Arterial Blood Sampling

Arterial blood gas sampling (ABG) is a medical technique used to check blood gas levels in the body by means of arterial blood. A small volume of blood is drawn using a thin needle and syringe to puncture the artery. Radial artery at the wrist is the easiest artery to feel and the most accessible and is used commonly.

The blood can also be drawn from an arterial catheter. Alternative sites of access include – the brachial artery at the antecubital fossa or the femoral artery in the groin. These arteries are not as superficial as the radial and may be harder to locate. There are more structures which may be damaged if healthcare worker is not familiar with anatomy, hence they should only be used under supervision.

A phlebotomist, nurse, or respiratory therapist is usually qualified to collect arterial blood for blood gas analysis. A wide skill set is required to collect arterial blood than venous blood sampling. Gentle handling of patients is generally required as most of the patients needing arterial blood sampling are often very ill.

Technician taking the blood sample should note down the oxygen concentration the patient is breathing since inspired oxygen concentration is critical for blood gas calculations. The sample is usually stored on ice to prevent metabolic activity and the analyst or biochemist is notified in advance about the sample.

Arterial blood gas determination is used to determine partial pressure of oxygen and carbon dioxide and it also reports pH of the blood, and the bicarbonate levels in blood. In addition, many gas analyzers are able to calculate concentrations of lactate, hemoglobin, several electrolytes, oxyhemoglobin, carboxyhemoglobin and methemoglobin in blood.

ABG testing is mainly used in pulmonology, to determine gas exchange levels in the blood related to lung function and has wide application in other areas of medicine. Possibility of disorders can be many and combinations are complex and difficult to interpretate, so calculators , nomograms, and rules of thumb are commonly used.

Appropriate positioning of patient can prevent a potential complication of tendon or nerve damage, while adequate pressure can prevent a hematoma and the use of aseptic technique eliminates potential chances of infection.

Sampling of arterial blood will be useful for patient management only if the sampling procedure is carried out according to an established, proven protocol. The validity of test results can be voided if any of the following occur: the sample is contaminated by air, improper anticoagulant or inappropriate anticoagulant concentration, flush solution (if sample is drawn from an indwelling catheter), or venous blood, the sample clots because of improper anticoagulation of the collection device, improper mixing, or exposure to air, and if the analysis is delayed.

Written by Phlebotomy Training specialist Dr Shahbaz A. Cheema, Course Director for Maxis Healthcare who run NHS Accredited Phlebotomy Training courses for medical and non medical practitioners. Learn the 3 Steps To Become a Phlebotomist