Shock is one of the leading causes of ICU admission, and is associated with a high risk of death, whatever its cause. Ad- renergic agents are the most commonly used vasopressor agents. Although the alpha-adrenergic properties of these agents raise blood pressure, they can also variably stimulate the beta-adrenergic and dopaminergic receptors. Accordingly, these agents have different haemodynamic profiles as well as different metabolic profiles. Minimal beta-adrenergic stimulation may be beneficial in preventing the decrease in cardiac output related to the increase in left ventricular afterload associated with the correction of hypotension. However, excessive beta-adrenergic stimulation (which can occur as the doses of these agents are adjusted for the vasopressor effect can have profound metabolic effects and promote arrhythmias. Whether these differences in haemodynamic and metabolic profiles impact out- come has long been undefined. Two randomized trials comparing dopamine and norepinephrine as the first vasopressor agent raised major concerns on the use of dopamine (which was associated with tachycardia and increased arrhythmic events, and may be associ- ated with an increased risk of death, especially in the subgroup of patients with cardiogenic shock). The place of epinephrine is not well defined: although this agent is associated with tachycardia, increased incidence of arrhythmic events, and undesired metabolic effects, their relevance to outcome has not been well established, as the studies were underpowered or biased by systematic addition of dobu- tamine. Altogether, these studies suggest that norepinephrine may be the first-choice adrenergic agent.
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