Dose range is 1-25 micrograms kg-1 per minute. Dobutamine was the first designer inotrope. It has predominant pi effects, which increase heart rate and contractility and hence cardiac output. It has mild p2 effects, which reduce systemic and pulmonary vascular resistance. Mild a effects may be unmasked in a patient on p blockers. The increase in cardiac work from administration of dobutamine can induce ischaemia in patients with cardiac disease - this is the basis of the dobutamine stress test. However, because of its vasodilatory properties, myocardial oxygen consumption is less than expected because of the reduction in afterload that occurs. These properties make dobutamine a logical first choice inotrope in ischaemic cardiac failure. Dobutamine has no effect on visceral vascular beds; the increased renal and splanchnic flow occur as a resultof increased cardiac output. The increase in cardiac output may increase blood pressure but, since systemic vascular resistance may be reduced or remain unchanged, the effect of dobutamine on systemic blood pressure is variable and depends to some extent on circulatory volume. The indications for and disadvantages of dobutamine are given in Box 6.2.
Box 6.2 Dobutamine indications and disadvantages Indications
• Low cardiac output states especially if due to ischaemic heart disease
• May not increase blood pressure
• Tachycardia and arrythmias
• Myocardial ischaemia
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