What the Letters in ABG Mean
ABG stands for Arterial Blood Gas, where the letters represent the type of blood sample (arterial) and the gases (oxygen and carbon dioxide) measured in that blood. 1, 2
Core Components Measured in an ABG
The key parameters reported in an ABG analysis include:
Primary Measurements
pH - Measures the acidity or alkalinity of arterial blood, with a normal range of 7.35-7.45. Values below 7.35 indicate acidemia, while values above 7.45 indicate alkalemia. 1, 3
PaO₂ (Partial Pressure of Arterial Oxygen) - Indicates oxygenation status, with normal values greater than 80 mmHg. This directly measures how much oxygen is dissolved in arterial blood. 1, 2
PaCO₂ (Partial Pressure of Arterial Carbon Dioxide) - Indicates ventilation status, with a normal range of 35-45 mmHg. Values above 45 mmHg suggest respiratory acidosis, while values below 35 mmHg suggest respiratory alkalosis. 1, 3, 2
HCO₃⁻ (Bicarbonate) - Reflects metabolic component of acid-base balance, with a normal range of 22-26 mEq/L. This helps determine if metabolic processes are contributing to acid-base disturbances. 1, 2
Additional Parameters
SaO₂ (Oxygen Saturation) - The percentage of hemoglobin saturated with oxygen, with normal values greater than 94% in most patients. 1, 3
Base Deficit/Excess - A sensitive marker for severity of shock and mortality risk, particularly useful in trauma and critically ill patients. 1
Lactate - Provides information about tissue oxygenation and perfusion, with elevated levels indicating shock states. 1
Clinical Significance
The "arterial" designation is critical because arterial blood provides more accurate assessment of oxygenation, ventilation, and acid-base status compared to venous samples, particularly in critically ill patients. 1, 3
The British Thoracic Society emphasizes that ABG analysis enables clear understanding of respiratory, circulatory, and metabolic disorders through systematic evaluation of these parameters. 3, 2