Blood Sampling: Arterial

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.

In case the patient is on arterial catheter, blood can be collected form catheter but this is only done by skilled phlebotomists or respiratory therapist. The brachial artery at the antecubital fossa or the femoral artery in the groin can be used as alternate sites for collection. The collection is difficult since these sites are deep seated and hard to locate. Other structures could be used if the healthcare worker is expert in anatomy; hence arterial blood collection from alternate sites is done only under proper supervision.

Arterial blood for blood gas analysis is usually extracted by a phlebotomist, nurse, or respiratory therapist. Taking arterial blood requires more skill than venous blood sampling. Patients who need arterial blood sampling are often very ill and require gentle handling.

Percentage oxygen concentration the patient is breathing must be noted before sampling as interpretation of blood gases is dependent on knowing the inspired oxygen concentration. The biochemist should know that sample is expected as even stored sample on ice should be analyzed swiftly so that continued metabolic activity by the cells does not alter the true result.

The pH of the blood, the partial pressure of carbon dioxide and oxygen, and the bicarbonate level can be determined by arterial blood gas analysis. Concentrations of lactate, hemoglobin, several electrolytes, oxyhemoglobin, carboxyhemoglobin and methemoglobin are also reported by many blood gas analysers.

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