الفهرس 
Anatomy of the AortaOnly 14 pages are availabe for public view
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Abstract
Anaesthesia for vascular surgical procedures is a high risk
specialty. This is attributable to two main factors. First, all the patients
are classified in American Society of Anesthesiologist (ASA) as group ill
and IV which are the highest risk groups. Second, repair of the arterial
lesion requiring surgical treatment may cause ischemic reperfusion
mjury. This can result in varying degrees oflocal cellular hypoxia and
tissue necrosis plus systemic organ failure involving the lungs, liver and
kidneys.
The patients should be assessed properly by taking good history
and doing through examination and investigations. Almost every patients
scheduled for vascular surgery is receiving regular oral medication from
one or more of the drug groups used for treatment of cardiovascular
diseases. The significance of these drugs is that they may interact with
intravenous and volatile anesthetics causing undue hypotension.
Resection and grafting of the abdominal aorta is performed for the
treatment of aneurysm and stenosing occlusive disease. The goals of
surgery and avoidance of rupture and relief of symptoms with restoration
and maintenance of blood flow to the viscera and legs. The anesthetic
technique is similar for all types of abdominal aortic disease. A controlled
airway with tracheal intubation and ventilation is essential because of the
huge abdominal incision. This may be supplemented with epidural
analgesia which is especially advantageous postoperatively. A regional
anaesthetic technique alone is inappropriate for such major body cavity
Fluid and blood losses are large compared to other abdominal
operations and adequacy of circulating volume is judged from
measurements of the central venous pressure and pulmonary artery
pressure. Because the operation involves a large abdominal incision with
evisceration of the intestines, the core temperature may decline by up to
3-4°C and so core temperature should be monitored by an oesophageal
probe.
Major disturbances of the circulation may arise at three points in
the operation: in association with placement of intra-abdominal retraction
and clamping and unclamping of the aorta. Removal of the intestines
from the abdominal cavity followed by placement of large retractors to
enable the aorta to be exposed may result in mechanical obstruction of
venous return VIa the inferior vena cava, resulting in hypotension.
Another cause of hypotension is associated with sudden. tachycardia and
facial flushing is the ”mesenteric traction syndrome”.
The consequences of cross clamping are similar regardless of the
.level at which the aorta is occluded, but the mangitude of the change is
greater the higher the level. Infrarenal cross clamping is the normal
of patients), with mechanical effects on the circulation and ischemic
consequences for the pelvis and lower limbs. The circulating effects are
increased PAOP, SVR, mean arterial pressure and decreased cardiac
output and preload.
Aortic unclamping results in restoration of blood flow to the
ischemic tissues and vasodilated blood vessels of the lower half. The
cardiovascular changes are broadly the opposite of those occurring during
cross :clamping. Thus the blood pressure and systemic vascular resistance
decrease (unclamping shock). The cardiac output, however, may decrease
further owing to decreased preload from pooling of blood in the
hyperemic lower extremities before returning to previous levels. There
may also be acute blood loss from the graft anastomosis site.
Unclamping shock can be reduced in several ways. Fist the surgeon
. can release the clamp slowly. Second, when bifuraction graft is used,
blood flow can be restored to one leg at a time. Third, anesthetist can
prepare for unclamping by stopping vasodilators and reducing the
concentration of volatile anaesthetic agent 5-10 minutes before the
anticipated release of clamp, and rapid infusion of colloids and
crystalloids. Renal and spinal cord protection are important goals in aortic
surgenes.
Surgery on the ascending aorta routinely employs median
sternotomy and cardiopulmonary bypass. Surgery on the aortic arch is
usually performed through a median sternotomy with deep hypothermic
circulatory arrest with focusing on achieving optimal cerebral protection.
All patients undergoing aortic surgery should be left intubated and
ventilated for 2-24 hours postoperatively.
Carotid disease is usually the result of atherosclerosis at the
bifurcation of the common carotid artery. It is also frequently
accompanied by coronary artery atherosclerosis, especially in
hypertensive, diabetics and elderly patients. This plaque at the carotid
bifurcation may produce symptoms either by reducing blood flow to the
brain, resulting in hemodynamic insufficiency, or by atheroembolic or
thromboembolic phenomenon.
Indications for carotid endarterectomy includes recurrent embolic
transient ischemic attacks or reversible ischemic neurologic deficits not
controllable with anticoagulant therapy, or transient ischemic attacks or
reversible ischemic neurologic deficits accompanied by critical luminal
narrowing of the carotid artery. Either of these presentations may be
accompanied by a history of stroke.
Careful neurological monitoring is mandatory. During general
anesthesia, methods used to determine adequacy of cerebral perfusion
have included, carotid stump pressure (CSP), regional cerebral blood
flow measurements, somatosensory evoked potentials (SEP),
electroencephalogram (EEG) and most recently, transcranial Doppler
(TCD).
As long as cardiovascular stability is maintained and the patient is
awake at the end of the operation, any of the commonly used induction
and maintenance anesthetic agent in combination with a short or
intermediate acting non-depolarizing muscle relaxant can be safely used.
Cervical plexus block (CPB) is another popular anesthetic technique. If
properly done, it offers many advantages. However three prerequisites are
. essential. A short surgical time (preferably less than 120 minutes),
Familiarity with the anesthetic technique, as well as patient understanding
and cooperation are all three required. It is preferred to perform a
superficial and deep cervical plexus block to improve the success of the
block.