saturday 2:15 lecture

Tourniquet Application and Hemoconcentration

• Tourniquet Analogy:

  • A tourniquet is compared to a traffic jam, slowing blood flow back to the heart.

  • Used correctly, it helps in blood sample collection but can cause issues if left on too long or too tight.

• Potential Issues:

  • Too Tight or Too Long:

    • Leaving the tourniquet on longer than one minute can lead to hemoconcentration.

    • Blood is still trying to return to the heart despite the tourniquet causing constriction.

    • Plasma can still pass through narrow spaces but red blood cells (RBCs) cannot.

  • Analogies for Cell Sizes:

    • RBCs are likened to semis (large), platelets to motorcycles (small), and white blood cells to Priuses (medium).

    • RBCs get stuck when trying to pass through constricted areas due to their size.

• Hemoconcentration Impact:

  • Leads to concentrated samples skewing test results, particularly affecting blood counts.

  • Important to ensure tourniquet application is correct and timely.

Factors Leading to Hemoconcentration

• Tourniquet Application:

  • Time: If the tourniquet is too tight, hemoconcentration can occur in as little as 30 seconds.

  • Fist Pumping:

    • Encourages potassium and other muscle-related substances to elevate in the blood.

    • A closed fist is acceptable, but continuous pumping can lead to rapid hemoconcentration.

• Mechanics of Blood Flow:

  • Squeezing a hand pushes blood out of capillaries, creating a concentrated area when blood is taken.

  • Color changes in the hand demonstrate changes in blood flow.

Hemolysis Explanation

• Definition:

  • Hemolysis refers to the destruction of red blood cells, which can affect laboratory results.

  • Hemolysis can occur when blood is under excessive pressure, particularly from a tourniquet or when cells are forced through narrow openings.

• Causes of Hemolysis:

  • Prolonged Tourniquet Use and Fist Pumping: Leads to excessive pressure, causing RBCs to burst.

  • Needle Positioning:

    • Incorrect angles can cause RBCs to break against the vein walls.

    • Being partially in the vein can restrict blood flow, adding pressure on cells.

Techniques to Avoid Hemolysis

• Using Appropriate Needle Sizes:

  • Smaller needles can lead to higher hemolysis rates due to increased pressure on cells.

  • Preferably, use larger gauge needles (21 or 22 gauge) for venipuncture to prevent hemolysis.

• Correct Syringe Use:

  • Pulling the plunger back too quickly creates excessive pressure, leading to hemolysis.

  • Match the speed of pulling the syringe to the blood flow speed to minimize risk.

Other Hemolysis Factors

• Impact of Dropping Tubes:

  • Dropping blood tubes can lead to hemolysis due to sudden impact.

• Inverting Tubes:

  • Aggressive inverting can also cause hemolysis.

Understanding Blood Contamination Risks

• Contamination Sources:

  • Bacteria from Skin: Not properly cleaning the site can lead to contamination.

  • Additive Contamination: Drawing improperly or using expired tubes can skew results.

Complications in Blood Draws

• Patient Complications:

  • Conditions like burns, scars, burns, or tattoos can affect visibility and access to veins.

  • Edema: Swelling increases the distance to veins, complicating access.

  • Scar Tissue: Can develop from repeated punctures, making veins hard to locate and access.

• Effect of IV Drug Use:

  • Frequent use causes significant scar tissue and limits accessible veins.

  • Plasma donations can lead to identifiable scars, allowing venipuncture from those sites, as they often remain accessible despite scarring.