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)?
- Hypotension or low blood pressure
- Hypovolemia or low volume
- Hypo-oxygenation or low perfusion
So, how does these three Hs cause ARF? Let’s go into a detailed explanation for each.
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.
What happens if there is not enough blood volume to push oxygen around the body or if an accident happened and the patient 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.
A great example would be a patient who has chronic obstructive pulmonary disease (COPD). Patient 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 patient is probably going into the oliguric phase or is currently in the oliguric phase.
ARF in Geriatric Patients
When you think about geriatric patients, they are dehydrated with decreased muscle mass. Reduced muscle mass means decreased fluid retention. Geriatric patients also have loss of appetite leading to hypovolemia.
Now, if geriatric patients 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 patient 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.