Blood Gases Level 1 Tutorial: Blood Gases
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Tutorial: Blood Gases
Learn an organized approach to arterial blood gas analysis, incorporating serum and urine electrolyte values into your more advanced levels of analysis.
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Tutorial: Blood Gases Compensatory Processes
Lessons
42
Times Practiced
1284
Cases Completed
1h 24m
Total Time spent
1m 24s
Average Time
Progress
Accuracy
Efficiency
Accuracy
Efficiency
1 Acidosis or Alkalosis Acidosis or Alkalosis
2 Shifting chemistry Shifting chemistry
3 Metabolic or Respiratory Metabolic or Respiratory
Current lesson 4 Compensatory Processes Compensatory Processes
5 Degree of Compensation Degree of Compensation
6 Abnormal Compensation Abnormal Compensation
7 Anion Gap Mechanism Anion Gap Mechanism
8 The Delta Delta and Acid Base Ddx The Delta Delta and Acid Base Ddx
9 Summary of Approach to ABGs Summary of Approach to ABGs
Compensatory Processes


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 pCO2. 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 pCO2) then you would expect a compensatory higher bicarb
  • if you identify a primary respiratory alkalosis (low pCO2) then you would expect a compensatory lower bicarb
  • if you identify a primary metabolic acidosis (low bicarb) then you would expect a compensatory lower pCO2
  • if you identify a primary metabolic alkalosis (high bicarb) then you would expect a compensatory higher pCO2
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.