Arterial blood gas analysis

Arterial blood gas analysis refers to the technical process of analyzing different types of gases and acid-base substances in various gases and liquids. Its specimens can come from blood, urine, cerebrospinal fluid and various mixed gases, but the most clinically used is blood. Blood specimens include arterial blood, venous blood, and mixed venous blood, among which the application of arterial blood gas analysis is most common. Basic Information Specialist classification: growth and development examination classification: blood examination Applicable gender: whether men and women apply fasting: not fasting Included items: buffer base (BB), carbon dioxide partial pressure (PCO2, PCO2), arterial oxygen partial pressure (PaO2), blood pH (pH), actual bicarbonate, residual base (BE, BD), oxygen saturation Warm reminder of carbon dioxide binding: maintain a normal mentality. Normal value 1. The pH value reference value is 7.35 to 7.45. <7.35 is acidemia, and >7.45 is alkalemia. However, normal pH does not completely rule out acid-base imbalance. 2, carbon dioxide partial pressure (PCO2) reference value 4.65 ~ 5.98kPa (35 ~ 45mmHg), multiplied by 0.03 is the H2CO3 content. Exceeding or lowering the reference value, said high and low carbonation. >50mmHg has a risk of inhibiting the respiratory center. It is the main indicator for judging various types of acid-base poisoning. 3, the total amount of carbon dioxide (TCO2) reference value of 24 ~ 32mmHg, representing the sum of CO2 and HCO3 in the blood, in the body affected by breathing and metabolism. Significantly decreased in metabolic acidosis and increased significantly in alkalosis. 4. The oxygen partial pressure (PO2) reference value is 10.64 to 13.3 kPa (80 to 100 mmHg). Below 60mmHg there is respiratory failure, <30mmHg can be life-threatening. 5. The oxygen saturation (SatO2) reference value is 3.5 kPa (26.6 mmHg). 6. The actual reference value of bicarbonate (AB) is 21.4 to 27.3 mmol/L, and the reference value of standard bicarbonate (SB) is 21.3 to 24.8 mmol/L. AB is an important indicator of metabolic acid-base imbalance in the body. Under certain conditions, SB also reflects metabolic factors. Both of them are normal and stable in acid and alkali. Both are low in metabolic acidosis (uncompensated), both of which are metabolic alkalosis (uncompensated), AB>SB is respiratory acidosis, AB<p>. 7. The residual base (BE) reference value is -3 to +3 mmol/L. The positive value indicates an increase and the negative value decreases. 8, anion gap (AG) reference value of 8 ~ 16mmol / L, is an important indicator of early detection of mixed acid-base poisoning. Judging the acid-base imbalance should first understand the clinical situation, generally based on pH, PaCO2, BE (or AB) to determine the acid-base imbalance, according to PaO2 and PaCO2 to determine hypoxia and ventilation. A pH outside the normal range suggests an imbalance. However, there may still be an acid-base imbalance in normal pH. PaCO2 exceeds normal warning of respiratory acid-base imbalance, and BE exceeds normal suggestion of metabolic acid imbalance. However, blood gas and acid-base analysis sometimes combined with other tests, combined with clinical dynamic observation, in order to get a correct judgment. Clinical significance In the past, because of the backward medical conditions, the determination of hypoxia can only be estimated by clinical symptoms, and the acid-base imbalance is only judged based on symptoms and CO2CP (carbon dioxide binding). Because clinical symptoms and CO2CP are affected by many factors, reliability is poor. Arterial blood gas analysis is a reliable indicator to determine whether the body has acid-base balance imbalance and hypoxia and hypoxia. At present, arterial blood gas analysis has become an indispensable test item in the diagnosis and treatment of hypoxemia and acid-base imbalance in clinical departments. 1. Hypoxemia is a common and complication that can endanger the life of a patient at any time. Many diseases can cause diseases such as respiratory diseases, heart disease, severe trauma, shock, multiple organ dysfunction syndrome (MODS), poisoning, etc. Various critical illnesses, as well as surgical anesthesia. Based on clinical symptoms and signs, it is impossible to make accurate judgments and estimates of hypoxemia and its extent. Arterial blood gas analysis is the only reliable indicator for diagnosing hypoxemia and determining its extent. Even if a ventilator can correct hypoxia and hypoxemia, many indications of the ventilator cannot be reasonably applied without the aid of arterial blood gas analysis monitoring. 2. In the process of critical illness treatment, acid-base imbalance is the most common clinical complication after hypoxemia. Timely diagnosis and correction of acid-base imbalance is of great significance for the treatment of critical illness. Arterial blood gas analysis is also the only reliable indicator for measuring and measuring the acid-base balance of the human body. Low results may be diseases: high altitude disease, elderly patients with pulmonary encephalopathy, metabolic acidosis in the elderly, sepsis and bacteremia, acute left heart failure in the elderly, respiratory failure in the elderly, pulmonary heart disease in the elderly, elderly lung Embolization, metabolic acidosis in the late neonatal period, high interstitial pneumonia in the elderly may be a disease: precautions for respiratory acidosis in the elderly Factors influencing arterial blood gas analysis: 1. Blood collection location: If the blood collection artery has an infusion, hemolysis and dilution may occur, causing K+ to increase and Ca2+ to decrease. If it is mistakenly collected as venous blood, because venous blood can not accurately reflect the arterial blood gas condition, its pH value is close to arterial blood under normal conditions, but when the body is sick, various metabolisms have different degrees of obstacles. There is a significant difference in the pH of the arteries and veins. 2. Blood collection and heparin concentration: Heparin concentration is the core guarantee for accurate blood gas analysis. Heparin dosage can cause dilution error, low pH, PaO2 value, high PaCO2 value, and pseudohypocapnia. However, if the amount of heparin is too small, the anticoagulant effect will not be achieved. The International Federation of Biochemistry (IFCC) recommends a final concentration of heparin in blood gas specimens of 50 u/ml. 3. Bubbles: Because the bubbles affect the pH of the blood gas, PaCO2, PaO2 detection results, especially the PaO2 value. The ideal blood gas sample should have air bubbles below 5%. 4. Specimen mixing degree: As with other anticoagulant specimens, insufficient mixing will increase the occurrence of blood coagulation, thereby affecting the accuracy of hemoglobin and hematocrit results. 5. Storage of specimens: Specimens for the detection of lactic acid must be stored in ice water before testing. Other test items can be stored for 1 h at room temperature or in ice water. 6. Sample inspection time: PaCO2, PaO2 and lactic acid detection must be completed within 15min. Other items such as pH, electrolyte, BUN, hemoglobin, blood sugar and red blood cell ratio are required to be completed within 1h. Inspection process 1. The main requirements for sample collection: Reasonable blood collection site, strict isolation of air, the patient is in anti-coagulation in a quiet state, immediately after the blood is taken for examination, the condition is allowed, it is best to stop taking oxygen for 30 minutes before taking blood, otherwise the concentration of inhaled oxygen should be indicated. 2. Blood collection site and method: Before the blood collection, the patient is quiet, avoiding tension and paralysis, so as not to drop PaCO2. The preferred site of blood collection is the femoral artery, radial artery or radial artery. In order to avoid the heparin dilution of the blood sample and affect the blood gas results, it is best to use a heparinized dry syringe to draw blood. However, this method is more cumbersome. At present, the disinfectant heparin solution (1000U/ml with normal saline) is used in the clinic to wet the inner wall of the 2ml syringe and fill the dead space of the syringe (heparin content is 40-50U). When the needle is inserted into the artery, the In principle, the arterial pressure is sufficient to push the needle core to allow the arterial blood to automatically enter the heparin-containing syringe. Generally, after taking 1 to 2 ml of blood, the plug is placed on the needle to make the air tightly sealed and immediately sent for inspection. If air is mixed in, it will affect the measurement results. Arterial capillary blood can be taken from the fingertips, earlobe or heel, but it is currently less clinically used. 3. Sample storage: The blood should be measured as soon as possible after blood collection. In principle, the sample should be measured within 20 minutes after extraction. If it needs to be placed, it should be placed in ice cubes (0 ° C) or placed in the refrigerator, but should not exceed 2 h. 4. Feasibility of venous blood to replace arterial blood for blood gas analysis: Blood gas analysis should be based on arterial blood in principle, but it is often difficult to see arterial puncture in patients in clinical practice, especially in infants and young children. At this time, venous blood is often used instead of arterial blood. 5. Record the patient's body temperature and oxygen concentration: The patient's body temperature can affect the pH, PaCO2 and PaO2 measurements. Especially in low temperature anesthesia surgery, the measured values ​​must be corrected. The oxygen concentration can affect the PaO2 value, and the physician should judge the effect of oxygen on the oxygen partial pressure. Not suitable for the crowd No taboos. Adverse reactions and risks No complications.

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