Normal ABG Results (US System of Measurements)
pH 7.35–7.45
PaO2 80–100 mm Hg
PaCO2 35–45 mm Hg
O2Saturation 95–100%
HCO 321–28 mEq/L
Base Excess -2 to +2 mEq/L
Normal ABG Results (SI Units)
pH 7.35–7.45
PaO2 10.6–12.6 kPa
PaCO 24.66–5.98 kPa
O2 Saturation 95–100%
HCO 321–28 mmol/L
Base Excess -2 to +2 mmol/L
Critical Levels: pH: <7.25 or >7.55; PaCO2: <20 or >60; PaO2: <45;
HCO3: <15 or >40; Base Excess: +- 3mEq/L
. 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- orhypercapnia), 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.
pH
■ 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, ametabolic acidosis and a respiratory alkalosis. One process dominates and the other partially
compensates.
■ In metabolic processes, the bicarbonate concentration in the blood changes. Bicarbonate is a
base controlled by the kidneys. Decreases in bicarbonate result in metabolic acidosis and
increases result in metabolic alkalosis.
■ In respiratory processes, blood pH is affected by carbon dioxide (CO2) levels. Though CO2 is
technically a gas, it is regarded as a respiratory acid—the only acid that can be exhaled. It is the
waste product of cellular metabolism and is carried by the blood to the lungs for excretion. If the
lungs are unable to excrete it, CO2 levels rise. Increased CO2 levels in the blood result in
respiratory acidosis. Decreased levels of carbon dioxide result in respiratory alkalosis.
PaO2
■ An indirect measure of oxygen content. Measures the tension (or partial pressure) of oxygen in
the blood.
PaCO2
■ 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.
HCO3-
■ 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.
