Arterial blood gas

Definition of arterial blood gas

blood is responsible for the transport and diffusion of nutrients throughout the body. Arterial blood circulates from the lungs to the tissues to supply oxygen. Venous blood returns to the lungs from the most distal tissues and carries mainly carbon dioxide, a waste product of cellular respiration. From this it follows that the amount of oxygen in arterial blood will be greater than in venous blood and, in the same way, the carbon dioxide dissolved in venous blood will be greater than in arterial blood.

The lungs and heart are involved in respiratory function. When one of these elements is injured, the diffusion of gases and cellular oxygenation will be altered. The arterial blood gasit is the exploration that allows to quantify oxygen and carbon dioxide in arterial blood. Thanks to this determination, it is possible to reach the diagnosis of respiratory, cardiac or metabolic problems that alter the correct circulation of oxygen.

It also allows to determine the degree of acidity or pH of the blood, being useful for the diagnosis of other pathologies such as diabetic ketoacidosis, or kidney failure.

How is the study done?

The analysis will be carried out in the hospital setting, in consultations or in laboratories for this purpose. The use of local anesthetic in the place of insertion of the needle is frequent, although sometimes its application can be dispensed with. The extraction may be carried out by the medical or nursing staff. The needle is inserted into the radial artery, which is located in the anterior or ventral region of the wrist. The area is located by palpation of the pulse. Puncture of the artery could lead to a spasm of the vessel or an occlusion by a thrombus. In order to avoid this complication, the Allen test should be performed, which consists of a simple test in which the circulation of the hand collapses by compressing the arteries of the hand, the ulnar and radial arteries, both located on the wrist. By repeatedly asking the patient to close and open the hand, the hand will turn pale. By ceasing to compress the ulnar artery, located on the most medial aspect of the wrist, in a healthy patient it will regain its usual coloration in about 15 seconds. If the normal color is not recovered, it is concluded that the circulation of the hand depends only on the radial artery, so it will be avoided to put the circulation at risk by means of a puncture and therefore the gasometry of the radial artery will be contraindicated.

Exceptionally, the brachial artery can be punctured at the level of the arm if the collateral circulation is insufficient or the anatomy does not allow the identification of the radial artery, as happens in some obese patients.

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Preparation for the study

It does not require any preparation. In patients who are undergoing oxygen treatment, the withdrawal of oxygen could be requested in the 20 minutes prior to the test, according to medical criteria.

What does it feel like during and after the study?

If local anesthesia is applied, an itching or burning sensation may be perceived in the area of ​​application. If you choose not to apply any anesthetic, it is possible that at the time of puncturing the artery a sensation similar to a cramp is perceived. These complaints quickly subside.

Study risks

It is a very common examination in the hospital setting that rarely presents complications. The most common will be presence of hematoma at the puncture site, that will send in a few days.

One of the most serious and feared complications is complete occlusion of the artery after puncture and ischemia of the hand. Its incidence is low and can be avoided in a large number of cases if care has been taken to assess the correct vascular supply to the hand through the patency of the ulnar artery (Allen's test).

Study contraindications

It does not present absolute contraindications. Special caution is required in patients on antiplatelet or anticoagulant treatment due to the higher incidence of bruising or bleeding after puncture.

Reasons why the study is carried out

An arterial blood gas analysis will be indicated in patients in whom it is necessary to complete the diagnosis or follow up on different pathologies that affect correct respiratory function. Arterial blood gas is useful to assess the indication for oxygen at home as well as the need for mechanical ventilation or other ventilatory support measures in patients with respiratory failure.