critical care medicine
How To Do Venous Blood Sampling
Step by Step Description of Venous Blood Sampling
Do a preliminary inspection (nonsterile) to identify a suitable vein: Apply a tourniquet, have the patient make a fist, and palpate using your index finger to locate a large-diameter vein that is nonmobile and has good turgor. To help distend and locate veins, tap a potential site with your fingertips. It may help to allow the arm to hang down, increasing venous pressure. Use a vein-finder device if a suitable vein is not readily seen or palpated. After identifying a suitable cannulation site, remove the tourniquet. Apply anesthetic if it is being used and allow adequate time for it to take effect (eg, 1 to 2 minutes for gas injector, 30 minutes for topical). Cleanse the skin site with antiseptic solution, beginning at the needle-insertion site and making several outwardly expanding circles. Wait for the antiseptic solution to dry completely. If applyingpovidone-iodine, wipe it off with alcohol and allow the alcohol to dry. If blood is being obtained for blood cultures, vigorously cleanse the site with alcohol for 30 seconds, allow the alcohol to dry, and then swab in outwardly expanding, overlapping circles usingchlorhexidineorpovidone-iodine. Wait for the antiseptic effect to occur (1 minute forchlorhexidineor 1.5 to 2 minutes for iodine). Wipe offpovidone-iodinewith alcohol and allow the alcohol to dry. For children, swab the site 3 times using only alcohol. After this point, do not touch the skin site with any nonsterile item. Try to access the vein efficiently and collect the blood sample within 30 seconds after tourniquet placement. Do not leave the tourniquet on for>1 minute. Reapply the tourniquet proximal to the selected insertion site. Do not have patients make a fist or let their arm hang down during the blood sampling, because these maneuvers may cause various erroneous laboratory values (eg, increased potassium, lactate, phosphate). Palpate with your gloved finger to locate the middle of the target vein. Apply gentle traction to the vein distally using the thumb of your nondominant hand to prevent the vein from moving. Traction may not be necessary for larger veins of the forearm or antecubital fossa. Tell the patient that the needlestick is about to happen. Insert the needle proximally (ie, in the direction of venous blood flow), with the bevel facing up, along the midline of the vein at a shallow angle (about 10 to 30 degrees) to the skin. Blood will appear in the needle hub (called a blood flash ) when the needle tip enters the lumen of the vein. Stop advancing the needle, lower the needle to better align it with the vein, and advance it into the vein an additional 1 to 4 mm, to ensure that it stays in position during blood collection. If no flash appears in the hub after 1 to 2 cm of insertion, withdraw the needle slowly. If the needle had initially passed completely through the vein, a flash may now appear as you withdraw the needle tip back into the lumen. If a flash still does not appear, withdraw the needle almost to the skin surface, change direction, and try again to advance the needle into the vein. If rapid local swelling occurs, blood is extravasating. Terminate the procedure: Remove the tourniquet and the needle and apply pressure to the puncture site with a gauze pad (a minute or 2 is usually adequate unless the patient has a coagulopathy). Keep the needle motionless. Begin to withdraw the blood sample and, when blood begins to flow, remove the tourniquet. When using vacuum tubes, push each tube fully into the tube holder, use care to avoid dislodging the needle from the vein. Fill multiple collection tubes in the proper sequence.* After removing a tube from the holder, gently invert the tube 6 to 8 times to mix the contents;do not shake the tubes. When using a syringe, pull back on the plunger gently to avoid damaging the blood cells or collapsing the vein. When blood collection is complete, gently hold a folded gauze square at the venipuncture site with your nondominant hand, and in one motion remove the needle and immediately apply pressure to the site with the gauze. Remove the tourniquet if you did not do so earlier. Have the patient or an assistant continue to apply pressure to the site. If you used a syringe to collect the blood, now transfer samples to collection tubes and bottles;* either insert the needle directly into the tops of the vacuum tubes, or remove the needle and attach a vacuum tube holder to the syringe. Do not inject blood into vacuum collection tubes; allow the vacuum to draw the blood into the tube. After blood has been added to a tube, gently invert the tube 6 to 8 times to mix the contents;do not shake the tubes. Deploy safety cover over the exposed needle. Deposit used blood-collection devices (with needles) into a sharps container. Do not recap non-safety needles prior to disposal unless a sharps container is not immediately available. Dress the site with gauze and tape or a bandage. * When multiple blood tests are to be done, blood should be allocated to the collection tubes in a proper sequence; first cultures, then tubes with anticoagulant, and then others. Note that the rubber tops of blood-culture bottles must be properly disinfected prior to introducing the blood sample (eg, by scrubbing each top with separate 70% alcohol wipes for 30 seconds and allowing it to air-dry). 