Dopamine

Dopamine is an endogenous **catecholamine** and the immediate metabolic precursor to norepinephrine. In veterinary critical care, it is primarily utilized as a continuous rate infusion (CRI) to manage hemodynamic instability, particularly hypotensive shock and acute heart failure, *after* adequate fluid resuscitation. ### Clinical Highlights * **Dose-Dependent Effects**: Dopamine's receptor affinity shifts dramatically based on the infusion rate, progressing from dopaminergic (vasodilation) to beta-1 (inotropic) to alpha-1 (vasopressor) effects. * **Renal Dose Controversy**: Historically, "low-dose" dopamine was used to promote diuresis in oliguric acute kidney injury. Modern evidence suggests it does not significantly improve Glomerular Filtration Rate (GFR) and is largely considered unproven or controversial in dogs, and potentially detrimental in cats. * **Strict Administration Rules**: Must be given via a dedicated IV line with a syringe pump or fluid pump. **Extravasation** causes severe tissue necrosis. > **Clinical Pearl**: Dopamine is ineffective and potentially dangerous if administered to a hypovolemic patient. Always restore intravascular volume before initiating vasopressor or inotropic therapy.

กลไกการออกฤทธิ์: Dopamine acts directly on **dopaminergic**, **β1-adrenergic**, and **α1-adrenergic** receptors, and indirectly by stimulating the release of endogenous norepinephrine from sympathetic nerve terminals. Its effects are highly dose-dependent: * **Low Dose (0.5–2 µg/kg/min)**: Primarily stimulates **D1 and D2 dopaminergic receptors** → vasodilation of renal, mesenteric, coronary, and intracerebral vascular beds. Increases renal blood flow and urine output, but does not appreciably increase GFR. * **Medium Dose (2–10 µg/kg/min)**: Stimulates **β1-adrenergic receptors** in the myocardium → increases intracellular cAMP → positive inotropic (increased contractility) and mild chronotropic (increased heart rate) effects. Improves cardiac output and organ perfusion. * **High Dose (>10–12 µg/kg/min)**: Overrides dopaminergic effects and strongly stimulates **α1-adrenergic receptors** in the vasculature → profound vasoconstriction → increases systemic vascular resistance (SVR) and blood pressure. Renal and peripheral blood flows are decreased at these rates.

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