Most illnesses, or even traumas, rely on labs for diagnosis, and particularly this acid/base balance deal. In all honesty, this is something that simply cannot be explained in one post because it involves knowing about metabolism, respiratory drive, homeostasis, cell energy, etc. But I would like to explain one thing that you may see most often, most subtly and that is metabolic acidosis. That can be a scary word and seem hard to understand, but I want to break it down for you.
First we have to understand respiration, not ventilation but respiration. Respiration is, in easy terms, the transfer of gases in the lungs. By now, we should all know that O2 goes in and CO2 comes out. Respiration is essentially transferring O2 into the blood stream and transferring CO2 out of the blood stream, into the lungs to be exhaled.
Now lets put that aside for now and talk about ischemia. Essentially, ischemia is when cells are starved of O2. We often understand this in terms of cardiology, but any cell can suffer ischemia. Ischemia can be caused by all sorts of things. COPD, CHF, sepsis, respiratory failure, and drug OD are just a few examples. What happens is oxygen cannot reach the cells for some reason and that's when we start to run into trouble.
Through food intake, we get what's called glycogen (essentially sugar) and through glycolysis, becomes pyruvate (I don't expect you to remember that). Pyruvate reacts with other enzymes (that we don't care about right now) in a process called "synthesis" to create adenosine triphosphate. That is a big word, so just remember ATP. ATP is pretty much just food for the cells. The synthesis may also be called Krebbs Cycle which you probably learned in class. This ATP is used in normal metabolism to create energy for the cells to make them happy and not lazy.
Now this is when ischemia comes in. For the synthesis to take place, there has to be oxygen, but if there's no O2 (or lack of), the metabolism turn into anaerobic metabolism (metabolism without O2). Since there is no O2, the pyruvate turns into lactate or lactic acid. This is when we become acidotic, hence forth, the "acidosis".
When we become acidotic, hydrogen ions are released. The body does not like that imbalance and will try to buffer it with bicarbonate (HCO3). The bicarb binds to the hydrogen ions creating "hydrogen bicarbonate". This new molecule breaks down and separates from H2CO3 to H2O and CO2. Look familiar? After it breaks down and separates, you end up with CO2 and water which now travels to the lungs to be exhaled. That is why someone with metabolic acidosis has HIGH CO2 (too much produced) and LOW bicarb (diminished by binding to hydrogen).
As a paramedic, you may not be able to initially tell if the patient is acidotic or not because you don't have labs to determine pH or bicarb. But there are some tricks to figuring it out. First is to get a good history. If the patient has a medical history or current issue that might cause acidosis (ischemia), take that into consideration. Next is to use you're ETCO2 device. If the person has a history that would lead you to suspect acidosis (such as infection from UTI), and the ETCO2 is high and respiratory rate is high, chances are, it's metabolic acidosis.
Let me explain how I came to that conclusion. The body has a compensatory mechanism (keeps everything in the body normal). When you see high CO2, it means one of two things. They are hypoventilating and not blowing enough off, or they are producing too much (acidosis). If the respiratory rate is high, you know that they aren't hypoventilating and holding it in. The hyperventilation is the body's natural way of getting rid of the CO2.
Now, let's take a couple things into account and I hope this makes things easier for you in regards to respiratory rate and ETCO2. If the cause of the changes is respiratory, the two will be opposite. Example could be hyperventilation from a panic attack, or hypoventilation from a kid holding their breath. If they are breathing too fast, they will start blowing off too much CO2 and that's why they say breath into a bag, to rebreathe that CO2. So if the rate is high and the CO2 is low, they are hyperventilating and the cause is respiratory. If they don't breath fast enough, they trap the CO2. In that case, you will see a low rate and high CO2. That's why when you see a high CO2 and a high rate, you know something metabolic (inside the body) is going on. That is how you can field diagnose sepsis (with vitals, temp, etc. along with it). Also remember that the initial hindrance to the metabolism is lack of O2, so their Spo2 will most likely be low as well and these patients need oxygen.
That is simple metabolic acidosis. It is important to understand this stuff because it may change the way you diagnose and treat patients in the field, especially in a critical care setting. A general treatment for this will be oxygen, fluids, and bicarbonate replacement. But chances are, you won't be messing with the bicarb in a pre-hospital setting.
I hope this has been helpful and I hope it has helped you to better understand a little of acid/base balance. Stay tuned, and I may have more posts in the future on acid/base.
