Large bowel obstruction Flashcards
What is the most common cause of a large bowel obstruction in adults?
Colonic malignancy.
What is the pathophysiology of a large bowel obstruction?
· Colon proximal to the cause of the mechanical obstruction dilates»_space;> increases colonic pressure and reduces mesenteric blood flow.
· This produces mucosal oedema with transudation of fluid and electrolytes into the colon lumen.
· This can produce dehydration and electrolyte imbalances.
· Progressively, the arterial blood supply is jeopardised with mucosal ulceration, full thickness wall necrosis and eventual perforation.
· This provides conditions for bacterial translocation, which can produce septic complications.
· The caecum is the usual site of rupture, as it has the largest diameter.
· A colonic volvulus arises from axial rotation of the colon on its mesenteric attachments - sigmoid most commonly affected.
· Once the volvulus has a 360° twist, then a closed loop obstruction is produced.
· Fluid and electrolyte shifts result from fluid secretion into the closed loop.
· This produces increased pressure and tension on the colonic wall, that eventually impairs colonic blood supply.
· This results in ischaemia, necrosis and perforation.
What is the prognosis of a large bowel obstruction?
· All causes carry a significant mortality and morbidity.
· No surgical treatment for sigmoid volvulus, recurrence rates are 40-60%.
What are the risk factors for a large bowel obstruction?
· Older age. · Females. · Institutionalised patients. · Mental illness. · Megacolon.
What are the common signs and symptoms of a large bowel obstruction?
· Colicky abdominal pain:
- Common to all causes of mechanical obstruction.
- Increasing constant pain.
- Pain on movement, coughing or deep breathing may imply perforation or impending perforation.
· Abdominal distention. · Tympanic abdomen. · Change in bowel habits. · Hard faeces on PR - faecal impaction. · Empty rectum - proximal obstruction. · Soft stools - partial obstruction. · Recent weight loss. · Rectal bleeding. · Abnormal bowel sounds. · Palpable rectal mass. · Palpable abdominal mass.
List the investigations would you request if you suspected a patient had a large bowel obstruction?
· FBC. · Electrolytes. · U&E's. · Amylase and lipase. · Coagulation studies. · Erect CXR. · Plain AXR. · Water-soluble (Gastrografin) enema.
What might a FBC show?
· Elevated WBC’s indicate an infective or inflammatory cause, or complication such as perforation or impending perforation.
· Anaemia can be found in the presence of an underlying malignancy, and is of a microcytic/iron deficiency picture.
What might happen to the electrolytes in the body?
· May be deranged from dehydration, fluid shifts or sepsis.
· The colon secretes potassium and bicarbonate in exchange for sodium chloride and water absorption, and this is disrupted in the obstructed colon, which may produce hypokalaemia.
What might U&Es show?
Elevated urea and creatinine. Urea is elevated more than creatinine depending on pre-morbid renal function.
What might happen to amylase + lipase?
Elevated with any significant intra-abdominal event.
What might coagulation studies show?
Prolonged INR, PTT and PT may be present in sepsis from perforation.
What might an erect CXR show?
· Free sub-diaphragmatic air indicates perforation and the need to consider urgent surgery.
· Absence of free air doesn’t exclude perforation.
What might a plain AXR show?
· Gaseous distension of large bowel.
· Level of obstruction may be determined by a cut-off beyond which the colon or rectum is empty of gas.
· Kidney-bean shape seen in volvulus.
· Intramural gas ominously suggests colonic ischaemia.
Suggest some differential diagnoses.
· Acute colonic pseudo-obstruction. · Chronic/Idiopathic megacolon. · Toxic megacolon. · Endometriosis. · Pseudomembranous colitis.
What are the treatment options for the acutely ill?
· 1st line - Supportive measures - NBM, Oxygen, IV fluids, catheter, NG tube, abx.
· If suspect perforation or impending perforation - Emergency surgery.
