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124 Cards in this Set

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Describe regions of cecum:
comma-shaped, divided into the dorsal located base, the body, and the ventrally, cranially directed apex
Describe regions of the cecal base:
separated into cranial and caudal portions, the cranial portion is referred to as the cupula
What is the cupula related to?
developmentally a portion of the ascending colon
Cecal base attachments:
attached dorsally to the ventral aspect of the right kidney, pancreas, and body wall, medial aspect of the base is attached to the transverse colon and the root of the mesentery
Describe cecal bands:
Dorsal, ventral, medial, lateral; dorsal cecal band is an extension of the ileocecal fold, which runs from the antimesenteric side of the ileum to the dorsal cecal band, lateral cecal band runs to the lateral band of the right ventral colon, forming the cecocolic fold, ventral band joins the medial band near the apex
Arterial supply to cecum:
predominately the medial cecal artery, with contribution from the lateral cecal artery, medial and lateral cecal arteries are branches of the cecal artery, branched from the ileocecal artery, from the cranial mesenteric artery
Cecum orifices:
ileocecal and cecocolic
Location of cecocolic orifice:
caudal and lateral to the ileocecal orifice
Cecal functions:
water and electrolyte absorption and microbial digestion
Volume of daily water absorption in the large colon:
equal to the volume of the extracellular fluid space
Region of large colon responsible for larger proportion of water absorption:
cecum
What controls cecal water movement?
predominately controlled by Na transport, but an osmotic effect of volatile fatty acids may play a role
What are the products of microbial fermentation?
volatile fatty acids
What facilitates movement of ingesta from the ileum to the cecum?
Migrating action potential complexes from the ileum
What are the patterns of motility in the cecum?
Patterns 1, 2, and 3 are responsible for mixing cecal ingesta. Pattern 1 begins at the apex and conducts toward the base. Pattern 2 begins at the caudal aspect of the base and conducts toward the apex. Pattern 3 begins at the cranial aspect of the base and conducts toward the apex. Pattern 4 is responsible for transmission of ingesta from the cecum to the RVC. It is a progressive pattern, beginning at the apex, through the base and cecocolic orifice, to the RVC
What is the motility of the RVC?
aboral and oral spike bursts. Aboral spike burst are associated with progressive motility. Oral burst allow the RVC to function as a reservoir and do not propagate to the cecum
What decreases cecal motility?
alpha 2, butorphanol
What increases cecal motility?
neostigmine, bethanechol, or erythromycin in normal horses
Dose of neostigmine:
0.025-0.033 mg/kg IV or SQ
Dose of bethanechol:
0.025 mg/kg
Dose of erythromycin:
IV as an infusion over 60 minutes at a dose of 0.10-1.0 mg/kg
Disease of the cecum:
impaction, intussusception, rupture, volvulus, infarction, or neoplasia
Types of cecal impactions:
Type 1 impactions have impaction of ingesta at the base or body of the cecum and are associated with temporary disruption of motility. Type 2 impaction have normal or fluid ingesta and are associated with cecal motility dysfunction
Predisposing factors for type 1 cecal impaction:
hospitalization, elective surgical procedure, and use of NSAIDs
Mechanism of type 1 cecal impaction:
temporary motility disruption is from the depression of gastrointestinal motility by general anesthetics, pain and restricted exercise
Predisposing factors for type 2 cecal impaction:
tapeworm (anaplocephala perfoliata) infection, inflammation, parasite induced thromboembolism, and dietary changes
Mechanism of type 2 cecal impaction:
Motility dysfunction is from interruption of cecal pacemaker function
Goals of medical management of type 1 impactions:
softening of ingesta to allow passage from the cecum to the RVC
Surgical approaches to the cecum:
VMC, 18th right rib resection
Surgical management of cecal impaction intra-operatively:
massage of impacted material, typhlotomy to lavage and removal of cecal content, or cecal bypass
Cecal bypass options:
cecocolic anastomosis (CCO), ileocolic anastomosis, or jejunocolic anastomosis
Cecal bypass candidates:
type 2 impactions but in horses with thickened cecal wall, minimal or no reflexive motility after evacuation, and an empty ventral colon, motilily dysfunction is suspected and bypass should be considered.
Typhlotomy candidates:
normal wall thickness, normal reflex motility after evacuation, and normal amount of large colon ingesta
Where is typhlotomy performed?
between the lateral and ventral cecal bands
The narrowest region of ascending colon:
left dorsal colon
Bands of the ascending colon:
The right and left ventral colons each have 4 bands, a medial and lateral dorsal (mesenteric) and a medial and lateral ventral (free) The pelvic flexure and left dorsal colon have 1 band, which joins with 2 other bands to have 3 bands on the right dorsal colon
Teniae functions in large colon:
mechanical support, maintenance of orientation in the abdomen, and allowing distention and contraction depending on fermentation
Composition of teniae:
smooth muscle and collagen
How does the composition of the teniae change?
depend on the location and function in the location, elastin is more prevalent in ventral colon teniae because of fermentation, while dorsal colon teniae have more smooth muscle as they are involved in transport of ingesta
Arterial supply to the ascending colon:
The ventral colon, including pelvic flexure, is supplied by the colic artery, a branch from the ileocecocolic artery, which is a branch of the cranial mesenteric artery. The dorsal colon is supplied by the right colic artery, a branch of the cranial mesenteric artery. The transverse colon and a portion of the small colon are supplied by the middle colic artery, also a branch of the cranial mesenteric artery.
Function of the ascending colon:
storage, microbial fermentation, and water absorption
How is feed propulsed in the ascending colon:
Transit is delayed by retropulsive activity initiated at the pelvic flexure pacemaker. Pelvic flexure activity results in the separation of small, well digested particles that are propelled aborally, and courser material which is propelled orally
Disease of the ascending colon:
large colon tympany, impaction, sand impaction, enterolithiasis, displacement, volvulus, colitis, and mural infarction
Risk factors for tympany and impaction of the ascending colon:
cribbing, increased hours stabled, recent change in exercise routine, increased interval from last deworming care, travel within 24 hours of development of the signs of colic, recent colic episode, recent lameness, increased interval from last dental care, tapeworm infestation, and grain diet high in soluble carbohydrates
Why do soluble CHO diets increase risk of tympany & impaction?
associated with less fiber, less water, and greater gas content
Enteral fluid advantages:
direct administration into the GI tract, stimulation of colic motility through the gastrocolic reflex, decreased expense and less precise fluid composition
Examples of cathartics:
mineral oil, dioctyl sodium sulfosuccinate, magnesium sulfate, sodium sulfate, raw linseed oil, and polyethylene glycol
What is mineral oil?
aliphatic hydrocarbon used as a lubricant and an intestinal transit marker
Dose of mineral oil:
5-10mL/kg
Disadvantages of MO:
can interfere with glucose absorption and chronic use can result in a foreign body-like reaction
What is dioctyl sodium sulfosuccinate (DSS)?
cationic surface active agent that lowers surface tension and facilitates penetration of the impacted mass with water and fat
Dose of DSS:
16.5-66 mg/kg
Function of MgSO4 and NaSO4:
increase colonic water content by osmotic activity
Dose of osmotic cathertics:
0.5-1 g/kg
Risk factors associated with sand impaction:
low volume of roughage in diet, access to sand, mineral content of soil, and geographic location
What other ascending colon disease is associated with sand impaction?
Large colon displacement or torsion can occur in 25-54%
Most common post-operative complication with surgical resolution of sand impaction:
diarrhea, peritonitis
Risk factors for enterolithiasis:
geographic location, breed, alfalfa hay, and longer duration of stabling
MOA of large colon displacements:
alteration of the normal motility pattern of the left colon, an increase in soluble carbohydrates in the diet results in an increase in gas production in the colon
Anatomy of LDD:
left dorsal and ventral colon move dorsally and lateral to the spleen to become entrapped within the nephrosplenic space, over the nephrosplenic ligament. The left dorsal colon is also usually rotated ventromedially such that it is ventral to the left ventral colon. As gas accumulates, the sternal and diaphragmatic flexures can migrate cranially and dorsally to become lodged in between the stomach and the left lobe of the liver.
MOA of LDD:
accumulation of gas and abnormal motility of the left dorsal colon
Efficacy of ultrasound and rectal palpation for diagnosis of LDD:
ultrasound 88, rectal palpation 61-72% accurate
Medical therapies for LDD:
fluid therapy & feed withholding, exercise with or without phenylephrine administration, or rolling under general anesthesia with or without phenylephrine administration
Surgical approaches for LDD:
flank laparotomy, flank laparoscopy, or ventral midline celiotomy
What effect does phenylephrine have?
alpha-1 agonist that causes vasoconstriction and splenic contraction, reducing the size of the spleen by 28% and thickness by 48%
Dose of phenylephrine:
3 ug/kg/min over 15 minutes, diluted in saline
Complications of phenylephrine:
Bradycardia, hypertension, fatal hemorrhage in older horses
How is the horse rolled for LDD?
horse is first placed in right lateral recumbency. The abdomen is vigorously balloted as the horse is rolled to dorsal, with or without hoisting the hind end. This procedure is repeated several times. The horse can be rolled from right lateral to left lateral, and either left to recover in left lateral or transitioned to sternal, back to right lateral, before allowing recovering in left lateral position.
Advantages of a standing flank laparotomy to correct NSE:
avoidance of general anesthesia, good access to the region, and ability to close the nephrosplenic space to prevent reoccurrence
Disadvantages of a standing laparotomy to correct LDD:
conversion to a ventral approach if diagnosis is incorrect and inability to address other potential GI lesions
Disadvantages of ventral celiotomy for correction of LDD:
general anesthesia and the associated costs, and longer post-operative recovery time
Under what conditions can standing laparoscopy be performed for LDD:
only if the left dorsal and ventral colons are not gas distended
Reoccurrence rates for LDD:
7.5-8.5%
How is LDD reoccurrence prevented?
closure of the nephrosplenic space, colopexy, or colon resection
Approaches for closure of the nephrosplenic space:
standing or recumbent flank laparotomy or a standing flank laparoscopy
Options to close the nephrosplenic space:
Cruciate sutures are placed between the ligament and the tip of the spleen using non-absorbable suture material, placement of polypropylene mesh to obliterate the space
MOA Right dorsal displacement:
retropulsive movements of the pelvic flexure, with migration of the left colon first cranially, then to the right, such that the right colon becomes located between the cecum and body wall
Risk factors for large colon volvulus:
recent foaling, recent dietary change, and recent access to lush pasture
Most common direction of LCV:
Dorsomedial volvulus, right ventral colon rotates medially and dorsally
How is LCV corrected?
From the left side, with the horse in dorsal, the base of the colon is manipulated in a clockwise direction
How is LCV correction to correct position verified?
normal position of the cecocolic ligament, normal position of the cecum, palpation of mesenteric attachment of right dorsal colon to the body wall, and palpation of the duodenum cranial to the right dorsal colon
Variables associated with poorer prognosis with LCV:
PCV greater than 50%, increasing PCV during surgery, decreasing TP, inability to maintain MAP, hypoxemia, persistent tachycardia during surgery, poor serosal color, dark red or black mucosa, no active bleeding from enterotomy, interstitial-to-crypt ration greater than 3:1, and less of greater than 95% epithelium
What is right dorsal colitis associated with?
use of NSAIDs and may be heightened in horses with a nervous disposition
What are the Surgical management options for RD colitis?
right dorsal bypass, resection of affected colon, large colon resection, or large colon bypass
Describe right dorsal bypass:
side to side anastomosis involving the right dorsal colon oral to the lesion to the proximal (oral) small colon
When do mural infarctions occurs?
strongylus vulgaris migration, severe colitis, or coagulopathy
Types of LC resection and anastomosis:
end to end or side to side
When is EE LC RA performed:
remove the colon within 4-5 inches of the cecocolic ligament
When is SS LC RA performed?
resection is close or proximal to the cecocolic ligament, EE places too much tension on the anastomosis and increases the risk of dehiscence
Describe EE LC RA:
after mesenteric vessel ligation, the right ventral colon is transected transverse to its long axis and the dorsal colon is transected at a 30 degree angle, with a shorter antimesenteric border. Anastomosis is started at the mesenteric border, from within the lumen, closed in 2 layers, with the outer layer inverting
Describe SS LC RA:
after mesenteric vessel ligation, the anastomosis can be created by hand or with stapling instruments, For hand sewn technique, the seromuscular layers of the dorsal and ventral colon are apposed. An incision is made parallel to this suture line in both the dorsal and ventral colon. Full thickness closure is performed, interrupted at 180 degrees to create the stoma. The seromuscular layers of the upper portion are closed with an inverting pattern. After the SS anastomosis is created, the ventral and dorsal colon are transected transverse to the long axis and the ends are closed in a 2 layer inverting pattern. For a stapled technique, ILA-100 or GIA-90 are fired twice and oversewn. After the stoma is created the colons and be transected and closed
What is the relation of the transverse colon?
dorsally to the pancreas and abdominal wall, and is connected by a short mesocolon to the root of the mesentery
Relation of the small colon:
occupies the left caudodorsal abdomen. It is related to the terminal duodenum by the duodenocolic fold
Teniae of the small colon:
has 2 teniae, mesenteric and antimesenteric
How are fecal balls formed?
by contractile activity of the longitudinal and circular muscles
Arterial supply to small colon:
caudal mesenteric artery. The proximal ¾ of the small colon is supplied by the left colic artery, a branch of the caudal mesenteric. The distal ¼ is supplied by the caudal rectal, also a branch of the caudal mesenteric artery
Examples of congenital small colon diseases:
atresia coli and colonic aganglionosis
Examples of obstructive small colon diseases:
impaction, enterolithiasis, and fecaliths
Examples of vascular small colon lesions:
intramural hematomas or mesocolon tears
Examples of strangulating small colon diseases:
lipomas, internal herniation, volvulus, or neoplasia
Risk factors for small colon impaction:
poor dentition, poor quality hay, decrease water intake, parasitism, lack of exercise, submucosal edema, motility disorders, increasing age, and breeds such as minis and ponies
Surgical approaches for small colon impaction:
ventral midline celiotomy or a flank laparotomy
How is small colon impaction resolved intra-operatively:
intraluminal fluid administration through the rectum and extraluminal massage, enterotomy, or resection and anastomosis
Most common complication of treatment of small colon impaction:
diarrhea and jugular thrombophlebitis
Fecalith:
inspissated fecal material as a result of poor quality diet, poor mastication, or reduced water intake
Phytoconglobate:
concretion of matted plant material formed into balls
Bezoars:
concretions of MgNH3PO4
Phytobezoars:
bezoars with plant material
Trichobezoars:
bezoars with hair
Phytotrichobezoars:
bezoars with both plant material and hair
When is meconium considered retained?
if the foal has not passed meconium by 12 hours of age and is straining to defecate
What increases risk of meconium impaction?
Failure to ingest colostrum, which stimulates passage of meconium
Differential diagnosis for meconium impaction:
ruptured bladder, atresia coli, ileocolonic aganglionosis, or enteritis
Medical treatment of meconium impaction:
enemas, but resolution has been reported to be high with retention enemas with 4% acetylcysteine. Addition of NaHCO3 enhances the activity of acetylcysteine, so should be added to either a commercial formula or a mixed formula. 100-200mL is administered and should be retained for 30-45 minutes with a gently inflated foley balloon catheter
What do intraluminal hematomas result in?
luminal obstruction and later, ischemic necrosis of the affected wall, which results in endotoxemia, shock, and possibly death
What is mesocolon rupture associated with?
parturition, either vigorous movement of the foal or as a sequella of type 3 or 4 rectal prolapse
Options for mesocolon rupture:
Resection and anastomosis can be attempted if there is viable colon proximal and distal to the lesion. Most cases subsequent to rectal prolapse do not have enough viable colon distally for RA, temporary or permanent colostomy should be considered
Ileocolonic aganglionosis:
lethal white syndrome, occurs in overo paint horse foals. The colon is stenotic with thin muscular walls and few myenteric plexuses. The condition results in megacolon and subsequently death.
Types of atresia coli:
Type 1 is membranous atresia, is characterized by a membranous diaphragm that occludes the lumen. Type 2 is cord atresia, which has a fibrous band or muscular cord like remenant connecting the blind ends. Type 3 is blind end atresia, which is most common in horses. There is an absence of a segment of intestine, with a gap in the mesentery as well as the disconnected ends.
Why are small colon enterotomies performed in the antimesenteric teniae?
stronger, have better apposition, have less intra-operative hemorrhage, and maintain appropriate lumen diameter
Options for small colon RA:
hand sutured single layer end to end, hand sutured double layer end to end, and triangulated end to end everting stapled anastomoses
Small colon surgical complications:
dehiscence, stricture, adhesions, and impactions of the enterotomy or RA site
Factors that affect small colon surgerical risks:
high concentration of collagenase, a high concentration of aerobic and anaerobic bacteria, and mechanical stress by firm fecal balls
Surgical repair options for atresia coli:
end to end or end to oblique end anastomosis, colostomy, or a pull through technique attaching the small colon to the anus