December 12, 2025

In this week’s column, we’ll start with a pre-test! Can you match the following terms? 

Why are these terms and knowledge of what they mean so important to us in EMS? Answer: They relate to the autonomic nervous system, which is crucial to the control of the cardiovascular, respiratory, digestive, urinary, and reproductive functions in the body. Many of the medications administered by us in the pre-hospital field act either directly or indirectly on the autonomic nervous system. 

Certain medications can either excite or mimic (be an agonist or mimetic), or block (be an antagonist or lytic) what the organ is designed to do. Some medications tend to work on the sympathetic (the fight or flight, or adrenergic) nervous system, while others concentrate on the parasympathetic system (rest and restore, cholinergic). Medications can also be grouped as Alpha, Beta 1 or Beta 2, based on which organs they work on. You might remember “Alpha for Arteries, Beta 1 for 1 heart, Beta 2 for 2 lungs.” This concept may appear to be very complicated, but when you break it down, it all makes sense.  

Take epinephrine, for example. This is a common sympathomimetic, meaning it mimics the "fight-or-flight" response, stimulating the sympathetic nervous system. The medication excites Alpha (vasoconstriction), Beta 1 (increased heart rate and strength), and Beta 2 (bronchodilation) receptors for a massive systemic response. This is exactly what we want to happen in drastic situations like cardiac arrest or anaphylactic reactions. Sometimes we want it to hit the entire system fast (0.1 mg/ml IV/IO) or sometimes a little slower (1.0 mg/ml IM) filtered through various muscles into the bloodstream. At other times, we want to target specific tissue as in stridor (racemic epi nebulized) and minimize systemic effects. In times of cardiogenic, neurogenic, or septic shock, or in cases of severe bradycardia, our epi administration is titrated (adjusted) to achieve your goals (10 mcg/ml of push dose epi, 1-5 ml or up to 50 mcg per dose if needed).  

Let’s look at another medication that is carried in our boxes. Metoprolol is commonly known as a beta blocker (recognize the “lol” ending?). This means it is a sympatholytic or blocks the effects of the sympathetic nervous system. It is often prescribed to patients to fight hypertension. The medication will slow down the rate and reduce the contractile force of the heart. Your protocol allows the use of metoprolol at a dose of 5 mg IV/IO over 1 minute for rate control in narrow complex tachycardia. Due to the potential danger involved, it is a medication that requires medical approval before administration.  

We'll review one final medication carried in our boxes that relates to the parasympathetic nervous system. Atropine is a common anticholinergic, meaning it blocks the effects of the parasympathetic system. It can also be called a parasympatholytic. It inhibits parasympathetic stimulation, allowing the sympathetic nervous system to dominate, which increases heart rate and cardiac output. These benefits are reasons we look to atropine in cases of unstable bradycardia, beta blocker overdoses, or organophosphate poisonings, administering 1 mg IV/IO every 3-5 minutes until resolution of symptoms.  

Pharmacology at the EMS level is not beyond your grasp of understanding. Next time you see medications listed as adrenergic, sympathomimetic, anticholinergic, antagonistic, Beta 2, etc., simply break it down. When you see an unfamiliar word, take a second to look it up! 

Until next time, stay safe! 

The UH EMS-I Team 

University Hospitals 

Pre-test answers: 

1:E; 2:C; 3:D; 4:B; 5:A