Blood Gas Analysis Specimen Collection Methods and Factors Affecting Results
Blood gas determination blood collection kit (with rubber stopper and needle), sterile swabs, aneroid, sterile cotton balls, and treatment tray. Here is my knowledge about blood gas analysis specimen collection methods and factors affecting the results.
I. Arterial blood gas specimen collection methods
1. puncture methods
1.1 Preparation of supplies
Blood gas analysis blood collection kit (with rubber stopper and needle), sterile cotton swabs, aneriodine Users who are willing to prepare their own anticoagulant blood collection needles can prepare a heparin dilution solution with 0.9% NS50ml + 2 sodium heparin injections (12,500U) for spare use and good aseptic storage. Before each blood gas draw, use a 2ml syringe to extract 2ml of heparin diluent, discard the heparin liquid after completely wetting the whole syringe, and the heparin liquid remaining in the dead space of the needle and head of the syringe can play an anticoagulant role. Less anticoagulant will make the blood agglutinate and block the flow path system of the blood gas analyzer, more anticoagulant will affect the results of blood gas and ion detection, and large doses of anticoagulant will seriously make the ionized calcium low and mislead the clinic.
1.2 Patient Preparation
The patient should be in a natural state, and should rest for 15min after the activity, and oxygen intake should be stopped 30min before the blood draw. Due to the patient's understanding of the collection of arterial blood less, easy to produce fear, the nurse should be targeted to do a good job of explaining the work, eliminating the patient's psychological concerns, stabilize their emotions, to avoid a variety of factors caused by excessive respiration or breathlessness caused by the blood gas error.
1.3 Assessment of the patient's arteries and selection of blood vessels
Most of the selection of arterial pulsation obvious, good elasticity, easy to fix, puncture site without hard knots of the blood vessels, commonly used blood collection sites in order: radial artery, brachial artery, femoral artery and dorsal artery, radial artery is the most suitable for arterial puncture blood collection. Generally choose the radial artery, because here the artery is fixed, easy to expose, not subject to the position and the operation of the location of the limitations; followed by the choice of the femoral artery and brachial artery, the patient is easy to accept, and the success rate is high, it is not easy to accidentally enter the vein or accidentally stab the deep nerve.
1.3.1 Adults: puncture with heparinized glass syringe or disposable syringe, blood collection site preferred radial artery, followed by the femoral artery
1.3.2 Pediatrics:
1.3.2.1, preferred use of the superficial temporal artery or scalp arterioles, strict disinfection, with heparinized No. 5 scalp needle connected to the 2 ml syringe, waiting for the arterial blood to the syringe papilla When the arterial blood flow to the nipple of the syringe, immediately use a small hemostatic forceps to clamp the scalp needle plastic hose head and tail respectively (about 0.5 ml of blood), and then pull out the needle and immediately mixing to send for inspection.
1.3.2.2, puncture with a heparinized syringe, the preferred site for blood collection is the radial artery, small infants can be used to take blood from the superficial temporal artery, the blood must be sealed.
1.3.2.3. When repeated arterial puncture is not possible due to technical constraints, preterm infants and small infants can use heparinized capillaries in the heel of the foot to collect blood from arterialized capillaries. Arterialized capillary blood collection, with not more than 42 ~ 45 ℃ wet towel hot compresses the skin at the site of blood collection for 5 ~ 15 minutes, so that the blood increases, blood flow accelerated to achieve arterialization, and then puncture, puncture should be deep, so that the blood flow is rapid and automatic outflow, discard the first drop of blood, can not be extruded, heparinization of the capillary to absorb (it is recommended to use the manufacturers of supporting the provision of the special capillaries), suction full of must be sealed, mixing and immediately after the Sent for examination. The PO2 of insufficiently arterialized capillary blood is low, and the effect on the results of PH, PCO2 and HCO3- determination is not obvious.
1.4 Positioning
Traditionally, the site of blood sampling is the strongest radial artery pulsation, which is used as the reference point for puncture. The point of entry for blood sampling is determined by the operator's feelings, and because the radial artery is thin, the beating point is striated, and the beating can be touched in a longer section, the error in the location of blood sampling is larger. Yang Lanjie reported that the positioning of the radial tuberosity as the base point, move 1cm to the ulnar side, and then move 0.5cm to the direction of the elbow that is the point of entry, the undergraduate use of this method of positioning, the success rate of puncture significantly improved.
1.5 Operation method
Assist the patient to take a comfortable position, expose and use a soft pillow to elevate the puncture site. Strictly disinfect the puncture site, open the blood gas determination blood collection kit packaging, pull the live plug to 1cm, disinfect the operator's left hand index finger and middle finger, according to the above positioning method to find the most obvious arterial pulsation and fix the artery, the right hand holding the syringe, the needle and the skin was 45?to 90?piercing the artery, the needle into the blood vessel wall there is a feeling of penetration, without the need to pull the plunger handle, the arterial blood automatically return to the blood, to the filling of the pre-programmed blood volume. After the blood volume, the needle is removed by pressing the eye of the needle at the puncture site with a cotton ball, and the patient is instructed to press for a period of not less than 5~10min, and then the needle is quickly stabbed into the rubber stopper, and the specimen is immediately palmed and rubbed and mixed for at least 5s to prevent the specimen from coagulating, and then labeled and immediately sent to be examined.
2, post-collection treatment
Immediately after blood collection, the tip of the needle or capillary suction vessels at both ends of the rubber cap or rubber cement seal, to prevent the entry of air bubbles, and immediately mixed to achieve the purpose of anticoagulant, and immediately sent to the examination, from the collection of blood to the examination should not be more than 20 minutes, so as to avoid the metabolism of the blood cells oxygen depletion, so that the decline in the PO2 and PH value PCO2 is elevated. If you can't measure immediately, the blood gas specimen should be stored in a container at 2 to 8 degrees Celsius, but even then the time to be measured should not be more than 2 hours.
2. Factors affecting the results of blood gas analysis
1. What are the types of samples for blood gas analysis?
The sample types for blood gas analysis are arterial blood samples, venous blood samples, and capillary blood samples.
Arterial blood samples. Arterial blood is the most commonly used type of blood for blood gas analysis because it provides the best information on oxygen uptake and transport, and the information obtained is stable and does not vary depending on the sampling point.
Venous blood samples, in general, are not recommended for blood gas analysis because they are influenced by the state of the peripheral circulation and cellular metabolism. It cannot be used to assess oxygen status, but it can reflect acid-base status (pH, pCO2, cHCO3) ctHb, FCOHb, FmetHb, FHbF, and ctBil.
Capillary blood samples, which can be used when arterial blood is not available, can be analyzed with the following parameters: ctHb, FOHb, FOHb, and ctBil. sO2, pO2, FOHb, and FHHb are only indicative. The results of sO2,pO2,FOHb,FHHb are for reference only, and can better reflect the following parameters: ctHb, FCOHb, FMetHb, FHbF, ctBil.
2. How do I choose a sampling point for blood gas analysis?
Arterial blood samples: the radial artery is most commonly used, because it is very superficial and easy to reach, no large veins around the vicinity, and there is a very good ulnar artery collateral circulation, easy to sample, in the puncture process, such as not touching the periosteum, the general pain is not sensitive. A modified Allen?s test is performed before radial artery sampling to determine the adequacy of collateral circulation. The brachial artery can be used but is not commonly used, due to the high risk of damaging the surroundings as it is not suitable for sampling because of its location. The femoral artery, although large and easy to puncture, has poor collateral circulation and is prone to inadvertent injury to the femoral vein and should be avoided in neonates and elderly patients.
Venous blood samples: the brachial vein is easy to sample.
Capillary blood samples: earlobes, fingertips, thumbs and heels for blood sampling; patients should be older than six months when heels and thumbs are used.
3. How do I choose an anticoagulant for blood gas analysis?
Dry heparin with sodium or lithium is recommended as the preferred anticoagulant, and liquid heparin should be avoided to avoid dilution of the sample. The following concentrations of heparin are recommended based on sample type: test tube: 7-30 IU/mL blood, syringe: 50-500 IU/mL blood, capillary: 50-100 IU/mL blood. If electrolyte measurements are included, use electrolyte-balanced heparin to minimize heparin-induced bias in electrolyte measurements for optimal results.
4. How do I prepare the patient for blood gas analysis sample collection?
The patient's respiratory status should be stable: the patient should be stabilized prior to sampling, with calm breathing and stable ventilation. Inform the patient of the sampling procedure to avoid unnecessary stress, which can cause hyperventilation. Hyperventilation is a major cause of blood gas errors and can increase alveolar ventilation, resulting in decreased pCO2, increased pH, and increased pO2.
5. How is the arterial catheter prepared for blood gas analysis?
The flushing solution in the arterial catheter must be completely removed from the system to avoid diluting the blood sample.
6. How do I prepare a capillary blood sample for blood gas analysis?
The capillary sampling site should be fully arterialized, and the arterialization should be warmed or gently massaged for 5-10 minutes to allow for local vasodilatation and congestion of the blood vessels, so that the capillaries are fully arterialized. If this requirement is not met, the blood sample will be only representative of the local tissues and will not respond to the patient's overall status. Otherwise, the pCO2 measurement may be low. Capillary blood cannot be used in patients with systolic blood pressure less than 95 mmHg, decreased cardiac output and vasoconstriction, or in newborns within the first few days of life.
7, blood gas analysis sample collection should pay attention to what?
It is important to note that blood sample testing should only be performed by specialized personnel, and to remember to handle blood samples and the instruments used to collect them with care. Use proper rubber gloves to prevent direct contact with the blood sample and always use sterilization techniques to prevent infection of the sampling site.
8. How is arterial sampling performed for blood gas analysis?
Arterial sampling: arterial puncture, be careful not to confuse venous blood with arterial blood samples, arterial blood (due to high pressure) than venous blood flow faster and lighter in color; immediately remove the air bubbles in it; immediately after sampling the sample with heparin mix. For arterial catheters, inhale the sample slowly to avoid hemolysis; remove air bubbles immediately; mix the sample with heparin immediately after sampling.
9. How do I collect a venous sample for blood gas analysis?
Venous samples: the hands and forearms should be immersed in water at 45 degrees Celsius for 20 minutes to arterialize the venous blood in the area, and then blood should be drawn from the veins of the arm (or back of the hand), but the blood should not be drawn with a pressure band, and should only be drawn slowly to avoid air bubbles. If a pressure band is used, the blood must be drawn in the first few seconds, and from time to time to flex the fingers or make a fist. Otherwise, the venous pO2 can be lowered, increasing the amount of acidic products.
10, blood gas analysis how to carry out capillary sampling?
For capillary sampling, use a lancet or other similar tool to puncture and the blood will flow out automatically without being squeezed, discard the first drop of blood as it may contain tissue fluid. The first drop of blood is discarded as it may contain tissue fluid. The collection is started from the middle of the second drop of blood to prevent air bubbles. It is forbidden to squeeze the blood collection point to avoid mixing some of the tissue fluid, which may cause deviations in instrumental measurements. It may also cause hemolysis of the sample (or part of it), resulting in high cK+ values. Sample analysis should be completed within 10 minutes. If storage is necessary, keep the sample at 0-4 degrees Celsius for a maximum of 30 minutes. NOTE: Use caution with measurements obtained with capillaries especially pO2.
11. How do I mix samples for blood gas analysis?
Mixed samples: Immediately after collection, mix the blood with heparin to avoid coagulation, which can clog the analyzer and cause unnecessary problems. To mix the sample, invert the sample and rotate it several times in your hand. Mixing wires or magnets may be used when mixing capillary tubes. Avoid mixing with too much force as this may cause hemolysis.
12. How do I collect a breath sample for blood gas analysis?
Breath gas sample, the patient's breath gas into the Douglas bag, connected to the syringe in the Douglas bag (minimum 20mL, contains a rubber tip). Fill, empty the syringe twice and inject the sample, then seal the syringe using the rubber tip.
13. How are samples for blood gas analysis stored?
The sample should be used immediately at all times and preservation of the sample should be avoided as much as possible. If immediate measurement of the sample is not possible, store it at room temperature for no more than 10 minutes. If prolonged storage is required, store at 0-4 degrees Celsius for up to 30 minutes. The following preservation methods are available: Ice water (with crushed ice or a cooling substance attached) may be used to store samples. Samples should not be placed directly into ice to avoid lysis of blood cells due to ice crystallization in the sample. Samples should be placed horizontally to avoid mixing of samples. Note: Samples with high estimated partial pressures of oxygen should be measured as soon as possible; PH and blood gas values should not be measured if air bubbles are present in the capillaries.
14. How do I prepare a blood gas analysis sample for analysis?
Arterial puncture and arterial catheterization samples: PH and blood gas values should not be measured if air bubbles are present in the sample. Shake and roll the sample in your hand several times to thoroughly mix the sample. Capillary samples: the sample should be mixed again before analysis, do not remove the mixing line before the sample is inhaled for measurement, slide the mixing line to the other end of the capillary tube where the sample is inhaled before inhalation and remove the rubber tips at each end of the capillary tube.
15. What is the effect of air bubbles in the blood gas analysis sample on the test results?
Air bubbles should be removed from the sample prior to mixing and stirring. Air bubbles can lead to potential errors if they are present at 5% compared to the blood sample content, and the effect of air bubbles will increase with storage time and mixing and stirring. The partial pressure of oxygen in air is higher than that of arterial blood, and the partial pressure of carbon dioxide is lower than that of arterial blood. According to the law of gases, the higher partial pressure flows to the lower partial pressure, which changes both the pO2 and pCO2 in the blood and renders it worthless for measurement.
16. What are the causes of errors in blood gas analysis in the pre-analytic phase of blood sample analysis? How can they be prevented?
The presence of air bubbles in the sample affects the parameter pO2, which should be removed immediately.
Precipitation in the sample, affecting the parameters Hct, pO2, pCO2, mix the sample before injecting into the analyzer.
Hemolysis, affecting parameters cK+, cCa2+, should avoid violent mixing, avoid storage temperature below 0°C.
Metabolism, which affects the parameters pO2, pCO2, cGlu, and cCa2+, should be avoided and stored at 0-4°C if necessary.
Sampling equipment structure, needle diameter is too small easily cause hemolysis, affect the parameters cK+, cCa2+, should choose the appropriate sampling equipment.
Liquid heparin causes dilution, affects parameters electrolytes and metabolites, Hct, pCO2, should use dry heparin tablets.
Heparin intervention affects, affects parameters electrolytes, especially cCa2+, electrolyte balanced heparin should be used.
Mixing of arterial blood into venous blood, affecting parameters pO2, sO2, standard sampling techniques should be used.
Unstable patient status, affecting parameters pH and blood gases, should be ventilated and adjusted for 20 minutes before sampling, informing the patient of the sampling procedure.
Leaking red blood cells, which affects the parameter cK+, should be stored at a temperature of 0-4°C for up to 30 minutes.
Placement in sunlight or other lights affects the parameter ctBil, the sample should be placed out of the light and measured as soon as possible, and the lights should be turned off before blood collection from patients undergoing phototherapy.
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