Vacuum Information and Courses from MediaLab, Inc.
These are the MediaLab courses that cover Vacuum and links to relevant pages within the course.
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|A process by which bacteria or other biological material are preserved through freeze drying under vacuum is termed:||View Page|
Insufficient blood volume may cause erroneous test results, and specimen rejection. When blood flow stops, it can mean several things:The bevel of the needle may be pressed against the wall of the blood vessel. If this is the case, moving the needle slightly may cause blood to begin flowing again.The vein may have collapsed due to the vacuum of the tube. If moving the needle slightly does not re-establish blood flow, you will have to recollect the patient.The needle may have gone all the way through the vein. Pulling the needle back slightly may cause blood to resume flowing.
The tube you are using may have insufficient vacuum. Try another tube. Never vigorously probe the patient's arm with a needle. At the first sign of discomfort the needle should be withdrawn. The patient may then be redrawn be yourself or another phlebotomist.Relevant topics: Insufficient volume, Partial collection tubes, What if no blood flows
|Multiple draw needles|
Multiple draw needles are used with vacuum collection tubes.They allow the collection of blood into multiple vacuum collection tubes during a single venipuncture.
They have a retractable sheath over the portion of the needle that penetrates the blood tube.
|Blood collection tubes: introduction|
A blood collection tube generally consists of a glass or plastic tube with a rubber stopper. It has a vacuum so that blood will flow into the tube.
Blood collection tubes may contain anticoagulants and/or other chemical additives.
|Butterfly needles continued|
Butterfly needles may be used with a syringe or a holder and vacuum collection tube system.
They are usually 21, 23, or 25 gauge.
|Syringe - Syringe blood collections|
Syringes may be used to collect blood from patients having small or delicate veins that might be collapsed by the vacuum of the evacuated tube system.Syringes may also be used to collect blood culture specimens.
|Syringe - Transferring blood to collection tubes|
After collecting the blood specimen into a syringe, properly activate the appropriate safety device, and dispose of the needle in a sharps container.Attach the syringe to a blood transfer device by twisting the needle tip into the hub of the device.Push a vacuum blood collection tube into the holder of the transfer device, and let the tube fill to the appropriate level.
Insufficient blood volume (short draws) within a collection tube containing anticoagulant will result in an incorrect ratio of blood to anticoagulant, and yield incorrect test results.Short draws can be caused by: A vein collapsing during phlebotomy.The needle coming out of the vein before the collection tube is full.Loss of collection tube vacuum before the tube is full. (Always keep extra tubes on hand.)
Preanalytical ErrorWhat is it?How does it happen?What is the result?HemolysisRed blood cells (RBCs) break and release contents of cell into plasma.Needle incorrectly positioned in vein; cells forced to squeeze through opening. Needle gauge too small; slow blood return into tube. Vigorous mixing or shaking of tube. Alcohol on skin that has not had sufficient time to dry. Some test results may be falsely elevated. (Potassium is especially affected by hemolysis.) Patient may have to be re-drawn. Clotted specimenClumped or clotted cells in specimen that requires anticoagulated or whole bloodInsufficient mixing of blood with anticoagulant in tube. Delay in mixing tube. Slow filling tube. Inaccurate test results for cell counts and clotting studies. Patient may have to be re-drawn. Tube filled to incorrect volumeToo little or too much blood in tube.Tube removed from needle too quickly. Vacuum in tube has been compromised due to use of tube past the expiration date (Results in a short fill). Manual fill of tube may lead to over-fill. Test results may be unreliable due to dilution errors. Patient may have to be re-drawn.
Fill blood collection tubes completely (until vacuum is exhausted) to ensure the correct blood to anticoagulant ratio necessary for accurate patient results. Specimens may be rejected by the laboratory if the tube is short-filled or over-filled. To avoid short-filling of tubes, the phlebotomist must ensure that the blood flow stops completely before removing the tube from the needle. When using a winged device (butterfly) to collect blood for coagulation studies (e.g., protime, aPTT), the phlebotomist must draw a light blue top "waste" tube before attaching another light blue top tube for testing. If the air in the tubing of the winged device is not displaced into a waste tube and is drawn into the tube used for testing, the tube used for testing will short-fill. The laboratory may reject the specimen because of invalid blood to anticoagulant ratio.
|Do Not Tamper With the Specimens|
A phlebotomist should not uncap a blood tube and pour blood between tubes or combine two partially filled tubes of blood into one. This may lead to over-fill of tubes and more importantly, invalid patient results. Combining two tubes with the same additive into one tube will alter the blood to anticoagulant ratio by doubling the amount of anticoagulant in the tube. When blood is being transferred from a syringe to a tube, the phlebotomist must not apply pressure to the plunger to force blood into the tube. This may cause over-filling of the tube and hemolysis of blood cells. With the aid of a transfer device, the tube will draw the amount of blood required to fill the tube based on the amount of vacuum in the tube.
|Blood Collection Systems and Devices|
The phlebotomist has a choice of several blood collection systems. Three that are commonly used are discussed on the following pages. Evacuated Tube SystemThe primary choice for a routine venipuncture that will be performed on an adult or an older child is a blood collection system that consists of a holder (or adapter), a needle that is pointed on both ends, and evacuated blood collection tubes. One end of the needle will pierce the vein and the other end will pierce the stopper of the evacuated tube so that blood will flow into the tube to fill the vacuum. A safety device is required on either the holder or the needle to comply with current standards for needle safety. Two examples of needle holders equipped with safety devices are shown on this page.
The syringe and needle combination should be the last equipment option that is considered; it is not as safe a choice as the self-contained blood collection systems because it involves more manipulation. However, the phlebotomist may choose to use a syringe to prevent vein collapse if the phlebotomist thinks that the vein is too fragile to withstand the pressure exerted by the vacuum as it pulls blood into the collection tube. A transfer device aids in the safe transfer of blood from the syringe into blood collection tubes. During blood transfer, do not manually push plunger as this may cause hemolysis of the specimen.
|Blood Tube Labeling Information|
Each tube used for blood collection is labeled by the manufacturer with important information. This information includes: tube volume in milliliters (mL), expiration date, lot number and, if applicable, the type of additive that is in the tube. Tube volume: Each tube contains a vacuum that allows a specific amount of blood to enter the tube. In a tube that contains an anticoagulant, the amount of blood that is drawn into the tube will establish the correct blood to anticoagulant ratio. Tubes not filled to the correct volume (over-filled or under-filled) may cause inaccurate test results. Expiration Date: An expiration date is stamped on all blood collection tubes, as shown in the image on the right. The tube manufacturer determines this date based on its studies of vacuum maintenance and anticoagulant effectiveness. The expiration date should be checked routinely; tubes that are past the expiration date should be discarded.If a blood collection tube is used past its expiration date, the vacuum may not draw the amount of blood needed to fill the tube completely. Short-filled tubes may not be acceptable for testing and the specimen would have to be recollected. If the tube contains an anticoagulant, it may not work effectively (may not prevent the blood from clotting). Lot Number: A lot number listed on the tube identifies a specific group of tubes that were manufactured at the same time. This information is important to know if a problem is identified with several collection tubes. If the defective tubes are all part of the same lot number, the manufacturer should be notified for replacement of the tubes. Additive: Most blood collection tubes contain a type of additive or chemical that, when mixed with the blood, will yield a specimen acceptable for testing. The various types of additives that are contained in blood collection tubes are discussed on the following page.
|Handle With Care|
Equipment: To successfully enter a hand vein, the phlebotomist must choose equipment that will allow needle entry at a very small angle. A winged device with a small gauged needle of 3/4 inch length is most often used to obtain blood from a hand vein. A syringe is usually attached to the end of the tubing of this device. By using a syringe, the phlebotomist can control the amount of pressure on the vein and avoid vein collapse. Evacuated tubes may collapse a vein by exerting too much pressure on the delicate vein. If available, smaller tubes containing less vacuum may be used.Insertion angle: The angle at which the needle is inserted into a hand vein is smaller compared to the angle of needle insertion into veins of the antecubital area. When drawing from a hand, the needle should be inserted into the vein at approximately a 15 degree angle to allow easier access of the surface hand veins. By inserting the needle at this angle, the risk of the needle going "through" the vein and puncturing the bony structures underneath is reduced.
|A phlebotomist was collecting a STAT prothrombin time (PT) and complete blood count (CBC) on a patient when blood flow unexpectedly stopped. The lavender top tube being drawn at the time was less than one-third full. The light-blue top tube had already been drawn for the prothrombin time.Before resorting to a second venipuncture, which of the following procedures should be attempted in order to adequately fill the lavender top tube?||View Page|