Coagulation Recap Flashcards
Explain the characteristics of the resting vs activated platelet membrane.
Negatively charged PS and PE are normally on the inner surface and neutral phosopholipids are on the outer surface (PC and syringomyelin). When the platelet is activated, PS and PE are exposed on the outer surface (now negatively charged).
Discuss actions of Flippase.
Moves PS and PE internally
Discuss actions of Floppase.
Moves PC outward
Discuss actions of Translocase.
The term for flippase/floppase combined- both are ATP dependent
Discuss actions of Scramblase.
Inhibits Translocase (ATP independent), leading to platelet activation.
Name the 4 most important platelet receptors and their functions:
- Integrin αIIbβ3 (previously GPIIb/IIIa): binds fibrinogen, fibrin, VWF under low shear conditions
- Integrin α2β1: binds collagen
- GP Ib-IX-V Complex: Binds VWF and thrombin under high shear conditions
- GP VI: binds collagen
List the 3 stages of thrombus formation during primary hemostasis.
Initiation
Extension
Stabilization/perpetuation
Discuss Initiation stage of thrombus formation during primary hemostasis.
Tethering and capture of platelets by exposure of subendothelial collagen leading to a monolayer of activated platelets
Discuss Extension stage of thrombus formation during primary hemostasis.
Additional platelets passing the area become activated due to locally high concentrations of platelet agonists.
Discuss Stabilization/perpetuation stage of thrombus formation during primary hemostasis.
Platelet plug is stabilized by binding between platelets/clot retracts.
How is initiation different under low and high shear conditions?
Under low shear, platelets bind directly to exposed collagen. Under high shear VWF is exposed which binds to collagen, then GP Ib-IX-V binds the plt to VWF (platelet “tethering”).
Name 8 ways to test platelet function.
- Blood smear or platelet count
- Clot reatraction test
- BMBT
- Platelet function analyzer (measures “closure time” in high shear conditions)
- Aggregometry (uses light transmission- more light is transmitted as the platelets aggregate)
- Cone and plate analyzers (CPA)- platelets adhere to a matrix in high shear conditions
- Viscoelastic analyzers
- Flow cytometry: assesses actual platelet receptors, etc by labeling the molecule or receptor of interest
Draw and label the classic coagulation cascade.
List the 4 phases of coagulation in the cell based model.
- Initiation
- Amplification
- Propagation
- Termination
Explain the Initiation phase of coagulation in the cell based model.
TF initiates the “extrinsic” pathway.
Factor 7 (circulating in activated form) binds TF, which activates X to Xa (small amount).
This forms a small amount of thrombin.
Xa can’t leave the cell surface (inactivated by AT and TFPI), but thrombin can.
Explain the Amplification phase of coagulation in the cell based model.
Small amount of thrombin diffuses away from the cell and activates stuff (platelets, FXI 🡪 FXIa, VWF cleaved off of FVIII 🡪 FVIIIa).
Explain the Propagation phase of coagulation in the cell based model.
FVIIIa and FIXa form “tenase” on the platelet surface which cleaves X to Xa (large amount) 🡪 large amount of thrombin formation (burst) 🡪 fibrin formation.
Thrombin activates FXIII to cross link fibrin.
Explain the Termination phase of coagulation in the cell based model.
Thrombin binds to thrombomodulin, which activates Protein C (along with cofactor Protein S) 🡪 inhibition of further thrombin formation. Antithrombin and TFPI also help to stop coagulation.
Explain the basic process of fibrinolysis.
Plasminogen is activated to plasmin, which breaks up fibrin into FDP’s.
List 2 fibrinolysis activators
Plasminogen activators:
tPA and uPA
List 4 fibrinolysis inhibitors:
- Plasminogen activator inhibitor (PAI)
- A-2 antiplasmin
- A-2 macroglobulin
- Thrombin activatable fibrinolysis inhibitor
Action of Plasminogen activator inhibitor (PAI)
Fibrinolysis inhibitor
Inhibits tPA and uPA
Action of A-2 antiplasmin and A-2 macroglobulin.
Fibrinolysis inhibitor
Inhibit plasmin
Action of Thrombin activatable fibrinolysis inhibitor
Fibrinolysis inhibitor
prevents binding of plasmin while thrombin is being produced (active clotting)
What is Virchow’s Triad?
Contributors to inappropriate thrombus formation. Vascular stasis, hypercoagulability, endothelial damage
What is a thrombus versus a thromboembolism?
Thrombus is a blood clot that forms in the vessel
Thromboembolism is when a clot or piece of clot breaks off and travels to a distant site
List diseases that predispose to hypercoagulability:
Cushing’s
Diabetes mellitus
Sepsis
SIRS- pancreatitis
Immune mediated diseases (IMHA, IMPA, etc)
Heartworm disease
Protein losing enteropathy
Protein losing nephropathy
Neoplasias- (particularly leukemia)
Post operative hemoabdomen- (particularly splenectomy)
What are the 2 different types of clots? How are they treated differently?
“White clot”: primarily platelets, form in arteries, mostly due to endothelial damage.
Treated with anti-platelet drugs.
“Red clot”: fibrin + RBC’s, form in veins, mostly due to stasis and hypercoagulability.
Treated with anti-coagulants.
What types of testing is most effective for evaluating hypercoagulability?
- Viscoelastic monitoring
- D-dimers and FDP’s
- Visualization of clots on imaging
- Measure endogenous anticoagulants (AT, Proteins C/S, TFPI)- decreased levels
- Concurrent prolonged coag times/low platelet count often indicate consumption (end-stages of DIC)
List the 3 classes of platelet inhibiting drugs and an example of each:
- ADP receptor antagonists: Plavix
- COX-inhibitors: Aspirin
- Integrin αIIbβ3 (previously GPIIb/IIIa) antagonists- block platelet/fibrinogen binding: Abciximab
Explain the mechanism of action and monitoring of unfractionated heparin. Draw a diagram!
UF Heparin:
binds to antithrombin, causing a conformational change, enhanced binding of AT to inactivate thrombin and Xa.
Can be monitored with aPTT (due to effect on thrombin) or Anti-Xa levels.
SQ or CRI.
Explain the mechanism of action and monitoring of low molecular weight heparin. Draw a diagram.
LMW Heparin:
Shorter chain compared to UF heparin.
Binds to antithrombin causing a conformational change and enhanced binding of AT to Xa.
Not long enough to inactivate thrombin.
Can only monitor with Anti-Xa levels.
Longer duration of action when given SQ.
Better bioavailability and more predictable dosing in animals.
List 5 procoagulant mechanisms in IMHA:
- Induction of TF expression on monocytes through RBC phagocytosis
- Induction of TF expression on endothelial cells by inflammatory cytokines and free Hb
- Microparticles expressing TF are released by monocytes, activated plt, endothelium, and RBC’s
- Damaged RBC’s/spherocytes/retics are procoagulant (activated surface- PS positive)
- Activated platelets are procoagulant (activated surface- PS positive)
- Decreased levels of anticoagulants (ie AT)
Define DIC
An acquired disorder of hemostasis characterized by activation and perpetuation of the coagulation and fibrinolytic pathways secondary to an inciting illness.
Initially there is microvascular and large-vessel thrombosis, which can lead to hypoxia and organ damage. Eventually, a consumptive coagulopathy (both platelets and coagulation factors become deficient) occurs, which leads to clinical hemorrhage.
Expected results of PT/aPTT with DIC.
Normal or prolonged.
Expected results of PLT count with DIC.
Decreased
Expected results of Antithrombin with DIC.
Normal or decreased.
Expected results of D-Dimer/FDPs with DIC.
Elevated
Expected results of Protein C with DIC.
Normal or decreased
Expected results of Fibrinogen with DIC.
Increased, normal, or decreased
Explain the reason for bleeding and expected diagnostic test results for Von Willebrandt’s disease.
PT/aPTT:
PLT count:
vWF:
BMBT:
Reason for bleeding: vWF deficiency
PT/aPTT: N/N
PLT count: N
vWF: low
BMBT: prolonged
Explain the reason for bleeding and expected diagnostic test results for Hemophilia A.
PT/aPTT:
PLT count:
BMBT:
Reason for bleeding: Factor VIII deficiency
PT/aPTT: N/prolonged
PLT count: N
BMBT:N
Explain the reason for bleeding and expected diagnostic test results for Hemophilia B.
PT/aPTT:
PLT count:
BMBT:
Reason for bleeding: Factor IX deficiency
PT/aPTT: N/prolonged
PLT count: N
BMBT:N
Explain the reason for bleeding and expected diagnostic test results for ITP.
PT/aPTT:
PLT count:
BMBT:
Reason for bleeding: Platelet deficiency
PT/aPTT: N/N
PLT count: <20k
BMBT: prolonged
Explain the reason for bleeding and expected diagnostic test results for Brodifacoum ingestion.
PT/aPTT:
PLT count:
BMBT:
Reason for bleeding: antagonism of vitamin K epoxide reductase
PT/aPTT: prolonged (PT first)
PLT count: N to slightly low (consumptive)
BMBT: N
Draw the vitamin K cycle and show where anticoagulant rodenticide takes effect
List the 3 proposed mechanisms for acute traumatic coagulopathy.
- DIC with a fibrinolytic phenotype
- Enhanced thrombomodulin-thrombin protein C pathway
- Marked sympathoadrenal response leading to catecholamine-induced endothelial damage
Explain the proposed mechanism for acute traumatic coagulopathy:
DIC with a fibrinolytic phenotype
Severe endothelial injury, hypoxia, and ischemia 🡪 marked thrombin generation 🡪 systemic fibrin formation 🡪Massive release of tissue plasminogen activator into circulation in response to thrombin/fibrin🡪 large amounts of plasminogen convert into plasmin (hyperfibrinolysis)
Explain the proposed mechanism for acute traumatic coagulopathy:
Enhanced thrombomodulin-thrombin protein C pathway
ATC not initially consumptive, but evolves from decreased thrombin degradation & increased thrombomodulin activity (from severe tissue injury & profound hypoperfusion) 🡪 enhanced activation of thrombin-thrombomodulin protein C anticoagulant pathway 🡪 protein C inhibits factor Va & VIIIa & suppresses plasminogen activator inhibitor-1 activity & thrombin activatable fibrinolytic inhibitor (TAFI) formation
Explain the proposed mechanism for acute traumatic coagulopathy:
Marked sympathoadrenal response leading to catecholamine-induced endothelial damage
Tissue injury 🡪 dose dependent sympathoadrenal response & release of catecholamines into circulation 🡪 damage endothelial glycocalyx 🡪 changes endothelium from antithrombitic to prothrombotic 🡪 body attempts to balance this by increasing antithrombotic & fibrinolytic components in blood (heparin-sulfate, soluble thrombomodulin, and tissue-plasminogen activator shed from damaged glycocalyx into blood)
List the 2 main initiators for ATC.
shock and tissue hypoperfusion
tissue injury
List the 4 contributing factors for ATC.
metabolic acidosis
hypothermia
hemodilution
systemic inflammation
What is the “lethal triad of death”?
Coagulopathy
metabolic acidosis
hypothermia
Explain the general recommended resuscitation strategy for hemorrhage to help reduce the risk of ATC
- Hypotensive resuscitation/permissive resuscitation: resuscitate only to MAP 60/SAP 80 for short term until hemorrhage is controlled. NOT if concurrent head trauma.
- Resuscitate bleeding with blood products (ideally fresh whole blood or 1:1:1), avoid high dose crystalloids
- Rapid control of hemorrhage- consider “damage control surgery”
- Consider antifibrinolytics (TXA or ACA)
Label the viscoelastic tracing (TEG and ROTEM) and explain what each section means.
- TEG= R-time
- ROTEM= CT
- Time to beginning of clot formation - TEG = K-time
- ROTEM= CFT
- Time from the end of R until 20mm apart
- Rate of clot formation - TEG = α -angle
- Rotem = α -angle
- The angle between the midline and the tangent to the curve
- Rate of clot formation - TEG = MA
- ROTEM = MCF
- Maximum distance between the 2 branches
- Measurement of clot strength - TEG = CL-30
- ROTEM = LY-30
- % clot lysis at 30 minutes
- Speed of clot breakdown - Coagulation
- Fibrinolysis
Provide a brief explanation/interpretation of the TEG tracing
Thrombocytopenia or platelet function defect
Provide a brief explanation/interpretation of the TEG tracing
Decreased coagulation factors
Provide a brief explanation/interpretation of the TEG tracing
Hypercoagulable state
Provide a brief explanation/interpretation of the TEG tracing
Hyperfibrinolysis
Explain the changes in RBCs secondary to storage (“storage lesion”)
- Documented association between storage time and adverse effects in critically ill patients, septic patients, and trauma patients (including increased risk of infections)
- RBC changes: altered energy metabolism, altered rheologic properties, oxidative damage, microparticle accumulation, hemolysis
- Decrease in pH of the unit
- Accumulation of pro-inflammatory substances/cytokines
- Release of free iron, which may increase oxidative stress
- Release of microparticles containing free hemoglobin
- Increased ammonia concentration
- Increased markers of hemolysis: potassium, arginase-1, free Hb
- Free Hb scavenges nitric oxide – less NO in capillaries may lead to decreased organ perfusion and MODS
What are strategies to combat storage lesions?
Consider using newer units (<14 days) in very critical patients or patients with hepatic dysfunction (due to ammonia)
Leukoreduction
Appropriate storage
Name that transfusion reaction and explain an appropriate response.
Patient develops a 103.5 fever mid-way through transfusion. Otherwise stable.
Febrile non-hemolytic reaction
Do nothing
Name that transfusion reaction and explain an appropriate response.
Patient develops facial swelling and hives 1 hour into transfusion
Allergic reaction
Slow or stop transfusion, give antihistamine +/- steroid
Name that transfusion reaction and explain an appropriate response.
Patient becomes tachycardic, tachypneic, hypotensive, vomits, and develops pigmenturia 20 min into transfusion.
Acute hemolytic transfusion reaction
STOP transfusion, supportive care
Name that transfusion reaction and explain an appropriate response.
Transfusion is given to a dog with bone marrow disease and PCV decreases back to baseline within 10 days.
Delayed immunologic hemolytic reaction
Do nothing
Name that transfusion reaction and explain an appropriate response.
Septic dog with no heart disease becomes dyspneic 2 hours post plasma transfusion with pulmonary infiltrates.
TRALI
Oxygen, prevent volume overload, volume limited ventilation if needed
Name that transfusion reaction and explain an appropriate response.
Cat becomes dyspneic 4 hours post transfusion with pleural effusion
Volume overload
Diuretics, O2, thoracocentesis
Define massive transfusion (there are 3 typical definitions)
- Full blood volume within 24 hours
- Half the blood volume in 3-4 hours
- > 1.5ml/kg/min of blood products over 20 min (bolus) = 90ml/kg/hr = 30ml/kg in 20 min
What treatments have shown a survival benefit in the veterinary literature for IMHA?
Prednisone
Individually adjusted doses of heparin (based on anti-Xa)
What treatments have shown a survival benefit in the veterinary literature for ITP?
Prednisone
Is elevated serum bilirubin/icterus for IMHA a positive, negative, or neutral prognostic indicator?
negative
Is elevated serum BUN for IMHA a positive, negative, or neutral prognostic indicator?
negative
Is elevated serum BUN for ITP a positive, negative, or neutral prognostic indicator?
negative
Is prolonged coagulation times for IMHA a positive, negative, or neutral prognostic indicator?
negative
Is hypercoagulable TEG for IMHA a positive, negative, or neutral prognostic indicator?
negative?
Is a HCT <20 for IMHA a positive, negative, or neutral prognostic indicator?
neutral
Is presence of melena for ITP a positive, negative, or neutral prognostic indicator?
negative
List 4 potential adverse effects of IVIG administration
1.Thrombosis/thromboembolism
2. Fluid overload- hyperosmolar solution
3. Hypersensitivity reactions
4. Acute renal failure- reported very rarely in humans, no reports in dogs
What is the significance of mild to moderate thrombocytopenia in most dogs with IMHA?
Consumption due to hypercoagulability- early DIC
List possible differentials for hemolytic anemia
- Fragmentation (ie DIC, splenic torsion, caval syndrome, hemangiosarcoma)
- Toxins (onions, garlic, acetaminophen, Zinc)
- IMHA (primary vs secondary)
- Heritable hemolysis (ie PFK deficiency)
- Infectious (mycoplasma, babesia)
- Hypophosphatemia
- Rapid osmolarity change
- Envenomation
- Histiocytic neoplasia
