Hemostatic disorders Flashcards
What are inherited forms of hypercoagulability in animals?
None reported in vet med
What are the components of the Virchow’s triad?
- endothelial damage
- hypercoagulability
- blood stasis/altered blood flow
List how the glycocalyx prevents excessive thrombosis
- heparan sulfate makes up most of the proteoglycans of the glycocalyx - binding site for antithrombin
- binds heparin cofactor 2 and thrombomodulin
- binds TFPI
- senses shear stress –> releases NO from endothelial cells –> vasodilation, PLT inhibition
NOTE inflammation => decreases glycosaminoglycan production => integrity of glycocalyx compromised => cannot bind anticoagulants as well
List 5 substances that can activate endothelial cells to release ultralarge multimers of vWF => platelet adhesion and tethering
- TNF-alpha
- histamine
- thrombin
- bradykinin
- vascular endothelial growth factor
What cleaves ultra large multimers of vWF?
ADAMTS13
How does TF induce inflammation?
induces NFkB –> TNF alpha production
Do dogs and cats have vWF in their platelet alpha granules?
only cats
What are the contents of NETS
DNA
histones
myeloperoxidase
neutrophil elastase
Describe how antithrombin can be reduced in systemic inflammation
- consumption (from thrombin generation)
- decreased production (negative acute phase protein)
- degradation by neutrophil extracellular traps
Protein S increases APC’s inhibition of FVa and FVIII xxxxx-fold
nearly 20-fold
How are Protein C and S affected in inflammation?
- negative acute phase proteins - produced less
- APC needs TM-thrombin complex for activation - TNF-alpha downregulates TM, endotoxin-activated neutrophils release elastases which cleaves TM
How does inflammation affect fibrinolysis?
TNF-alpah and IL-1 => lead to delayed but profound PAI-1 release - more than tPa => fibrinolysis decreased
NETs integrate into clots and delay fibrinolysis
List changes contributing to a hypercoagulable state in systemic inflammation or sepsis
- TF expression (tissue damage, microparticle circulatin etc.)
- EC activation (TF expression, ultra large multimers of vWF expression, etc.)
- disruption of the glycocalyx (unable to bind and present important anticoagulants)
- decreased Protein S and C
- fibrinolysis inhibition (high PAI-1 levels, NETs inhibiting fibrinlysis)
Can you use Antithrombin activity to predict risk of thrombosis in PLN?
No, has failed to uniformly predict risk of thrombosis in people
List the procoagulant mechanism in IMHA
- excessive TF expression
- cell free heme => decreases NO bioavailability + upregulates endothelial cell adhesion molecules
- NET formation (inflammation, hypoxia, exposure to free heme)
- augmented thrombin generation from hemolysis (increased microparticles and procoagulant erythrocyte membrane)
- PLT activation showed conflicting results in studies
What are the 3 most common neoplasias to cause DIC in dogs
hemagiosarcoma
mammary carcinoma
adenocarcinoma of the lung
What coag panel changes should raise concern for a consumptive coagulopathy in patients with systemic inflammaiton?
- PLT count drop
OR - PT prolongation by 20% or more
In cats with spontaneous echocontrast, how common was coagulopathy?
in 50% in one study
How commonly are both pelvic limbs affected in FATE?
75%
How common is an underlying cardiomyopathy in FATE. How commonly has this cardiomyopathy been previously known of?
- 90%
- < 10%
What is the 5P rule of FATE?
- Pallor (purple or pale toes)
- Polar (cold extremeties)
- pulselessness
- paralysis
- pain
List diagnostic tools to differentiate for FATE
- 5Ps
- toe nail cut to the quick and not bleeding
- absence of doppler flow
- visualization of the thrombus on US
- thermal imaging
- angiography
- glucose/lactate difference of peripheral limb versus central blood
What was assessed in the BLASST study?
thrombolytic therapy with tPA compared to placebo in FATE
showed discharge rates of 45 versus 30%
What are positive and negative prognostic indicators in FATE?
unilateral limb paralysis (70% survival to discharge versus 25% if both limbs affected)
negative:
* lower rectal temp (most consistent across studies)
* CHF present
* lower HR
* higher P cc
* absence of motor function
* higher affected limb lactate at admission
List the complications of thrombolytic therapy in FATE
- AKI
- hyperkalemia
- clinical bleeding
- coagulation abnormalities
What was assessed in the REVEAL study on FATE?
the cummulative risk for fate in cats with HCM or HOCM
1 year 3.5%
5 years 9.5%
10 years 11.3%
What did the FATCAT study assess in FATE?
clopidogrel versus aspirin in cats with previous FATE
recurrence rate 75% in aspirin group and 49% in clopidogrel group
time to recurrence of FATE or cardiac death 11.5 months for clopidogrel, 4.3 months for aspirin
What clinical sign has been associated with increased transfusion requiredments and mortality in ITP?
melena at time of hospital admission
What is the DOGiBAT score
score assessing bleeding - grades for 9 different anatomic sites
correlated with transfusion requirements and inversely correlated with platelet count
Where do autoantibodies bind on PLTs in ITP?
fibrinogen receptor (GPIIIbIIIa, integrin alphaIIb-beta3)
vWF receptor (GPIbIX)
Which Pattern Recognition Receptor is expressed on platelets?
TLR-4
In uremia-associated platelet dysfunction is aggregation, activation, or adhesion affected? What laboratory finding is this supported by?
adhesion
diminished vWF binding ability despite normal vWF concentration
will clinically resemble vWF disease
List classes of drugs that can affect platelet function
- antiplatelet drugs (clopidogrel, aspirin)
- NSAIDs (conflicting data)
- PDE inhibitors (Sildenafil, Pimobendan)
- NO donors (nitroprusside, nitroglycerin)
- antithrombotics (heparin, factor X inhibitors)
- fibrinolytic drugs
- antimicrobials (beta-lactams, cephalosporins)
- serotonin reuptake inhibitors
- synthetic colloids
- Vitamin E
How are synthetic colloids suspected to affect platelet function?
- binding of colloidal molecules to GPIIbIIIa (integrin alphaIIbbeta3) and GP1b
- interfers with vWF/FVII complex formation => eliminated faster
- interfers with intracellular signaling function
List the 3 Types of vWD
Type 1 - reduced quantities of all vWF multimers - Dobermans common
* bleeding following procedures
Type 2 - reduced quality of vWF, reduced high molecular weight vWF
* more severe bleeding diatheses, spontaneous mucocutaneous bleeding
Type 3 - complete absence of vWF
* spontaneous vWF, life-threatening hemorrhage after trauma or procedures, spontaneous mucosal bleeding
List 5 types of congenital thrombocytopathies
Glanzman Thrombasthenia
* absent or reduced GPIIbIIIa
Bernard-soulier Syndrome
* GBIb-IX-V abnormalities
* macrothrombocytopenia
P2Y12 and P2Y2 abnormalities
* greater swiss mountain dogs
Chediak-Higashi syndrome
* persian cats
* intrinsic platelet storage pool defect - cannot store dense granules
Canine Scott Syndrome
* impairment of platelet-dependent thrombin formation
* cannot perform scrambling of platelet phospholipids - cannot externalize phosphatidylserine
What are Tier 1, 2, and 3 diagnostics to evlauate for platelet disorders?
Tier 1:
* PLT count
* PLT size/morphology
* clotting times
* vWF concentration
* vWF binding assay
Tier 2:
* BMBT
* Platelet function analyzer
* Clot retraction
* Platelet aggregometry
Tier 3:
* Flow cytomety
* Western blot analysis
* Molecular testing
* Whole-genome sequencing
What is the recommendation for patients requiring invasive procedures but getting anitplatelet drugs?
discontinue at least 5-7 days before procedure
What is assessed by BMBT?
Platelet function
What are normal values for BMBT?
What could affect the results besides platelet function?
< 3 min dog
< 2 min cat
blood viscosity, hematocrit
List methodologies for platelet function analysis?
- BMBT
- bench-top platelet function analyzer (PFA-100)
- aggregometry
- flow cytometry
- Platelet mapping viscoelastic testing - insensitive
What is added to blood to measure aPTT?
kaolin and phospholipids
With synthetic colloid administration is PT or aPTT typically prolonged?
aPTT
What is the suspected cause for hypercoagulable TEG tracings in anemic patients?
recent ex vivo model showed hypercoagulable tracing in impacted by plasma proteins and available fibrinogen as opposed to packed cell volumes
What are typical coag panel changes in DIC?
- prolonged PT, aPTT
- hypofibrinogenemia
- elevated D-dimers
- reduced antithrombin activity
List 4 differentials for hyperfibrinolysis in dogs
- Greyhound dogs
- Trauma-induced coagulopathy
- Hemoperitoneum
- Liver disease
List drawbacks of BMBT
- operator dependent variability
- insensitive for mild defects of platelet function
- has shown unreliable in predicting surgical bleeding
What percentage decrease of clotting factors is necessary for prolongation of PT, aPTT, or ACT?
60-70% for PT aPTT
90% of ACT
Which clotting time can be affected by PLT counts?
ACT - PLT < 10k can prolong ACT
How long should hypotensive resuscitation be applied for?
What is a contraindication for it?
No longer than 90 min (MAP of 60 mm Hg)
ICH - want MAP of 90 mm Hg
What are the 2 effects of Desmopressin?
- release of vWF from endothelial weibel palade bodies
- enhances density of platelet surface glycoproteins - enhances adhesion
List interventions that can bed used to stop epistaxis
- benign neglect - often stop on their own
- ice-packing
- sedation
- phenylephrine infusion into nasal cavity (diluted in saline or lidocaine)
- nasal packing - risk of penetration into the cranial vault!
- yunnan baiyao orally or topical - anecdotal
- antifibrinolytic agents
- foley catheter insertion and inflation
- carotid artery ligation
How is platelet production regulated?
By the hormone thrombopoietin
up or downregulated by circulating PLT numbers, PLTs bind to thrombopoietin therefore if less PLTs circulating less is bound and more active –> stimulating megakaryocytes
List platelet’s trophogens and what is their function?
- platelet-derived growth factor
- vascular endothelial growth factor
- fibroblast growth factor
- stem cell factor
- sphingosine-1-phosphate
keep endothelial tight-junctions tight - if PLT counts < 20-25k -> not enough trophogens and RBC extravasation
only happens with thrombocytopenia, not PLT dysfunction
Why is bleeding into the brain rare with thrombocytopenia?
endothelial tight junctions there do not rely on trophogens
How do the clinical signs of thrombocytopenia and thrombocytopathia differ
Both PLT dysfunction and thrombocytopenia can cause ecchymoses (bruising) but petechiation is only caused by thrombocytopenia (note: trophogens!)
List causes of PLT sequestration.
- splenomegaly
- neoplasia
- severe hypothermia
usually only causes mild thrombocytopenia
How does vincristine improve platelet counts?
- induces platelet release from megakaryocytes
- reduces phagocytosis of opsonized platelets
Where are tPA and uPA produced?
tPA - endothelium
uPA - mesothelial cells, fibroblasts, epithelia, monocytes, endothelium
What triggers tPA release?
- bradykinin
- histamine
- alpha-adrenergic agonists
- PAF
- acetylcholine
What are the half-lives of uPA and tPA?
uPA 8 min
tPA 1-4 min
Name 2 plasma proteins that inhibit plasmin directly
- alpha-2-antiplasmin
- alpha-2-macroglobulin
Name 2 inhibitors of tPA and uPA
- PAI-1
- protease nexin
What endogenous antifibrinolytic has been shown to be upregulated in dogs with sepsis?
TAFI
PAI-1
Describe the role of thrombomodulin in acute coagulopathy of trauma
- endothelial damage + catecholamine surgery => thrombomodulin release
- binds thrombin => TM-T complex activates APC
- APC inhibits not just FVa and FVIII but also PAI-1
- low PAI-1 levels while endothelium releases excessive PA => hyperfibrinolysis
Which snake types cause hyperfibrinolysis and does it happen?
Eastern and western diamondback rattlesnakes
tPA-like substance in venom
Explain how hypofibrinolysis occurs in sepsis
TNF-alpha, lipopolysaccharides, TGF-beta, IL-1
=> induce endothelial PAI-1 synthesis
Describe the euglobulin clot lysis time
test to assess speed of clot lysis
cold acetic acid causes precipitation of euglobulin fraction (plasminogen, tPA, fibrinogen) => clots with thrombin and then the time until dissolution is monitored
largely replaced by viscoelastic testing
List tests of fibrinolysis
- ECLT (euglobulin clot lysis time)
- tPA assays
- plasminogen assays
- PAI-1 assays
- TAFI assays
- alpha-2-antiplasmin assays
- Viscoelastic testing
What is aproptin?
serine protease inhibitor (i.e., plasmin) - inhibits fibrinolysis
used in human coronary artery bypass grafting - anecdotally in dogs - no published reports though
What are the main findings of the CRASH-2 trial?
in human patients with hemorrhagic shock TXA administration within 3 hours improved mortality without increasing risk of thrombotic events
Are antifibrinolytic drugs safe in cats?
unknown at this time
experimental studies showed sezireus and myocardial injuries from TXA - but administration was not consistent with what would be done clinically
no studies showing safety at this time
What are available recombinant tPA products?
alteplase
reteplase
tenecteplase
Why doesn’t the Hageman trait typically lead to clinical signs of bleeding?
FXII deficiency - contact pathway not necessary for cell-based model of coagulation - more so activated in systemic inflammation and other disorders
will show up as elevated aPTT but not cause bleeding in otherwise healthy patient
What is the onset of action time and duration of action of Desmopressin?
onset of action 30 min
duration of action 2 hours
What is HASHTI?
6 step measure protocol for anticoagulant-associated coagulopathy
H: Hold further doses
A: Antidote if available
S: Stabilize and Support
H: Hemostatic measures
T: Transfusion
I: Investigate for bleeding source
What is the antidote for heparin overdose?
Protamine
* works fast for UFH - within 5-10 min, effect monitored with aPTT or ACT
* not as efffective for LMWH - cannot fully reverse it, effect difficult to monitor without anti-factor Xa assays
side effect: histamine release and anaphylaxis
What are the 2 fibrinolysis phenotypes of DIC and what conditions have each been reported?
Suppressed fibrinolytic type DIC
* most common in sepsis
* increased PAI-1
* causes microthrombosis and increased risk of MODS and death
Enhanced fibrinolytic type DIC
* augmented fibrinolytic activity and hemorrhage
* seen with different cancers in people
* reported with hemangiosarcoma in a dog
List diagnostic criteria supporting diagnosis of DIC
- underlying disorder known to cause DIC
- thrmbocytopenia
- prolonged PT APTT (>25-50%)
- decreased fibrinogen cc
- red cell fragmentation (schistocytes, acanthocytes)
- increased FDP and d-dimer cc
List the causes of coagulopathy in liver disease
- cholestasis/biliary duct obstruction - decreased Vit K absorption - decreased carboxylation of clotting factor II VII IX X Protein C and S
- thrombocytopenia from decreased synthesis of thrombopoietin, consumption with DIC, splenic-platelet sequestration due to portal hypertension
- platelet dysfunction from signaling dysfunction
- dysfibrinogenemia from failure of liver removing sialic acid from fibrinogen
- hyperfibrinolysis - decreased clearance of tPA, decreased PAI-1, TAFI, alpha-2-antiplalsmin
What are risk factors for bleeding complications after percutaneous ultrasound-guided biopsy of the liver
- dogs PT > 1.4
- cats aPTT > 1.4
- PLT count < 86k
What is the difference between TAC and ACOTS and RAC?
TAC - trauma-associated coagulopathy => includes both the early endogenous causes of coagulopathy and resuscitation-induced coagulopathy
ACOTS - endogenous coagulopathy from trauma and shock
RAC - resuscitation-associated coagulopathy
Name 3 potential causes of acidosis in TAC.
hyperlactatemia from tissue hypoxia and catecholamine release
chloride-rich fluid administration
citrate administration with blood products
How are platelets activated in ACOTS?
suspected:
wide-spread ADP release - prematurily activates and consumes platelets
