- How the exam is done
- What is it for
- Reference values and how to understand the exam result
- What is the difference in arterial and venous blood gases
Arterial blood gas analysis is a blood test normally performed on people admitted to the Intensive Care Unit, which aims to verify that the gas exchanges are occurring correctly and, thus, to assess the need for extra oxygen.
In addition, it is an exam that can be requested during hospitalization to assist in the diagnosis of respiratory, kidney or serious infections, in addition to verifying whether the treatment is being effective and, thus, can be used as one of the criteria that can influence the discharge from the patient.
How the exam is done
Arterial blood gas analysis is performed by collecting a blood sample from the artery of the arm or leg. This type of collection is quite painful, as it is a more invasive collection. The collected blood is taken to the laboratory for biochemical tests to check blood pH, bicarbonate concentration and partial pressure of CO2.
Arterial blood gases should not be performed in case of peripheral arterial disease, as there may be difficulties in drawing blood, coagulation problems or if the person is using anticoagulants. In such cases, the doctor may order other tests to identify the diseases that are causing respiratory changes.
What is it for
Arterial blood gases are requested by the doctor to:
- Check lung function, especially in asthma or bronchitis and in case of respiratory failure - Know what the symptoms are and how the treatment of respiratory failure is done; It helps to evaluate the pH and acidity of the blood, which is useful to assist the diagnosis of renal failure and cystic fibrosis, for example; Assess the functioning of the metabolism, which is important in the identification of heart disease, stroke (stroke) or type II diabetes, for example; Functioning of the lungs after surgical procedure or transplantation.
In addition, blood gas analysis is also requested in case of drug overdose. This exam is not common, it is not performed in clinics or in routine consultations, being only requested by the doctor in more severe cases.
Reference values and how to understand the exam result
The normal values of the arterial blood gas analysis are:
- pH: 7.35 - 7.45 Bicarbonate: 22 - 26 mEq / L PCO2 (partial pressure of carbon dioxide) : 35 - 45 mmHg
The following table indicates some examples of altered arterial blood gas values:
| pH | Bicarbonate | PCO2 | state | Common causes |
| Less than 7.35 | Low | Low | Metabolic acidosis | Renal failure, shock, diabetic ketoacidosis |
| Greater than 7.45 | High | High | Metabolic alkalosis | Chronic vomiting, hypokalemia |
| Less than 7.35 | High | High | Respiratory acidosis | Lung diseases, such as pneumonia, COPD |
| Greater than 7.45 | Low | Low | Respiratory alkalosis | Hyperventilation, pain, anxiety |
The arterial blood gas examination indicates how the lung is working, that is, if the gas exchanges are being carried out in the correct way, thus indicating the person's condition, which may be acidosis or respiratory or metabolic alkalosis. Understand what metabolic and respiratory acidosis, metabolic alkalosis and respiratory alkalosis mean.
This test is not sufficient to close the diagnosis, it only suggests respiratory, renal or metabolic disorders, and other complementary tests, such as X-rays, CT scans, other blood tests and urine tests, are usually requested by the doctor so that the diagnosis can be closed and the treatment can be started according to the cause of the change in blood gas analysis.
What is the difference in arterial and venous blood gases
Arterial blood gases determine the exact values of the amount of oxygen and whether the kidneys and lungs are functioning properly, which helps in the diagnosis of lung, kidney diseases and infections.
Venous blood gas analysis, on the other hand, is performed as a second option when collection in the artery is not possible, with collection being made in the vein, and its main objective is to assist in the diagnosis of peripheral arterial diseases or blood clotting problems.
