Chapter 12, part 2 Flashcards
Purpose of the colon
Extracts water, sodium, short-chain fatty acids (SCFAs), and some vitamins from the stool
Excretes potassium
What percentage of water and sodium is recovered by the colon?
90% of each
How much water can the colon absorb a day?
Where does most of this absorption occur?
6 L/day
Most occurs on the right side
What is the primary energy source of the colon?
SCFAs -Butyrate -Propionate -Acetate Also creates osmotic gradient, driving solute absorption
Bacterial population of the colon
Bacteroides (anaerobe): MC bacteria overall
E. coli is the MC aerobe
What are the three patterns of colonic motility?
Retrograde
Segmental
Mass movements
Retrograde colonic motility
Anti-peristaltic that starts near the hepatic flexure and moves toward the cecum
Results in slowing of colonic transit and increasing fecal mixing
Where does segmental motility occur?
What does it do?
Transverse and left colon
Propels stool forward over small distances (increasing stool mixing)
What do mass movements do?
Progress along the length of the colon and can move a column of stool up to 1/3 the length of the bowel
During these, pressure is the highest in the sigmoid colon
What supplies extrinsic control of the colon to stimulate and inhibit motility?
Parasympathetic and sympathetic neurons
What are the two plexuses of the intrinsic neurons?
Myenteric (Auerbach)
Submucosal (Meissner)
Where is the myenteric (Auerbach) plexus?
At junction between longitudinal and circular layers of muscularis propria
How is the submucosal (Meissner) plexus formed?
In the submucosa from nerve fibers that perforate the circular muscle layer
Gastrocolic reflex
Ingestion of a meal results in increased colonic tone
How does nl defecation occur?
Initial trigger leads to rectal distention, which leads to internal sphincter relaxation
Puborectalis relaxes, which leads to strengthening of anorectal junction
External anal sphincter relaxes and intra-abdominal pressure increases
Rectal contents evacuated
What is the purpose of the rectum?
Reservoir for stool
Filling of this leads to the urge to defecate as the internal sphincter relaxes
Appendicitis
Inflammation of inner lining that can be d/t obstruction of the lumen by a fecalith or d/t infection
Sx of appendicitis
Periumbilical pain migrating toward RLQ
Nausea
Anorexia
Labs of appendicitis
LFTs
Pancreatic enzymes
Rads of appendicitis
CT of abdomen and pelvis
U/s- for peds or pregnant pts (non-compressible tubular structure)
Tx of appendicitis
Appendectomy
If small abscess or phlegm: do IV abx initially followed by interval appendectomy after 4-6 wks
Large abscess- drainage catheter in addition to abx therapy
Diverticular dz
Outpouchings of the colonic wall
Most commonly d/t high intraluminal pressure in areas of anatomic weakness where small arterioles traverse the colon wall
What is the MC site for diverticular dz?
Sigmoid colon
Diverticulosis
Usually asymptomatic
Common cause of lower GI bleeding
Diverticulitis
Infection and inflammation resulting from perforation of a diverticulum
S/sx of diverticulitis
Localized abd pain (at sigmoid, MC) Change in bowel habits Anorexia Nausea Fever/chills Urinary urgency
Labs/rads of diverticulitis
Leukocytosis
Do CT scan of the abdomen
Tx of uncomplicated diverticulitis
Bowel rest, analgesia prn, and abx
-Can be outpatient if pt is afebrile and stable vital signs
-Must be able to tolerate oral intake
If they don’t meet these criteria: admit for bowel rest, IV abx and serial evaluations
-Abx for 10-14 days
Need colonoscopy 6 wks after resolution of sx
What is considered complicated diverticulitis?
Presence of abscess, fistula, obstruction, or free perforation
Tx of complicated diverticulitis
Greater than or equal to 4 cm pericolonic abscess: percutaneous drainage
Smaller abscesses: abx and observation
Once resolved, should consider elective colectomy
What can abscesses in diverticulitis lead to?
Erode adjacent organ
Fistula
What is the most common fistula in diverticulitis?
How is this confirmed?
Colovesical fistulas (pneumaturia and recurrent UTIs) Confirm with CT (air in the bladder without previous cath= colovesical fistula)
Tx of abscess in diverticulitis
Broad spectrum abx until inflammation resolves then elective resection
Hinchey classification
Stratify severity of diverticular dz complicated by perforation
Hinchey classification I
Small, confined pericolonic or mesenteric abscess
Hinchey classification II
Larger, walled-off pelvic abscess
Hinchey classification III
Generalized purulent peritonitis
Hinchey classification IV
Generalized fecal peritonitis
Tx for Hinchey classification I-II
Abx and percutaneous drainage
Then elective colectomy and anastamosis
Tx for Hinchey classification III-IV
Surgical emergencies that require immediate exploration
Hartmann’s procedure: segmental resection, proximal end colostomy, and closure of the rectal stump
Could also do laparoscopic lavage- treats diverticulitis with purulent peritonitis
Cause of large bowel obstruction
Typically caused by neoplasms
Sx of large bowel obstruction
Similar sx to SBO Abd pain Distention Obstipation N/V
What is the MCC of nonmechanical colonic obstruction?
Colonic pseudo-obstruction Can cause a closed-loop obstruction btwn the valve and point obstruction Leads to progressive distention Leads to vascular compromise Leads to possible perforation
When would you need prompt surgical exploration in a large bowel obstruction?
If s/sx of sepsis or peritonitis
Imaging for large bowel obstruction
Plain abdominal XR and upright CXR adequate to show free intra-abdominal air
Profound dilation of cecum (10-12 cm) indicates impending perforation
Can do CT- if not obvious dx, can do water soluble contrast enema
Volvulus- what is it?
What area is most common in the rest of the world?
What area is most common in the US?
Twisting loop of colon around the axis of its mesentary
Causes closed loop obstruction
Sigmoid area
Cecum: rotation of the cecum and terminal ileum around the mesentery
Sx of volvulus
Acute or chronic abdominal pain
Distention
Vomiting
Initial tx of volvulus
Prompt IV resuscitation followed by detrosion of the sigmoid
When will a rigid protoscopy or flexible endoscope be successful for a volvulus?
Rush of gas and stool from dilated proximal colon
Cecal bascule
Variant of cecal volvulus that occurs when floppy cecum flips anteriorly and superiorly, becoming fixed
S/sx of cecal volvulus
Abdominal pain
Distention
N/V
Rads of cecal volvulus
X-ray
Coffee bean sign
Tx of cecal volvulus
Surgical resection with right colectomy
Most pts with ______ will present with obstruction
Colon CA
What is the mainstay of tx for malignancies causing obstruction?
Surgery
What is the tx for proximal lesions in malignant obstructions?
Right colectomy
Tx for distal lesions in malignant obstructions
Proximal diversion with loop colostomy
Other option: Hartmann’s procedure (resection of colonic segment and creation of an end proximal colostomy)
Can also do endoluminal stenting for palliative care
Sx of colonic pseudo-obstruction (Ogilvie’s syndrome)
Similar sx to LBO, but characterized by large dilation proximal to the colon WITHOUT mechanical obstruction
Dx of colonic pseudo-obstruction
Water soluble enema to r/o mechanical etiology
Tx of colonic pseudo-obstruction
Initial tx- NG tube decompression, NPO, IVF, cessation of narcotics and anticholinergics, and correct electrolyte abnormalities
If it doesn’t resolve, neostigmine and endoscopic decompression
