Arterial Blood Gases (ABGs) Critical Lab Values

Arterial Blood Gases (ABGs) Lab and Diagnostic Procedure

  • Collect in an air-free heparinized syringe. Send in ice slurry to lab immediately.

ABGs provide information about acid-base balance and the levels of O2 and CO2 in the blood.

ABG results may indicate decreased O2 levels (hypoxia), decreased or increased CO2 levels (hypo- or hypercapnia), acidosis (decreased pH), alkalosis (increased pH), and the degree of compensation.

ABGs are drawn to establish the diagnosis and severity of respiratory failure and manage patients with respiratory dysfunction, cardiac failure, renal or hepatic failure, trauma, multisystem failure, diabetic ketoacidosis, sepsis, and other serious conditions.



An indicator of hydrogen ion concentration. Controlled primarily by the ratio of bicarbonate ions (HCO3 -) to carbonic acid (H2CO3). The body can tolerate only small changes in blood pH. Levels outside this range lead to coma and death because vital proteins lose structural integrity and function.

Acidosis and alkalosis refer to processes that alter the pH of blood.

Metabolic acidosis, metabolic alkalosis, respiratory acidosis, and respiratory alkalosis are the four ways in which pH is altered. A patient often has two processes occurring simultaneously; for example, a LABS A-F 8 metabolic acidosis and a respiratory alkalosis. One process dominates and the other partially compensates.


  • An indirect measure of oxygen content. Measures the tension (or partial pressure) of oxygen in the blood.


  • Measures the partial pressure of carbon dioxide in the blood. CO2 content is controlled by the lungs, and PCO2 is therefore a measure of how adequately the lungs are ventilating.

O2 Saturation

  • Indicates the oxygen content of the blood expressed as a percentage.


  • Indicates the bicarbonate ion concentration in the blood, which is regulated by the kidneys. It is directly related to blood pH.

Base Excess/Deficit

  • A calculated result that indicates the number of buffering anions in the blood and reflects the metabolic component of the patient’s acid-base balance.

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