Acute mesenteric ischemia; anatomy, pathophysiology and management

Acute mesenteric ischemia is one of the most problematic causes of acute abdominal pain. In this presentation, etiologies of acute mesenteric ischemia, their diagnostic evaluation and treatment are discussed.

1. Acute mesenteric ischemia Dr. Pezhman Kharazm Assistant Professor of Vascular S urgery Golestan University of Medical Sciences

2. Anatomy Three main  mesenteric arteries provide the arterial  perfusion to the gastrointestinal system:  C eliac  artery ( CA) S uperior  mesenteric artery (SMA ) Inferior mesenteric artery (IMA)

3. Anatomy CA:   Foregut  (distal esophagus to duodenum), hepatobiliary system, and  spleen SMA: Midgut  (jejunum to  mid-colon) IMA: Hindgut  (mid-colon to rectum).

4. Types of Acute mesenteric ischemia Arterial: Non occlusive mesenteric ischemia (NOMI) Occlusive: Emboli thrombosis Venous

5. Acute arterial  mesenteric ischemia  The superior mesenteric  artery is the  most commonly involved  vessel.  

6. Acute arterial  mesenteric ischemia Acute   thrombotic:   U nderlying   mesenteric  atherosclerosis I nvolves  the origin of the mesenteric arteries while sparing the  collateral   branches Acute   embolic : O riginate  from a cardiac source  Frequently   occur  in patients with atrial fibrillation or following myocardial infarction Non occlusive  mesenteric  ischemia : L ow  flow state in otherwise  normal  mesenteric  arteries M ost  frequently occurs in critically ill patients on vasopressors. 

7. Clinical Manifestations Abdominal pain out of proportion to physical  findings   S udden   onset  of  abdominal  cramps in patients with underlying cardiac or atherosclerotic disease, often associated with bloody diarrhea, as  a  result of mucosal sloughing secondary to  ischemia Fever N ausea V omiting A bdominal  distention  Diffuse  abdominal  tenderness, rebound , and rigidity are late signs and usually indicate bowel  infarction  and necrosis.

8. NOMI The typical patient who develops  nonocclusive  mesenteric  ischemia  is an elderly patient who has multiple comorbidities,  such  as congestive heart failure, acute myocardial infarction  with  cardiogenic shock, hypovolemic or hemorrhagic shock,  sepsis , pancreatitis, and administration of digitalis  or vasoconstrictor  agents such as epinephrine.  Abdominal  pain is  only present  in approximately 70% of these patients. When  present.   In  the absence of abdominal pain,  progressive abdominal  distention with acidosis may be an early sign of ischemia and impending bowel infarction

9. Diagnostic Evaluation D ifferential   diagnosis: P erforated   viscus Intestinal   obstruction Pancreatitis Cholecystitis N ephrolithiasis .  Laboratory  evaluation is neither  sensitive  nor specific in distinguishing these various diagnoses. 

10. Laboratory findings C omplete  blood count  (CBC): hemoconcentration  and leukocytosis.  Arterial blood gas (ABG): Metabolic   acidosis  as a result of  anaerobic metabolism .  S erum   amylase:  may  be elevated and indicate  a diagnosis of pancreatitis but is also common in the setting of intestinal  infarction. Increased lactate  levels, hyperkalemia, and azotemia may occur in the  late stages  of mesenteric ischemia.

11. Imaging studies Plain abdominal  radiographs :   To  exclude other causes of abdominal pain such as intestinal obstruction, perforation, or  volvulus   Pneumoperitoneum ,  pneumatosis   intestinalis , and gas in the portal vein may indicate  infarcted  bowel.  R adiographic  appearance of an  adynamic  ileus with a gasless abdomen is the most common finding 

12. Imaging studies Upper  endoscopy,  colonoscopy,  or  barium  radiography : Not indicated   Moreover B arium  enema is contraindicated if the diagnosis of mesenteric ischemia is being  considered .  

13. Imaging studies Duplex  ultrasonography:   A valuable  noninvasive means  of  assessing the patency of  the mesenteric   vessels    Spiral  CT with three-dimensional reconstruction   MRA  

14. Imaging studies M esenteric   arteriography: The definitive diagnosis of mesenteric vascular disease   Should   be performed  promptly in any patient with suspected mesenteric  occlusion. Mesenteric  emboli  typically  lodge at the orifice of the middle colic  artery, Mesenteric  thrombosis, in contrast, occurs at the most proximal  SMA, which tapers off at 1 to 2 cm from its origin.  Nonocclusive  mesenteric ischemia produces an  arteriographic  image of segmental mesenteric  vasospasm  with a relatively normal-appearing main SMA trunk 

15. Treatment Initial   management:   F luid   resuscitation S ystemic  anticoagulation with heparin   Sodium   bicarbonate H emodynamic  status  monitoring: C entral  venous  catheter P eripheral  arterial  catheter Foley   catheter A ntibiotics  

16. operative management  P atients  in a moribund condition with acute abdominal symptoms should undergo immediate surgical exploration, avoiding  the  delay required to perform an arteriogram

17. Acute Embolic Mesenteric Ischemia P rimary   goal : T o  restore arterial perfusion with removal of  the  embolus from the vessel. The abdomen is explored through a  midline  incision The transverse colon is lifted superiorly, and  the  small intestine is reflected toward the right upper quadrant . The SMA is approached at the root of the small bowel  mesentery A transverse   a rteriotomy  is made to extract the embolus,  using  standard balloon embolectomy  catheters

18. Following the restoration of SMA flow, an assessment of intestinal viability must be made, and nonviable bowel must be  resected: Intraoperative  intravenous fluorescein injection  and  inspection with a Wood’s  lamp Doppler  assessment of  antimesenteric  intestinal arterial pulsations.  A  second-look procedure should be considered in  equivocal cases   24  to 48 hours following embolectomy.

19. Acute Thrombotic Mesenteric Ischemia U sually  involves a severely atherosclerotic vessel, typically the proximal CA and  SMA R equire  a reconstructive procedure   to  bypass the proximal occlusive  lesion.   The   bypass may  originate from either the aorta or iliac artery. 

20. Endovascular treatment Catheter-directed   thrombolytic therapy   Is  a potentially useful treatment modality for acute  mesenteric   ischemia C an  be initiated with  intra-arterial delivery  of thrombolytic agent into the mesenteric thrombus    Has  a higher probability of restoring mesenteric blood flow success when performed  within  12 hours of symptom onset.  Successful  resolution of  a  mesenteric thrombus will facilitate the identification of the  underlying  mesenteric occlusive disease  process Subsequent  operative mesenteric revascularization or mesenteric balloon angioplasty and stenting may be performed electively to correct the mesenteric stenosis.

21. Drawbacks  of  endovascular interventions D oes  not  allow  the possibility to inspect the potentially ischemic intestine following restoration of the mesenteric  flow A  prolonged period of time may be necessary in order to achieve  successful catheter-directed thrombolysis,  Therefore ,  C atheter-directed   thrombolytic  therapy  for  acute  mesenteric  ischemia  should only be considered in selected  patients.  

22. Non occlusive Mesenteric Ischemia The  treatment of  non occlusive  mesenteric ischemia is primarily  pharmacologic: S elective  mesenteric arterial catheterization followed by infusion of  vasodilatory   agents: T olazoline Papaverine This  must be coupled with the cessation of other  vasoconstricting   agents. Concomitant  intravenous heparin should be  administered  to prevent thrombosis in the cannulated  vessels   Treatment  strategy thereafter is dependent on the patient’s clinical response to the vasodilator therapy.

23. Mesenteric vein thrombosis 80% of patients have some type of hypercoagulopathy Tumors (compressive or paraneoplastic effects), intra abdominal infections (appendicitis complications or pancreatitis), trauma, and cirrhosis are other causes Clinical manifestations are similar to other causes of acute msenteric ischemia Doppler ultrasonography and contrast enhanced CT scan can diagnose MVT. Treatment is fluid resuscitation, bowel rest, anticoagulation, and in selective cases mesenteric vein thrombolytic therapy Laparotomy should be avoided unless severe peritoneal signs are present

24. Thank you