الفهرس 
Anatomical and Physiological Considerations of Cerebral CirculatilonOnly 14 pages are availabe for public view
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Abstract
The general principle of endovascular neurosurgical procedures involves the placing of special catheters into the arterial circulation of the head, neck or spinal cord through a transfemoral artery approach and through the utilization of special techniques (superselective anesthesia functional examination (SAFE)) it is now possible to safely and accurately access distal target vessels to allow placement of embolic materials and drugs.
The brain is supplied by the two internal carotid and two vertebral arteries. These four arteries anastomose on the inferior surface of the brain and form the circulus or the Circle of Willis. The spinal cord is supplied by three distinct longitudinal vessels; an anterior spinal artery that runs down along the anterior median sulcus and supplies the anterior 80%of the spinal cord, and two spinal arteries that supply the posterior 20% of the spinal cord
The venous drainage of the brain is by veins that lie in the subarachnoid space. The veins pierce the arachnoid matter and the meningeal layer of the dura to drain into the cranial venous sinuses.
The general goals of endovascular neurosurgical procedures in cerebrovascular disorders are:
1. Defenitive treatment for certain disorders.
2. Adjunctive therapy to surgery or radiotherapy.
3. Palliative treatment e.g. for malignant and inoperable tumors.
The great improvement in basic applications of interventional methods including development of fluoroscopic equipments and non ionic contrast materials, development of angiographic techniques, high resolution fluoroscopy, high speed DSA and magnetic resonance angiography and improvement of embolic materials and catheters as well as a better understanding of the neurovascular anatomy, all these allowed for an unprecedented access into the distal cerebral and spinal vasculature and thus opened new therapeutic windows.
The goals of anesthetic management for endovascular neurosurgical procedures are:
1. To render a patient immobile, painless and comfortable.
2. To provide optimum hemodynamic and intracerebral conditions for successful performance of the procedure.
3. To allow for perioperative evaluation of neurologic function.
4. To assist in treating complications.
The anesthetic management for endovascular neurosurgical procedures includes:
A) Preoperative management:
1. Preoperative clinical assessment:
The usual preanesthetic evaluation of the patient is performed with particular emphasis on certain aspects of the patient’s history of allergies, medications, cardiovascular and pulmonary diseases and a thorough neurological evaluation.
2. Preoperative laboratory evaluation:
Particular emphasis should be placed on evaluation of the hemostatic function.
3. Premedication:
Appropriate premedication drugs should be chosen with certain primary goals in mind which include anxiolysis, sedation, amnesia and decreasing autonomic adrenergic discharge these goals could be met safely with benzodiazepines. Other drugs may be used to provide other effects e.g. Reduction of gastric acidity, anti-sialogogue effect and decrease nausea and vomiting.
B) Monitoring:
The quality of monitoring devices should be utilized in endovascular neurosurgical procedures must be equal to those used in major neurosurgical operating theaters. Special monitoring considerations include direct arterial blood pressure monitoring, pulse oximetry, temperature monitoring central venous pressure, pulmonary artery pressure monitoring and central nervous system monitoring.
C) Anesthetic techniques:
The two basic techniques are general anesthesia and managed anesthesia care with conscious sedation. The choice of anesthetic technique is detected by physiologic status of the patient, the duration and type of interventional neuroradiology team.
a) Managed anesthesia care with conscious sedation:
Goals of anesthetic choice for intravenous sedation are to alleviate pain, anxiety and discomfort, provide patient immobility and allow rapid recovery. Its main advantage is the ease awake neurologic examination can be carried out during the procedure. Another advantage is the absence of hemodynamic changes that would associate endotracheal in general anesthesia.
Another important value of managed anesthesia care is that allows the performance of SAFE. This helps to decide whether the catheter is positioned in a hazardous position proximal to a vessel irrigating expressive regions of the brain or if the area can be safely embolized without neurologic sequelae.
The two main techniques that have been proposed for managed anesthesia care are:
- Neuroleptic Analgesia: by infusion of a solution mixture of DROPeridol and fentanyl o produce analgesia, amnesia and cardiovascular stability.
- Propofol infusion: in this technique, a base of neuroleptic analgesia is developed by titration of fentanyl, midazolam and DROPeridol. This is followed by infusion of a propofol drip, which is titrated to develop an unconscious patient airway.
b) General anesthesia:
Indications:
i. Small children and uncooperative adult patients.
ii. Specific procedures to improve the quality of imaging and to allow more accurate placement of embolic materials.
The advantages of general anesthesia in endovascular neurosurgical procedures are:
i. With new agents, a rapid induction with minimal hemodynamic changes, good control of depth of anesthesia and a smooth rapid emergence can be achieved.
ii. Provides better management of PaCO2 and management of induced hypotension and deliberate hypertension is facilitated.
iii. Provides Respiratory immobility if required to improve imaging quality.
iv. Avoids time loss in the case of neurologic emergencies for securing airway.
Conduct of general anesthesia for endovascular neurosurgery:
The main goal while providing general anesthesia is to achieve a smooth induction and recovery without hemodynamic changes and straining that may associate a badly managed intubation of the trachea or recovery period and may jeopardize the whole procedure and affect the morbidity of the lesion. Maintenance of general anesthesia is best done by continues propofol infusion plus inhalational anesthetics at low concentrations which allow rapid changes in the depth of anesthesia and rapid recovery.
The proper performance of these procedures requires a multidisciplinary team that actively interrelates. Anesthetists have an active role in the manipulation of ventilation, systemic and cerebral hemodynamics (induced hypotension and deliberate hypertension) and anticoagulation to provide optimum conditions for performance of these procedures. Anesthetists also have an unquestionable role in the prevention and management of morbidity and mortality during endovascular neurosurgical procedures. Many of the risks encounteres in this arena are the same as those encounteres during traditional operative neurosurgery (aneurismal rupture and ischemia from vascular occlusion) and hemodynamic complications following irradiation of AVMs. Anesthetists must be also prepared for the management of complications that may arise from the use of contrast media and embolic materials.
d) Postoperative Care:
The patient is kept under observation with particular observation of the neurological state and the blood pressure of the patient. During the post procedure period, the blood pressure should be maintained 10-20 % lower than the patient’s blood pressure prior to the procedure.