ABGs Nursing Normal Lab Values

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Overview of ABGs Nursing Lab Values

  1. Arterial Blood Gas
    1. Obtained directly from artery
      1. Venous samples contain Deoxygenated blood – we want to measure accurate oxygen levels in an ABG
    2. Measures Acid-Base Balance of blood
    3. Assess full oxygenation capacity
    4. Arterial results show what’s happening in the body SYSTEMICALLY

Nursing Points

  1. Lab values include
    1. pH
    2. pCO2
    3. HCO3
    4. PaO2
    5. SaO2
    6. Lactic Acid
    7. Base Excess (or Deficit)
    8. Electrolytes (in some facilities or units) 
      1. K – Potassium
      2. Mg – Magnesium
      3. Na – Sodium
      4. Ca – Calcium

ABG Lab Value Assessment

  1. pH
    1. 7.35-7.45
    2. Measurement of the level of acidity or alkalinity
  2. pCO2
    1. 35 – 45 mmHg
    2. The amount of carbon dioxide in the blood
  3. HCO3
    1. 22 – 26 mEq/L
    2. Level of bicarbonate
  4. PaO2
    1. 80 – 100 mmHg
    2. On ROOM AIR (21% FiO2)
    3. Amount of oxygen in the blood
  5. SaO2
    1. 95-100%
    2. Saturation of hemoglobin with oxygen in arterial blood
      1. In other words, how well the hemoglobin molecules bind to oxygen
  6. Lactic Acid
    1. 0.5 – 1 mmol/L
    2. Produced during anaerobic metabolism
      1. Meaning, if tissue isn’t getting oxygen, lactate is produced as a byproduct instead of CO2
      2. Critical value for sepsis patients
  7. Base Excess (or Deficit)
    1. -2 to 2
    2. Indicates level of “extra” base (alkaline)
    3. Negative (base deficit) indicates acidosis
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Hey guys, my name is Brad and welcome to nursing.com. And in today’s video, what we’re going to be doing is we’re going to discuss arterial blood gases, also known as ABGs. I’d like to dive in a little bit into what the different types of lab values for ABGs are, as well as, what the normal reference ranges are, and what can happen whenever alterations in ABGs occur. Without further ado, let’s dive in. 

And whenever we’re taking a look at ABG lab values, it’s important to understand that arterial blood gases reflect acid-base balance, as well as O2 load, which we’re going to come to see here momentarily. Now, these here are a lot of the, these are the lab values associated with an arterial blood gas sample. And what we’re going to do is we’re going to go over them one by one. 

The very first thing here is going to be our blood pH. Now, before I actually reveal what this is, let’s recall, maybe from high school chemistry, right, whenever we’re talking about pH scale. This pH scale goes from zero, which is the most acidic that you could get to seven, which is completely neutral, all the way up to 14, which is the most basic that you can get, right? The closer that you get to zero, the more acidic you are, the closer you get to 14, the more basic you are, right? This is the entire pH scale. Now, whenever we’re talking about a blood pH, the actual pH of our blood itself, a normal reference range of 7.35 to 7.45. Our entire reference range is zero to 14, but our blood pH is this incredibly narrow range of like right here of 7.35 to right here, 7.45. This is important to know, right? Because our blood pH is an incredibly narrow reference range. It’s so small. So any alteration in our CO2 or our bicarbonate as we’re going to come to see can, completely throw off that incredibly narrow blood pH range. And the reason why it’s so important to keep that blood pH in such a narrow reference ranges, is because should our blood pH get too acidic or too acidotic or too alkalinic, or too basic. And this is whenever cellular degradation and destruction can occur. We can actually have destruction of the cells of our body. So, that’s our normal reference range of 7.35 to 7.45. Again, remember, should we get less than 7.35 we’re getting more acidic. Should we go higher than 7.45, we’re getting more basic. Okay. We got that. 

Now,CO2 is our next thing. A normal reference range for CO2 in an ABG is 35 to 45. It’s important to remember, CO2 is controlled by our respiratory system, so by our lungs, and it’s important to think of CO2 as an acid. It’s crucially important. CO2 is an acid. So think about it. The more CO2 that you have, the higher your CO2, the more acidic you’re going to be, right. The more acidic that blood pH is going to be. And at that blood pH is getting more acidic. We’ll remember that means that our blood pH is getting less than 7.35. 

All right, bicarbonate is our next thing. A normal reference range for bicarbonate is 22 to 26. Let’s remember bicarbonate is controlled by our renal system, by our kidneys. The entire point of bicarbonate is it acts as a buffer to neutralize free hydrogen ions, right? Free hydrogen ions are an acid. Bicarbonate, acts as a buffer, binding with these free hydrogen ions, reducing acidity. Okay. So the higher your bicarbonate, the more basic that you’re going to be, right, and the more basic you are, that means you’re going higher than 7.45. Just trying to tie these concepts together. 

PaO2 is classified as 75 to 100 millimeters of mercury. This is the normal reference range for a PaO2.  And this is pretty much an arterial view of how well our patient is oxygenating. We remember that we get our SPO2, our peripheral oxygenation measurement, through that little finger probe in the hospitals. That’s a measurement of how well oxygen is perfusing our peripheral tissues. But this PaO2 is the true clinical indicator, cellularly, as far as how well we’re oxygenating. SaO2, this is again, is basically that finger probe with a normal reference range of 95 to 100%.  

And your base excess. We’re going to recall that a normal base excess is negative four to plus two (-4 to +2). And think about base excess as the amount of excess base that we have in our body. 

Now let’s talk about some alterations in this normal blood pH of 7.35 to 7.45, right? I think I’ll write it up here again, just so we remember, 7.35 to 7.45. What are some types of things that can occur that can cause alterations in these arterial blood gases? So the first thing is acidosis. Let’s recall that acidosis is defined as a blood pH less than 7.35, right? The closer that we get to zero on that pH scale, the more acidic we get. Now, there are two different things that can control this, right? We’ve talked about our CO2 and we’ve talked about our bicarb. Okay, well, what are the two different ways in which acidosis can occur? Remember CO2 is an acid. So if we have a CO2 greater than 45, that is going to cause us to become acidic. Higher CO, more acidotic we get.  In cases such as COPD whenever patients chronically retain CO2. Bicarbonate, how could we become acidotic through bicarbonate, through the release of bicarbonate from those kidneys. This occurs whenever we have a bicarbonate level, less than 22. Remember bicarb is basic. It’s alkalinic. It’s going to bind with those free acidic hydrogen ions to increase blood pH and reduce acidity. If our bicarbonate is low, if those buffers are low, if that base is low, then we’re going to become acidotic.

Alkalosis, right? This is whenever we have a blood pH greater than 7.45. Again, remember the closer that you get to 14 on that pH scale, the more alkalinic you get, right? And how can this occur through CO2 or through bicarb, okay? Think about CO2. This occurs whenever your CO2 is less than 35 in instances where a patient is in a panic attack, for instance, and you’re panting, breathing very quickly. You’re blowing off all of your CO2 causing your CO2 to be less than 35, causing your blood pH to become more alkalinic. And with bicarbonate, remember it’s a base itself. Remember it is a buffer itself. So if we’re becoming alkalinic, then this is because our bicarbonate is greater than 26. Too much base, too much binding of those free hydrogen ions. We’re depleting too much acid pushing our blood pH towards a more alkalinic environment.

And very quickly partial/full compensation. We’ll dive into this more with some reference material here below on how to maybe solve these on exam questions, but just understand that partial and full compensation is essentially the body’s attempt either from a respiratory standpoint or from a renal standpoint, to try and compensate for either an acidotic blood pH or for an alkalinic  blood pH.

And so to summarize some of our key points surrounding arterial blood gases, also known as ABGs. Remember the ABGs are reflective of that acid base balance, right? They’re reflective of that very narrow blood pH range of 7.35 to 7.45, and the different ways in which both CO2 from the lungs, as well as bicarbonate from the kidneys can help affect that blood pH. We’re also going to remember all of those lab values that are associated with ABGs and what each individual one means, as well as, the proper reference ranges. Also remember that assessment/pathophysiology that is, you know, directly influences whether a patient becomes acidotic or goes into alkalosis. And also remember that physiology, how the lungs help control CO2 and how the kidneys help control the release of bicarbonate. 

I hope this is, that this little down and dirty on ABGs helped you guys. I hope that this information helps you moving forward, not only for exam purposes, but as well as your clinical practice. Guys go out there and be your best selves today. And as always, happy nursing.


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