We'll learn what metabolic alkalosis is all about in this lesson and how the respiratory system tries to save you from this potentially life-threatening condition.
When an Ion Goes Missing
Fans of documentary crime shows are well aware that sometimes people go missing because they are taken away, get lost, or because they just want to go missing on their own and leave their old lives behind. In a quirky way, this has to do with acidic ions in your body that also go missing as a result of disease states. And just like people and families suffer as a result of a missing loved one, your body suffers as a consequence of this missing ion.
Metabolic alkalosis is a condition that occurs as a result of decreased hydrogen ion concentration or increased bicarbonate ion concentration not as a result of primary respiratory issues. The hydrogen ion is acidic and the bicarbonate ion is basic. If too much acid is lost or too much of a base is gained, then our body becomes alkaline due to an absolute or relative base excess. As a result, alkalemia ensues. Alkalemia is an abnormally high pH of the blood, > 7.45.
Let's examine the reasons as to why this pathological state can occur. Our first possibility in a criminal investigation of a missing person's case is that someone went missing or got lost as a result of a criminal act or by accident, such as when people leave their home and get lost in the woods. It doesn't really matter which one occurs because the person is unfortunately gone.
Well, anything that causes the loss of hydrogen out of the body can cause metabolic alkalosis. One possibility is the loss of hydrogen through kidney excretion. A condition called hyperaldosteronism causes the excess secretion of hydrogen (and potassium) out of the body by way of the kidneys.
Another way by which hydrogen can be lost from the body is through vomiting. Your stomach is full of acid. By vomiting a lot or for a long period of time, we deplete our body's stores of acid, and this leads to a rise in the pH of our body (alkalosis), which subsequently causes the pH of our blood to increase (alkalemia). In either case, the acid is lost in excess, and relative to this loss, the amount of bicarbonate has increased in the body. Bicarbonate is basic and hence we're stuck with alkalosis.
While people may get lost or kidnapped, sometimes they just disappear and hide on their own. Maybe they're hiding from the IRS somewhere abroad or from a criminal gang while in the witness protection program. The end result is that they're still there. They're alive; they're just hidden from view.
Our acidic hydrogen ions also employ this strategy in certain instances, with the end result of alkalosis. Here's one reason how. Sometimes our body loses too much potassium. This can occur as a result of the hyperaldosteronism I just discussed or by the administration of specific diuretics (also known as water pills), among other causes. If potassium is lost in excess from the body and blood, which we term hypokalemia, then the body must do something about this. Just as Newton's third law of motion implies an action must have a reaction, the same deal goes for our biological systems that always react to a certain event.
From your basic cellular biology classes you should've learned that potassium is the main intracellular (within cells) ion. It, like hydrogen, carries a positive charge. If potassium is lost from the body, it is also lost from within our cells. Since the cells lose positively charged potassium ions, they become more negative.
Cells don't like this; they want to maintain an electrochemical balance. Therefore, cells react by telling the positively charged hydrogen ions to leave the blood and enter inside to restore the appropriate electrical charge. This means the hydrogen ions essentially hide away inside of our cells. This, as before, causes alkalemia (a high blood pH).
Okay, lastly I want to discuss the final overarching cause of alkalosis. This is when too much bicarbonate (our base) is added to our system. This happens when bicarbonate is administered, paradoxically, to treat acidosis. The exact details of why this occurs are beyond the scope of this lesson, but you can think of it as a couple (the hydrogen ions) walking down the street, only to be surrounded by a mob (bicarbonate that's injected into a person) out of nowhere. There's not much the two people can do; they're overwhelmed and alkalosis results.
Compensation, Tests, and Treatment
Okay, enough of the crime scene details. During metabolic alkalosis, the body tries to compensate for this by decreasing the breathing rate. You heard me correctly. You probably know that if you stop breathing then carbon dioxide cannot be exhaled out of the body, meaning it builds up within your body.
If your breathing rate is decreased by the lungs, something known as hypoventilation, then CO2 builds up in the body. CO2 is acidic and causes the pH to drop back down to normal or as close to normal as possible. We term this compensation by the respiratory system as compensatory respiratory acidosis, since it acidifies our body as compensation for the primary metabolic alkalosis.
Therefore, on test results, metabolic alkalosis leads to a high pH, a high bicarbonate level, and a high level of the partial pressure of arterial carbon dioxide (PaCO2). Again, in alkalosis, the absolute or relative levels of bicarbonate increase. Bicarbonate is basic. A base has a high pH, so pH increases. To compensate for this the lungs retain CO2; levels of CO2 (as measured by PaCO2) rise as compensation. It's all pretty straightforward.
In fact, there's a really simple way to remember that all the important test values increase. Think about it. Alkalosis, by definition, causes a high pH. There's no way around that indisputable fact. So long as you remember that, then just remember that all the other values follow in the same direction - up. Everything is high in metabolic alkalosis.
As a very quick side note, don't think that the kidneys just sit still and do nothing to try and mitigate a metabolic problem (alkalosis in our case). They do try; it's just that unlike respiratory compensation, which is quick in onset, the ability of the kidneys to excrete excess bicarbonate takes several days to reach maximum potential.
In cases where the kidneys are so sick that they cannot do this, then dialysis (the artificial cleaning of the blood) may be necessary to treat metabolic alkalosis. However, in less severe cases, the underlying cause of the metabolic alkalosis, such as hyperaldosteronism, must be identified and treated to stop this process.
This lesson went over metabolic alkalosis, which is a condition that occurs as a result of decreased hydrogen ion concentration or increased bicarbonate ion concentration. As a result of this, alkalemia ensues. Alkalemia is an abnormally high pH of the blood, > 7.45. Many things can cause metabolic alkalosis, including vomiting, hyperaldosteronism, and hypokalemia, or low levels of potassium in the blood.
As the pH of the blood rises, since basic bicarbonate ions accumulate in the body, the respiratory system decreases the breathing rate, resulting in hypoventilation. This increases the amount of CO2 in the body in order to acidify the blood. This is termed compensatory respiratory acidosis. Therefore, on a blood test metabolic alkalosis results in a high pH, high bicarbonate, and a high PaCO2.
Once you have finished reviewing this lesson you should be able to:
- List three ways that metabolic alkalosis can occur in the body and what it involves
- Discuss how the body reacts to alkalemia
- Describe how to test for metabolic alkalosis and how to treat it