What are the 4 major causes of acute mesenteric ischemia?
Superior Mesenteric artery embolism (50%)
Superior Mesenteric Thrombosis (15-20%)
non-occlusive ischemia (20-30%)
Mesenteric venous thrombosis
Circulation to the intestines: -what are the main 2 arteries? -regulated by which hormones? -innervated by which nerves? -
2 main arteries SMA and IMA.
*more blood is shunted there after eating.
Regulation:
- if not adequate perfusion pressure renin and vasopressin come in to improve perfusion.
- Vasopressin causes mesenteric vasoconstriction and venous dilation, reduces portal venous pressure in patients bleeding from potral HTN.
-innervated by sympathetic nervous system.
Hallmark Clinical Presentation of Ischemic bowel?
Other sx
severe cramping, abd pain(worst they’ve ever had) out of proportion of PE findings, poorly localized.
*wont find peritoneal signs, might have bruits.
Sx:
- sudden or gradual onset
- prior episode
- n/v
- bloody diarrhea
- as ischemia worsens:
- -abd distension
- -absent bowel sounds
- -peritoneal signs
- -+/- feculant odor to breath
Risk factors associated with acute mesenteric arterial embolism
- advanced age
- Coronary artery dz
- cardiac valvular dz
- hx of afib
- aortic surgery
- aortic dissection
- CHF
What are the clinical syndromes associated with occlusive and non-occlusive ischemic bowel?
- Occlusive:
- -mesenteric arterial embolism
- -mesenteric arterial thrombosis
- -mesenteric venous thrombosis
- Non-occlusive:
- -hypoperfusion
Mesenteric Arterial embolism
- median age & gender
- often occludes which artery?
median age 70YO and 2/3 are women
Occludes SMA, 6-8cm beyond arterial origin near the middle colic artery and affects the jejunum.
Mesenteric arterial thrombosis
- etiologies
- usual site of blockage?
- sx
Etiologies:
- atherosclerotic dz
- trauma
- infection
Usual site of blockage: SMA or celiac axis
Sx:
dont usually develop until significant blockage.
-discomfort so bad that they lose weight b/c they dont want to eat. 15min post prandial they get crampy pain and diarrhea.
Which has a more favorable prognosis, Mesenteric arterial embolus or thrombus?
-Mesenteric arterial EMBOLUS has more favorable prognosis.
Mesenteric Venous Thrombosis:
- MC in which age group
- onset
- MC site?
- sx
MC age group 48-60YO
Onset: can be acute or develop over the course of a few weeks.
MC site: superior mesenteric vein or intestinal strangulation from hernia or volvulus.
*if involves portal vein d/t liver dz.
Sx:
- insidious onset of sx
- pain diffuse and nonspecific but later becomes constant
- anorexia
- vomiting
- diarrhea/constipation
- hematemesis
Mesenteric Venous thrombosis:
- Risk factors
- pathophysiology
Risk factors:
- hypercoagulable state*
- portal HTN*
Pathophysiology:
-decreased mesenteric venous blood flow results in bowel wall edema**, results in systemic hypotension & increase in blood viscosity. This results in diminished arterial flow leading to submucosal hemorrhage and bowel infarction.
Non-occlusive mesenteric ischemia
- etiology
- risk factors
- pathophysiology
- mortality rate?
- sx
etiology:
- result of splanchnic hypoperfusion & vasoconstriction
Risk factors:
-atherosclerotic dz
HPathophysiology
-mesenteric vasospasm
High mortality; 70%
Sx:
- progressive abd pain, bloating, n/v, mental status changes(d/t poor perfusion of brain)
- 25% dont have abd pain
Sx of ischemic colon?
Dx?
mild abd pain, tenderness present
rectal bleeding, bloody diarrhea
Dx: colonoscopy
*90% of pts are over age of 60YO
Summary of MC causes of each of the following:
- Arterial emboli
- Arterial thrombosis
- Venous thrombosis
- Nonocclusive mesenteric ischemia
Emboli: atrial fibrillation, MI
Arterial thrombosis: atherosclerotic dz
Venous thrombosis: hypercoagulable, neoplasm
Nonocclusive: low flow states
Work up for bowel ischemia?
- Lab
- Imaging;
- -abd xrays
- -CT of abd***
What may be seen on labs of ischemic bowel dz?
- increased WBC w/ predominance of immature cells
- increased HCT
- increased amylase, increased phsophate
- increased serum lactate
- metabolic acidosis
- any pt with abd pain and metabolic acidosis has intestinal ischemia until proven otherwise*
WHat may be seen on plain xrays with ischemic bowel dz?
- pneumotosos intestinalis
- portal venous gas
- thickened bowel wall with thumb-printing
- air fluid levels
- dilated bowel loops
- gasless abd
Pneumatosis intestinalis:
- what is this?
- suggestive of what dz?
What: gas cysts in the bowel wall, not gas in the bowel lumen.
*requires surgical removal.
Suggestive of necrotizing enterocolitis.
Portal Venous Gas:
- what is this?
- cause
WHat: accumulation of gas in the portal vein and its branches.
-Cause: ischemic bowel, intra-abd sepsis
What is the first step in evaluation of acute abd? What is the next step?
What is the preferred imaging study?
Upright and supine plain abd x-rays are the 1st step in eval of acute abd.
CT is the next step if the dx is not made on plain films.
Preferred imaging study is CT.
- can be with IV and PO contrast.
- oral contrast necessary for eval of mucosal thickening of the bowel wall.
CT findings?
Bowel wall thickening: MC in ischemic colitis, colonic infarction, and venous occlusion
Bowel dilation
Fat stranding(fluid in fat, seen on anything causing inflamm) and ascities
Varying degrees of attenuation
Pneumatosis and portomesenteric gas
MR angiography:
better at dx venous occlusions
Tx of Ischemic Bowel
Hemodynamic monitoring: correct hypotension, hypovolemia
Cardiac monitor, venous access, O2
- correction of metabolic acidosis
- broad spectrum abx
- NG tube for gastric decompression
- vasopressors that have less effect on mesenteric perfusion (dobutamine, low dose dopaine, milrinone)
- anticoagulation unless actively bleeding.
- correction of arrhythmias
- THEN imaging
- -may start with plain films or CT, but if strong suspicion should proceed DIRECTLY to angiography
- at angiography can give papaverine (anti-spasmodic) directly in to relieve mesenteric vasoconstriction.
-if peritoneal signs may proceed directly to the OR for surgical repair.
What is gold standard dx study for acute arterial ischemia?
Mesenteric angiography
Tx of:
- Mesenteric aterial embolus
- mesenteric arterial thrombus
- Mesenteric venous thrombus
- nonocclusive mesenteric ischemia
MAE: surgery and embolectomy or local infusion of thrombolytic therapy
MAT: surgery w/ thrombectomy + revascularization or heprinization
MVT: heparinization + resection of infarcted bowel.
Non-occlusive mesenteric ischemia:
- papaverin infusion during angiography
- reverse underlying conditions
- repeat angiography can be done in 24hrs
- surgical exploration reserved for pts w/ peritoneal signs
