HEMOSTASIS SURGICAL BLEEDING TRANSFUSIONS Flashcards
hemostatic process
- Process involves interaction between blood vessel wall, platelets, and coagulation proteins
- When systems coordinate, a clot is laid down initially to stop bleeding, followed by eventual clot lysis and tissue remodeling.
- Abnormal bleeding can result from diminished thrombin generation (eg, due to factor VIII deficiency) or enhanced clot lysis (eg, due to alpha-2-antiplasmin deficiency).
- Conversely, excessive production of thrombin can lead to thrombosis
⦁ decreased clot formation or increased clot breakdown –> abnormal bleeding
phases of hemostasis
1) endothelial injury & formation of platelet plug
2) clotting process by coagulation cascade
3) termination of clotting by antithrombotic mechanisms (plasmin, antithrombin, protein S & protein C - degrade factors 5a & 8a)
4) Removal of clot by fibrinolysis
protein S & protein C
aid in prevention of clotting cascade
degrade factors 5a & 8a
factor 5 leiden
excessive production of factor 5 –> excessive clot formation
ADP function
adenosine diphosphate
released from platelets upon platelet activation and functions to recruit additional platelets and amplify platelet aggregation
ADP is released from platelets when stimulated –> recruits more platelets to the site of injury
Plavix / Clopidogrel blocks platelet activation by ADP
PLATELET ACTIVATION
After injury to vessel wall
⦁ Vasoconstriction for about 60 seconds
⦁ Next platelets adhere to site of vascular injury; physiologic platelet stimuli – Collagen and thrombin (further activates platelets), ADP.
⦁ ADP adenosine diphosphate is released from platelets upon platelet activation and functions to recruit additional platelets and amplify platelet aggregation
(this is where Plavix works - prevents platelets from being able to signal to one another for aggregation)
PLATELET ADHESION
After activation platelets undergo significant shape changes that make the platelets extremely adhesive.
Platelet adhesion is primarily mediated by the binding of platelet surface receptor GPIb/IX/V complex to von Willebrand factor (VWF) in the subendothelial matrix
Von Willebrand Factor (VWF)
lines vessels; acts as bridging molecule at sites of vascular injury for platelet adhesion; also acts as a carrier protein for factor 8 (needed for fibrin formation)
von Willebrand disease
deficient or abnormal function of VWF = most common of inherited bleeding disorders;
platelets can’t adhere to vessel, and factor 8 gets broken down faster and can become deficient too (leading to hemophilia A)
PLATELET AGGREGATION
Results in platelet-platelet cohesion.
Results in both exposure of and conformational changes in the GPIIb/IIIa receptor on the platelet surface, leading to binding of both immobilized VWF and fibrinogen
fibrinogen is secreted from
platelets (but still has to be converted to fibrin…from thrombin)
platelets contain 2 types of granules
alpha & dense
platelets secrete substances from their granules (alpha & dense granules)
ADP (platelet recruitment / activation)
growth factor - helps with tissue repair
fibrinogen - helps solidify platelet aggregation
tissue factor (factor 3) is also known as
thromboplastin
coagulation pathway summary
- Various coagulation factors are activated to generate fibrin
- Extrinsic Pathway
⦁ begins with thromboplastin (= tissue factor = factor 3)
⦁ thromboplastin / TF / factor 3 -> activates factor 7 to 7a -> activates factor 10 to 10a - Intrinsic Pathway
⦁ Requires factors 12, 11, 9 and 8 to convert factor 10 to 10a - Common Pathway
⦁ involves factor 10, 5, 2 (prothrombin) and 1 (fibrinogen)
⦁ factor 13 = fibrin stabilizing factor; creates crosslinks to hold fibrin strands together
thrombin (2a) then activates which clotting factors
5, 7, 8, 11, 13
which electrolyte is ESSENTIAL to the clotting cascade
CALCIUM
PTT = \_\_\_\_\_\_\_\_\_\_ pathway PT = \_\_\_\_\_\_\_\_\_\_\_ pathway
PTT = intrinsic
PT = extrinsic
intrinsic pathway is activated by
extrinsic pathway is activated by
Intrinsic pathway is activated by damage directly to the blood vessel and the exposure of collagen to the circulating platelets within the blood.
The extrinsic pathway is activated by many things.
Intrinsic pathway = think injury*
in order for factor 9a to activate factor 10, need
factor 8!
damage / collagen exposure activates factor 12 -> 12a
12a activates 11 -> 11a
11a activates 9 -> 9a
9a activates 8 -> 8a
9a + 8a together activate factor 10 -> 10a
INTRINSIC VS EXTRINSIC PATHWAY
INTRINSIC PATHWAY
⦁ damage / collagen exposure activates factor 12 -> 12a
⦁ 12a activates 11 -> 11a
⦁ 11a activates 9 -> 9a
⦁ 9a activates 8 -> 8a
⦁ 9a + 8a together activate factor 10 -> 10a
EXTRINSIC PATHWAY
⦁ damage / exposure of tissue factor (3) = activates 3 -> 3a
⦁ 3a activates 7 -> 7a
⦁ 7a activates 10 -> 10a
factors 1-7 = also called….
⦁ Factor I – Fibrinogen ⦁ Factor II – Prothrombin ⦁ Factor III – Tissue factor ⦁ Factor IV – Calcium ⦁ Factor V – Labile factor ⦁ Factor VI – not used anymore ⦁ Factor VII – proconvertin
factor deficiencies
Factor 8 – Hemophilia A Factor 9 – Hemophilia B = Christmas Factor 10 - Stuart-Prower Factor 11- Hemophilia C Factor 12 - Hageman factor deficiency Factor 13 - fibrin stabilizing factor
rarest factor deficiency
factor 13 deficiency
clot forms, but breaks down quickly, because factor 13 is what stabilizes the fibrin to hold platelets together
normal platelet count
140,000 - 400,000
H&P for bleeding issues
- HISTORY = most important step
⦁ ask about meds: OTC, ASA, Clopidogrel (Plavix), Warfarin (Coumadin) - ASA, plavix = antiplatelet = used to prevent clots in arteries
- Warfarin (& heparin) = anticoagulant = used to slow clotting in veins (DVT)
- PE = look for signs of a bleeding disorder
evaluation (labs) for bleeding
⦁ platelet count
⦁ PT (prothrombin time) = extrinsic pathway
⦁ PTT (partial thromboplastin time) = intrinsic pathway
⦁ bleeding time
⦁ thrombin time
PLATELET COUNT
verifies that patient has an adequate number of platelets available in circulation; if abnormal = can order a blood smear to look at the platelets under a microscope
normal = 140,000 - 400,000
PROTHROMBIN TIME (PT)
- evaluates the extrinsic pathway
- measures the ability of the blood to form a stable thrombi
- evaluates factors 7, 10, 5, prothrombin (2) and fibrinogen (1)
- most common use = MONITORING WARFARIN
- PT is reported with INR (international normalized ratio) = ratio of a patient’s prothrombin time to a normal (control) sample
most common use for PT
monitoring warfarin therapy
why is PTT normal in a patient with factor 7 deficiency
because PTT measures the intrinsic pathway, and factor 7 is in the extrinsic pathway (PT)
most common use for PTT
evaluate UNFRACTIONATED HEPARIN therapy
PARTIAL THROMBOPLASTIN TIME (PTT)
Intrinsic pathway
- evaluates the adequacy of factors 12, 11, 10, 9, 8, 5, 2 (prothrombin), 1 (fibrinogen)
- most commonly used to evaluate UNFRACTIONATED HEPARIN therapy
- PTT = normal in patients with factor 7 deficiency…because PTT measures the intrinsic pathway, and factor 7 is in the extrinsic pathway (PT)
BLEEDING TIME
- Two incisions with lancet on the forearm
- Time from injury to cessation of bleeding from both wounds is measured
- Normal range is 5-10 minutes
- Prolonged time may indicate;
⦁ Thrombocytopenia (low platelets)
⦁ Medication (ASA) - (anti-platelet- prevents coagulation)
⦁ Von Willebrand disease (factor needed for platelet to adhere to vessel & acts as carrier protein for factor 8
THROMBIN TIME
- Evaluates fibrinogen-to-fibrin conversion with an external source of thrombin
- Prolongation may indicate: ⦁ Low fibrinogen levels ⦁ Abnormal fibrinogen ⦁ Fibrin and fibrinogen split products ⦁ Heparin (anti-coagulant = binds to antithrombin and intensifies action - inhibits thrombin activation & inhibits factor 10 from converting to 10a)
heparin MOA
anti-coagulant = binds to antithrombin and intensifies action - inhibits thrombin activation & inhibits factor 10 from converting to 10a
reversed with protamine sulfate
warfarin MOA
inhibits synthesis of vitamin K - calcium dependent clotting factors (2, 7, 9, 10) - ***7 = warfarin = think extrinsic
warfarin = reversed with vitamin K
PT (extrinsic) & PTT (intrinsic) meet at factor
10
X marks the spot!