Intra-operative bleeding presents a larger obstacle to endoscopic visualization. Blood obscures the anatomy of the surgical field and dirties the endoscope lens causing greater difficulty with visualization. This situation increases the risk of complications, including brain injury, orbital or optic nerve injury, and catastrophic bleeding from major vessels (e.g., internal carotid artery) 1.
Endoscopic sinus surgery (ESS) is a minimally invasive technique used to restore sinus ventilation and function in patients with recurrent acute or chronic infective sinusitis in whom medical therapy has failed. The term ESS is used to draw attention to the potential for reestablishing natural mucociliary clearance mechanism, drainage and aeration of sinuses, whilst maintaining as much of the normal anatomy as possible. Over last few years this technique has become popular worldwide due to its minimally invasive nature and preservation of mucosa2.
Continued bleeding into the surgical field during ESS not only impairs endoscopic vision but can lead to complications3. Compared with conventional anesthesia, total intravenous anesthesia (TIVA) has been previously reported to result in reduced blood loss when used for FESS. However, few recent studies point out that TIVA may not significantly reduce blood loss 4-5.
Controlled hypotension has been used to reduce bleeding and the need for blood transfusions, and provide a satisfactory bloodless surgical field . Controlled hypotension is defined as a reduction of the systolic blood pressure to 80-90 mm Hg, a reduction of mean arterial pressure (MAP) to 50-65 mm Hg or a 30% reduction of baseline MAP 6. The physiological principle which underlies hypotensive anesthesia is a natural survival mechanism. When profuse bleeding occurs, the blood pressure drops. This drop leads to a reduction or cessation of the bleeding, blood pressure stabilization, and recovery. Accordingly, reducing the patient's blood pressure during surgery can potentially reduce
overall bleeding. Since bleeding in the surgical field is also reduced, the surgical field operating conditions are improved 7 .
Pharmacological agents used for controlled hypotension include those agents that can be used successfully alone and those that are used adjunctively to limit dosage requirements and, therefore, the adverse effects of the other agents. Agents used successfully alone include inhalation anaesthetics, sodium nitroprusside, nitroglycerin, trimethaphan camsilate, alprostadil (prostaglandin E1), adenosine, remifentanil, and agents used in spinal anaesthesia. Agents that can be used alone or in combination include calcium channel antagonists (e.g. nicardipine), beta-adrenoceptor antagonists (beta- blockers) \[e.g. bisoprolo, propranolol, esmolol\] and fenoldopam. Agents that are mainly used adjunctively include ACE inhibitors and clonidine. New agents and techniques have been recently evaluated for their ability to induce effective hypotension without impairing the perfusion of vital organs 8.
Calcium channel blockers are drugs that block the entry of calcium into the muscle cells of the heart and arteries. Thus, by blocking the entry of calcium, calcium channel blockers reduce electrical conduction within the heart, decrease the force of contraction (work) of the muscle cells, and dilate arteries which reduces blood pressure and thereby the effort the heart must exert to pump blood 9.
Although calcium channel blockers have a similar mechanism of action, they differ in their ability to affect heart muscle vs. arteries, and they differ in their ability to affect heart rate and contraction. For example; verapamil (Covera-HS, Verelan PM, Calan), reduces the strength and rate of the heart's contraction and are used in treating abnormal heart rhythms10.
Beta-blockers antagonise the effects of sympathetic nerve stimulation or circulating catecholamines at beta-adrenoceptors which are widely distributed throughout body systems. Beta1-receptors are predominant in the heart (and kidney) while beta2- receptors are predominant in other organs such as the lung, peripheral blood vessels and skeletal muscle11.
