Respiratory acidosis - causes, symptoms, diagnosis, treatment, pathology

What is respiratory acidosis? With respiratory acidosis, “acidosis” refers to a process that lowers blood pH below 7.35, and “respiratory” refers to the fact that it’s a failure of the respiratory system carrying out its normal pH- balancing job.

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0:03 - 0:16: What’s “Respiratory Acidosis”?
1. “Acidosis” refers to a process that lowers blood pH below 7.35.
2. “Respiratory” refers to the fact that it’s a failure of the respiratory system carrying out its normal pH balancing job.

0:17 - 0:41: Inhalation and Exhalation
Now normally during an inhalation, the diaphragm and chest wall muscles contract to pull open the chest and that sucks in air like a vacuum cleaner.
Then during an exhalation, the muscles relax, allowing the elastin in the lungs to recoil, pulling the lungs back to their normal size and pushing that air out.
Ultimately, the lungs need to pull oxygen into the body and get rid of carbon dioxide.

0:44 - 1:51: pH Fluctuations, PCO2 and Minute Ventilation
Carbon dioxide binds to water in the blood and forms carbonic acid, which then dissociates into the hydrogen ions and bicarbonate ions.
So in order to prevent pH fluctuations, the carbon dioxide concentration, or the partial pressure of carbon dioxide concentration called PCO2, needs to be kept within a fairly narrow range.
For this reason, the lungs maintain the ventilation rate they need to get rid of carbon dioxide at the same rate that it’s created by the tissues. If PCO2 starts to rise and pH starts to fall, chemoreceptors that are found in the walls of the corroded arteries and in the wall of the aortic arch start to fire more, and that notifies the respiratory centers in the brain stem that they need to increase the respiratory rate in the depth of breathing.
As the respiratory rate and depth of each breath increases, the minute ventilation increases - that’s the volume of air that moves in and out of the lungs in a minute. The increased ventilation helps move more carbon dioxide out of the body, which reduces the PCO2 in the body and raises the pH.

1:54 - 3:13: Causes of Respiratory Acidosis
In respiratory acidosis, the normal mechanism of ventilation is disturbed and minute ventilation becomes inadequate to balance the pH. This can be due to a number of problems.
2:05 - 2:21: Slow Firing Rate of Respiratory Centers
Sometimes the problem is not the lungs themselves but the respiratory centers in the brain stem. After a stroke or medication overdose, like with opiods or barbiturates, the respiratory centers can slow their rate of firing, so breathing becomes extremely slow or stops entirely.
2:23 - 2:41: Neuromuscular Disorder or Malfunction of Diaphragm or Chest Wall Muscles
It could also be due to a neuromuscular disorder, like myasthenia gravis, where the nerves don’t effectively stimulate the muscles to contract.
Sometimes the diaphragm or chest wall muscles don’t work properly, which can happen after severe trauma or due to obesity when the chest wall is too heavy for the muscles to lift it.
2:43 - 2:53: Airway Obstruction
Another reason is airway obstruction, which might happen if a child swallows an object, like a peanut, and it lodges in the right main stem bronchus, preventing the lungs from fully ventilating.
2:55 - 3:13: Impaired Gas Exchange
Finally, there might be impaired gas exchange between the alveoli and capillaries. That might happen if alveoli are damaged from chronic obstructive pulmonary disease, or if fluid accumulates within the alveoli like in pneumonia, or if fluid collects between alveoli and the capillary walls like in pulmonary edema.

3:15 - 3:35: Consequences
In all these situations, the result is that the lungs can’t efficiently get rid of carbon dioxide. The carbon dioxide accumulates in the blood, so the partial pressure of carbon dioxide rises, usually above 45 mmHg. This causes a decrease in the blood pH, often reducing it below 7.35.

3:36 - 5:41: Defense mechanisms of the body
To compensate for this decrease, the body is designed with several mechanisms.
3:41 - 3:46: The Still-working Respiratory Centers
If the respiratory centers are working, then they try to increase the rate and depth of ventilation.
3:47 - 5:39: Bicarbonate Ions and Basic Molecules
If that doesn’t work, then some of the excess carbon dioxide diffuses across cell membranes, especially into red blood cells, where it reacts with water molecules and forms carbonic acid, which eventually gets converted into hydrogen ions and bicarbonate ions. The key here is that this bicarbonate can quickly escape to the circulation, trying to counteract the increased partial pressure of carbon dioxide and keeping the pH from getting too low.
At the same time though, free hydrogen ions are generated, which could very well make the intracellular environment acidic. Fortunately they can be bound and neutralized by various basic molecules within the cells, mainly exposed NH2 or amine groups in proteins like hemoglobin.
The concentration of these proteins though is too low compared to the amount of excess carbon dioxide molecules floating through the blood. What this means is that if all of the carbon dioxide molecules tried to hide inside the cells, they’d give rise to a whole lot of hydrogen ions that have no spare protein to bind to. Therefore this would mess with the intracellular pH.
So essentially, only a small amount of carbon dioxide molecules find their way to the cells. As a result, the amount of bicarbonate that’s generated is too little, about 1 mEq/L (one milliequivalent per liter) for each 10 mmHg increasing partial pressure of carbon dioxide in order to have a substantial effect on pH.
For example, if partial pressure of carbon dioxide has an acute rise of 20 mmHg, let’s say it moved from 40 to 60, then this mechanism could only result in a rise of plasma bicarbonate by 2 mEq/L, from its reference value of 24 up to 26, which doesn’t have a big impact on pH. Therefore the pH remains very low during this acute phase of the disorder.

5:42 - 6:34: Minute Ventilation and the Kidneys
Fortunately, if minute ventilation hasn’t decreased to life-threatening levels, then within about three or five days, the kidneys start sensing that pH is too low and step up to help correct the imbalance. More specifically, the cells of the proximal convoluted tubules start generating and re-absorbing more bicarbonate into the bloodstream. In fact, the kidneys are pretty effective in doing this since they managed to increase the concentration of bicarbonate about 4 mEq/L for each 10 mmHg increase in partial pressure of carbon dioxide. So if the partial pressure of carbon dioxide went up from 20 to 40 mmHg, which is a 20 mmHg increase, plasma bicarbonate would increase by 8 mEq/L, going from its reference value of 24 to 32 mEq/L. This can lead to a substantial increase in the pH, bringing it closer to its normal range again.

6:36 - 6:59: Recap
Alright, as a quick recap, respiratory acidosis happens when the lungs fail to eliminate excess carbon dioxide which builds up in the blood, causing blood pH to fall below 7.35. It’s divided into an acute and a chronic phase according to the absence or presence of renal compensation, respectively, which raises bicarbonate concentration in the blood.

[ralphvincentdomingo]

This topic could've been a 2hrs discussion if our prof were to discuss it, lol.