# Step 2: CO₂ – ABG Interpretation (Nursing)

by Rhonda Lawes

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00:00 And here's our old friend, the couch of homeostasis.

00:03 Now you look in the middle, you have the pH of 7.35 to 7.45, since we're in step 2, we're looking at the CO2 level.

00:12 So above the couch where it says acidotic or alkalotic, we're referring to CO2 levels so make sure you write in CO2 above acidotic and CO2 above alkalotic.

00:25 So you see on the red size of the couch, we have excess CO2.

00:29 The more CO2 you have, that means that the level of CO2 is greater than 45 remember normal for CO2 is 35 to 45 so if I have a number that's higher than 45, that means I have excess CO2.

00:44 If I have a number of less than 35 for this CO2, then I'm moving towards alkalotic because I have less CO2 or acid in my system.

00:54 So in step 2, the more CO2 I have, the higher that CO2 number will be if it's greater than 45, then its an abnormal value.

01:04 If it's lower than 35, that's also an abnormal value and I would label it alkalosis.

01:11 Okay, so too much CO2 means I have too much additional acid in my blood and I would expect a CO2 that's greater than 45.

01:19 If it's less than 35, we know we have the opposite issue, that would be not enough CO2 and I would label that alkalotic.

01:28 Okay, so you look at the CO2 and label it as acidosis or alkalosis.

01:34 So as CO2 that's less than 35, I would label as alkalotic, Ig I have a CO2 that's greaterthan 45, I would label that as acidotic.

01:45 Ready? Let's try some examples but first, remember think if we can think through what happens when you have through too much CO2 or not enough CO2? What are the clinical things that could happen? Well before I go through the rest of the slide, I want you to pause the video and see if you can come up with some reasons before we talk about them.

02:08 Okay, welcome back.

02:09 Now let's see if you can walk through these with me and see if they make sense.

02:13 Anything that causes you to retain CO2 could be like holding my breath, which you know I did that as a little kid until I passed out.

02:20 I would really not recommend it, I wasn't getting my way, and I though that would be an effective way to do it.

02:25 Yeah again, wouldn't recommend it.

02:28 COPD - that's another reason why you would have retained CO2.

02:32 If someone is suffocating, or for any reason the respirations are depressed, that would cause a patient with too much CO2 .

02:42 See, this is a great time to bring up that ABGs are nothing more than a measurement.

02:48 They're worthless without your clinical judgement.

02:52 They just let you know where the patient was at that instant that you drew the blood for the arterial blood gases.

02:57 What you have to figure out is what got them to that point of imbalance and correct it.

03:03 Now looking at not enough CO2, that's anything that causes me to blow off CO2 like hyperventilating and stress.

03:11 Now your patient might be in pain or they might just be like two junior-high girls in the cafeteria.

03:15 Remember they always wear those matching outfits but when a really cute boy walks in, they start hyperventilating.

03:22 Those are the ones that pass out from hyperventilating.

03:26 Or they could be on a ventilator, someone who is very ill and we're overoxygenating them like we have their ventilator volumes too fast or too big.

03:35 So those are just some reasons that someone might end up with too much CO2 - not breathing efficiently enough or not enough CO2 because they're hyperventilating.

03:47 So let's go get some examples, are you ready? So you look at the CO2, we're in step 2.

03:53 Step 1 was look at the pH and label it.

03:56 Step 2 is look at the CO2 and label it.

03:59 We know that CO2 in the blood acts as an acid.

04:02 So if I have more acid than normal I'm gonna label that acidotic.

04:07 If I have a lower CO2 level than normal I'm going to label that alkalotic.

04:13 So, the first one is a CO2 of 30.

04:16 Well I know the normal levels for CO2 is 35 to 45 (mmHg).

04:22 30 is less than normal so I'm gonna label that? Right, alkalotic.

04:32 Let's do another one.

04:34 CO2 of 48.

04:37 Alright so normal is 35 to 45, so a number of 48 is higher than normal that means I have extra CO2 onboard - that's extra acid, that's going to make it Acidosis, good, you're getting it that's really good.

04:58 Okay, so a CO2 of 50.

05:01 Wait a minute, 48 was high, no follow the rules.

05:05 If a CO2 of 50 that's higher than normal, that means I have extra acid, so I would label that Acidosis Let's do a couple more.

05:18 CO2 of 28.

05:20 Oh ok, that's lower than the normal of 35 to 45, that means I have less acid available so I would label that alkalosis.

05:35 Last example, CO2 of 33 Okay, so I would think that through where normal is 35 to 45.

05:47 This is lower than normal, I have less acid available, so that's gotta be alkalosis.

05:53 That's it, that's how you look at the CO2 and label it as acidosis or alkalosis.

06:04 Extra CO2 - acidosis, not enough CO2 - alkalosis

The lecture Step 2: CO₂ – ABG Interpretation (Nursing) by Rhonda Lawes is from the course Interpretation of Arterial Blood Gases (ABGs) (Nursing).

### Included Quiz Questions

1. Holding the breath
2. Chronic obstructive pulmonary disease
3. Suffocation
4. Hyperventilation
5. Severe diarrhea
1. Hyperventilation
2. Overoxygenation
3. Emphysema
4. Suffocation
5. Depressed respirations

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