In the prehospital setting, they do not provide us with many tools to treat hypotension, but they do provide us with some effective ones. I always like to stick to basic interventions first - oxygen and trendelenburg - identifying the cause and rapid transport to definitive care; but, what if that is not enough? The large bore IV with fluid challenge and then dopamine administration comes next. By this point, I should be getting close to the emergency room. Easy, right?
I love the drug Dopamine! Effective and interesting to administer in the field. Weight based drugs that require a drip administration are fun. We do not have pumps on our trucks, so calculating the drip rate required from the concentration on hand, for the patient’s weight in kilograms, to the desired dose over a certain time period - all in your head - is one of those skills that can quickly impress the FNG (Friendly New Guy). But you have to know what you are doing! Each patient must be individually titrated to the desired hemodynamic response. At the wrong dosage, Dopamine will either be ineffective or dangerous to the patient.
Dopamine, a simple organic chemical in the catecholamine family, plays a number of important physiological roles in the body. As an intravenous medication acting on the sympathetic nervous system, Dopamine produces effects such as increased heart rate and blood pressure. But you know that! However, because dopamine cannot cross the blood–brain barrier, dopamine given as a drug does not directly affect the central nervous system. On the other hand, I like to joke around that the increased cerebral perfusion pressure will have an effect on the brain. You never know, the patient might even wake up and thank you before you arrive at the ER. This could be a good time to ask him an important question I have come to contemplate.
"Are you on any MAOIs?"
Why is that important? Well, once again, I am happy you ask!
Dopamine's onset of action occurs within five minutes of intravenous administration, and with dopamine's plasma half-life of about two minutes, the duration of action is less than ten minutes. If monoamine oxidase (MAO) inhibitors are present, however, the duration may increase to one hour. "D'oh!!!"
I think this means we can inadvertently overdose a patient on dopamine. Maybe that is why my last patient started those runs of VT after the administration?!? The more you know!!!
How about that!
(For my two faithful followers: If you can recall, I have written about manoamine oxidase inhibitors before - in my post "Do you want some cheese with that MAOI?" In that post, I mentioned a little about the function of manoamine oxidase. MAO inhibitors act by impeding the activity of monoamine oxidase, thus preventing the breakdown of neurotransmitters and endogenous catecholamines, such as dopamine. It is one of my favorite posts. Check it out. Hope you enjoy it, too.)
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