We just went over this today in lecture, and my instructor made it SOOOOO simple.
Draw a grid like a tic-tac-toe board. Label the columns across the top Acid, Normal, and Alkalotic. Down the left side label the rows pH, PaCO2, and HCO3. Fill in the grid....first row is <7.35, 7.35-7.45, and >7.45. Those are values for pH. Then fill in the second row with >45, 35-45, and <35. Those values are for PaCO2. The last row is <22, 22-26, and >26. Those represent HCO3. Okay, now look at your ABG lab report. Say the pH was 7.49, the PaCO2 was 48, and the bicarb was 37. Tie in those values in your grid. You should have 7.49 under alkalotic, 48 under acid, and 37 under alkalotic. Look at the pH first to see if it's acidic, normal, or alkalotic. The next value in the same column will tell you if it's respiratory or metabolic (PaCO2 reflects respiratory, and HCO3 reflects metabolic). It's as simple as which column has two values in it
Acid Normal Alk
pH <7.35 7.35-7.45 >7.45
PaCO2 >45 35.45 <35
HCO3 <22 22-26 >26
Then you can get into whether or not it's compensated