The effect of Dexmedetomidine vs Magnesium sulphate for controlled hypotension in Spine surgeries

Controlled hypotension is a technique to reduce blood loss and the need for blood transfusion during surgery by improving the visibility of surgical site and decreasing the blood pressure until hypotension is achieved. Nowadays, newer and more sensitive spine surgery devices are getting introduced like microsurgical techniques and minimally invasive techniques which has successfully made to stabilize every segment of the spine. In spine surgeries, there are chances of increased bleeding due to the close network of epidural venous plexus. Due to increased bleeding and decreasing the visibility of the surgical field there is an increased chance of severing a nerve.

Controlled hypotension means to reduce Mean Arterial Pressure (MAP) to 60-70 mmHg or a 30% decrease in the baseline value. Decrease in intraoperative blood pressure leads to a direct reduction in bleeding from surgically injured arteries and arterioles. This decreases the intraoperative blood loss and facilitates surgical exposure and further reduces transfusion dependence.

Numerous pharmacological agents have succeeded in controlling MAP. The ideal agent used for controlled hypotension should be easy to administer, have a short onset time, effect that disappears quickly when administration is discontinued, rapid elimination without toxic metabolites, negligible effects on vital organs and predictable and dose-dependent effects.

Magnesium sulphate

Magnesium sulphate causes hypotension by :

1.    limiting the outflow of calcium from the sarcoplasmic reticulum

2.    acts as a vasodilator by increasing the synthesis of prostacyclin

3.    inhibiting angiotensin converting enzyme (ACE) activity.

Magnesium sulphate also has analgesic action due to its antagonistic effect at N-methyl D-aspartate (NMDA) receptors which inhibits norepinephrine release by blocking N-type and partially L-type calcium channels.

 Dexmedetomidine

Dexmedetomidine is a highly selective α2-adrenoceptor agonist with sedative, anxiolytic and analgesic characteristics.

Dexmedetomidine activates central 2A and imidazoline type 1 receptors which causes decrease in norepinephrine release and leads to a decrease in blood pressure and heart rate.

There have not been many studies comparing the effect of magnesium sulphate and dexmedetomidine with each other in spine surgeries. Hence our study aims to bridge the gap between these two drugs for achieving hypotension to decrease bleeding and increase the surgical visibility without any adverse effects of the drug. This observational study is designed with the aim of obtaining clinical evidence on a potentially different effect of dexmedetomidine versus magnesium sulphate in hypotensive anaesthesia during spine surgery.