A blood test for the gas composition occupies a rather important place in medicine, since it can be used to determine how saturated the body is with air. And this, in turn, makes it possible to determine the effectiveness of therapy, as well as diagnose a person's primary form of hyperventilation and respiratory failure.
What is this analysis?
If we explain the features of the analysis of arterial blood gases in a clear language, then we can note that this study shows how well the lungs transport oxygen to the blood.
During the passage of blood through the lungs, it is saturated with oxygen. After that, blood transports oxygen throughout the body. In parallel with this, with the help of the lungs, carbon dioxide is removed from the blood. Blood sampling is carried out precisely from the artery for the reason that arterial blood still does not have time to transfer oxygen to other tissues, as a result, it becomes possible to really assess the ratio of these gases in the body.
Thus, through the analysis of blood for gases, you can find out about its acidity, the degree of oxygen and carbon dioxide. Based on the data obtained, it can be concluded that the lungs work, namely, how they deliver oxygen to the body.
Blood passing through the lungs is saturated with oxygen. Then it spreads throughout the body to all organs. In this case, the blood is cleansed of carbon dioxide by the lungs. It is important to take a test before the blood clears, so it is taken from an artery. This allows you to measure the actual concentration of gas impurities in the blood.
Measurable indicators
Blood gas analysis allows you to study these indicators:
- Partial pressure of oxygen. This value is responsible for how easily oxygen is transported from the lung tissue to the blood.
- The partial pressure of carbon dioxide. Allows you to explore how easily carbon dioxide is removed from the blood.
- Acidity. The acidity level indicates the amount of hydrogen ions in the blood.
- Bicarbonate. This is a substance that helps maintain the required level of acidity in the blood.
Indications
A blood gas test is required in the following cases:
- there is a need to identify pathology of breathing and lung disease;
- for monitoring the course of therapy of pulmonary diseases;
- to identify the need for additional oxygen (mechanical ventilation method);
- for measuring the acid-base balance in people suffering from heart or kidney failure, diabetes mellitus, insomnia, severe infections.
Features of the analysis
The analysis of arterial blood gases does not require special preparation, the only thing that needs to be done is to inform the doctor about the drugs used and the presence of various allergic reactions.
Before taking blood from an artery, an initial assessment of the state of blood flow is performed. To do this, they press an artery and analyze the degree of blanching of the distal region of the body. If the blood flow is weak, then other blood vessels are used to collect blood. Most often, blood is taken from the hand.
After a blood sample of 2 ml is taken, the puncture site is pressed for 5-10 minutes. It is mandatory to take into account the high pressure present in the arterial bed.
Complications
Since the collection of biomaterial for the analysis of blood gases is performed from the artery, a number of complications may develop:
- hematoma at the injection site;
- dizziness and a feeling of nausea directly during the collection of biomaterial;
- bleeding;
- occasionally a needle can damage the nerve ending.
Distorting factors
When passing a blood gas analysis, there are a number of factors that can cause distortion of the final results:
- increased or decreased body temperature;
- anemia or erythrocytosis - these pathologies impair the quality of oxygen, which is carried together with the blood;
- immediately before the delivery of the biomaterial there was contact with tobacco.
Indicators of acid-base balance
Analysis of the composition of gases in the blood includes the study of acid-base balance, the norm of which varies depending on age:
- adults - 7.35-7.45;
- children - 7.31-7.47.
As a result, it is concluded that if the value of the acid-base balance is less than 7.35, then the body contains an excessive amount of carbon dioxide. An indicator of more than 7.45 indicates an exceeded alkali content.
The study of oxygen pressure
The norm of oxygen pressure also differs depending on age:
- adults - 4.7-6;
- children - 4.3-8.1.
When passing a blood gas analysis, this indicator may be within normal limits or be reduced. In the latter case, the formation of hypoxia is diagnosed, which is accompanied by an increase or decrease in the amount of carbon dioxide.
Carbon dioxide pressure indicator
The norm of such an indicator as carbon dioxide pressure also completely depends on age. In both cases, the pressure is in the range of 35 to 45 mm.
If the studied indicator is less than 35 mm, then this indicates a violation of hyperventilation. The body is deficient in carbon dioxide. With an indicator of more than 45 mm, an excess of carbon dioxide is diagnosed, which entails a decrease in the heart rate and the development of a patient's feelings of anxiety.
Bicarbonate rate
Depending on the age of the patient, the following normal indicators of bicarbonate content are distinguished:
- adults - 22-28;
- children - 15-25.
If the value is below normal, then this may be a sign of the development of renal pathologies, dehydration, or a metabolic form of acidosis. Exceeding the norm often develops with excessive use of steroids, hyperventilation and the metabolic form of alkalosis.
Acidosis and alkalosis
Speaking in plain language, the analysis of blood gases determines whether the body receives enough oxygen. You should also understand what acidosis and alkalosis are. These pathologies are among the conditions that signal the body about the complete depletion of its protective functions, as a rule, this is due to malfunctions in the acid-base balance.
In this case, acidosis is of several types:
- Respiratory acidosis is a pathology that is characterized by a decrease in acid-base balance and an increase in carbon dioxide pressure. The development of a pathological condition occurs due to a decrease in breathing volume. A similar condition can develop against the background of pneumonia, exacerbation of bronchial asthma or obstructive bronchial diseases. By analyzing blood gases, a diagnosis is made of the presence or absence of respiratory failure.
- Metabolic acidosis - develops due to a decrease in the amount of bicarbonates and an increase in the amount of acid released. This condition can develop against the background of renal failure or diabetes.
Alkalosis is a condition characterized by an increase in blood acidity as a result of the accumulation of alkaline elements.
There are several types of such a condition:
- Compensated Type. A violation of the acid-base balance is observed, in which the acidity is normal, and only minor shifts are present in the buffer systems.
- Uncompensated type. Acidity indicators go beyond the normal range; this is most often caused by an excessive content of bases and a small number of physiological and physicochemical mechanisms for regulating the acid-base balance.
When passing a blood test for gases, the same preparation rules must be followed as when passing a general blood test. A few days before the examination, fatty, fried, salty and spicy foods should be excluded from the diet.
As a rule, the patient receives a transcript of the results of the study after a few days, a maximum of a week. With the results, the patient goes to the doctor and, under his guidance, starts treatment.