INTRAOPERATIVE COMPARISON BETWEEN ISOFLURANE AND NITROGLYCERIN FOR HYPOTENSIVE ANAESTHESIA

Abstract

Introduction
All surgeries involve cutting of the blood vessels which will obviously result in bleeding.
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Deliberate hypotension is a method to produce a controlled and safe reduction in the intravascular pressure, while preserving organ perfusion. By enhancing the visualization of the surgical field, hypotension allows accurate delineation of lesions thereby causing fewer traumas to the delicate structures. Therefore intricate operations may be performed easily, exactly and therefore more successfully. Extensive surgical procedures are associated with considerable haemorrhage during and after surgery. The concept of intentionally decreasing arterial BP to hypotensive levels during surgery was first proposed by Cushing in 1917 for intracranial surgery and was introduced into clinical practice by Gardner in 1946.
Since then, this technique has been variously named as controlled hypotension, Induced hypotension, deliberate hypotension and hypotensive anaesthesia. Deliberate hypotension is defined as the intentional reduction of the systemic perfusion pressure. Most studies define deliberate hypotension as reduction in systolic blood pressure (SBP) to 80- 90mm Hg (30% decrease in the SBP from the baseline pressure). According to another definition, deliberate hypotension is a decrease in the mean arterial pressure (MAP) to 50-65 mm Hg in normotensive patients.
Main purpose of hypotensive anaesthesia is to decrease intraoperative blood loss, thereby improving operating condition or decreasing the need for blood transfusions.
Different techniques have been used to achieve controlled hypotension.
1. PHYSIOLOGIC TECHNIQUES:-
Body positioning, the haemodynamic effects of mechanical ventilation, and changes in heart rate
and circulatory volume can be used with drugs to lower blood pressure to the desired level. The appropriate use of physiologic maneuvers helps decrease the dose of potentially toxic drugs
needed to produce hypotension.
2. PHARMACOLOGIC TECHNIQUES:- These includes:-
Volatile Anaesthetics -- Halothane, Isoflurane, Sevoflurane,Enflurane, Desflurane.
Directly acting vasodilators -- Sodium Nitroprusside, Nitroglycerine, Hydralazine, Adenosine.
Ganglion Blocking Agents -- Trimethapan
Beta Blockers -- Propanolol, Esmolol
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Combined α & β blocker -- Labetalol
Calcium channel blocker -- Nicardipine
Prostaglandins -- PGE1
Spinal and Epidural Anaesthesia
The ideal hypotensive agent should have a predictable, dose dependent effect, rapid onset and
recovery, quick elimination without producing toxic metabolites and should not disrupt auto
regulation of vital organs.
Nitroglycerine is an organic nitrate which causes direct nonspecific, vascular smooth muscle
relaxation, consequently decreasing both preload and after load on heart leading to fall in both
systolic and diastolic blood pressure.
Isoflurane is a halogenated methyl ether and a potent inhalational anaesthetic. Isoflurane produces rapid hypotension by decreasing peripheral vascular resistance without myocardial depression . It also provides better myocardial perfusion than halothane or enflurane . With isoflurane baroreflex activity is better mained in hypotensive anaesthesia .It 14 has rapid onset and recovery , more potent peripheral vasodilating effect .It also has the ability to protect the brain from hypoxia due to decrease in cerebral metabolic rate . (Artru 1984 : Michenfelder etal in 1987 ). With these advantages , Isoflurane has been gaining increasing interest recently as a
hypotensive agent in induced hypotension . Isoflurane has been used as the sole agent to induce hypotension in orthoganthic surgery and has significantly reduced blood loss and improved the quality of surgical field .
Since both these drugs are safe and easily available , an attempt has been made to study comparing Nitroglycerine with Isoflurane as hypotensive agents during spinal surgeries in the Operation theatres of SCB Medical College and Hospital ,Cuttack.