Arterial Blood Gas Interpretation

Posted by e-Medical PPT Monday, September 27, 2010
An arterial blood gas (ABG) is a blood test that is performed using blood from an artery.The most common puncture site is the radial artery at the wrist, but sometimes the femoral artery in the groin or other sites are used. The test is used to determine the pH of the blood, the partial pressure of carbon dioxide and oxygen, and the bicarbonate level. Many blood gas analyzers will also report concentrations of lactate, hemoglobin, several electrolytes, oxyhemoglobin, carboxyhemoglobin and methemoglobin. Arterial blood for blood gas analysis is usually extracted by a phlebotomist, nurse, or respiratory therapist.
The syringe is pre-packaged and contains a small amount of heparin, to prevent coagulation or needs to be heparinised, by drawing up a small amount of heparin and squirting it out again. Once the sample is obtained, care is taken to eliminate visible gas bubbles, as these bubbles can dissolve into the sample and cause inaccurate results. The sealed syringe is taken to a blood gas analyzer. If the sample cannot be immediately analyzed, it is chilled in an ice bath in a glass syringe to slow metabolic processes which can cause inaccuracy. Samples drawn in plastic syringes are not iced and are analyzed within 30 minutes.

The pH indicates if a patient is acidotic or alkalemic.
A low O2 indicates that the patient is not respiring properly, and is hypoxemic. At a PaO2 of less than 60 mm Hg, supplemental oxygen should be administered.
The carbon dioxide partial pressure (PaCO2) indicates a respiratory problem.A high PaCO2 (respiratory acidosis) indicates underventilation, a low PaCO2 (respiratory alkalosis) hyper- or overventilation.
The HCO3− ion indicates whether a metabolic problem is present (such as ketoacidosis). A low HCO3− indicates metabolic acidosis, a high HCO3− indicates metabolic alkalosis.

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