4.3.5: Haemostatic disorders - Thrombosis and DIC Flashcards
What does thrombosis result from? (Physiology)
3 abnormalities:
* Endothelial injury
* Alterations in blood flow (either stasis or turbulence, stasis probs more important)
* Hypercoagulability
What is hypercoagulability and what might it result from?
Hypercoagulability: defined as an abnormally activated haemostatic system that predisposes a patient to thrombosis. This can result from:
* Hyperfunctional platelets
* Activation of coagulation with generation of excessive thrombin
* Deficiency of inhibitors
Hypercoagulability is a characteristic feature of DIC. It occurs in conditions known to initiate DIC e.g. severe inflammation, sepsis, cancer, IMHA (dogs), GI disorders associated with endotoxaemia e.g. strangulating obstructions, colitis in horses
How do you test tertiary haemostasis?
Tertiary haemostasis: breakdown of the clot.
* Test for fibrinolysis by testing levels of fibrinogen and its degradaton products, FDPs, e.g. D-dimer
* High D-dimers = lots of clots being broken down
* Can also theoretically test for levels of inhibitors e.g. antithrombin III -> if this is low, there is a risk of thrombosis
When might D-dimers be elevated?
When the animal is in a pro-thrombotic state
Examples
* Feline thromboembolic disease
* Protein-losing nephropathy/ enteropathy -> clotting factors are being lost
* Hyperadrenocorticism -> steroids cause a thromboembolic state
1
Platelet count, BMBT, platelet function, vWF
2
WBCT, APTT, OPST (PT), specific factors
3
D-dimers (FDPs)
FDP: fibrinogen degradation products
Describe the pathogenesis of DIC
Disseminated intravascular coagulation (DIC)
* a.k.a. death is coming
* This occurs when there is excessive activation of the haemostasis pathways (this has been triggered by something)
* At the start, you are more prone to making clots
* Then, you have no clotting factors and platelets because you used them all up, so then you bleed
* This all happens subclinically until it doesn’t because it’s catastrophic
Describe the clinical presentations of DIC and species differences
- Cats like to clot (they favour thrombotic disease)
- Dogs like to bleed
DIC can present in various ways:
* Chronic/ silent/ subclinical
* OR acute/ fulminant in dogs -> there is profuse spontaeous bleeding (primary and secondary haemostasis suggested) with possible signs secondary to anaemia or parenchymal organ thrombosis i.e. end organ failure
True/false: DIC always occurs secondary to an inciting cause.
True
Examples of inciting causes:
* Endothelial damage e.g. electrocution, heat stroke, sepsis
* Platelet activation often viral e.g. FIP, endotoxaemia, neoplasia
* Release of tissue procoagulants e.g. trauma, pancreatitis, bacterial infections, erythema multiforme and some neoplasia (haemangiosarcomas)
* Basically anything
If a neoplasia is the cause of something, going for either haemangiosarcoma or lymphoma is often a good idea. They cause most things so usually a safe bet.
What is overt DIC and what clinical signs might you see?
Overt DIC: the disease is clinically detectable.
* Widespread microvascular thrombosis decreases blood flow to vital tissues causing hypoxic injury, cell death, and organ failure -> high morbidity and mortality
* Sometimes there is only the overt phase of DIC, if the inciting cause is bad and acute enough
How can you test for DIC?
No single pathognomonic test for DIC
* Confirm and identify an intiating disease e.g. infectious cause
* Identify haemostatic abnormalities:
* Thrombocytopaenia / dropping platelet count
* Prolonged clotting time (PT/ aPTT)
* Low antithrombin III
* Hypofibrinogenaemia as coagulation factors get used up
* High FDPs/ D-dimers
* Schistocytes, keratocytes, acanthocytes - although this is non-specific
Treatment of DIC
- Must identify and treat underlying cause, otherwise is hopeless
- Supportive care: fluid therapy to increase tissue perfusion, and for shock, correction of acidosis etc.
- Could do transfusion but limited evidence for this
- Could give heparin -> this acts to halt intravascular coagulation and decreases activity of the fibrinolytic system, but only works if you have sufficient antithrombin
Which virus in rabbits can cause DIC?
Rabbit haemorrhagic disease virus (RHD2)
* Incubation period 3-9 days
* Some animals remain subclinical and may shed the virus for several weeks
* Less virulent and lower mortality than RHDV classical form
b) PCV and coag is most appropriate
* PCV willl tell us whether we need to transfuse/ what our starting point pre-transfusion is
* Coagulation profile will show us where the cascade is failing -> in this case we are considering a genetic coagulopathy
* A blood smear and manual platelet count are always good but will not save you here
