What is Arterial Blood Gas?

An arterial blood gas (ABG) is a type of blood test which measures the pH or acidity of the blood, as well as gases, such as oxygen and carbon dioxide. The test is usually performed on people if they have breathing problems, such as emphysema and asthma. It helps doctors evaluate whether the lungs are functioning efficiently

When we inhale we breathe in oxygen, which is transported from the lungs into the bloodstream. During exhalation, carbon dioxide is released and also travels through the blood. Two of the most important factors an ABG measures is the level of both the carbon dioxide and the oxygen level in the blood.

The level of carbon dioxide affects the pH of the blood, which is why it’s considered a critical factor measured by an arterial blood gas. Excess carbon dioxide makes the pH lower and causes a condition know as respiratory acidosis. This can lead to various symptoms, including confusion, headaches, coma and possibly death.

An arterial blood gas also measures oxygen in the blood in two ways. The first measurement is called the partial pressure of oxygen (Pa02). This measures how efficiently the oxygen moved from the lungs into the bloodstream. The second measurement is the oxygen saturation level, which means how much oxygen is in the blood.

Many types of blood draws are obtained from a vein. An arterial blood gas is taken from an artery. It is usually drawn from the radial artery, located in the wrist, or the brachial artery, which can be felt on the inside of the arm at elbow level. Specially trained medical personal can draw an arterial blood gas, including, doctors, nurses, respiratory therapists and lab technicians.

Medical personnel performing an ABG will first do an Allen’s test. This test confirms that the patient has collateral circulation to the hand. The radial artery, along with the ulnar artery, supplies blood to the hand. Although unlikely, if the radial artery is damaged during the blood draw, it’s important to ensure the ulnar artery is supplying blood to the hand.

The next step is swabbing the wrist with an alcohol swab to prevent infection. Because arteries are not seen, the technician will feel for a pulse. Once the pulse is located, the tech will insert the needle and blood will flow into the syringe. After the needle is removed, pressure is applied to the artery for a few minutes to ensure bleeding has stopped. The blood sample is then ran through a special machine which can provide the lab values.