Bowel obstruction - Summary Medicine PDF

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Met3a learning outcome objectives covering bowel obstruction...

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BOWEL OBSTRUCTION (1) Know the volumes of fluid secreted in the GI tract Total fluid intake = 9.0L/day 2L = ingested water from diet 7L = secreted from GIT 

Saliva – 1500/day

 

Gastric juice – 2500ml/day Bile – 500ml/day

 

Pancreatic juice – 1500ml/day Intestinal secretions – 1000ml/day

Around 7L are absorbed in the small intestine, leaving 2L to pass into the large intestine Around 1.8L of this is absorbed, with around 200ml being lost in faeces

Be able to differentiate mechanical and adynamic obstruction Mechanical  

Physical obstruction to the passage of bowel contents through the bowel lumen High amount of pain

Adynamic obstruction (ileus) = functional obstruction due to reduced bowel motility  

Bowel sounds are absent Pain tends to be less than mechanical obstruction

Know the difference between simple and complicated obstruction Simple = one obstructing point with no vascular compromise Complicated = obstruction associated with an ischaemic bowel or bowel at risk of perforation

Understand the difference between simple and strangulating intestinal obstruction Simple = one obstructing point with no vascular compromise Strangulating = blood supply to the bowel is compromised, patient is peritonitic with sharper, more constant and localised pain

Understand the term closed loop obstruction = obstruction at two points (e.g. sigmoid volvulus) forming a loop of grossly dilated bowel at high risk of perforation Causes = hernias, adhesions, volvulus

Be able to differentiate between small and large bowel on abdominal X-ray and CT Small bowel

  

Central location of dilated bowel loops Presence of valvulae convientes >3cm = dilated

Large bowel 

Peripheral location of dilated bowel loops

 

Presence of haustra >6cm = dilated

Understand the pathophysiological changes that occur in bowel obstruction In early course of obstruction, intestinal motility and contractile activity increase in attempt to overcome the obstruction Obstruction leads to distention of the proximal bowel segment with solids, fluids and gas, resulting in pain and increased tension on the abdominal wall Later in the course of obstruction, the bowel becomes fatigues and dilates, with contractions becoming less frequent and less intense As the bowel dilates, water and electrolytes accumulate in the bowel lumen and wall, resulting in third spacing leading to rapid dehydration Increased tension impairs blood supply, resulting in necrosis, loss of barrier function and perforation Loss of barrier function allows translocation of luminal bacteria and toxins, resulting in bacteraemia, toxaemia and septicaemia

SMALL BOWEL OBSTRUCTION (1) Know the causes of small bowel obstruction Luminal 

Foreign body

 

Bezoars Gallstone

 

Food particles A. lumbricoides

Mural    

Neoplasms  lipoma, polyps, leiomyoma, haematoma, lymphoma, carcinoma, secondary tumours Crohn’s TB Stricture

 

Intussusception Congenital

Extraluminal   

Hernia



Volvulus

Postoperative adhesions Congenital adhesions

Understand the classification of small bowel obstruction Mechanical vs functional SBO High vs low SBO Simple vs closed loop Simple vs complicated (complicated = indicates compromise of the circulation to a segment of bowel with resultant ischemia, infarction, and perforation) Partial vs complete (partial obstruction allows some liquid contents and gas to pass through the point of obstruction, whereas complete obstruction impedes passage of all bowel contents)

Know the clinical features of small bowel obstruction Symptoms 

Cramping abdominal pain (usually periumbilical)

 

Nausea and vomiting Obstipation (inability to pass flatus or stool)

Signs  

Dehydration  tachycardia, orthostatic hypotension, dry mucous membranes Abdominal distension

 

Hernia Tinkling bowel sounds



Abdominal tenderness (if peritonitic)

 

Masses on palpation Empty rectum on PR exam



Abdominal scars – could indicate past bowel surgery adhesions?

Know the cardinal signs of small bowel obstruction Rapid onset of: 

Pain (abdominal cramps around epigastric and umbilical regions)



Severe vomiting

 

Absolute constipation (obstipation) Abdominal distention

Know the appropriate imaging in the investigation of acute abdominal pain including: plain radiography (erect chest X-ray and abdominal Xray), abdominal ultrasound scan, CT scan, contrast studies Erect chest x-ray = if perforation has occurred, can show pneumoperitoneum Abdominal x-ray = shows dilated small bowel (>3cm) loops centrally with valvulae convientes. Thumb-printing can suggest ischaemia. Can also suggest cause, such as gallstone ileus (pneumobilia + gallstone in RIF + SBO = Rigler’s triad) or volvulus Abdominal ultrasound = can show free fluid, masses, patterns of peristalsis, Doppler for mesenteric blood flow CT scan = defines the level, degree and cause of obstruction, can show the degree of ischaemia and can indicate free fluid and gas in the peritonium

Contrast study = gastrografin (iodine-based contrast agent) can be used for acute abdomen. Barium follow through or enema can be used in more chronic cases to define the level of the obstruction and differentiate mechanical from adynamic obstruction

Know the complications that can result from small bowel obstruction including: ischaemia, perforation and biochemical derangement Ischaemia 

If strangulation of bowel loops occur, blood supply can become impaired, leading to ischaemia



Causes of strangulation o External = hernial orifices, adhesions/bands



o

Interrupted blood flow = volvulus, intususspection

o

Increased intraluminal pressure = closed loop obstruction

o

Primary = mesenteric infarction

Once the blood supply is compromised, the bowel loses its mucosal barrier function, and rapid translocation of bacteria can lead to sepsis

Perforation 

If the bowel becomes excessively dilated, it is at risk of perforation



Risk especially high with closed loop obstructions, such as in volvulus

Biochemical derangement 

Vomiting  loss of K+, H+ and Clo  metabolic alkalosis



Third spacing of bowel secretions  loss of Na+ and H20

Understand the acute management of small bowel obstruction Drip and suck  NG tube to remove obstruction to give bowel rest (and make NBM) and intensive fluid resuscitation as patients can be severely dehydrated Correct electrolyte imbalances (usually use Hartmann’s or plasmolyte for fluids as contain K+) IV antibiotics if ischaemia suspected

Know the conservative treatment of small bowel obstruction Fluids and electrolytes Analgesia IV antibiotics if ischaemia suspected Reassessment every 4 hours and repeat abdominal x-rays Indications for surgery = lack of response over 24-48 hours seen by: increasing pain, distention or tenderness, NG aspirate changing from non-feculent to feculent Surgery after 3 days if no improvement

Know the indications for surgical intervention  

Peritonitis Closed-loop obstruction

 

Bowel ischaemia Bowel necrosis



Perforation

Know the surgical treatment of small bowel obstruction Exploratory laparotomy and proceed  

Resection of any necrotic small bowel Enterolithotomy for gallstone ileus

Exploratory laparoscopy with adhesiolysis may be used when adhesions are suspected as the cause

Know the possible post-operative complications of surgical treatment for small bowel obstruction Short bowel syndrome  

If large amounts of bowel are resection, the bowel may be too short to absorb adequate nutrients This results in malnutrition, dehydration and persistent diarrhoea

 

Patients require nutritional supplementation Patients may even need a bowel transplant

Anastomotic leak Further episodes of obstruction due to adhesion formation

LARGE BOWEL OBSTRUCTION (1) Know the normal function of the large bowel Absorption of large amounts of fluid to concentrate faecal matter Transmission of faecal matter from the small bowel to the anus

Know the causes of large bowel obstruction Colorectal cancer (most common cause) Constipation Diverticular disease Benign stricture (due to radiotherapy, anatsomatosis, iscahemia) Volvulus (caecal or sigmoid) Crohn’s disease Foreign body

Know the classification of large bowel obstruction

Partial vs complete Simple vs complicated Simple vs closed loop

Know the clinical features associated with large bowel obstruction Symptoms    

Colicky abdominal pain Distention Obstipation Change in bowel habit



Tenesmus

Signs 

Distended abdomen

 

Tenderness Tinkling bowel sounds



PR exam o Empty rectum if proximal complete obstruction o

Rectal masses

o

Hard faeces if faecal impaction

o

Soft faces if partial obstruction

Know the complications that can result from small large obstruction: (ischaemia, perforation and biochemical derangement) Ischaemia  



If strangulation of bowel loops occur, blood supply can become impaired, leading to ischaemia Causes of strangulation o External = hernial orifices, adhesions/bands o

Interrupted blood flow = volvulus, intususspection

o

Increased intraluminal pressure = closed loop obstruction

o

Primary = mesenteric infarction

Once the blood supply is compromised, the bowel loses its mucosal barrier function, and rapid translocation of bacteria can lead to sepsis

Perforation 

If the bowel becomes excessively dilated, it is at risk of perforation



Risk especially high with closed loop obstructions, such as in volvulus

Biochemical derangement 

Vomiting  loss of K+, H+ and Clo  metabolic alkalosis



Third spacing of bowel secretions  loss of Na+ and H20

Know the imaging modalities available to interpret cause of large bowel obstruction including: plain radiography (erect chest X-ray and abdominal Xray), abdominal ultrasound scan, CT scan, contrast studies Erect chest x-ray = if perforation has occurred, can show pneumoperitoneum Abdominal x-ray = shows dilated small bowel (>6cm) loops peripherally with visible haustra. Thumb-printing can suggest ischaemia. Can also suggest cause, such as sigmoid/caecal volvulus CT scan = defines the level, degree and cause of obstruction, can show the degree of ischaemia and can indicate free fluid and gas in the peritoneum Contrast study = contrast enema can be used in more chronic cases to define the level of the obstruction and differentiate mechanical from adynamic obstruction Sigmoidoscopy = indicated in the case of volvulus as can be therapeutic

Know the conservative treatment for large bowel obstruction Resuscitation with NG tube, IV fluids and IV antibiotics Endoscopic stenting = may be appropriate for the elderly, in palliative care or as a bridge to surgery Sigmoidoscopy (flexible or rigid) with insertion of rectal tube can resolve sigmoid volvulus can should be left in situ for 24 hours with AXR to confirm decompression

Know the indications for surgical intervention and the consequences of resection of the large bowel  

Peritonitis Closed-loop obstruction

  

Bowel ischaemia Bowel necrosis Perforation

Know the surgical treatment of large bowel obstruction Exploratory laparotomy Identify cause If perforation  Irrigate bowel and resect perforated segment Hartmann’s procedure is the most preferred operative approach for distal colonic lesions, including complicated sigmoid volvulus, diverticular disease and colonic cancer Subtotal colectomy is preferred if there is a combination of a distal obstruction (e.g. sigmoid cancer) with a proximal perforation (e.g. caecal perforation) Caecopexy (anchoring of caecum) may be possible if caecum is still viable. Otherwise resection ± ileostomy is indicated For unresectable lesions, a defunctioning loop ileostomy (or colostomy if rectal obstruction) to defunction the bowel and relieve obstruction

Know the possible post-operative complications of surgical treatment

Persistent diarrhoea Complications of stoma Anastamotic leak

ILEUS AND PSEUDO-OBSTRUCTION (1) Understand the difference between ileus and pseudo-obstruction and their relative causes Ileus   

= bowel obstruction due to loss of peristalsis of the bowel wall (i.e. a functional rather than mechanical defect) Usually affects the small bowel Causes o Post-operative after bowel handling (onset usually 2-3 days after surgery) o Intraperitoneal inflammation (e.g. due to peritonitis) o

Ischaemia

o

Myocardial infarction

o o

Pneumonia Hypothyroidism

o

Diabetes

o o

Spinal and pelvic fractures Retroperitoneal haematoma

o

Metabolic abnormalities

o

 Hypokalaemia  Hyponatraemia  Uraemia  Hypomagnesia Drug induced  

Morphine TCAs



Calcium channel blockers

Pseudo-obstruction 

= acute dilation of the colon in the absence of any mechanical obstruction in severely ill patients

 

Also known as Ogilvie’s syndrome Affects the large bowel



Usually occurs in very sick, elderly patients with: o Chest infection o o

Myocardial infarction Cerebrovascular event

o

Renal failure

o

Electrolyte disturbance

Differentiate between adynamic and mechanical bowel obstruction In ileus:

 

Bowel sounds are absent (compared to hyperactive in mechanical BO) Pain tends to be less severe than in mechanical BO

  

X-ray = gas distributed diffusely throughout the small and large bowel with lots of distal air Contrast study = no obvious transition point showing obstruction point CT = gold standard to differentiate between ileus and mechanical obstruction

In pseudo-obstruction: 

Presents with rapidly progressing abdominal distension, usually with no/little associated pain



Usually other medical history that point towards this condition



X-ray = colon dilation, most prominent in the caecum and ascending colon

Understand the treatment of ileus/pseudo-obstruction Ileus 

Rule out mechanical causes

 

Drip and suck Usually resolves spontaneously in 2-4 days

Pseudo-obstruction  

Rule out mechanical causes Drip and suck

 

If caecum >12cm, consider colonoscopic decompression IV neostigmine (reversible AChE inhibitor) to stimulate muscarinic parasympathetic receptors to enhance colonic motor activity...