ABG - Arterial Blood gas - taking a sample

Arterial blood gas (ABG) sampling by direct vascular puncture is a procedure often practiced in the hospital setting. The relatively low incidence of major complications,[1] its ability to be performed at the patients bedside, and its rapid analysis make it an important tool used by physicians to direct and redirect the treatment of their patients, especially in patients who are critically ill.

ABG sampling is usually performed on the radial artery because the superficial anatomic presentation of this vessel makes it easily accessible. However, this should be done only after it has been demonstrated that there is sufficient collateral blood supply to the hand. In cases where distal perfusion is compromised and distal pulses are diminished, femoral or brachial artery puncture can be performed instead.

The brachial artery commences at the lower margin of the tendon of the teres major. Passing down the arm, it ends about 1 cm below the bend of the elbow, where it branches into the radial and ulnar arteries. The radial artery commences at the bifurcation of the brachial, and passes along the radial side of the forearm to the wrist. For more information about the relevant anatomy, see Arterial Supply Anatomy.

ABG sampling provides valuable information on the acid-base balance at a specific point in the course of a patient's illness. It is the only reliable determination of ventilation success as evidenced by CO2 content. It constitutes a more precise measure of successful gas exchange and oxygenation. ABG sampling is the only way of accurately determining the alveolar-arterial oxygen gradient (see the A-a Gradient calculator).

Because the results of ABG sampling only reflect the physiologic state of the patient at the time of the sampling, it is important that they be carefully correlated with the evolving clinical scenario and with any changes in the patients treatment.