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Module title = Tutorial: Blood Gases
Lesson title = Compensatory Processes
This is lesson 4 of 9 in this module
Your body likes to have a normal pH (can you blame it?). Therefore, when one abnormal mechanism starts to push the pH into the abnormal range of either acidosis or alkalosis, a
second process
will become engaged and try to push the pH back toward a normal value. This mechanism is called
secondary compensation
. This is normal.
Rule #1:
the compensation is ALWAYS in the opposite "pH direction."
if you have a primary
acidosis
problem, the compensatory mechanism will be make the pH more
alkalotic
if you have a primary
alkalosis
problem, the compensatory mechanism will make the pH more
acidotic
Rule #2:
the compensation is ALWAYS the opposite mechanism as the primary disturbance.
if the primary disturbance is
respiratory
, the secondary compensatory mechanism must be
metabolic
if the primary disturbance is
metabolic
, the secondary compensatory mechanism must be
respiratory
Rule #3:
The compensation process
never over-corrects
the pH.
if the primary disturbance is acidosis, the pH will
always
be < 7.40 after compensation
If the primary disturbance is alkalosis, the pH will
always
be > 7.40 after compensation
Rule #4:
If Rule #1 is violated, then the patient has a
mixed primary disturbance.
if there is a metabolic
acidosis
and a respiratory
acidosis
, then both processes are
primary
if there is a metabolic
alkalosis
and a respiratory
alkalosis
, then both processes are
primary
this is called a
mixed acid base disturbance
Respiratory compensation starts within 30 minutes and is maximal within a few hours. Metabolic compensation takes about 3-5 days for maximal compensation. Kidneys are a little slower than lungs to make changes.
So how do you go about determining if a compensatory process is occurring? You need to go through these steps in this order:
Step 1:
look at the pH. What is the acid/base disturbance?
Step 2:
look at the bicarb and the pCO
2
. Which element is driving the pH?
Step 3:
is there an "opposite process" to the primary process occurring?
This is how you answer the question for step 3 (there are 4 scenarios):
if you identify a primary
respiratory
acidosis
(high pCO
2
) then you would expect a compensatory higher bicarb
if you identify a primary
respiratory
alkalosis
(low pCO
2
) then you would expect a compensatory lower bicarb
if you identify a primary
metabolic
acidosis
(low bicarb) then you would expect a compensatory lower pCO
2
if you identify a primary
metabolic
alkalosis
(high bicarb) then you would expect a compensatory higher pCO
2
Notice the very predictable pattern? I probably did not have to outline all 4 scenarios for you; you could have predicted them yourself because you are brilliant.
Lesson 4 of 9
That was the last lesson!