# Arterial Blood Gas --- An **arterial blood gas** or **ABG** lab is a reading of the respiratory gases in the blood, and is used to test [[acid-base balance|blood pH]] and acidosis or alkalosis. >[!science] Normal Values >The normal value of ABGs are: > >- For  pH, the normal range is **7.35 to 7.45** >- For PaCO2, the normal range is **35 to 45 mmHg (respiratory determinant)** >- For PaO2, the normal range is **75 to 100 mmHg** >- For HCO3, the normal range is **22 to 26 mEq/L (metabolic determinant)** ![[acidosis and alkalosis.png]] - [[Acidosis]]: This means the [[acid-base balance|blood pH]] is below 7.35, which can either come from: - retaining too much CO2: [[acidosis#Respiratory Acidosis|respiratory acidosis]] - not making enough (or loosing too much) bicarbonate: [[acidosis#Metabolic Acidosis|metabolic acidosis]] ## Compensation When the body senses our ABGs are out of balance, it **compensates**, or at least tries to. It does this between two major pathways, the kidneys making or excreting bicarb (a base), and the lungs expelling or retaining CO2 (an acid) - pH normal? - CO2/HCO3 normal => Normal - CO2/HCO3 abnormal => fully compensated - One is causing the problem, the other is fixing it - pH off? - CO2/HCO3 are off - if one is also off => partially compensated - is the other one normal => not compensated ___