STEP 2:
Respiratory Acidosis: Where the pH<7.40 AND [pCO2]>40, that is the partial pressure of carbon dioxide is greater than the normal 40. Again, 40 is normal. Don’t memorize a range.
Metabolic Acidosis: pH<7.40 AND [pCO2]<40**
Respiratory Alkalosis: pH>7.40 AND [pCO2]<40
Metabolic Alkalosis: pH>7.40 AND [pCO2]>40
Note that in a respiratory process, the pH and pCO2 go in the opposite direction and in a metabolic process the pH and pCO2 go in the same direction. This is because CO2 (carbon dioxide) acts as an acid in the body.
**When a metabolic acidosis is present, we must look for an anion gap (AG). AG=[Na]-[Cl]-[HCO3]. If the patient’s albumin is low, the anion gap changes. The correction for albumin is cAG= AG + 2.5(4-Albumin) for albumin measured in g/dL.