i have a problem with mixed acid base disorders

Jonathank · Feb 7, 2011

I'm sure if you realize it or not- or if this even helps you- but: if the unit is mm Hg, you're measuring pressure rather than concentration. Concentration is expressed in units like osmolarity or osmolality.

Nurse Kyles, BSN, RN · Feb 7, 2011

this is how my instructor taught us about acid/base imbalances:

acidosis----------------------------------------------------------------alkalosis

ph

paco2:

hco3:

paco2= respiratory

hco3= metabolic

you will notice that the paco2 is from largest to smallest. this is to simplify this to make it easier.

step 1: using this chart plot where your ph goes. does it indicated acidosis, alkalosis or normal?

if the values are normal, there are a couple of possibilities. everything could be normal, in which case the other abg values are going to be in normal range. aother possibility is that compensation has taken place. with compensation the paco2 and hco3 will be out of range in opposite directions.

step 2: next you plot your hco3 & paco2 on the chart. the value that matches (is on the same side as the ph) is the primary component that is causing the acid or alkalosis.

step 3: determine if compensation is occurring: look at the "opposite component"

*if it is within the normal range, there is no compensation occurring.

*if it is outside the normal range (but on the opposite side of the primary component), compensation is occurring.

*if there is compensation but the ph is still outside the normal range, there is partial compensation. if both "components" are out of range but the ph has returned to the normal range, the imbalance has been fully compensated. (the body will not over-compensate).

to practice:

abg values:

ph: 7.55

paco2: 40

hco3: 30

acidosis x alkalosis

ph:

paco2:

hco3: x

i plotted the values using blue xs

step 1: plot the ph on the chart. it is on the right side which indicates alkalosis

step 2: plot hco3 & paco2. the x that matches the ph indicates the problem. the arrow is on the right side which indicates metabolic alkalosis.

step 3: determine compensation. since the paco2 is in range, while the other values are out of range, this shows no compensation.

step 3: indicates no compensation, since paco2 is in normal range.

answer: metabolic alkalosis, with no compensation.

another practice:

abg values:

ph:7.3

paco2:55

hco3: 25

acidosis x alkalosis

ph:

paco2: x

hco3:

step 1: acidosis

step 2: paco2 is on the same side matching the ph. this indicates respiratory acidosis

step 3: hco3 is in range, so compensation is not occuring.

practice:

abg values:

ph: 7.3

paco2: 55

hco3: 30

acidosis x alkalosis

ph:

paco2:x

hco3: x

step 1: ph indicates acidosis

step 2: co2 is elevated and "matches" ph so it is respiratory acidosis;hco3 is elevated indicating compensation

step 3: partial compensation is occurring since ph is low but almost normal range; hco3 is elevated as kidneys release bicarb to counteract the extra co2 retained by the lungs.

i hope this helps you! good luck! :coollook:

Jonathank · Feb 8, 2011

Kylee has given you a pretty definitive tutorial there. I would just point out that there are different ways to assess compensation or lack thereof. Don't get thrown if you're book/class defines it differently.