Bleeding Disorders Flashcards
What is the appropriate coagulation model?
Cell-based model: explains deficiencies in traditional clotting cascade model and why the absence of some factors is greater than the absence of others
What does prothrombin time measure? What is a normal prothrombin time? Do we use prothrombin time?
Extrinsic pathway (tissue factor pathway) and common pathway - assess deficiency in PT, liver disease, antiplatelet drugs, warfarin
11-14 seconds
Prothrombin time (PT) = test used to help detect and diagnose a bleeding disorder or excessive clotting disorde
International normalized ratio (INR) = calculated from a PT result and is used to monitor how well the blood-thinning medication (anticoagulant) warfarin (Coumadin®) is working to prevent blood clots.
What is an INR?
International normalized ratio (standardized PT value)
measures coagulation function of extrinsic (tissue factor) pathway. Normal value = 1
Used to monitor warfarin
ideal for low intensity warfarin therapy = INR of 2-3
ideal for high intensity warfarin therapy (like mechanical heart valve) = INR of 2.5-3.5
what does aPTT measure? what is normal? what can it detect?
activated partial thromboplastin time measures the intrinsic pathway
normal = 25-35 seconds, assess intrinsic pathway problems such as heparin, von Willebrand dz, hemophilia
what is a normal platelet count?
150-450k per mL
what is von willebrands disease?
most common inherited bleeding disorder = 1% of population
vWF binds factor VIII in circulating blood, unbound factor VIII is destroyed
What is the MOA of warfarin?
inhibits the synthesis of vit-K dependent coagulation proteins (2, 7, 9, 10) and proteins C, S, and Z
How should you treat a patient that is on warfarin who needs dental surgery?
Med consult
Get INR within 24 hrs of surgery
Have to discontinue warfarin for several days due to long half life
JADA 2009 - suggest INR of up to 4 is acceptable for most dental procedures
Morimoti - perio surgery can be performed with INR less than 3 using local hemostatic measures
why are people on direct anticoagulants?
medication fo choice for patients w/ Afibb, hx of venous thromboembolism (PE)
do not require lab monitoring, have rapid and short onset (differs from warfarin)
MOA of Pradaxa
Factor 2a (thrombin) reversible inhibitor DIRECT THROMBIN INHIBITOR
12-15 hr half life (needs to be discontinued at least 24 hrs pre-op). Cannot be measured with PT, INR, or PTT
MOA of Xarelto/Eliquis
Direct factor Xa inhibitors (thus inhibit the formation of the fibrin clot)
Have a half life of 6-12 hrs
Metabolized by liver CYP3A4 enzyme thus has dietary and drug interactions (grapefruit juice)
No defined therapeutic range . Cannot be measured with PT, INR, or PTT
What happens if patient who is taking Xa inhibitor has a bleeding emergency?
Reversal agent - Xa protein that acts as a decoy for the ZA inhibitor, must be given via IV infusion
why are people on antiplatelet drugs?
Prevention of recurrent MI, stroke, TIA, coronary thrombosis, and within 1 year of cardiac stent placement
what are examples of antiplatelet drugs?
aspirin, clopidogrel (plavix)
what is the MOA of aspirin?
Irreversibly inhibits platelet cyclo-oxygenase and impairs platelet aggregation
What is the MOA of Plavix?
Plavix (clopidogrel) -inhibits the fibrinogen receptor on the platelet
Use of these drugs prolongs bleeding time
What are examples of higher-risk dental procedures for bleeding?
3 or more extractions
GBR
definitely consult with general physician
What are examples of low risk dental procedures that do not require interruption of anticoagulation therapy?
Implant placement
Soft tissue biopsy
Dental extractions of less than 3 teeth that are not surgically complex
What are common drug interactions with warfarin?
Amoxicillin, Augmentin, Metronidazole, Clinda, NSAIDs,
what are common drug interactions with direct oral anticoagulatants?
NSAIDs, azole antifungals, clarithromycin, erythromycin
What are local hemostatic agents that you would be prepared to use in a bleeding emergency?
Collaplug - physical effect to stabilize clot (bovine collagen dressing)
Gelfoam - absorbable gelatin sponge - physical stabilization of clot
Surgicel/Actcel - cellulose. physical stabilization
CANNOT USE SURGICEL & TOPICAL THROMBIN TOGETHER. SURGICAL INACTIVATES TOPICAL THROMBIN
Topical thrombin - directly converts fibrinogen to fibrin
Tranexamic acid - competitive inhibitor of plasminogen activation
Explain the intrinsic pathway
Intrinsic pathway = PTT pathway
Injury to blood vessels leads to: -activation of 12 > 12a 12a activates 11 > 11a 11a activates 9 > 9a 2a activates 8 > 8a
8,9, and Calcium activate
10 to become 10a
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