If hypotension is unresponsive to fluid therapy, or fluids cannot be used, pharmacological interventions with inotropes or vasodilators are indicated. In some patients, this approach may be further justified to increase vascular tone for a transient period parallel to the initiation of fluid therapy to prevent irreversible lesions of momentarily hypoperfused core organs. T§b.!§...5. summarizes the pharmacological profile and specific indications for drugs most commonly used in treating hypotension.
Sympathomimetic drugs are administered to increase vasoconstrictor tone by their effect on peripheral a-receptors and/or to increase heart rate and myocardial contractility by their effects on cardiac b1-receptors and a-receptors. Phosphodiesterase inhibitors such as amrinone improve cardiac contractility by increasing cyclic AMP production but they also cause vasodilation. Once blood pressure has been restored to levels adequate to sustain perfusion of vital organs, vasodilator therapy may enhance cardiac output by reducing the ventricular afterload. Vasodilators may also be useful to decrease pulmonary artery wedge pressure in the presence of hydrostatic (cardiac) pulmonary edema.
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