Didactic Encyclopedia


Custom Search

What is a gas analysis | Diseases and conditions: Medical tests.


Gas analysis

The gases is a diagnostic test that is used most often in hospitals and medical emergencies. With it you can know the number of gases that are dissolved in the blood. It consists of collecting a small amount of venous or arterial blood for later analysis in the laboratory. The types of gases according to the source of collection can be divided:
Arterial venous gas: collected blood from one vein either, just as is done when a routine blood test. With this blood gas analysis is not very useful because the blood flowing through the veins always will be poor in oxygen and rich in carbon dioxide, but it is useful to know the blood pH and bicarbonate levels.
Arterial blood gases: collects blood from an artery, usually the radial artery in the wrist. It is somewhat painful, but it is the only blood that allows us to know what is the amount of oxygen that passes into the blood from the lungs. It is the test most used and the only one that allows for the diagnosis of respiratory failure.
With this test can identify situations in which the human body's metabolism is altered, and also check if the situation is so serious as to require intensive treatment in an ICU. Does not involve large costs, injury to the patient is minimal, and the benefits are great.

When an arterial gas becomes

The gases is a test that is very frequently used in medicine because it is a minimally invasive to the patient and can provide lots of useful information. Why it calls routine to detect abnormalities that compromise the level of gases and body metabolism. Some of these situations are:
Respiratory failure: although it could be suspected when a person presents a respiratory failure, can only be diagnosed through an arterial blood gases. Respiratory failure situations can be diverse, some of them would be asthma, COPD, pulmonary fibrosis, acute Lung edema, etc.
Hyperventilation: when a person breathes very quickly and emotionally can eject more than should be carbon dioxide, and blood would have been less. This produces metabolic alterations of calcium (tetany) and blood pH (alkalosis).
Situations of acidosis: venous or arterial gas analysis allows to know the levels of blood pH. There are situations in which the acid levels in blood are too high. Some of the most important are Diabetic Ketoacidosis (you cannot use glucose and ketone bodies are produced) and sepsis (oxygen is not used and it produces lactic acid).
Alterations of renal metabolism: the functioning of the lungs is linked to the kidney. When an arterial gas is disturbed it can mean the alteration of one of the two systems. Bicarbonate which is reabsorbed in the kidney tubules can help guide us in one direction or another.

Preparation for a gas analysis

If you are performing an arterial gas these are the issues that you must take into account:
Duration: takes very little time. The collection of the blood sample consists of a small puncture to remove a small tube of blood.
Entry: admission is not needed, but it should be done in a hospital with adequate asepsis conditions environment, and to carry the sample to the laboratory in less than half an hour. Anyway, it is usually done in patients admitted with neumologicos problems or emergency situations.
Is necessary to be accompanied?: no.
Drugs: is not necessary to take any prior medication. It must be said to the doctor all medications you are taking at that time. Some medications can alter the normal characteristics of the gases, as diuretics, for example.
Food: is a test that is not altered by eating in the hours before, so it is not necessary to save fast.
Clothing: don't need a garment special, just to wear sleeves allowing to discover the arm for blood collection.
Documents: it is advisable to carry your health card, but at the time of you gas analysis do not usually ask you for any identification.
Pregnancy and lactation: test can be taken without modifying any attitude. It is better that the doctor knows you are pregnant because the gases may be slightly different.
Contraindications: there are no contraindications.

How a gas analysis

When you get to the inquiry or to the emergency room doctor will make you some general questions about your state of health (important diseases, risk factors, lifestyle, workplace, etc.), and above all insist the symptoms that have led you to consult. After perform you a general physical examination, and assess the realization of an arterial gas if it believes it may be useful for diagnosis and treatment.
At the same time, a doctor or a nurse shall draw you needed blood for testing. If it is an arterial venous blood from the front of the elbow, as an any blood test should be extracted. But most often, it is necessary to obtain a sample of arterial blood, and so you will have to draw blood the radial artery located on the wrist, or the blood humeral which is on the inner side of the elbow.
First clean the surface of the skin with an antiseptic substance to eliminate germs. After the health will feel the pulse of the artery which want to puncture and when it located puncionará with a sterile needle. It's difficult to make technique and that takes practice. If it is correct, then leaves bright red blood enters the syringe; It tends to fly out because the artery has a high pressure. Prick is rather painful, but when you remove blood from routine. But it only lasts a few seconds, so you have to keep calm and hold.
When you are finished collecting the sample they will be placed you at the point of puncture cotton and will ask you that strong pressure for 10-15 minutes. That will let bleeding and prevent the formation of a hematoma. The sample is sent then to the laboratory, where will discuss it with a unit specialized in as. Results, which may be interpreted by the doctor will be in 30-60 minutes.

Complications of arterial gas

Rarely appear complications when performing a gas analysis. It's a test with little risk, and the few complications that may appear are not serious. Some of them are:
Gases without success: happens with enough frequency that is not able to extract blood from the artery on the first try, even in toilets with experience. When this happens there to repeat it, which produces another prick is painful to the patient, even if they do not increase other risks.
Local infection: whenever you go through the skin the risk of an infection. Today it is very rare to appear, since the antisepsis measures are extreme for the gases.
Hematoma: is common to spill some blood from the artery puncionada to the surrounding tissues. To avoid this is should be compressed the artery for a few minutes after the extraction.
Haemorrhage: it is extremely rare, since the needle that punctures are made points artery is very thin and bleeding is usually self-limiting within minutes.

Gas analysis results

The results of the gases consist of a series of values of different blood components that have been analyzed in the laboratory, as with other analytical blood or urine. The values that are studied are:
Partial oxygen (pO2) pressure: analyzes the amount of oxygen that is dissolved in the blood. Normal results vary between 75 mmHg and 100 mmHg. It is considered that a person develops respiratory failure when the pO2 is less than 60 mmHg. You can only be analyzed in arterial blood.
(PCO2) carbon dioxide partial pressure: is to analyze the amount of carbon dioxide dissolved that there is in the blood, as well as with the pO2. Normal results vary between 35 mmHg and 45 mmHg. If the level is low you can indicate respiratory alkalosis; If they are high it may indicate respiratory acidosis. You can only be analyzed in arterial blood.
blood pH: is to analyze the number of protons (H +) that are dissolved in the blood, and which add acidity to the plasma. Normal values vary between 7.35 and 7.45. If the pH is lower than the person presents acidosis or acidemia; If it is higher, it will present alkalosis or alcalemia. You can analyze in arterial and venous blood.
Saturation of oxygen (SatO2): Although the pO2 is the method that has been established for diagnosing respiratory failure, sometimes is not the most accurate. It should take into account that the oxygen in the blood is partly dissolved and partly attached to hemoglobin. PO2 analyzes only the dissolved, and to find out the attached to hemoglobin to be studied oxygen saturation. Analysed using studies of light polarized in the blood sample. Normal values are usually between 95-100%, although sometimes above 90% you can be normal. It can be studied only in arterial blood.
Bicarbonate (HCO3): the amount of bicarbonate in the blood depends on the resorption that occurs in the. He is responsible for neutralizing acid in the blood, so it will be increased when there is a situation of acidosis in time, and decreased when a lasting alkalosis. Normal values vary between 22-28 mEq. You can analyze in arterial and venous blood.
Published for educational purposes
This web site does not provide medical advice, diagnosis or treatment
Diseases and conditions


Custom Search