Malignant Bowel Obstructio Flashcards
Malignant Bowel Obstruction - Definition
Bowel obstructive symptoms due to the presence of an intra-abdominal malignancy.
Often occurs in context of advanced disease.
May be secondary to non-malignant (post-surgical adhesions, radiotherapy bowel damage) or malignant causes (more likely as cancer becomes more advanced, or if primary CA is ovarian)
Most common cancers where malignant bowel obstruction is seen
- Gyne cancers (particularly ovarian - as many as 40% of patients with ovarian CA)
- GI cancers (esp colorectal)
Cancers metastasizing to the abdomen (esp lung, breast, malignant melanoma).
Pathophysiology of MBO
Mechanical (more common, where the lumen is occluded) or functional (less common)
Mechanical:
- Extrinsic occlusion of the lumen (compression of the bowel due to progression of the tumour, mesenteric or omental masses, adhesions, etc.)
- Intraluminal occlusion of the lumen (primary or metastatic tumour)
- Intramural occlusion of the lumen (intestinal linitis plastica - proliferation of the cancer through the intestinal tissue resulting in thickening and rigidity)
Functional (dysmotility)
- Motility disorder without mechanical occlusion
- Carcinomatosis (infiltration of the mesentery, bowel muscle, or nerves)
- Paraneoplastic syndrome
- Celiac plexus involvement
- Cancer related neuropathy
- Decreased motility secondary to meds (e.g. opioids)
- Bowel motility problems secondary to other illnesses like DM
Contributory causes:
- inflammatory edema
- fecal impaction
- constipating meds
- dehydration
Common symptoms of MBO
- Nausea and vomiting (due to fluid accumulation proximal to obstruction, leading to bowel distention and secretion of water/sodium into the lumen)
- Colicky pain (bowel contracts to overcome obstruction)
- Abdominal pain (Inflammatory response to bowel distention and damage to epithelium, with production of prostaglandins, vasoactive intestinal peptides and nociceptive mediators)
- Late stage - systemic hypotension, sepsisdue to ongoing inflammatory response and splanchnic vasodilation, as well as passage of bacteria through the intestinal wall. Ultimately, may result in perforation.
Differential diagnosis of MBO
- Severe constipation
- Check for history consistent with preceding constipation, drug use associated with constipation, in activity, check for hypercalcemia, hypokalemia, hypothyroidism
- On exam, look for palpable fecal masses
- Rectal exam for hard feces, and if rectum is empty but distended, consider obstipation at a higher level
- AXR flat plate to assess for MBO - Opioid bowel syndrome
- Opioids alter GI motility
- Up to 4% of patients with cancer may develop nausea, vomiting, mild abdo discomfort, constipation, gaseous abdo distention, and weight loss.
Presentation of MBO
- More common in advanced stages and often slowly progressive with multiple episodes of partial obstruction
- Intestinal strangulation, ischemia, and perforation are uncommon
- Radiographic testing may not always confirm the diagnosis, or may changes may predate the onset of symptoms - maintain a high index of suspicion
Symptoms:
- N/V (intermittent or continuous). May be undigested stomach contents or feculant depending on level of obstruction
- Continuous pain (bowel distention, tumour mass, hepatomegaly)
- Colicky pain (occurs only in mechanical obstruction)
- Abdominal distention (variable)
- Constipation (intermittent or complete, with absence of flatus)
- Diarrhea (may occur initially as a result of bacterial liquefaction of fecal material blocked in the sigmoid or rectum)
Common signs of MBO on exam
Inspection
- abdominal distention (varies - if extensive peritoneal tumour spread, likely to be less)
- visible loops of distended bowel or peristalsis
Palpation
- masses
- organomegaly
- ascites
- tenderness (including rebound tenderness)
Auscultation
- bowel sounds increased or decreased
- absent in late obstruction, peritonitis, and functional bowel obstruction
- succession splash when the stomach is filled with ++ fluid (e.g. in GOO)
Rectal exam
- palpable masses
- rectal shelf
- rock hard stool (significant constipation)
- ballooned empty rectum (colonic obstruction higher up)
Signs of dehydration
Syndrome of gastric outlet and proximal SBO
- Severe n/v, early in the course, large amounts of undigested food
- emesis may be bile stained if upper SBO
- Vomiting of saliva and gastric juices may be almost odourless
- Epigastric distention, no colicky pain
- BMs may occur with the fecal matter consisting of intestinal cellular debris and bacteria
Syndrome of distal small bowel MBO
- N/V moderate to severe
- Moderate generalised abdominal distention
- If mechanical, upper or central abdominal colic
- Constipation to varying degrees, occasionally diarrhea
Syndrome of large bowel MBO
- N/V late, smaller amounts, feculent emesis eventually
- Significant abdominal distention
- Central to lower abdominal colic
- Colicky pain not as severe as in higher obstructions
- Often preceding history of alternating diarrhea and constipation before complete obstruction occurs
Investigation of MBO
- Basic labs (CBC, lytes, cr) - other causes of symptoms
- AXR
- Dilated loops of bowel, air fluid levels on an upright film proximal to the obstruction, decreased or absent intra luminal gas distal to the obstruction
- In functional obstruction, will show uniform gaseous distention through the GI tract
- Limited in showing the cause/location of obstruction, when there is tumour encasement of the bowel (as bowel cannot distend in this circumstance), and if there are multiple levels of obstruction. - XR with gastrograffin or barium contrast
- Shows the site and extent of the obstruction and the presence of multiple sites of obstruction
- NEVER use barium if a partial bowel obs is suspected, as the barium can worsen the obstruction
- May be more useful in more proximal obstruction - CT
- useful for identifying case of the obstruction, staging, and for assisting in the choice of invasive tx (e.g. surgery or stenting)
- superior results in assessment of abdominal symptoms
Indications for surgery in MBO
- Surgery is controversial in MBO, but may be required for patients with non-malignant obstruction related to previous surgery or radiation
- No prospective randomized trials
- Potential pitfalls include re-obstruction, inadequacy of symptom relief, and post-op morbidity and mortality
- Surgery would be a better option than stenting for palliation in patients who have a longer prognosis (>60 days), few comorbidities, and single site of obstruction near the gastric outlet.
Options:
- Complete resection (most useful with GI primary where negative margins are possible)
- Operative bypass
- Lysis of adhesions
- Diverting stoma (minimum of 100cm of small bowel before a stoma in order to maintain nutrition, risk of fluid balance problem)
Intraluminal stents for Upper MBO - indications and risks
- Surgery would be a better option for palliation in patients who have a longer prognosis (>60 days), few comorbidities, and single site of obstruction near the gastric outlet.
- Stenting better for those with short length of tumour, single site of obstruction near the pylorus or proximal 2/3 of the duodenum, with intermediate to high performance status and life expectancy > 30 days
- May be placed in upper and lower bowel with good relief of symptoms
- Cannot be done for long obstructions or beyond the length of the endoscope
- Lasers may be used to canalize through tumours to allow stent placement
Risks:
- Aspiration during procedure (risk can be mitigated with GA and intubation)
- Perforation (7-14%)
- Migration
- Reobstruction (long term failure rate of 25-30%)
Medical management of MBO
- Bowel decompression
- Chemo (poorly studied)
- Rads (may be effective in some cases)
- Pain relief (opioids)
- Anti-emetics
- Anti-secretory agents (ocreotide, buscopan, glycopyrrolate)
- Corticosteroids
- IV hydration and bowel rest
Bowel decompression for MBO
- NG tube inserted to decompress gas and fluid in the bowel
- Generally a temporary measure for severe symptoms as a bridge to surgical or other medical tx
- May be unnecessary with adequate antisecretory therapy
Risks:
- Provides incomplete relief of symptoms
- Uncomfortable
- Long term morbidity (erosion of the nares, nutritional deficiency, aspiration pna)
Venting gastrostomy or enterostomy
Indicated for patients in whom pharmacological management is not effective, or for very high gastric outlet or upper SBOs that cannot be bypassed
Allows patients to partake in the social experience of eating/drinking
Can do gastrostomy or jejunostomy depending on position of stomach (or if stomach has been removed)
Pharmacologic approach to MBO
- Provide clear written instructions. Typically, start antisecretory therapy, steroid, anti-emetic. Consider IVF if patient unable to tolerate PO fluids and NG tube for severe symptoms
- If partial response to any pharmacologic therapy is not seen in 24 hrs, reassess
- Reassess every 48 hrs as the clinical picture evolves
Pain relief in MBO
Opioids
- Relief of pain
- Decrease in abnormal motility contributing to colic
- Administer parenterally (subcut) to ensure absorption
PO Loperamide
- May be useful as an antimotility agent, but no clear evidence
Antisecretory agents may also provide pain relief (may give buscopan 40 - 120mg/day) or glycopyrrolate in addition to opioids for colicky pain if opioids alone are ineffective)
Anti-emetics in MBO
- No clear data to prefer one anti-emetic over another
- Antidopminergic drugs often used (e.g. haldol 5-15mg/day)
- No evidence for aprepitant or ondansetron
- Never use metoclopramide (useful in partial SBO) in complete bowel obs or if patient has colic as it will be worsened by the prokinetic effect
Complete relief of N/V due to MBO with anti-emetics alone is usually not possible due to hypermotility and then pooling of secretions and distention of the bowel.
Anti-secretory agents in MBO (rationale, dosing, action, side effects)
- Much of the symptoms attributable to MBO are related to the abdominal distention, pain, and N/V due to a large volume of intestinal secretions.
- Anti-secretory therapy should be seen as first line even if the patient is being considered for surgery
- Give subcut, 300-600mcg/daily in divided doses or continuous infusion
Octreotide (somatostatin analogue)
- Give subcut, 300-600mcg/daily in divided doses or continuous infusion
- Inhibits release of gastrin, cholecystokinin, vasoactive intestinal peptide, and pancreatic enzymes, decrease bowel secretions overall
- Also decreases neurotransmission in the nerves of the GI tract, decreasing peristalsis, splanchnic blood flow, and increasing absorption of fluids
Side effects:
- dry mouth
- long term, can be associated with hyperglycemia and biliary sludging
May give buscopan or glycopyrrolate in addition to octreotide
Corticosteroids in MBO (rational, mechanism, dosing)
MOA: likely anti-emetic, analgesic, anti-inflammatory effect that decreases peritumour edema
Dexamethasone 6 - 16mg PO daily
Poor evidence but widely used, does not appear to affect survival
Discontinue if no response within 4-5 days. If there is a response, wean down over time to a minimum effective level
Hydration in MBO
IV or subcut hydration in case of severe fluid imbalance or severe electrolyte abnormalities. Rates should be lower if antisecretory agents are being used and patient is not severely dehydrated
Once secretions, nausea and pain are controlled, most patients can tolerate clear fluids PO until the obstruction resolves
Nutrition - role of TPN or nutritional supplementation
Likely not to improve QOL for patients with survival of less than 3 months
For patients with slow growing tumours involving the GI tract, sparing other major organs, TPN trial in the case of weight loss from starvation may be considered.
For patients who are severely malnourished and in home a surgery is planned but cannot be enterally fed, may be appropriate to consider for 7-10 days preop to decrease rate post op infections, periop mortality, and LOS. Post op duration should be defined preop and generally should be < 10 days.
How to manage patients between episodes of MBO at home
- Maintain adequate hydration
- Give regular metoclopramide to keep intestinal contents moving through areas of partial obstruction
- Maintain daily soft BMs
- osmotic laxatives with PEG, or lactulose
- use bisacodyl supps PRN
- avoid high enemas - Soft or liquid low residue diet (poor evidence)
- Meds in the home for future events (anti-emetics, antisecretory drugs, antimotility agents, opioids) for use as soon as cramps, distention, nausea or vomiting occur
As episodes become more frequent and close together, complete irreversible bowel obstruction is more likely imminent
