Hemostasis Flashcards
4 Steps Involved in Primary Hemostasis
- Adhesion of plts to damaged vascular wall
- Activation of plts
- Aggregation of plts
- Production of fibrin
What do each of the 4 steps of primary hemostasis require?
Adhesion requires VIII:vWF
Activation requires thrombin (Factor IIa)
Aggregation requires ADP and thromboxane A2
Production of fibrin requires all the pathways
What is the normal plt count?
Plts have an average life-span of _____ days.
150,000-400,000 cells/mL
8-12 days
Approx. ____% of the plt pool is sequestered in the spleen.
33%
When vascular endothelium is damaged and the subendothelium of the blood vessel is exposed, vWF anchors plts to the _____ layer of the _______.
Collagen
Subendothelium
vWF is synthesized and released by ________.
Endothelial cells
What is the most common inherited coagulation defect?
von Willebrand’s disease
____________ should be suspected in any patient with an increased bleeding time despite a normal plt count and normal clot retraction.
von Willebrand’s disease
What is the first line treatment for von Willebrand’s disease?
DDAVP - causes release of endogenous stores of vWF
Increased plt adhesion in 30 min that lasts for 4-6 hrs
SE in children = hyponatremia
*DDAVP causes thrombocytopenia in type 2B von Willebrand’s disease
Other options: cryoprecipitate, Factor 8
Cryoprecipitate contains which factors?
Factors 1, 8, 13
After plt activation by thrombin (Factor IIa), what 2 mediators are released?
- Thromboxane A2
- ADP
*These 2 mediators promote plt aggregation by uncovering fibrinogen receptors - fibrinogen (Factor I) attaches to its receptors and links the plts
The fibrinogen receptor is known as…
GPIIb/IIIa
Fibrinogen (Factor I) _______ plts.
Aggregates
How does aspirin work?
Renders cyclooxygenase I non-functional
Acetylation of cyclooxygenase
Prevents the conversion of arachidonic acid to thromboxane A2
WithOUT thromboxane A2 - plt aggregation is impaired
Persists for the life of the plt (8-12 days)
What is the rate-limiting enzyme in the conversion of arachidonic acid to thromboxane A2?
Cyclooxygenase
NSAIDs vs. Aspirin
Produce the same effects as aspirin BUT the depression of thromboxane A2 production is temporary (approx. 24-48 hrs) NOT permanent like aspirin (8-12 days)
How does clopidogrel (Plavix) work?
Anti-ADP agent
Persists for the life of the plt (8-12 days)
How does Eptifibatide and Abciximab work?
Anti-fibrinogen receptor (GPIIb/IIIa) drugs
Result - no linking of plts
What is the most common acquired blood clotting defect?
Inhibition of cyclooxygenase production by aspirin and NSAIDs
Most common cause of plt dysfunction
List the synonyms for clotting factors I, II, III, IV, VIII, XIII.
I Fibrinogen II Prothrombin III Tissue factor IV Calcium VIII:vWF von Willibrand's XIII Fibrin-stabilizing factor
All clotting factors are from the liver EXCEPT ____________.
3: vascular wall, traumatized cells
4: diet
8: vascular endothelial cells
Which clotting factors are Vit K dependent?
2, 7, 9, 10
Protein C, S
Explain the role of fibrin in blood coagulation.
After plts aggregate, fibrin is woven into plts and cross-linked
Cross-linking of fibrin strands requires Factor XIII
Now the clot is insoluble and stable!
Extrinsic Pathway
Damage outside of blood vessel
Release of thromboplastin/Factor 3/tissue factor
7 is activated
3a + 7a + 4 = 10 is activated
Intrinsic Pathway
Exposure of blood to collagen 12 is activated 11 is activated 9 is activated 9a + 8:Ca + 4 = 10 is activated
Final Common Pathway
10a + 5a + 4 = 2 is activated (prothrombin to thrombin)
Thrombin (2a) converts fibrinogen (1) to fibrin (1a)
In the presence of Factor 13, fibrin cross-linking occurs
What is the primary physiologic initiator of coagulation?
Thromboplastin
Factor 3
What helps position clotting factors on the surface of the plt so biochemical rxns can occur?
Calcium
Coumadin acts on the _________ and final common pathways.
Coumadin is assessed by _____ and _____.
Extrinsic
PT and INR
Heparin acts on the _________ and final common pathways.
Heparin is assessed by _______ and ______.
Intrinsic
PTT and ACT
Hemophilia A What is it? Cause? Affects males or females? Is it common? Treatment?
Factor 8:C deficiency Sex-linked recessive genetic disorder Carried by female, affects males 2nd most commonly inherited coag disorder Tx - FFP, cryoprecipitate, 8 concentrate
Hemophilia B
What is it?
Treatment?
Christmas disease
Factor 9 deficiency
Tx - 9 concentrate
What is the most important clue to a clinically significant bleeding disorder in an otherwise healthy patient?
History
What is the most common reason for coagulopathy in patients receiving massive blood transfusions?
Lack of functioning plts
Plts in stored blood are nonfunctional after how many days?
1-2 days
Abnormalities of coagulation owing to dilution of what 2 factors may also be an issue other than lack of functioning plts in a patient who is receiving massive blood transfusions?
- Factor 5
2. Factor 8
What is the only acceptable clinical indication for transfusion of PRBCs?
To increase the oxygen carrying capacity of blood
What factors are present in FFP?
ALL factors EXCEPT plts
One unit of PRBCs will increase Hct by ____% or 1 g/dL.
3-4%
*1 mL/kg PRBCs will increase Hct 1%
One unit of plts will increase plt count by ________ mm3.
5,000-10,000/mm3
How does heparin work?
Heparin binds to ATIII
Increases the effectiveness of ATIII 1,000-10,000x
What is the purpose of antithrombin III?
Activated ATIII binds to Factor 2a (thrombin) and Factor 10a (to a lesser degree 9, 11, 12)
After binding, ATIII removes them from circulation
Anticoagulates the blood
Where is ATIII made?
ATIII strongly inhibits which 2 factors?
ATIII partially inhibits which 3 factors?
ATIII is a required cofactor for what?
Liver
Factors 2a, 10a (final common pathway)
Factors 9a, 11a, 12a (intrinsic pathway)
Heparin
Acquired ATIII deficiency states are found in patients with…
Cirrhosis of the liver
Nephrotic syndrome
What is the most common reason a patient is unresponsive to heparin?
What would you do to fix it?
An ATIII deficiency Give FFP (includes all coag and anticoag factors made by the liver)
How does warfarin work?
Binds to the Vit K receptor in the liver
Inhibits production of the Vit K dependent clotting factors (2, 7, 9, 10)
*D/c 3-5 days pre-op
How does protamine work?
Combines electrostatically/ionically with heparin
Protamine is positively charged (basic), heparin is negatively charged (acidic)
*Neutralization rxn
What is an option if the patient has developed heparin-induced thrombocytopenia and you still need anticoagulation?
Direct thrombin inhibitors
Hirudin, Ximelgatran, Argatroban
Coagulation Tests - Normal Values Bleeding Time Plt Count PT PTT ACT Fibrinogen
Bleeding Time: 3-10 min Plt Count: 150,000-400,000 cells/mL PT: 12-14 sec PTT: 25-35 sec ACT: 80-150 sec Fibrinogen: > 150 mg/dL
Describe the clot-busting role of plasmin.
Plasminogen (inactive form of plasmin) is incorporated into a clot as the clot is formed
Tissue-type plasminogen activator (tPA) and urokinase-type plasminogen activator (uPA) convert plasminogen to plasmin
Plasmin breaks down fibrin
Where is plasminogen synthesized?
Liver
Facts about tPA
Incorporated into the forming clot
Produced by endothelial cells
Release is stimulated by thrombin and venous stasis
What is the most widely used thrombolytic agent for intra-arterial infusion into the peripheral arterial system and grafts?
Urokinase
How does aprotinin work?
Anti-fibrinolytic agent
Inhibits plasmin
Fibrin breakdown is slowed
Decrease intra-op blood loss
How does epsilon aminocarproic acid (Amicar) and tranexamic acid work?
Displace plasmin from fibrin
Prevent the breakdown of fibrin
What is the result of inhibiting plasmin?
Fibrin that is formed breaks down slowly
So bleeding is decreased
What are the risks of aprotinin?
Increases the risk of perioperative MI
May exacerbate renal dysfunction
May cause a primary allergic rxn after the first dose
May cause a severe anaphylaxis after a second dose or greater dose
Name 4 commonly encountered problems associated with abnormal hemostasis.
- DIC
- Liver disease
- Renal disease - uremia
- Multiple transfusions
Disseminated Intravascular Coagulation (DIC)
Describe.
Diagnosis?
Manifestation of an underlying disease process
No lab test for DIC
Lab tests reflect consumption of clotting factors + enhanced fibrinolysis
What OB emergencies are associated with DIC?
Abruptio placentae
Amniotic fluid embolism
What are the most common precipitating factors for acute DIC in surgical patients?
Shock
Ischemia
Infection
Lab Abnormalities in DIC
Decreased: plts, Factors 1, 2, 5, 8, 13
Increased: fibrin degradation (split) products
What is the most common cause of an isolated high PT?
Liver disease
How does liver disease affect coagulation?
What is the Tx?
Thrombocytopenia from hypersplenism
Increase lytic activity d/t poor clearance of tPA
Plt dysfunction from elevated fibrin split products
Synthesis of ALL coag factors is decreased (except Factor 8)
Tx - replace clotting factors with FFP, cryoprecipitate, and Vit K
How does uremia affect coagulation?
What is the Tx?
Plt dysfunction - impaired adherence and synthesis of thromboxane A2 and ADP
Fibrinogen and other clotting factors are decreased
Fibrinolytic system is impaired
Tx - dialysis, elevation of Hct, cryoprecipitate, DDAVP
Are plt transfusions helpful in uremia?
NO, they are ineffective
The transfused plts rapidly become abnormal
What are the issues associated with massive blood transfusions?
Deficiencies of plts, Factors 5 and 8
Diffuse bleeding during massive transfusion is generally caused by…
Thrombocytopenia
What is the best test of primary hemostasis or plt function?
Bleeding time
What antiplatelet agent prevents ADP-induced plt aggregation?
Ticlopidine
*D/c 14 days prior to surgery
Post-op bleeding with continued oozing from wounds and catheter sites suggests what disorder?
DIC
What is DDAVP?
Analogue of ADH
Used as a substitute for ADH to concentrate the urine
Used to treat von Willebrand’s (Type 1) - stimulates the release of existing vWF from endothelial cells
What is the onset time of heparin?
< 1 min
What 3 problems can administration of protamine cause?
- Systemic hypotension
- Pulmonary HTN
- Allergic rxns
* Adverse events are d/t histamine release
What is the max recommended dose of Protamine?
50 mg within 10 min
*Rapid injection may cause histamine relase - facial flushing, bronchoconstriction, tachycardia, hypotension
What is the protamine dose?
1 mg of protamine for every 100 units of heparin predicted to still be circulating
What are the 3 antidotes of warfarin?
- Vit K
- Fresh whole blood
- FFP
When should the last dose of LMWH be given prior to surgery ?
12 hrs before the procedure
*Restart 12 hrs after the procedure
Neuraxial interventions should be delayed ___ hrs after a dose of LMWH.
10-12
If a neuraxial cath is in place and a dose of heparin/LMWH is given, how long should you wait before removing the cath?
Heparin - 2-4 hrs WITH a normal PTT or ACT (wait 1 hr after removal b4 redosing)
LMWH - 10-12 hrs (wait 2 hrs after removal b4 redosing)
Erthropoietin
Where is it made?
What stimulates the release?
What does it do?
Kidneys make 90%, liver makes 10%
Released in response to hypoxia
Stimulates bone marrow to produce and release RBCs
*At high altitudes, inspired PO2 and PaO2 are low - erthropoietin is stimulated
What is the normal life span of a RBC?
120 days
Where dose the breakdown of Hgb occur? What are the breakdown products?
Liver
Iron + porphyrin
*Porphyrin is converted to bilirubin
What globin chains does normal Hemoglobin A have?
2 beta globin chains
2 alpha globin chains
What is the most important determinant of blood viscosity?
Hematocrit
What clotting factor is not a plasma protein?
Factor 4 calcium
What is the function of Protein C?
Vit K dependent anticoagulant
Thrombin (2a) activates protein C
Protein C then promotes fibrinolysis by… Promoting release of tPA from endothelial cells
Destroying plasminogen activator inhibitor
Cleaves Factors 5a and 7a
What abnormality would be found with several days of aspirin therapy?
Prolonged bleeding time
What are 5 compensatory mechanisms to increase oxygen delivery in chronic anemia?
- Increased CO
- Increased 2,3 DPG levels
- Increased P50 (right shift)
- Increased dissolved O2
- Decreased blood viscosity - increased flow
Aplastic anemia is due to what?
What is the most common cause?
Lack of functioning bone marrow
Cancer chemotherapeutic drugs
Megaloblastic anemia aka pernicious anemia develops when their is a deficiency of what?
Lack of either Vit B12 OR folic acid
RBCs fail to mature
RBCs are large and immature
What kind of RBCs result in iron deficiency anemia?
Hypochromic
Microcytic
Deficiency in glucose-6-phosphate dehydrogenase (G6PDH).
What is the most common clinical manifestation of this disorder?
What % of the black population?
What 2 drugs should be avoided?
Chronic hemolytic anemia 1% of the black population 1. Nitropursside 2. Prilocaine *Vulnerable to cyanide toxicity Also: Aspirin, PCN, Stretomycin, Sulfonamides, Quinidine, Doxorubicin, Methylene blue *May trigger a hemolytic crisis 5 days after administration
What is the hereditary defect in thalassemia?
Impaired synthesis of the…
Alpha globin strands - alpha-thalassemia
Beta globin strands - beta-thalassemia
What is the principle sign seen in thalassemia?
Anemia
What disease results from a mutation on each of the beta-globin strands of Hemoglobin A?
Has a valine instead of glutamate at the 6th position
Hemoglobin S results
Sickle cell anemia
What does it mean with the patient has sickle cell trait?
Heterozygous (HbA 60% and HbS 40%)
Sickling rarely occurs
*10% of black Americans
What hematocrits are seen in patients with sickle cell anemia?
18-30%
> 70% of total hemoglobin is HbS
*0.5% of black Americans
What is the problem of HbS?
When partial pressure of O2 is low and HbS releases O2, HbS molecules attach to each other and form aggregates - sickle shape
What 3 ways does HbS differ from HbA?
HbS has a…
- Lower affinity for O2 (P50 = 31 mmHg)
- Less soluble in aqueous solution
- Polymerizes and precipitates upon deoxygenation
At what PO2 does sickling being?
PO2 < 50 mmHg
What is the lifespan of RBCs in a patient with sickle cell anemia?
10-15 days
How do you prevent sickling?
Keep the patient warm and hydrated
Supplement with oxygen
Maintain a high CO
Avoid stasis - vasoconstriction, tourniquets, pressure
What is the goal of partial exchange transfusion in a patient with sickle cell disease?
Increase the normal Hgb to 50% and achieve a Hct of 35-40%
What are the most abundant factors in FFP?
Factor 5 and 8
Must FFP be ABO compatible?
Yes
Which factor has the shortest 1/2 life?
Factor 7
4-6 hrs
Does FFP or cryoprecipitate have more fibrinogen in it?
Cryoprecipitate
Virchow’s Triad
- Endothelial injury
- Stasis or turbulent blood flow
- Hypercoagulability
What is thrombin time (TT)?
Evaluates the ability of thrombin to convert fibrinogen to fibrin
Normal TT 9-11 sec
Does plt count measure plt function?
NO - bleeding time measures quality and quantity of plts
*Bleeding time is NOT a reliable test of clotting - BUT it is the best test of plt function
Spontaneous bleeding occurs when plt count falls below…
20,000 per mL
What 3 herbals can cause anemia?
- Garlic
- Ginseng
- Ginkgo
* D/c 2 weeks prior to surgery
Which is of greatest cause for concern? Increased PT Increased PTT Increased bleeding time Increased ACT
Increased bleeding time