Blood Flashcards
Primary haemostats involves
Platelet plug formation: sub-endothelial matrix, vWF, platelets
Secondary haemostats involves
Fibrin formation from fibrinogen via thrombin
Cross links & stabilises the clot
Testing if you suspect primary coagulopathy
- platelet count
- consider buccal mucosal bleeding time
- measure von Willebrand’s factor - ELISA
Testing if you suspect secondary coagulopathy
- one stage prothrombin time + activated partial thromboplastin time
(if would need to wait for external tests can opt for whole blood clotting time + activated clotting time) - Check serum biochemistry - liver function
Extrinsic pathway is initiated by
Tissue factor exposed on damaged tissue or released from activated endothelial cells
- binds factor 7
= principle initiator of the coagulation cascade
Intrinsic pathway
Amplifies coagulation cascade response
Start with factor 12 activation by surface contact (-ve charge) or thrombin.
APTT
Activated partial thromboplastin time - tests intrinsic and common pathways
Prolonged if clotting factors <30% normal level
OSPT
One stage prothrombin time - tests extrinsic common pathway.
Sensitive to fact VII deficiency.
Test for factor VII deficiency
one stage prothrombin time
Emergency clotting test
Whole blood clotting time - plain glass tube, see how long it takes to clot - intrinsic + common pathways.
Disorders of primary haemostasis
- thrombocytopenia
- thrombocytopathia
- vWF deficiency
Clinical signs primary haemostats
petechiae (±pupura) & ecchymosis
± bleeding from mucosal surfaces - melena epistaxis, haematuria
- excessive bleeding after sx
- occasional CNS bleeding
only a small amount of blood leaks out before it is sealed by a fibrin clot.
Pre-surgery in Dobermans
Do a buccal mucosal bleeding time test - if prolonged delay sx and test for vWF.
Disorders of secondary haemostasis
- inherited deficiencies of coagulation factors e.g. Haemophilia A = factor VIII deficiency.
- acquired deficiencies of coagulation factors - liver dz, warfarin toxicity.
Clinical signs of secondary haemostasis disorders
- Bleeding into body cavities, joints, bruising (rarely petechiae)
- Haematomas - excessive bleeding following sx, trauma, venepuncture.
- Mucosal or surface bleeds less common
more severe bleeding as platelet plug forms but is unstable - washed away.
Mixed primary and secondary coagulation disorders
DIC
Angiostrongylus vasorum infection
Indicators of thromboembolic disease
- increased fibrin degeneration products
- high D-dimer levels
- high Antithrombin III levels - increased risk of thrombosis
TEG
thromboelastography - used to detect hyper & hypocoagulable states
Citrated whole blood used <4hrs old
ECC & referral only
Blood volume of a cat
60-70ml/kg
Blood volume of a dog
88ml/kg
Clinical signs of >20% blood loss
Increasing pulse rate, increased respiratory rate, decreasing blood pressure, pale mms, weakening pulses.
If conscious - confusion or abnormal behaviours
Below PCV 21%
Oxygen carrying capacity severely compromised
What are the 3 plasma proteins?
Albumin, globulin, fibrinogen
High PCV/Hb is linked to
Dehydration
Stress
Polycythemia - e.g. myeloproliferative disease or over production of erythroprotein.
Broadly a lack of platelets is due to
reduced production,
consumption e.g. DIC
haemorrhage
Potential tx is sx required and dog has reduced vWF
Desmopressin - stimulates release from the vascular endothelium.
Cyroprecipitate containing vWF
Blood product options
- whole blood
- plasma
- packed rbcs
- cryoprecipitate
Whole blood transfusion is used for
Blood losses >30% in eunaemic patients
Clotting disorders
Severe anaemia - care if normovolaemic
Blood typing/cross matching
Not essential in 1st transfusion for dogs
Essential for cats
Plasma transfusion is used for
Hypoproteinaemia
Clotting disorders - fresh or fresh frozen
Packed red cell transfusion is useful for
Anaemic but normovolaemic patients - increased oxygen carrying capacity.
Suspension diluted before administration.
Cyroprecipitate
Formed from centrifuging thawed fresh frozen plasma - used in clotting factor deficiencies to avoid plasma volume overload
Potential blood products for clotting factor disorders
Whole blood, plasma, cyroprecipitate
Potential blood products for anaemia
Whole blood, packed red cells
Autotransfusions
Can be planned for surgery if blood loss expected.
10d prior provided the animal is not anaemic - take <10% circulating volume, store at 4degrees until sx.
Potential problems with transfusions
Transfusion reactions - if severe IV haemolysis can - renal failure & DIC Volume overload Bacterial contamination Emboli - insufficiently mixed/ no filter Hypocalcaemia if large vols Disease/exfoliating tumour transmission.
