Emergency Pharmacology: A Highlight on Vasopressors (Dopamine)

Vasopressors are life-saving drugs that are commonly seen in an emergency setting. But what are vasopressors, and what are their mechanisms of action?

Vasopressors Defined

Vasopressors are types of medications that exert pressure on the veins, on the vascular beds to promote vasoconstriction. When this happens, there is an increase in blood flow to the heart, lungs, and the brain. Aside from these organs, the kidneys are also directly affected by vasopressors.

Upon administration of vasopressors, the kidneys are alerted to hold all the fluid in the body or what is also known as fluid retention, causing dilation in the renal cavity or arteries; this will be explained further as we go along.

Examples of Vasopressors

There are many examples of vasopressors available in the market, but there are only two that are commonly utilized inside the hospital, especially in emergency scenarios. These drugs are:

  • Norepinephrine (Levophed)
  • Dopamine

Between the two, we’ll focus our attention on dopamine.

Dopamine

Dopamine is usually the first line of drug given to anyone who is suffering from hypotension.

Much like any other vasopressors, the introduction of dopamine is going to prompt vasoconstriction, putting pressure on the vessels. The primary goal for the administration of dopamine is to increase blood pressure. Aside from boosting blood pressure, dopamine can also inadvertently increase heart rate.

As mentioned, the kidneys are also going to be affected through perfusion, holding the fluid in to retain blood and distribute it to the rest of the body.

Hypotensive Crisis

Vasopressors are given especially during a hypotensive crisis. A hypotensive crisis is a situation wherein the body is losing a lot of blood drastically, which can either be caused by the following:

  • Trauma, example: gunshot wound
  • Excessive vomiting
  • Diarrhea

Any of these events can lead to hypovolemic shock, which is a deficiency of blood or fluids within the vascular spaces. If there is the extremely low amount of blood perfusion, it will compromise the distribution of oxygen. Remember, without oxygen, the body will eventually expire.

The Function of the Kidneys

So, during a hypotensive crisis, the kidneys will swoop in to save what is left of the little blood in the body by ceasing the mechanism of urination. The kidneys will not allow pee to go out of the body, keeping it inside the vascular spaces until blood pressure will rise naturally.

Route of Dopamine

Dopamine is usually given with an intravenous infusion as a piggyback or slow infusion; this will help increase blood pressure and dilate the renal arteries. This is true during emergencies.

Dopamine and ARF

Dopamine is also given to clients who are suffering from acute renal failure (ARF). When the kidneys are failing, dopamine will ignite the opening up of the renal arteries, causing more perfusion by shunting blood down to the kidneys so the client won’t go into chronic renal failure, and potentially losing the kidneys.

How does one determine that there is low perfusion in the kidneys?

The mean arterial pressure (MAP) determines how much blood flow is getting around the body. Normally the MAP is from 85 – 100. However, if there are problems with the kidneys, the MAP will go below 65. If this happens, the perfusion becomes compromised. To prevent this, dopamine is given.

For our next lecture, we’ll be focusing on the second vasopressor we’ve mentioned – norepinephrine (Levophed). Check it out in Simple Nursing’s website and YouTube channel.

Identifying the Most Common Causes of Acute Renal Failure

Aside from pouring cement (toxins) into your washer machines (kidneys) which could automatically create massive destruction (renal failure), there are other ways that the kidneys can go into acute renal failure and these ways are broken down into three Hs.

What are the three Hs that contribute to the development of acute renal failure (ARF)?

  1. Hypotension or low blood pressure
  2. Hypovolemia or low volume
  3. Hypo-oxygenation or low perfusion

So, how does these three Hs cause ARF? Let’s go into a detailed explanation for each.

Hypotension

So, you’re wondering, “What does blood pressure have to do with kidney function?”

Well, without oxygen, the body breaks down and dies. If you don’t breathe, you die. If you put a rubber band around your finger, it will turn purplish-blue and eventually die. This is the same with your kidneys.

If there’s low blood pressure, there will be hypoperfusion. And if there’s hypoperfusion, there won’t be sufficient blood and oxygen that’s going to be delivered into the kidneys. Therefore, the primary concern in acute renal failure is how much oxygen the kidneys are receiving.

But how is oxygen delivered to the kidneys?

First, oxygen is breathed in and goes into your respiratory tract to get exchanged with carbon dioxide. Oxygen is then carried by hemoglobin that is present in your red blood cells and takes oxygen into the heart to be distributed or pumped to the different parts of the body. Basically, this is how the body receives oxygen.

If there is hypotension, there will be low blood pressure and the kidneys will receive an insufficient amount of oxygen due to the inefficient push of blood from the heart.

Hypovolemia

What happens if there is not enough blood volume to push oxygen around the body or if an accident happened and the client bled out? Is there going to be sufficient oxygen-carrying blood to transport oxygen around the body?

If there is decreased volume, there won’t be enough blood to circulate the body; thus, hypo-oxygenation will also occur.

Hypo-oxygenation (hypoperfusion)

A great example would be a client who has chronic obstructive pulmonary disease (COPD). Client with COPD has dysfunctional lungs that are unable to exchange oxygen with carbon dioxide. Without proper oxygen-carbon dioxide exchange, there won’t be enough oxygen-carrying hemoglobin to transport O2 down to the kidneys.

What Is MAP?

Low blood pressure will be equivalent to hypoperfusion and hypo-oxygenation. So the question now is, how does one measure if there’s enough blood pressure? This is where mean arterial pressure (MAP) comes in.

Mean arterial pressure directly correlates with the amount of blood that carries oxygen the kidneys are receiving. The magic number of your MAP is 65. If the MAP drops below 65, this means that your kidneys are not getting enough perfusion and your client is probably going into the oliguric phase or is currently in the oliguric phase.

ARF in Geriatric Clients

When you think about geriatric clients, they are dehydrated with decreased muscle mass. Reduced muscle mass means decreased fluid retention. Geriatric clients also have loss of appetite leading to hypovolemia.

Now, if geriatric clients are taking blood pressure medications and the kidneys are not getting enough blood volume to filter the drugs, this will cause toxicity and directly leads to decreased MAP.

Furthermore, if the geriatric client is a chronic smoker and develops COPD like emphysema and chronic bronchitis, this will also cause acute renal failure that is caused by hypo-oxygenation. With the geriatric community, this is called as the synergistic effect.

So remember, the three Hs of acute renal failure are: hypotension, hypovolemia, hypo-oxygenation that all lead to one major issue – perfusion.