What is the perioperative medication management of hypotension?

Updated: Jan 09, 2018
  • Author: Nafisa K Kuwajerwala, MD; Chief Editor: William A Schwer, MD  more...
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Answer

Hypotension can occur at any time during surgery as a result of blood or fluid loss and from the effects of vasoactive anesthetic drugs. Medications used to treat coexisting cardiovascular disorders may also exacerbate hypotension.

Phenylephrine is a selective alpha-1 adrenergic agent that causes peripheral vasoconstriction. It is useful in the treatment of hypotension associated with spinal anesthesia, as well as in patients with coronary artery disease or aortic stenosis to increase coronary perfusion pressure. It can be administered in bolus doses of 40-100 mcg through a peripheral intravenous line or an infusion of 10-20 mcg/min. It has a rapid onset of action and short duration of action (5-10 min).

Serum calcium levels are decreased with the administration of heparin and albumin or after a transfusion of blood preserved with citrate. Low serum concentrations of ionized calcium are associated with myocardial depression and decreased peripheral vascular resistance. Calcium ions increase myocardial contractility and have a variable effect on systemic vascular resistance. However, calcium is best used in the treatment of hyperkalemia and hypotension in patients who are hypocalcemic and are receiving calcium channel blockers. Calcium should be administered as a slow intravenous bolus of 0.5-1 g.

Dopamine is used in the treatment of cardiogenic shock, CHF, and following cardiac surgery. It has 3 different actions at 3 pharmacologic doses. When administering in the range of 0.5-2 mcg/kg/min, it increases renal blood flow and urine output via DA1 receptors, which are postsynaptic and act on renal, mesenteric, splenic, and coronary vascular smooth muscle to mediate vasodilation through stimulation of adenylate cyclase and increased production of cAMP. [8] At 3-10 mcg/kg/min, it increases inotropy and chronotropy, augmenting cardiac output. Finally, at more than 10 mcg/kg/min, it increases total peripheral resistance.

Dobutamine is a β-adrenergic receptor agonist with minimal α-adrenergic receptor agonist activity. It is a positive chronotropic and inotropic agent with pulmonary and systemic vasodilatory effect. It decreases total peripheral resistance and increases cardiac output, without the tendency to cause tachycardia that may be evident with dopamine. It is useful in low cardiac output states when an increase in left ventricular end-diastolic volume and pulmonary vascular resistance is not desirable. It is administered as an infusion of 5-15 mcg/kg/min.

Epinephrine is a naturally occurring catecholamine found in the adrenal medulla. It is an α- and β-adrenergic receptor agonist (β-adrenergic receptor predominance at lower doses) that increases cardiac contractility and the heart rate, accentuates systolic and mean blood pressures, and serves as an effective bronchodilator. It should be used as an infusion, starting at 1-4 mcg/min, and then titrated to cardiac output and blood pressure.

Norepinephrine causes vasoconstriction and has positive inotropic action without increasing the heart rate. It has primarily α-, with minimal β2 -receptor, activity. It should be used as an infusion, starting at 1-4 mcg/min and titrated to blood pressure.

Milrinone is a noncatecholamine inotropic agent (phosphodiesterase inhibitor) with hemodynamic properties similar to those of dobutamine. Inhibition of myocardial type III phosphodiesterase leads to an increase in myocardial cAMP, which increases the influx of intracellular Ca2+ and has a positive inotropic effect independent of β-adrenergic receptor stimulation. It increases cardiac inotropy and slightly decreases total peripheral resistance, thereby improving cardiac output. It causes pulmonary and coronary vasodilation.

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