part 2

• Hemoconcentration

  • Tourniquet application causes localized venous stasis, or stagnation of the normal venous blood flow. (A similar term for this is venostasis, the trapping of blood in an extremity by compression of veins.)
  • This results in hemoconcentration, a decrease in the fluid content of the blood with a subsequent increase in nonfilterable large molecule or protein-based blood components such as RBCs.
• Ways to Help Prevent Hemoconcentration During Venipuncture

  • Ask the patient to release the fist upon blood flow.

  • Choose an appropriate easily recognizable vein.

  • Do not allow the patient to pump the fist.
• Hemolysis

  • Hemolysis results when RBCs are damaged or destroyed and the hemoglobin they contain escapes into the fluid portion of the specimen.
  • The red color of the hemoglobin makes the serum or plasma appear pink (slight hemolysis), dark pink to light red (moderate hemolysis), to dark red (gross hemolysis), and the specimen is described as being “hemolyzed”
• Hemolysis can erroneously elevate certain analytes, especially potassium. (There is 23 times as much potassium in RBCs as in plasma.)

  • Hemolysis also elevates ammonia, catecholamines, CK and other enzymes, iron, magnesium, and phosphate.

  • RBC counts can be decreased by hemolysis.
• IV valves are designed to prevent backflow of IV solution by allowing fluid to move in only one direction.
• Partially Filled Tubes Evacuated tube system (ETS)

  • Tubes should be filled until the normal amount of vacuum is exhausted.
  • Failing to do so results in a partially filled tube, referred to as a short draw.
  • Short-draw serum tubes such as red tops and serum separator tubes (SSTs) are generally acceptable for testing
• Excess EDTA in underfilled lavender-top tubes can shrink RBCs, causing erroneously low blood cell counts and hematocrits and negatively affecting the morphological examination of the RBCs on a blood smear.
• Excess heparin in plasma from underfilled green-top tubes may interfere with the testing of some chemistry analytes.
• Excess sodium fluoride in underfilled gray-top tubes can result in hemolysis of the specimen.
• Specimen contamination is typically inadvertent and generally the result of improper technique

  or carelessness, such as:

  • Allowing alcohol, fingerprints, baby powder, or urine from wet diapers to contaminate newborn screening forms or specimens, leading to specimen rejection.
  • Filling tubes in the wrong order of draw.
  • Ex: drawing a potassium EDTA tube before a serum or plasma tube for chemistry tests can lead to EDTA contamination of the chemistry tube and cause false hyperkalemia (high potassium) and hypocalcemia (low calcium).
• Wrong or Expired Collection Tube

  • If you are not certain of the type of tube required for a test, consult the procedure manual before collecting the specimen.
  • expired anticoagulant may allow the formation of microclots.
  • expired tubes may have lost vacuum and result in short draws if used.
• Troubleshooting Failed Venipuncture

  • important steps to remember are: stop, assess, and correct.
• Needle Position Insertion

  • use visual cues to help determine if the needle is correctly positioned in the vein.
  • Make all needle adjustments slowly and precisely to avoid injuring the patient.
• Correct needle position; blood can flow freely into the needle

  
• Needle not inserted far enough; needle does not enter the vein.

  
• Needle bevel partially out of the skin; tube vacuum will be lost.

  
• Needle bevel partially into the vein; causes blood leakage into tissue

  
• Needle bevel partially through the vein; causes blood leakage into tissue.

  
• Needle bevel completely through the vein; no blood flow obtained.

  
• Needle bevel against the upper vein wall prevents blood flow.

  
• Needle bevel against the lower vein wall prevents blood flow.

  
• Needle bevel penetrating a valve prevents blood flow.

  
• Needle beside the vein; caused when a vein rolls to the side, no blood flow obtained.

  
• Collapsed vein prevents blood flow despite correct needle position.

  
• Needle Not Inserted Far Enough

  If the needle is not inserted far enough, it may not penetrate the vein at all This can happen if the vein is located more deeply than normal (e.g., if the patient is obese or extremely overweight). In this case, there will be no blood flow at all. To correct this problem, slowly advance the needle forward until blood flow is established.