Fluids and electrolytes

bikeridingnursee · Oct 24, 2008

this is how i was taught. i will take most of this directly from my instructors worksheet.

you gotta know the normal arterial blood gas (abg) levels!

i will list the normal values here for reference for the example:

pH 7.4 (7.35-7.45)(7.37-7.42)

PO2 80-100 mmHg

02Sat 95% or greater

PCO2 35-45 mmHg (some say 37-42)

HCO3 22-26 meq/L

the PCO2 is considered the respiratory parameter which is controlled by the lungs (and is acidotic). so if the PCO2 is above 40 (the normal mean) this is resp. acidosis, below 40 is resp. alkalosis. we'll get to which system is causing the problem later.

metabolic parameter is standard bicarbonate (which is basic) is controlled by the kidneys. if HCO3 is below 24 (the normal mean) that means that this is metabolic acidosis because there is less base, if it is above 24 there is more base and therefore is metabolic alkalosis.

if one system is unbalanced, the opposite system will try to compensate in order to bring the pH back to normal.

how do we decide which system is causing the imbalance in pH and which system is compensating for the other system? follow these steps:

1. first part look at the pH level. if it is above 3.40 this is considered alkalosis (can be either resp. or met. but we'll get to that. if it is below 3.40 it is considered acidosis (again could be resp. or met.)

2. now look at the PCO2. - is it acid or alkaline?

3. now look at the HCO3- is it acid or alkaline?

4. put the answers together for conclusion.

heres an example.

pH 7.45 -------------------------------------------high (less acid), alkaline

PaCo2 (resp. acidic factor) 40--------------------------normal

HCO3 (metabolic, basic factor) 30----------------------high (more base) metabolic alkaline

= uncompensated metabolic alkalosis

ex. 2

pH 7.11----------------------low, (less base) acidosis

PaCO2 25--------------------low, (less acid) alkalosis

HCO3 4----------------------low, (less base) acidosis

= metabolic acidosis with partially compensated resp. alkalosis

bikeridingnursee · Oct 24, 2008

please add to this if i confused things as i am a new nurse...

but one more thing, to know if it is compensated or not, i was taught like this...

using example 2. from above,

the pH is acidic and after looking through the ABG's you determine that the PACO2 which is respiratory is alkalotic and the HCO3 is low resulting in less base causing metabolic acidosis.

you know that the reason the pH is out of whack is because of the metabolic acidosis because the pH is also acidotic. you can see that the respiratory system is trying to conpensate for the metabolic system by decreasing the amount of PaCO2 which is acidic to create a more alkaline environment, hence the resp. alkalosis.

f the pH was acidic but you had a high PACO2 (resp. acidosis) and a high HCO3 (metabolic alkalosis) it can probably be determined that the main cause is the PACO2 and the HCO3 is trying to compensate and balance the acidity level.

hope im not just confusing you more.

DreamingTree · Oct 25, 2008

same explanation, but i'll phrase it a bit differently. make a chart:

acidosis alkalosis

7.35 ph 7.45

45 co2 35

22 hco3 26

sorry -- the chart won't work on here. i hope you get the idea of how it should look. put all acidotic values on one side, alkalotic on the other. for some reason, the post edits out my spacing.

follow these steps:

1. look at ph (using the chart). this is how you determine acidosis versus alkalosis.

2. look at co2 & hco3 (again, chart). which value is out of whack?

----> if your co2 is > 45 and the ph is acidotic, then you have respiratory acidosis.

----> if co2 is

----> if hco3 is

----> if hco3 is > 26 and the ph is alkalotic, then you have metabolic alkalosis.

3. now consider if compensation is taking place. this is a bit trickier to explain, but....here goes:

----> compensated: ph will be away from it's norm (7.40), but within the range (7.35 - 7.45)

----> uncompensated: ph is outside of the range ( 7.45)

----> if ph is on the acidic side, but compensated (w/in range), look at co2 & hco3. choose the value that is out of whack on the acidic side. this will determine if it is resp. acidosis or metabolic acidosis. the other value will be out of whack on the alkalotic side because the body is trying to compensate. hco3 increases to compensate for resp. acidosis. co2 decreases to compensate for metabolic acidosis. make sense?

until it becomes second nature, keep making a chart (like i did above), and put checkmarks next to the values that are abnormal. the value matches the ph (hco3 or co2) will give you the final answer.

good luck!

disclaimer: all info blatantly stolen from a former nsg instructor's lecture. she made it all seem so easy....