الفهرس 
INTRODUCITONOnly 14 pages are availabe for public view
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Abstract
In vertebral fixation surgeries, patients lose a lot of blood during the course of surgery. This could result in severe patient complications during and after surgery, also make the surgical visualization in bloody field difficult and the duration of surgery more prolonged. With the new anesthetic agents, drugs, and monitoring techniques; this problem has been addressed.
Controlled hypotension is defined as a reduction of systolic blood pressure to (80-90mmHg), a reduction of mean arterial pressure (MAP) to (60-70mmHg) or by 30% of the baseline. Controlled hypotension is a commonly used technique to limit blood loss and improve visualization of the operative field during vertebral fixation surgery.
Many anesthetics and vasoactive drugs have been used successfully to produce deliberate hypotension, including volatile anesthetics (eg. isoflurene), direct-acting vasodilators (eg. hydralazine, nitroglycerin, sodium nitroprusside), autonomic ganglion-blockers (eg. hexamethonium, pentolinium), β-adrenergic receptor blockers (eg. propranolol, atenolol), α-adrenergic blocking agents (eg. prazosin, prostaglandin E1 (eg. alprostadil) and calcium channel blockers (eg. nefidipine, amlodipine).
Drugs used to produce controlled hypotension must be easy to administer,
have a short onset time, an quick offset time on discontinuation, a rapid
elimination without toxic metabolites, negligible effects.
Nitroglycerin (NTG) is a directly acting vasodilator (mainly venous)which decreases cardiac preload, decreases left ventricle filling pressure and decrease blood pressure with coronary vasodilatation (increasing coronary perfusion). It has been used to achieve induced hypotension because of its rapid onset (1- 2minutes), rapid offset (3-5minutes), titrability, limited interaction with anesthetic drugs and low coast. However, it causes reflex t