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GS22 General Surgery and Thoracic Surgery Small Bowel Obstruction Etiology
Toronto Notes 2019
Table 7. Common Causes of SBO
Intraluminal
Intussusception Gallstones Bezoars
Intramural
Crohn’s
Radiation stricture Adenocarcinoma
Extramural
Adhesions from previous surgeries (75% SBO) Incarcerated hernia
Peritoneal carcinomatosis
MUST DO
Rule out CRC in constipated patient
Send for TURP in patient with BPH (treat intra- abdominal HTN)
Increased Risk of Perforation with Distention as seen on Abdomen Imaging • Small bowel ≥3 cm
• Distal colon ≥6 cm
• Proximal colon ≥9 cm
• Cecum ≥12 cm
Patients presenting with a SBO in setting of “virgin” abdomen should have surgery ASAP – EXCEPTION: malignant obstruction from history and imaging
In a non-virgin abdomen – adhesional SBOs resolve spontaneously with NGT decompression 70% of time
Top 3 Causes of SBO (in order)
ABC
Adhesions
Bulge (hernias) Cancer (neoplasms)
Causes of SBO
SHAVING
Stricture
Hernia
Adhesions
Volvulus Intussusception/IBD Neoplasm Gallstones
• threetypes
■ partial SBO: only a portion of intestinal lumen is occluded, allows passage of some gas & fluid, low
risk of strangulation
■ complete SBO: the lumen of the intestine is occluded, no passage of gas or stool, at higher risk of
strangulation
■ closed-loop obstruction: segment of intestine is obstructed both proximally and distally (e.g.
volvulus), leading to rapid rise in intraluminal pressure from gas and fluid that cannot escape, high risk of strangulation due to bowel wall ischemia
Risk Factors
• priorabdominalorpelvicsurgery • abdominalwallorgroinhernia
• historyofmalignancy
• priorradiation
Clinical Features
• 1)distinguishmechanicalobstructionfromileus;2)determineetiologyofobstruction;3)recognize partial from complete SBO; 4) differentiate simple from complicated (e.g. strangulated) obstruction
• symptoms: colicky abdominal pain, nausea/vomiting, obstipation
■ vomiting is more prominent with proximal than distal
■ more feculent vomitus suggests more established obstruction because of bacterial overgrowth
■ continue passage of gas and/or stool 6-12 h after onset of symptoms suggest partial than complete
obstruction
• signs:abdominaldistention(mostprominentifobstructionatdistalileum),hyperactiveproceedingto
minimal bowel sound
• strangulatedobstruction:abdominalpaindisproportionatetophysicalexamfindingssuggestintestinal
ischemia
■ may have tachycardia, localized abdominal tenderness, fever, marked leukocytosis, and lactate
acidosis
Investigations
• radiological
■ abdominal x-ray (3 views): triad of dilated small bowel (>3 cm in diameter), air-fluid levels on
upright film, paucity of air in colon (high sensitivity, low specificity as ileus and LBO can present
similarly)
■ CT: discrete transition zone with proximal bowel dilation, distal bowel decompression, and
intraluminal contrast does not pass the transition zone
◆ most importantly to rule out ischemic bowel/strangulation: pneumatosis intestinalis (free air
in bowel wall) and thickened bowel wall, air in portal vein, free intraperitoneal fluids, and
differential wall enhancements (poor uptake of IV contrast into the wall of the affected bowel) ■ other
◆ less used: upper GI series/small bowel series (if no cause apparent, i.e. no hernias, and no previous surgeries)
◆ may consider U/S or MRI in pregnant patients • laboratory
■ may be normal early in disease course
■ creatinine, and hematocrit to assess degree of dehydration
■ fluid, and electrolyte abnormalities; metabolic alkalosis due to frequent emesis; amylase elevated ■ if strangulation: leukocytosis with left shift, elevated lactate (late signs)
Treatment
• IVisotonicfluidresuscitationandurineoutputmonitoringwithcatheter
■ SBO related vomiting and decrease PO intake leads to volume depletion
• NGtubeinthestomachforgastricdecompression;decreasenausea,distention,andriskofaspiration from vomiting
• NPO
• Partial SBO/Crohn’s/Carcinomatosis: conservative management with fluid resuscitation and NG tube
decompression
■ 48 h of watchful waiting; if no improvement or develops complications, surgery
• CompleteSBO,ifnoclinicalfeaturesofstrangulation,shortcourseofconservativemanagementwith fluid resuscitation and NG tube decompression with frequent re-examination by surgical team
■ duration of observation varies from hours to a few days
■ if SBO fails to resolve, or if symptoms of strangulation develop, then surgery