1. Dr. Mohamed E. Mustafa
Dept. of Surgery
SMC

2.  Ischemic colitis is a rare but possibly fatal
complication of aortic reconstruction.
 Its diagnosis is often delayed, resulting in
significant patient morbidity and mortality.
 To avoid this complication, the vascular
surgeon must:
1. Be aware of the preoperative, intra operative,
and postoperative risk factors.
2. Be knowledgeable of the vascular anatomy
and the many vascular collaterals that may
protect the colon when blood flow is reduced.

3.  The reported incidence of colonic ischemia in
patients undergoing aortic surgery ranges from
0.2 to 10%.
 Colonic ischemia has been detected in 6% of
patients undergoing aortic reconstruction who
had routine post operative colonscopy.
 60% of patients routinely studied following
repair of a ruptured AAA will have evidence of
ischemia.

4.  Pre Operative:
 1. Age
 2. Ruptured AAA
 3. Renal Disease
 4. Coagulopathy
 5. Loss of collaterals from a previous colectomy/
GI surgery.
 6. Occlusive disease of the internal
 iliac arteries and superior mesenteric arteries.
 7. Prior pelvic radiation therapy

5.  Intra Operative:
 1. Intraoperative embolization of the
inferior mesenteric artery from
manipulation of the aortic aneurysm.
 2. Insertion of an aortobifemoral graft
 3. Increasing the length of cross-clamp
and operative time.
 4. ligation of one or both of the IIA.

6.  Post Operative:
 1. Hypoxemia
 2. Hypotension/Hypovolemia
 3. Use of vasoactive drugs.

7. Anatomy

9.  Colon receives arterial flow from 3 main
vascular beds:
1. Superior Mesenteric Artery
2. Inferior mesenteric Artery
3. Internal Iliac Arteries.
 These are usually interconnected by collaterals.

10.  Cecum and Ascending colon: Terminal
branches of SMA, mainly the ileocolic artery.
 Transverse colon: supplied by 2nd
branch of the
SMA, the middle colic artery (There is a
significant anatomical variation in MCA; up to
20% of individuals may not have an MCA.
 Left colon, Sigmiod colon and superior part of
the rectum: Inferior mesenteric artery.

11.  Collaterals:
 Collateral arteries may be an important source
of blood to the colon if one of the major arteries
is occluded.
 Marginal Artery: runs parallel to the
mesenteric edge of the colon. There are 2 parts
of the marginal artery , the Arc of Riolan and
the marginal artery of drummond, which refer
to the parts of the artery that run next to the
distal transverse and splenic flexure.

12.  Meandering mesenteric:
 This is a more centrally located artery
connecting the MCA and the IMA. It can
become quite large and provide important
collateral flow.
Based on pre op aortograms, the meandering
artery has been found in 35% of pts with
aortoiliac occlusive disease and 27% of pts with
aortoiliac aneurysm. Its presence should alert
the surgeon that there is an abnormality in the
mesenteric circulation.

13. Methods of Intra Operative
Assessment of Bowel
Viability during Aortic Repair

14.  1. Clinically
 2. Doppler Ultrasound
 3. IV Fluroscien
 4. IMA Stump Pressure
 5. Sigmoid Intramural pH
 6. Photoplethysmography ( Pulse Oximetry)
 7. Laser Doppler Flowmetry

15.  Loss of arterial pulsation of the supplying
mesenteric artery.
 Blue/black color of bowel
 Loss of bowel sheen
 Los of peristaltic activity
 Temperature
 Studies have shown that using clinical
judgment has an Overall accuracy of 87%
 Predictive value (69%)
 Predictive value in first laparotomy (58%)

16.  In 1978, Ernst et al. proposed measuring IMA
stump pressures in pts undergoing AAA
repair.
 Pressures were measured pre- & post-
aneurysm repair with an 18 gauge
angiocatheter inserted either directly into the
IMA or by threading the catheter into the
orifice of the IMA from within the aneurysm
sac.

17.  The study included 52 patients undergoing
AAA repair.
 39 of the 52 patients had IMA stump pressures
measured. All had postoperative colonoscopy.
One of the 39 patients on colonoscopy had
evidence of mild mucosal ischemic colitis. This
patient had an IMA stump pressure of
 37mmHg, whereas all the other patients had
IMA stump pressures greater than 40mmHg.

18.  Expansion of this study was done in 1983 to
include 64 pts. Of the 64 patients, pelvic blood
flow could not be restored in 3.
 Two of the patients had stump pressures
greater than 40mmHg, had their IMA ligated,
and did not develop colonic ischemia.
 One patient had an IMA stump pressure of less
than 40mmHg, did not have IMA
reconstruction, and developed ischemic colitis.

19.  Two other patients were found to have an IMA
stump pressure less than 40mmHg.
One patient underwent IMA reimplantation
and did not develop ischemic colitis, and the
other patient had the IMA ligated and
developed colonic ischemia.

20.  Thus, it was recommended that if the IMA
stump pressure following aneurysm repair is
greater than 40mmHg or if the IMA was
chronically occluded, then the IMA could be
ligated without ischemic colitis occurring.
 However, Schiedler et al., found 5 (21%)
patients among 24 who had stump pressures
lower than 40 mmHg who did not develop
ischemic colitis.

21.  Thus, the reliability of this technique has been
questioned.
 This technique cannot be applied to many
patients undergoing aortic reconstruction for
occlusive disease.
 In addition, IMA stump pressure
measurements may not prevent the
postoperative development of ischemic colitis
in patients with marginal or normal IMA
stump pressures who become hypotensive in
 the perioperative period.

22.  Hobson et al., using a doppler US probe against the
antimesenteric border of the colon suggested that if the
arterial signals were present during temp. occlusion of
the IMA, then there is adequate collateral flow to
prevent colonic ischemia.
 The significance of lost or reduced arterial signals is not
known as no controls were used in this study.
 The weakness of this method is that it is a qualitative
method, and may be dependent on where the probe is
placed.
 Also, Doppler signals may be present despite less than
adequate perfusion to prevent colonic ischemia.

24.  This can be measured using a tonometer, which
is a silicone balloon permeable to co2, which is
filled with saline and introduced transanally
into the colon.
 Once the co2 in the saline filled balloon
equlibriates with the co2 of the mucosa, the
Pco2 in the balloon and the arterial blood
HCo3 can be entered into the Henderson-
Hasselbalch equation to get the intamural pH.

25.  Fiddian-Green’s study showed that there was a
sensitivity of 100% and specificity of 87% in
predicting ischemic colitis when the
intramural pH was < 6.86.
 This method has the advantage that it can be
used not only intraoperatively, but also during
the post operative period to detect ischemic
colitis.

26.  However, its accuracy is dependent on several
factors:
 the balloon being in the proper position in the
sigmoid/descending colon.
 The co2 in the balloon accurately reflecting
mucosal co2
 Good apposition of the balloon to the mucosal
surface

27.  Using IV fluorescein and a UV light (woods
light), tissue perfusion can be assessed by the
uptake of fluorescein by the examined tissues.
 In a retrospective study, IV fluorescein was
used in 186 pts.
 3 fluorescein patterns were identified:
 Normal (169 pts)
 Patchy uptake (11 pts)
 Absent (4 pts)

28.  None of the pts with normal or patchy uptake
developed clinical evidence of colonic
ischemia.
 The recommendations of this study was that
pts with an absent or patchy fluorescein
pattern should undergo IMA reconstruction.

29.  Disadvantages of this method include:
 1. It provides a qualitative, not quantitative
result.
 2. It assesses mainly serosal, and not mucosal
blood flow.
 3. Difficulties in reusing fluorescein accurately
in the same pt.

30.  Pulse oximetry detects alteration in reflected
infrared light as a function of Hb absorption and
has been a widely accepted reflection of o2
saturation.
 Ouriel et al. did a study on pts undergoing aortic
reconstruction which showed:
 colonic ischemia did not occur in 28 pts in which
the pulsality did not change from the baseline.
 2 pts had loss of pulsality & developed ischemic
mucosal changes based on post op colonoscopy.


31.  The disadvantages of this method are:
 1. when pulsatility is lost, there is no longer the
ability to accurately measure transcolonic o2
saturation.
 2. Pulse oximetry is unable to differentiate
potentially recoverable mucosal ischemia from
complete irreversible ischemia.

33.  LDF uses monochromatic light that is reflected
from moving RBCs and is conducted back to a
photodiode. The signal is then processed &
expressed in millivolts, which is directly
proportional to the velocity of blood.
 Ahn et al. found that colonic LDF values in 62
pts varied between 5 & 42ml/min per 100g.
 LDF has been shown to be more sensitive than
doppler US in detecting bowel ischemia.

34.  Lynch et al. compared Doppler US, laser
Doppler and fluorometry in a dog model of
small bowel ischemia.
 It was found that Laser doppler Index (=
Experimental segment velocity/reference
segment velocity x 100) had the greatest
sensitivity in detecting ischemic bowel at 94%
sensitivity.

36.  The earlier Ischemic colitis is identified in the
post op period, the lower the mortality.
 Because there is no 100% accurate method of
intraoperatively predicting ischemia, one must
look for post op signs suggesting Ischemic
colitis

37.  1. Diarrhea – occurs in 40% of post pts
developing ischemic colitis
 2. Bloody Diarrhea : highly suggestive of
Ischemic colitis, but only occurs in 25% of pts.
 3. Peritonitis or severe abdominal pain occurs
only in 12% of pts.
 4. Acidosis, raised LDH, Leucocytosis


38.  Late Signs:
 Low Cardiac output
 Coagulopathy
 Multi organ failure
 Flexible sigmoidoscopy/colonoscopy is the
investigation of choice.