstruction.
- Small bowel obstruction – Dilated >3cm, central abdominal location, and valvulae conniventes visible
- Large bowel obstruction – Dilated >6cm, or >9cm if at the caecum, peripheral location, and haustral lines visible
What is the management of bowel obstruction?
Conservative
- NBM
- IV fluids - patients often depleted due to third spacing + urinary catheter + fluid balance chart
- NG tube if vomiting and gastric contents aspirated
- Refer to surgeons +/- arrange for surgery within 6hrs if suspecting ischaemia or strangulation
- Analgesia - opioids e.g. IV morphine sulfate
- Antiemetics - not prokinetic ones like metoclopramide
Small bowel obstruction:
- Complicated: Emergency surgery e.g. laparoscopic - if peritonitis, strangulation or bowel ischaemia
- Uncomplicated: Non-operative for 72hrs - if no resolution of adhesional obstruction, then surgical management
Large bowel obstruction:
- Conservative - for diverticulitis give abx and fluids, monitoring for complications
- Flexible sigmoidoscopy - for volvulus
- Enemas/manual removal - large bowel obstruction caused by faecal impaction
- Emergency surgery- if perforation
- Bowel stenting - for malignant cause with palliation only
What is the definitive management of different causes of SBO?
What are the 3 main types of surgery for LBO?
Right hemicolectomy - ileocaecal valve is removed and caecum
Hartmann’s - sigmoid colon is removes with formation of iliac fossa colostomy
Subtotal/total colectomy - for obstructing lesions in descending or sigmoid colon when caecum has torn. Ileosigmoid or ileorectal anastomosis can be done if patient is well enough
What is the prognosis with bowel obstruction?
- 2/3 uncomplicated cases of obstruction are caused by adhesions
- these usually resolve in 4days with conservative management
A 68-year-old male presents to the surgical assessment unit with a one-week history of increasing abdominal pain and discomfort with constipation. On further questioning he gives a history of alteration in bowel habit and intermittent blood mixed in the stool over the past three months. He has lost ½ stone in weight. He is not taking any medication and has no other history to note.
What is the most likely diagnosis and why?
Colorectal malignancy with bowel obstruction - typical or a left sided/rectal carcinoma. No evidence of sepsis or ileus making megacolon, infection and abscess formation unlikely.
What is the most likely site of rupture in large bowel obstruction?
Caecum - it has the thinnest bowel wall
Law of Laplace
Is US useful in obstruction?
Ultrasound will be of limited use in the presence of bowel obstruction as gas will degrade the images
More useful investigations:
- DRE
- Rigid sigmoidoscopy
- Erect chest radiograph
- AXR
- ECG
What does this x-ray show?
- Gross caecal dilatation with loss of haustra - ileocaecal valve is competent
- T - transverse colon with gas and there is absence of gas on the left side of colon so it can be deduced that the colon is obstructed near the splenic flexure
- G - gas in the extraperitoneal tissues. This patient had an obstructing carcinoma at splenic flexure and the caecum was perforated.
What does this x-ray show?
- Erect film showing multiple loops of dilated small bowel and multiple fluid levels.
- The obstruction was caused by a small carcinoma of the medial wall of the caecum encroaching upon the ileocaecal valve.
Note: erect abdominal films are rarely taken nowadays
What does this AXR show?
Large bowel dilatation in keeping with obstruction extending into the pelvis
The large bowel is dilated – note haustrations to identify and peripheral distribution. There is no gas in the rectum making pseudo-obstruction unlikely. No thumb-printing is evident to suggest ischaemia. Note also right hip replacement.
What does this x-ray show?
Mid small bowel obstruction.
- Dilated small bowel loops fill the upper left quadrant and centre of the abdomen
- The small bowel distal to the obstruction is collapsed and is not visible on this film.
- have valvulae conniventes (plicae circulares [P]) extend across the whole width of the lumen
- faecal loading of the ascending colon (F)
- small amount of gas in the sigmoid colon (S) .
- Note also the metallic tip of the nasogastric tube and the incidental radiopaque gallstone.
What happens to the ileocaecal valve after large bowel obstruction?
It usually becomes incompetent allowing small bowel to distend and delaying the onset of obstructive symptoms
Define pseudo-obstruction.
Pseudo obstruction = Ogilvie syndrome in the acute setting; characterised by dilatation of the colon due to an adynamic bowel, in the absence of mechanical obstruction.
Differences:
- Usually has normal bowel sounds/inaudible.
- In most cases resolves with conservative measures.
- Related to e.g. retroperitoneal inflammation, haemorrhage, neurology , biochemical abnormalities, certain drugs (anticholinergics).
What is the pathophysiology of pseudo-obstruction?
Unknown
May be due to interruption of autonomic nervous system so that there is no smooth muscle action in bowel wall
What are the complications of pseudo-obstruction?
Toxic megacolon
Bowel ischaemia
Perforation
Therefore must still be managed where possible.
What are the causes of pseudo-obstruction?
-
Electrolyte imbalance or endocrine disorders
- Including hypercalcaemia, hypothyroidism, or hypomagnesaemia
-
Medication
- Including opioids, CCBs, or anti-depressants
-
Recent surgery, severe illness, or trauma
- Includes MI
-
Neurological disease
- Includes Pd, MS and Hirschsprung’s disease
What are the clinical features of pseudo-obstruction?
- Abdo pain
- Distension
- Constipation - or passing abnormal stools, or paradoxical diarrhoea
- Vomiting - LATE sign
Check for focal tenderness as this is a warning sign of ischaemia
What investigations would you do in pseudoobstruction?
Bloods:
- U&Es
- Ca2+
- Mg2+
- TFTs
Imaging:
- CT contrast (1st line) - must exclude mechanical obstruction
- AXR - limited for diagnosis as will look the same as in mechanical obstruction so best to do CT contrast
Other:
- Motility studies e.g. colonic transit time test
- Colonoscopy +/- biopsy
What is the management of pseudo-obstruction?
Usually conservative management is sufficient (1-3)
- NBM
- IV fluids
- NG Ryles tube to aid decompression
- +/- Endoscopic decompression - done if there is no resolution within 23-48hrs; flatus tube is inserted into the region
- +/- Neostigmine IV - anticholinergic trial if still no resolution
- +/- Segmental resection +/- anastomosis - or caecostomy or ileostomy
List 5 signs that indicate that a patient may need fluid resuscitation urgently.
- SBP <100mmHg
- HR >90
- Cold
- cap refill >2 s
- RR >20
- NEWS 5
- Passive leg raising suggests fluid responsiveness
Define closed loop obstruction.
Closed loop obstruction is when a single segment of bowel is obstructed at two sites.
