Effects of Nitroglycerin Versus Labetalol on Tissue Perfusion During Deliberate Hypotension

Hypotensive anesthesia is associated with the risk of reduced tissue perfusion. The usual target mean arterial pressure during deliberate hypotension is 50- 65 mmHg; however, the status of peripheral perfusion under this target is not well investigated. Nitroglycerin and Labetalol are commonly used drugs to achieve deliberate hypotension. Nitroglycerin is a direct vasodilator and its main action is through venodilation, while labetalol combines a selective α1 and non selective beta-adrenergic blocking activity. Both drugs were previously compared during deliberate hypotension with regard to surgical field quality and blood loss. No study to date compared the effects of both drugs on peripheral perfusion when used for induction of deliberate hypotension. The Peripheral Perfusion Index (PPI) is the ratio between pulsatile and non-pulsatile components of peripheral circulation. Measurement of PPI is based on analysis of the pulse oximetry signal. PPI showed increasing popularity as a non invasive monitor of peripheral perfusion. Serum lactate is another frequently used marker of global tissue perfusion.The aim of this study is to compare the influence of nitroglycerin and labetalol on tissue perfusion when used for induction of deliberate hypotension during FESS operations. Tissue perfusion will be evaluated using PPI and serum lactate as markers of peripheral and global tissue perfusion respectively.