Bowel Obstruction

#med #disease #y2023 #gi

Presentation :

Abdominal pain, nausea, vomiting, constipation-to-obstipation, and distention
Classic exam findings include: abdominal distension, tympany to percussion, and high-pitched bowel sounds
Small bowel obstructions (SBOs) are more common than large bowel obstructions (LBOs)
Classic findings to differentiate SBO from LBO:

	SBO	LBO
Pain	Intermittent, colicky, improves with vomiting	Continuous
Tenderness	Focal	Diffuse
Vomiting	More frequent, larger volume, bilious	Intermittent, feculent

Pathophysiology :

Classified as a partial, complete, or closed loop
- Closed-loop obstruction: complete obstruction distally and proximally closing off a given segment of small/large intestine
Arises from either mechanical or functional processes.
- Mechanical:
  - Intrinsic
    - Intussusception
    - Malignancy (CRC, Bowel wall tumors like lipoma or sarcoma)
    - Stricture
    - Diverticula (inflammation of acute diverticulitis leads to scar formation and fibrosis which gradually narrows the lumen of the sigmoid colon resulting in an intrinsic compression of the lumen)
    - Foreign body impaction
    - Inflammatory (IBD, TB)
  - Extrinsic
    - Post-surgical adhesions
      - At least two-thirds of patients with previous abdominal surgery have adhesions
    - Malignancy (Extraluminal mass effect)
    - Inguinal and umbilical hernias
    - Volvulus
    - Endometriosis
- Functional:
  - Colonic Pseudo Obstruction (Ogilvie's)
  - Ileus:
    - Opiates
    - Post-surgical
    - Post-inflammatory
  - Constipation
LBOs are less common and compromise only 10% to 15% of all intestinal obstructions.
- The most common cause of all LBOs is adenocarcinoma, followed by diverticulitis and volvulus.

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Acute obstruction subsequently causes:
- Dehydration, and electrolyte imbalances 2/2 emesis: hypochloremia, hypokalemia, hyponatremia
- Metabolic alkalosis:
  - Emesis causes loss of gastric HCl
  - Dehydration stimulates renal proximal tubule reabsorption of bicarbonate and loss of chloride, which perpetuates metabolic alkalosis (and hypochloremia)
- When intraluminal pressure exceeds venous pressures, loss of venous drainage exacerbates edema and congestion of the bowel. Congestion in turn may compromise arterial flow, causing ischemia, necrosis, and ultimately perforation.
  - A closed-loop obstruction, in which a segment of bowel is obstructed proximally and distally, may undergo this process rapidly and is considered a surgical emergency
  - Intestinal volvulus, the prototypical closed-loop obstruction, causes torsion of arterial inflow and venous drainage, immediately compromising bowel viability

Diagnostic Testing:

Confirm the diagnosis of small and large bowel obstruction w/ an abdominal CT with IV or PO contrast.
- IV contrast: if suspected high grade obstruction or concern PO contrast would be poorly tolerated/unlikely to reach the site of obstruction
- PO contrast: if suspected low grade obstruction or contraindication to IV contrast
- Allows for visualization of the transition point, the severity of obstruction, potential etiology, and assessment of any life-threatening complications.
- XR accurately diagnoses intestinal obstruction in only about 60% of cases; its use is generally limited to initial evaluation of unstable patients
Routine bloodwork: CBC, BMP (hypoK, hypoCl), consider lactate
- The development of metabolic acidosis, especially in a patient with an increasing serum lactate level, may signal bowel ischemia. (typical is alkalosis if significant vomiting/dehydration)
LBOs:
- Contrasted enemas can be used to further characterize: aid with the diagnosis of volvulus, can differentiate mechanical from functional obstructions
- Water soluble contrast is the preferred contrast as it is better absorbed by the peritoneum in case of a perforation and does not hamper visibility on subsequent CT scans
- Bowel diameter over 10 cm is associated with an increase in the risk of perforation

Treatment :

Supportive care: IVF resuscitation, correction of electrolyte/pH derangements, restrict oral intake/NPO
NG tube placement for most cases
Consider catheterization to monitor I/O (though comes w/ risk of infection, reduced mobility)
As compared to SBOs, LBOs typically fail conservative mgmt
If febrile/leukocytosis start abx to cover GNR + anerobes (ie, Zosyn, Cipro/Flagyl)
Surgical admission/consultation is recommended
Surgical exploration is recommended in patients who:
- Clinically deteriorate at any point during hospitalization
- Failure to improve w/ 3-5d of nonoperative management (may go longer if surgical team is frequently reassessing)
- Irreducible or strangulated hernia
  - Patients with resolution of SBO after reduction of a hernia should be scheduled for elective hernia repair.
- Signs of peritonitis, clinical instability, leukocytosis, leukopenia, and acidosis are concerning for abdominal sepsis, ischemia, or perforation, and mandate immediate surgical exploration
Endoscopic dilation/stenting may be offered in some cases (mass, stricture)
In select patients with adhesive or partial SBO, oral administration of hypertonic water-soluble contrast media may have therapeutic effects and assist in resolution. Although the risk of vomiting and aspiration should be considered, a systematic review and meta-analysis of 14 prospective trials demonstrated significant reduction in the need for surgery and shortened hospital stays in patients who received water-soluble contrast media.Ref

Prognosis:

Pts with SBO from adhesions are at high risk of recurrence if non-operative management is used

References:

Created on: Friday 09-01-2023