Hemorrhage and Coagulation

A

Normal Blood Volume and Composition

• 1.

  Total blood volume (TBV) = 70 mL/kg total body weight (80 mL/kg for newborns)

• 2.

  Total volume red blood cells (RBCs) = TBV × hematocrit

  • a.

    Approximately 26 mL/kg for male patients, 24 mL/kg for female patients

  • b.

    Can be measured using chromium-tagged erythrocytes, but this is not often performed clinically

• 3.

  Total plasma volume = TBV × (1 − hematocrit)

B

Classes of Hemorrhagic Shock ( Table 11.1 )

• 1.

  Class I and II classically are managed with crystalloid.

  TABLE 11.1

  Classes of Hemorrhagic Shock

  	I	II	III	IV
  Blood loss (mL)	<750	750–1500	1500–2000	>2000
  Blood loss (% blood volume)	<15	15–30	30–40	>40
  Pulse rate/min	<100	100–120	120–140	>140
  Blood pressure	Normal	Normal	Decreased	Decreased
  Pulse pressure	Normal	Decreased	Decreased	Decreased
  Respiratory rate/min	14–20	20–30	30–40	>35
  Urine/output (mL/h)	>30	20–30	5–15	Negligible
  Mental status	Normal	Mildly anxious	Anxious, confused	Confused, lethargic

• 2.

  Class III and IV typically require blood products.

C

Typing, Screening, and Crossmatching

• 1.

  Typing—serologic compatibility established for donor and recipient A, B, O, and Rh antigen groups

• 2.

  Screening—tests recipient blood for presence of common antibodies (indirect Coombs test)

• 3.

  Crossmatching—tests for compatibility of recipient blood with a specific blood product to be infused. Test mixes donor’s RBCs and recipient’s serum, drawn less than 72 hours before test takes place.

D

General Blood Product Administration Guidelines

• 1.

  Allow 30 minutes for frozen products to thaw or for cold products to be warmed. Products should be warmed to 33°C–35°C before or during infusion.

• 2.

  Ensure the patient has appropriate intravenous or intraosseous access.

• 3.

  Before administration of blood product, the patient’s name, medical record number, blood product ordered, blood type, and product’s expiration date should be checked, ideally by two people together.

• 4.

  Use a standard blood filter to remove clots or large aggregates of cells.

• 5.

  Check vital signs at minimum before beginning infusion, 15 minutes into infusion, and after completion of transfusion of each unit.

A

Complete Blood Count

• 1.

  Hemoglobin (13.5–18.0 g/dL in males, 12.0–16.0 g/dL in females); hematocrit (40%–54% in males, 38%–47% in females)

• 2.

  Platelets: from 150,000 to 400,000/mm ³ ; 50,000/mm ³ is required for normal hemostasis.

B

Prothrombin Time

• 1.

  Evaluates production of vitamin K–dependent factors (II, VII, IX, X); indicates function of extrinsic pathway

• 2.

  Increased when functional volume of one or more factors is less than 50% (reference range, 12–14 seconds)

C

International Normalized Ratio

• 1.

  Developed because of laboratory variations in prothrombin time (PT) results caused by variations in thromboplastin (PT test reagent) activity; used to modulate warfarin therapy (reference, 1.0)

D

Activated Partial Thromboplastin Time

• 1.

  Evaluates function of intrinsic pathway

• 2.

  Increased when functional volume of one or more factors is less than 50% (reference range, 40–60 seconds, varies by laboratory)

E

Activated Clotting Time

• 1.

  Similar to activated partial thromboplastin time (aPTT) but designed to measure clotting time after administration of heparin. It correlates linearly with concentration of heparin in blood. Normal range 70–180 seconds, and therapeutic range varies with indication.

F

Bleeding Time

• 1.

  Evaluates platelet function and blood vessel integrity (reference range, 2.5–5.5 minutes)

• 2.

  Assessed with small cut on patient’s skin

G

Platelet Function Tests

• 1.

  Multiple available technologies, including several point-of-care tests

• 2.

  Alternative to bleeding time for diagnosis of congenital and acquired platelet disorders

H

Thrombin Time

• 1.

  Measures polymerization of fibrinogen

I

Fibrinogen

• 1.

  Normal fibrinogen levels are 200–400 mg/dL, functional level is greater than 150 mg/dL. Affects PT and aPTT when less than 50 mg/dL

J

Viscoelastic Tests

• 1.

  Point-of-care functional assessment of clot formation, strength, and lysis. Two available technologies: thromboelastography (TEG) and rotational thromboelastometry (ROTEM)

  • a.

    Similar technology and comparable results ( Fig. 11.1 )

    

  • b.

    TEG more prevalent in North America; ROTEM more prevalent in Europe

• 2.

  Useful to distinguish between medical and surgical bleeding and to guide ongoing blood product resuscitation

A

Whole Blood

• 1.

  Must be ABO identical, crossmatch required

• 2.

  Banked whole blood usually stored in 500-mL units

• 3.

  Stored at 4°C in citrate/phosphate/dextrose preservative for up to 21 days

• 4.

  Contains all blood components

  • a.

    This is a poor source of platelets, which lose function after stored for 24 hours in whole blood.

  • b.

    Clotting factors are stable in whole blood for up to 12 days, except factors V and VIII.

  • c.

    Storage lesion: Intracellular 2,3-diphosphoglycerate (DPG) and adenosine triphosphate are reduced during storage; hemoglobin dissociation curve shifts to the left (more affinity for oxygen); pH decreases; and lactate, ammonia, and potassium increase.

• 5.

  Indications

  • a.

    Used during mass casualty or military operations. May be supplied by fresh donations

  • b.

    Burn surgery—used perioperatively when large losses of blood, platelets, and bleeding factors are expected

  • c.

    Decreases donor exposure but generally less widely available than blood components

• 6.

  Autologous blood

  • a.

    This may be collected before surgery for perioperative use, although use is increasingly uncommon with improved disease screening.

  • b.

    Up to 5 units may be collected over 40 days before surgery.

  • c.

    Erythropoietin is given to hasten generation of blood cells.

• 7.

  Fresh whole blood

  • a.

    Administered within 48 hours of donation

  • b.

    May be more effective than component therapy but usually administered untested for infectious disease due to time constraints

  • c.

    “Walking blood bank”—group of donors tested frequently when transfusions are likely (military operations)

B