Norepinephrine noradrenaline

Norepinephrine is also an endogenous catecholamine secreted by the adrenal medulla and the terminal endings of postganglionic nerve fibers. It is a potent a-agonist with moderate br and minimal b2-activity. Therefore it induces marked peripheral vasoconstriction with a resultant rise in blood pressure and often a fall in cardiac output. Importantly, the fall in cardiac output does not always occur early, but slowly over time. Hence norepinephrine can limit tissue oxygen availability. Concurrent use of dobutamine may prevent this. Norepinephrine may also be combined with phosphodiesterase inhibitors (e.g. milrinone) to achieve an additive inotropic effect of the adrenergic and non-adrenergic agents, while the vasodilator and vasoconstrictor effects counterbalance each other. Norepinephrine can also be combined with epoprostenol (prostacyclin) or prostaglandin E1 in the treatment of severe right heart failure.

An attractive effect of norepinephrine is that the predominant a-adrenergic effects result in limited tachycardia. Hence, the addition of norepinephrine can be considered in the presence of hyperkinetic septic shock associated with severe tachycardia unresponsive to fluids. Nevertheless, the increased afterload related to the vasopressor effects leads to increased myocardial workload and can precipitate acute cardiac failure, myocardial ischemia, and pulmonary edema.

Indications

Severe circulatory shock

Norepinephrine is indicated when arterial hypotension persists despite the administration of dopamine at doses of 20 to 25 pg/kg/min. Right ventricular failure

Pulmonary hypertension with arterial hypotension can compromise right ventricular function by decreasing right ventricular coronary perfusion. Norepinephrine can be beneficial in restoring coronary perfusion pressure in such circumstances, but this pattern is rare and, when it occurs, is manifest by profound cardiovascular collapse. In right ventricular failure it may be combined with a pulmonary vasodilator such as prostaglandin E ..

Septic shock

Norepinephrine may be useful for maintaining tissue perfusion pressure in severe circulatory collapse associated with sepsis ( Marik and Mohedi,n,..1994).

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