dobutamine

Dobutamine is another inotropic agent we use in the ICU. It’s referred to as a catecholamine—our word for an organic compound that is released by the adrenal medulla during the fight-or-flight response—but dobutamine is synthetic. It’s actually a structural analogue of isoprenaline (Isuprel), and is administered as a racemic mixture (*important fact*).

This medication is administered primarily for patients in cardiogenic shock, but is also utilized heavily in the advanced heart failure population. It can be a home infusion for those patients. It’s also used for stress testing, interestingly enough. Make sure you hold the beta-blocker that morning.

Dobutamine acts on three different receptor sites on the surface of the myocardial cell. It directly stimulates the beta-1 receptors, the beta-2 receptors, and the alpha receptors. The fact it’s a racemic mixture ensures that the alpha activity of dobutamine is balanced. Because dobutamine (unlike dopamine) does not act on dopamine receptors, it doesn’t promote the release of norepinephrine. This means it won’t increase afterload despite its action on the sympathetic nervous system.

  • Beta-1 activity: agonist, increases contractility and heart rate
  • Beta-2 activity: agonist, resulting in vasodilation of blood vessels in skeletal muscle tissue, as well as dilating bronchioles
  • Alpha-1 activity: balanced agonist and antagonist activity via the (+) and (-) isomers

The effects of dobutamine are dose-dependent. The primary hemodynamic factor followed for titration of the drip is cardiac index. Standard dose range is 2.5-20 mcg/kg/min, and may be titrated by 2.5 mcgs every 15 minutes or so. Increase in heart rate is more marked starting around 12 mcg/kg/min.

Dobutamine increases myocardial metabolism and oxygen consumption. This mechanism results in worsened myocardial ischemia and angina may occur. Hence its use during stress testing…

Effects on other systems

Nausea and vomiting can be quite pronounced, as activation of the beta-2 receptor sites slows gastric motility. This effect can be worse in patients who are diabetic, as well as those who have received anesthetic medications.

Dobutamine stimulates glycogenolysis in skeletal muscle and gluconeogenesis in the liver, which raises blood sugar, as well as insulin secretion in the pancreas, to drive said serum glucose into the cell. If your patient is a diabetic, however…

It increases renin secretion from the kidney. This results in activation of the RAAS, which is a mechanism for hypertension.

It inhibits histamine release.

PRIMARY CONSIDERATIONS: Administration of dobutamine can contribute to down-regulation of the beta-receptors. It’s also proarrythmogenic, and can precipitate ventricular and supraventricular arrhythmias, as well as cause chest pain from angina.

dopamine

I’m not talking about the dopamine already present in your system that allows you to like things and enjoy life. I’m talking about the intravenous drip used as an inotrope in the intensive care unit.

Dopamine is a primitive drug.

I mean that literally. Also, it smells bad. Seriously. Open the bag and take a whiff–sulfur, yum.

Dopamine is the precursor to norepinephrine and epinephrine. It’s a neurotransmitter that acts centrally and peripherally, once metabolized, on the sympathetic nervous system. The sympathetic nervous system is that fight-or-flight response we all remember from the last time we did CPR.

We used dopamine all the time when I was growing up as a nurse. The doctors would write for “renal dose dopamine” and we knew that meant 1-3 mcg/kg/min, titrate to urine output greater than 50cc/hr.

We ran it in septic patients all the time, based on the theory it would protect the kidneys and the gut from the low perfusion state induced by sepsis. We would run it before levophed–back then, levophed was the last drug you reached for. We’d use it to give our fresh hearts a little kick to get them extubated and make their numbers look good, help them have adequate urine output without lasix.

So how does dopamine induce diuresis?

It causes “diuresis” by decreasing aldosterone secretion in the adrenal cortex. Aldosterone is what encourages your kidneys to retain sodium at the distal renal tubule. This causes water retention. If you block aldosterone, you prevent the retention of sodium and water. It also, at low doses, increases renal blood flow & GFR, promoting the excretion of sodium. As we know, H2O can’t think for itself but merely follows sodium every where it goes.

It also inhibits insulin secretion. This is one reason why patients (particularly type 2 diabetics or patients who have received anesthetic medications) on dopamine drips will have a higher serum glucose. We didn’t worry about it much back then, because all of our patients were on insulin drips anyway.

Dopamine has another strange effect: it affects the release of thyroid-stimulating hormone and inhibits prolactin release. Consider hypo- or hyperthyroidism if your patient begins exhibiting unexplained heart rate/blood pressure changes while on a dopamine drip that hasn’t been titrated.

The effects of dopamine are dose-dependent.

  • Low dose effects (1-2 mcg/kg/min) include vasodilation of the renal and mesenteric blood vessels by acting on the dopaminergic 1 & 2 receptors.
  • Moderate dose effects (2-10 mcg/kg/min) are primarily beta-1, enhancing contractility and heart rate.
  • Higher doses than 10 mcg/kg/min act overwhelmingly on the alpha-1 receptors, causing vasoconstriction.

PRIMARY CONSIDERATIONS: causes tachyarrhythmias, particularly in hypovolemic patients. At high doses, profound vasoconstriction will occur, which can cause necrosis, gangrene, and even compartment syndrome if infused through a peripheral IV.

#CCRN #CSC #CMC #AACN

welcome

This is the post excerpt.

All scenarios are made up, everyone came out of it okay, and all views expressed are my own. Don’t get medical advice here, folks. Do the right thing. Go see a doctor, vaccinate your kids, plant a tree.

Something smart should go here, but I’m fresh out. One of these days maybe I’ll find some more smart.

My grandmother always told me that, if ignorance is bliss, I should check to see if I have the right kind of ignorance, since I don’t appear blissful enough. Thanks, grandma.