HYDRALAZINE

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Hydralazine is a direct-acting vasodilator that primarily acts on the smooth muscle cells of arterioles, causing relaxation and a reduction in systemic vascular resistance. While its primary use is in the management of hypertension, hydralazine also has important roles in the context of anesthesia:

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1. Intraoperative blood pressure control: During surgery, maintaining stable blood pressure is essential for patient safety and optimal surgical outcomes. Hydralazine can be used to manage intraoperative hypertension and achieve desired blood pressure targets by reducing systemic vascular resistance.

2. Management of hypertensive emergencies: In rare cases, patients may develop hypertensive emergencies during the perioperative period, which require rapid blood pressure reduction to prevent end-organ damage. Hydralazine, with its rapid onset and relatively short duration of action, can be administered intravenously to quickly lower blood pressure in these situations.

3. Pre-eclampsia and eclampsia management: Hydralazine is often used in obstetric anesthesia to manage severe hypertension in patients with pre-eclampsia and eclampsia. This helps to prevent maternal and fetal complications related to high blood pressure during pregnancy and delivery.

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Here are the main steps in hydralazine's mechanism of action:

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1. Interaction with the vascular smooth muscle: Hydralazine enters the vascular smooth muscle cells in the walls of arterioles.

2. Modulation of intracellular calcium: Although the exact mechanism is not fully understood, it is believed that hydralazine interferes with calcium movement and handling within the vascular smooth muscle cells. One hypothesis is that hydralazine increases the efflux of calcium from the cell or inhibits the influx of calcium, which reduces intracellular calcium concentrations.

3. Smooth muscle relaxation: The decrease in intracellular calcium levels leads to relaxation of the vascular smooth muscle, causing dilation of the arterioles.

4. Decreased systemic vascular resistance: As the arterioles dilate, systemic vascular resistance decreases, which lowers blood pressure.

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                                                                                         Key points about Hydralazine

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• Direct acting arteriolar vasodilator.

 

• Causes greater decrease of diastolic than systolic blood pressure.

 

• May cause hyperdynamic circulatory state.

 

• Arteriolar dilatation may be associated with stimulation of the sympathetic nervous system leading to tachycardia, increased myocardial contractility, increased plasma renin activity, increased aldosterone, increased sodium, and water retention.

 

• Hydralazine is subject to polymorphic acetylation; slow acetylators generally have higher plasma levels.

 

• Lupus erythematosus-like syndrome can develop after prolonged use.

 

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