small bowel obstruction١٣/٠١/١ ٣ pathophysiology with onset of obstruction, gas and fluid...

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SMALL BOWEL OBSTRUCTION

Ahmad kachooyi MD

Assistant Professor

Qom Medical University

EPIDEMIOLOGY

١. Intraluminal (e.g., foreign bodies, gallstones,

or meconium)

٢. Intramural (e.g., tumors, Crohn's disease–

associated inflammatory strictures)

٣. Extrinsic (e.g., adhesions, hernias, or

carcinomatosis)

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Intra-abdominal adhesions related to prior

abdominal surgery account for up to ٧% of the

cases of small bowel obstruction.

Less prevalent etiologies for small bowel

obstruction include hernias, malignant bowel

obstruction, and Crohn's disease

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PATHOPHYSIOLOGY

� With onset of obstruction, gas and fluid

accumulate within the intestinal lumen

proximal to the site of obstruction

� colicky pain and the diarrhea that some

experience even in the presence of complete

bowel obstruction.

� strangulated bowel obstruction; If the

intramural pressure becomes high enough,

intestinal microvascular perfusion is impaired,

leading to intestinal ischemia, and, ultimately,

necrosis.

� partial small bowel obstruction; only a portion

of the intestinal lumen is occluded, allowing

passage of some gas and fluid.

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� complete small bowel obstruction;

development of strangulation is more likely.

� closed loop obstruction; a segment of intestine

is obstructed both proximally and distally (e.g.,

with volvulus). A rapid rise in luminal pressure,

and a rapid progression to strangulation

CLINICAL PRESENTATION

� colicky abdominal pain, nausea, vomiting, and obstipation.

� Continued passage of flatus and/or stool beyond �to ١٢ hours after onset of symptoms is characteristic of partial rather than complete obstruction.

� abdominal distention

� Bowel sounds may be hyperactive initially, but in late stages of bowel obstruction, minimal bowel sounds may be heard

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LABORATORY FINDINGS

� hemoconcentration and electrolyte

abnormalities

� Mild leukocytosis

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FEATURES OF STRANGULATED OBSTRUCTION

� abdominal pain often disproportionate to the

degree of abdominal findings

� tachycardia, localized abdominal tenderness,

fever, marked leukocytosis

� Acidosis

� need for early surgical intervention

DIAGNOSIS

� focused on the following goals:

� (a) distinguish mechanical obstruction from

ileus

� (b) determine the etiology of the obstruction

� (c) discriminate partial from complete

obstruction

� (d) discriminate simple from strangulating

obstruction

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HISTORY

� prior abdominal operations (suggesting the

presence of adhesions)

� presence of abdominal disorders (e.g., intra-

abdominal cancer or inflammatory bowel

disease)

EXAMINATION

� search for hernias (particularly in the inguinal

and femoral regions)

� The stool should be checked for gross or occult

blood, the presence of which is suggestive of

intestinal strangulation.

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RADIOGRAPHIC EXAMINATION

� The abdominal series consists of ;

١. a radiograph of the abdomen with the patient

in a supine position,

٢. a radiograph of the abdomen with the patient

in an upright position,

٣. a radiograph of the chest with the patient in

an upright position.

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RADIOGRAPHIC EXAMINATION

� The finding most specific for small bowel

obstruction is the triad :

١. dilated small bowel loops (>٣ cm in diameter)

٢. air-fluid levels seen on upright films

٣. a paucity of air in the colon

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� False-negative findings on radiographs :

١. when the site of obstruction is located in the

proximal small bowel

٢. when the bowel lumen is filled with fluid but

no gas , preventing visualization of air-fluid

levels or bowel distention; closed-loop

obstruction

COMPUTED TOMOGRAPHIC (CT) SCANNING

� The findings of small bowel obstruction

include :

١. a discrete transition zone with dilation of

bowel proximally , decompression of bowel

distally

٢. intraluminal contrast that does not pass

beyond the transition zone

٣. a colon containing little gas or fluid

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COMPUTED TOMOGRAPHIC

� provide evidence for the presence of closed-

loop obstruction and strangulation

� Closed-loop obstruction is suggested by the

presence of a U-shaped or C-shaped dilated

bowel loop associated with a radial distribution

of mesenteric vessels converging toward a

torsion point.

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COMPUTED TOMOGRAPHIC

� Strangulation is suggested by thickening of the

bowel wall, pneumatosis intestinalis (air in the

bowel wall), portal venous gas, mesenteric

haziness, and poor uptake of IV contrast into

the wall of the affected bowel.

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CT SCAN

� performed after administration of oral water

soluble contrast, or diluted barium

� The water soluble contrast has been shown to

have prognostic and therapeutic values

� appearance of the contrast in the colon within

٢� hours is predictive of nonsurgical resolution

of bowel obstruction.

LIMITATION OF CT SCANNING

� low sensitivity (<٠%) in the detection of low-grade or partial small bowel obstruction

� A subtle transition zone may be difficult to identify in the axial images obtained during CT scanning

� In such cases, contrast examinations of the small bowel, either small bowel series (small bowel follow-through) or enteroclysis, can be helpful.

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THERAPY

� fluid resuscitation is integral to treatment

� Isotonic fluid should be given intravenously

� indwelling bladder catheter placed to monitor

urine output.

� Central-venous or pulmonary-artery catheter

monitoring may be necessary to assist with

fluid management, particularly in patients with

underlying cardiac disease.

THERAPY

� Broad-spectrum antibiotics are given by some

because of concerns that bacterial

translocation may occur in the setting of small

bowel obstruction;

� NG tube

� The standard therapy for complete small bowel

obstruction generally has been expeditious

surgery

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COMPLETE SMALL BOWEL OBSTRUCTION

� some have advocated nonoperative

approaches in management of these patients,

� closed loop obstruction is ruled out

� no evidence of intestinal ischemia.

� Such patients need to be observed closely and

undergo serial exams

� Clinical signs and currently available laboratory

tests and imaging studies do not reliably permit

the distinction between patients with simple

obstruction and those with strangulated

obstruction before the onset of irreversible

ischemia.

� the goal is to operate before the onset of

irreversible ischemia.

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� Conservative therapy, in the form of NG

decompression and fluid resuscitation is the

initial recommendation for:

١. Partial small bowel obstruction

٢. Obstruction occurring in the early

postoperative period

٣. Intestinal obstruction due to Crohn's disease

�. Carcinomatosis

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PARTIAL OBSTRUCTION

� progression to strangulation is unlikely to occur

� most patients with partial small obstruction

whose symptoms do not improve within �٨

hours after initiation of nonoperative therapy

should undergo surgery.

EARLY POSTOPERATIVE PERIOD OBSTRUCTION

� ٧�٠% patients undergoing laparotomy

� Patients undergoing pelvic surgery, especially colorectal procedures, have the greatest risk

� The presence of obstruction should be considered if symptoms of intestinal obstruction occur after the initial return of bowel function or if bowel function fails to return within the expected ٣ to days after abdominal surgery.

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EARLY POSTOPERATIVE PERIOD

� usually partial and only rarely is associated with

strangulation.

� a period of extended nonoperative therapy (٢ to ٣

weeks) consisting of bowel rest, hydration, and

total parenteral nutrition (TPN) administration is

usually warranted.

� if complete obstruction is demonstrated or if signs

suggestive of peritonitis are detected, expeditious

reoperation should be undertaken without delay.

CARCINOMATOSIS

� limited prognosis

� Management must be tailored to an individual

patient's prognosis and desires

� relief of the obstruction may be best achieved

by a bypass procedure

� avoiding a potentially difficult bowel resection

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OPERATIVE PROCEDURE

� adhesions are lysed

� tumors are resected

� hernias are reduced and repaired

� affected intestine should be examined, and

nonviable bowel resected

CRITERIA SUGGESTING VIABILITY

� normal color

� Peristalsis

� marginal arterial pulsations

. In borderline cases:

١. Doppler probe

٢. administered fluorescein dye in the bowel wall

under ultraviolet illumination

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"SECOND-LOOK" OPERATION

� if the viability of a large proportion of the

intestine is in question, a concerted effort to

preserve intestinal tissue should be made

� the bowel of uncertain viability should be left

intact and the patient re-explored in ٢� to �٨

hours

OUTCOMES

� The majority of patients who are treated

conservatively for adhesive small bowel

obstruction do not require future readmissions;

� less than ٢٠% of such patients will have a

readmission over the subsequent years with

another episode of bowel obstruction.٢٣

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PREVENTION

� adhesion prevention:

١. Good surgical technique

٢. careful handling of tissue

٣. minimal use and exposure of peritoneum to foreign bodies

In patients undergoing colorectal or pelvic surgery, hospital readmission rates of greater than ٣٠% over the subsequent ١٠ years have been reported for adhesive small bowel obstruction.

PREVENTION

� Use of laparoscopic surgery, when possible,

has been strongly promoted

� adhesion prevention :hyaluronan-based agents,

such as Seprafilm