An arterial blood gas (ABG) test measures oxygen and carbon dioxide levels in blood as well as acid-base balance. It is useful for diagnosing and managing patients with respiratory issues or those in intensive care. The test provides information on oxygen saturation, partial pressures of oxygen and carbon dioxide, bicarbonate levels, and total carbon dioxide. Blood is collected from an artery, usually in the wrist, and must be analyzed within 30 minutes to provide accurate results used to guide treatment plans. Abnormal levels can indicate issues like hypoxemia, hypercapnia, or metabolic acidosis and alkalosis.

1. Dr. Nishith A. Vachhani A.B.G. Page 1 of 2
ARTERIAL BLOOD GAS
Introduction
 Disorders of acid–base balance can lead to severe complications in many disease states, and
occasionally the abnormality may be so severe as to become a life-threatening risk factor.
 The process of analysis and monitoring of arterial blood gas (ABG) is an essential part of
diagnosing and managing the oxygenation status and acid–base balance of the high-risk patients,
as well as in the care of critically ill patients in the Intensive Care Unit.
 An arterial-blood gas (ABG) test measures…
‑ Oxygenation of blood through gas exchange in the lungs.
‑ Carbon dioxide elimination through respiration.
‑ Acid-Base balance or imbalance in extra-cellular fluid (ECF).
 Many blood-gas analyzers will also report concentrations of
lactate, hemoglobin, several electrolytes, oxyhemoglobin, carboxy
hemoglobin and methemoglobin.
Indications of ABG
‑ Establishing diagnosis.
‑ Guides treatment plan.
‑ Ventilator management.
‑ Improvement in acid/base management; allows for optimal function of medications.
‑ Acid/base status may alter electrolyte levels critical to a patient’s status.
Site of Arterial Blood Collection
‑ Radial artery (In forearm – antecubital fossa)
‑ Femoral / Brachial artery (in the groin area)
‑ Arterial catheter
Collection of Specimen
‑ Pre-heparinized (0.05 ml for 1 ml of blood) syringe and needles (20, 23 and 25 gauge, of different
lengths)
‑ A safety syringe with a needle cover that allows the syringe to be capped before transport.
‑ A bandage to cover the puncture site after collection;
‑ A container with crushed ice for transportation of the sample to the laboratory.
‑ Locate the radial artery by performing an Allen test.
‑ Disinfect the sampling site on the patient with 70% alcohol and allow it to dry.
‑ Holding the syringe and needle like a dart, use the index finger to locate the pulse again.
‑ Advance the needle into the radial artery until a blood flashback appears, then allow the syringe
to fill to the appropriate level. DO NOT pull back the syringe plunger.
‑ Withdraw the needle and syringe; place a clean, dry piece of gauze or cotton wool over the site.
‑ Expel air bubbles, cap the syringe and roll the specimen between the hands to gently mix it. Cap
the syringe to prevent contact between the arterial blood sample and the air, and to prevent
leaking during transport to the laboratory.
‑ Label the sample syringe.
‑ Analyze within 30 min.

2. Dr. Nishith A. Vachhani A.B.G. Page 2 of 2
Parameters:
1) Arterial Blood pH & H+
:
‑ Indicates Acid/Base status of body.
‑ Normal pH: 7.35 – 7.45 ‑ Normal H+: 35 – 45 nmol/L
‑ Acidemia: If pH is <7.35 & H+ >45 nM
‑ Alkalemia: If pH is >7.45 & H+ ,35 nM
2) Oxygen saturation (SaO2):
‑ Oxygen saturation (SaO2) is a measurement of the percentage of how much hemoglobin is
saturated with oxygen.
‑ Normal: 94% to 100%
‑ Oxygen is transported in the blood in two ways: oxygen dissolved in blood plasma (pO2) and
oxygen bound to hemoglobin (SaO2).
‑ About 97% of oxygen is bound to hemoglobin while 3% is dissolved in plasma.
3) Partial pressure of oxygen (PaO2):
‑ PaO2 is the partial pressure of oxygen in the alveoli.
‑ It is a driving force for diffusion of oxygen across the alveolar membranes, through pulmonary
capillary walls, and into the arteriolar blood flow and erythrocytes for transport throughout
the body into peripheral tissues.
‑ Normal: 10-13 kPa. 75 to 100 mm Hg.
‑ Hypoxemic: A low PaO2 indicates that the patient is not oxygenating properly.
‑ At a PaO2 of less than 60 mm Hg, supplemental oxygen is required.
4) Partial pressure of carbon dioxide (PaCO2):
‑ PaCO2 is the carbon dioxide partial pressure in alveoli.
‑ Indicates respiratory components.
‑ Normal: 4.7-6.0 kPa. 38 to 42 mm Hg.
‑ The carbon dioxide partial pressure (PaCO2) is an indicator of CO2 production and elimination.
‑ A high PaCO2 (hypercapnia) indicates under ventilation.
‑ A low PaCO2 (hypocapnia) indicates hyper or overventilation.
5) Bicarbonate (HCO3):
‑ Blood brings bicarbonate to your lungs, and then it is exhaled as carbon dioxide.
‑ Bicarbonate is excreted and reabsorbed by your kidneys.
‑ It regulates body's pH balance.
‑ Normal: 22 to 28 mEq/L.
‑ A low HCO3 indicates metabolic acidosis. It is found in diarrhea, kidney disease, and liver
failure etc.
‑ A high HCO3 indicates metabolic alkalosis. It causes a pH increase in tissue. It can happen
from a loss of acid, such as through vomiting and dehydration)
6) Total CO2:
‑ This is the total amount of CO2, and is the sum of HCO3 and PCO2.
‑ Normal: 23 - 30 mmol/L, 100 - 132 mg/dL
7) O2 Content:
‑ This is the sum of oxygen dissolved in plasma and chemically bound to hemoglobin.
‑ Normal: 16 – 22 ml O2/dl blood.