Comparison of intravenous Magnesium Sulphate vs Dexmedetomidine in improving visualization of surgical field in functional endoscopic sinus surgery. A randomized controlled study

Functional endoscopic sinus surgery (FESS) is a revolution in the surgical procedures for chronic sinus and other paranasal sinus diseases, by making it the procedure of choice. It is minimally invasive, shortens procedure duration, minimizes surgical scar, reduces complication rate and reduces the discomfort of the patient.

However, there can be serious complications associated with FESS like orbital injuries, optic nerve injuries, CSF leak etc. due to close proximity of the blood vessels, nerves and the orbital and intracranial cavities, whose incidence can be increased with excessive bleeding during surgery.

The major requirement for functional endoscopic sinus procedure is a relatively bloodless surgical field to provide better visualization and successful outcome of the procedure despite the high vascularity of the surgical area.This can be achieved by controlled hypotensive technique which is an accepted technique worldwide. Controlled hypotensive technique is by maintaining a mean arterial pressure of 60-70 mmHg which reduces the bleeding from the surgical site thereby resulting in less blood loss, better visualization leading to reduction in complications and surgeons satisfaction is also improved.

The ideal agent used for controlled hypotension should have certain characteristics like ease of administration, shorter onset and offset time, negligible metabolism without any toxic metabolites and minimal effect on various organ systems.

Controlled hypotension involves reducing arterial blood pressure 30– 40% below its normal range or reducing MAP (mean arterial pressure) to 65 mm of Hg reversibly and maintaining it at that level throughout the surgery.

Various methods have been used to achieve controlled hypotension like positioning, pharmacological methods and arteriotomy. Pharmacological drugs sodium nitroprusside,NTG, hydralazine,volatile anaesthetic, intravenous anaesthetics like propofol and betablockers have been used with various success rates.

Dexmedetomidine is a potent highly selective alpha 2 receptor agonist. It has the property of sedation, analgesia and anxiolytic. It causes sympatholysis by acting at central alpha 2a receptor and imidazoline type1 receptor and presynaptic blockade of the release of norepinephrine, thereby causing controlled hypotension.

Magnesium Sulphate causes stabilization of the cell membrane and intracytoplasmic organelles by inhibiting the activation of NA-K ATPase and Ca- ATPase enzyme. It also limits Ca2+ outflow from sarcoplasmic reticulum by inhibiting L-type Ca channels in sarcoplasmic reticulum. In addition Mg2+ acts as a vasodilator by increasing the synthesis of prostacyclin, as well as by inhibiting ACE (angiotensin converting enzyme) activity.

Since there are only very few studies on comparing these two drugs in producing controlled hypotension, our aim is to compare these two drugs in terms of satisfaction of surgeon, visibility of the field, blood loss, hemodynamic profile and to note any complication if any.