Thrombophylaxis Flashcards
A 61 year old with colon cancer requiring laparotomy for hemicoloectomy, what VTE prophylaxis should be used?
VTE risk calculation using Caprini model 0-1 very low 2- low 3- moderate 5 - high (6% risk)
multiple considerations
High risk:
major open surgery
malignancy
age age >61
pharmacological for 4 weeks
mechanical
- elastic stockings (concern re: pressure sores)
- intermittent pneumatic compression (only 2 randomised studies performed).
25 year old post MVA with multiple injuries (external fracture pelvis fixation with large proximal DVT), what therapy would you use?
- IVC filter in patients with proximal DVT with contraindication to anticoagulation
Not recommended for primary prevention in orthopaedic and non-orthopaedic surgery.
What are some complications for IVC filters?
- early - jugular/femoral thrombosis
- pneumothorax
- late - IVC perforation, IVC thrombosis, filter migration and fracture
of patients with filters
- 7% failed retrieval
- ‘minor complication rate’ of 3.5% with (see above)
- 115 day mean insertion time
73 year old with aortic stenosis and 70% stenosis of mid right coronary artery. Previous CABG and post op had arrest requiring CPR - became hypoxic, given adrenaline. Used heparin intraop. What is likely cause? How would you diagnose it?
HITS
- transient drug induced platelet activating immune disorder
- autoantibodies target PF4 heparin complex
- risk factors UFH>LMWH>fondaparinux
surg>medical>obs/pead
female >male
DDx: non immune heparin associated thrombocytopenia (type 1)
Pathogenesis
- PF4 (platelet factor 4) antibody binds and activates surface of platelet causing thrombosis
Diagnosis
- clinical syndrome, not all antibodies result in thrombosis (thrombocytopenia first but progress to thormbosis), bleeding is not a feature
- ELIZA assay - higher level correlates increased likelihood of HITS (cutoff differs based on site)
- platelet activation assay gold standard (only in Sydney).
- Auto-HIT platelet aggregometry
What is the 4T score for diagnosis of HIT?
T - thrombocytopenia
(>50% nadir 2, 30-50% nadir 1, <30% 0)
T - timing of plt reduction\
(day 5-10 2, >day 10 1, <4 days 0)
T - thrombosis
(new 2, progressive 1, none 0)
oTher cause (no 2 possible 1 definite 0)
score of 6-8 = high, 4-5 intermediate 0-3 low
What is the management of a patient with HIT?
- isolated - stop heparin and anticoagulate (as 30 day risk of thrombosis up to 50% despite heparin cessation)
Anticoagulation
- cease heparin
- direct thrombin inhibitor - lepirudin
- delay warfarin until normal platelets
- overlap anticoag with warfarin for 5 days at least
What do you do in a patient who has ?HIT preop?
1) HIT antibody testing
- if negative use heparin
- if positive - use lepirudin or bivalirudin intraop
HIT antibodies generally disappear within 100 days
- for cardiac surgery if there are antibodies then bivalirudin can be used (direct thrombin inhibitor)
68 M with AF on warfarin for a mechanical Mitral valve for elective TURP - what anticoagulation periop?
high risk based on CHEST guidelines
- require bridging
- stop warfarin 5 days preop
- start LMWH full dose 1mg/kg b.d. INR <2
- stop LMWH 24hrs preop
- start prophylactic heparin postop (high risk bleeding procedure)
- reintroduce therapeutic dose when bleeding controlled
73M tripped on footpath fell onto face with PMHx: HTN, PPM, hyperlipidaemia, AF, TIA, prostate cancer
- was on dabigatran
Reduced GCS with last dose dabigatran 0800 that morning
mildly prolonged INR/APTT, TCT normal, normal renal function dabigatran level (therapeutic several hours later)
patient had large subdural haemorrhage
What is your management of a patient on NOAC with bleed?
- initiate resus measures
- order coag screen
- check FBE, UEC, LFT and G+H
- stop the drug and delay restarting oral anticoag until bleeding controlled
Mild bleeding
- local haemostatic measures
- antifibrinolytic agent (e.g. TXA orally or topically 15mg/kg QID)
Mod-severe
- mechanical compression, surg intervention
- TXA IV 15-30mg/kg +/- infusion
- fluid replacement
- blood products
- consider PO charcoal if <2hrs since ingestion dabigatran or <8hrs rivaroxaban
- HDx consideration for dabigatran
- trial PLEX for rivaroxaban as protein bound
consider idarucizumab
What are the mechanisms of NOACs?
Dabigatran
- direct thrombin inhibitor
- peaks 1-3hrs
- half life 12-17hrs
- renal excretion primarily
- reversal with idarucizumab
- prolonged APTT/INR
- indication (stroke, thromboprophylaxis)
Rivaroxaban
- F10z inhibitor
- peaks 1-3hrs
- half life 7-11hrs
- renal excretion 50%
- reversal nil
- prolonged APTT/INR
- indication (stroke, thromboprophylaxis, tx of DVT)
What are the coagulation cascade implications of NOACs?
- intrinsic pathway (APTT, Factors 8,9,11,12 and common pathway)
- extrinsic (PT/INR, factor 7 and common)
rivaroxaban/dabigatran affect lower on the coagulation cascade with thrombin/factor 10a
can’t give clotting agents like FFP (more reagents)
66M with AF and CHADS2 score of 2 treated with warfarin. Presents with altered conscious state after falling off a ladder and an INR of 2.8. CT showing parenchymal haemorrhage. How would you manage this patient pre-neurosurg?
reversal
- withhold
- administer vitamin K
- transfusion therapy (FFP and prothrombin complex concentrates (4 factor)
Australia has 2,9,10 and low 7
reversal of warfarin urgently give FFP as it contains factor 7.
1) withhold warfarin
2) IV vitamin K 5-10mg
3) FFP 15mls/kg
4) PCC 25-50units/kg + 1-2units FFP
Explain the mechanism of action of warfarin and some issues with its use
Inhibits factors 2,7,9,10 by liver (and protein c and s) as vitamin K antagonist (blocking synthesis)
4-10days to stable anticoagulation
INR aim 2-3 except high risk valves 2.5-3.5
Downsides - narrow therapeutic margin - delayed onset of action interaction with drugs - dietary effects - warfarin 1-2% risk bleeding per year
hepatic clearance Cytochrome P450 2C9 and vitamin K epoxide reductase
For a patient with mechanical AVR what do you do with warfrin pre umbilical hernia repair?
continue warfarin
- minor dental
- minor derm
- cataract surg
withhold warfarin 5 days preop
- restart postop
Semiurgent
- IV vitamin K 3mg 12-18hrs preop
What is the risk of DVT or PE? How do we estimate it?
- 2 in 1000 patients have VTE with 8% in hospital mortality in Australia
- may account 10% of deaths related to hospital admission with more common than MI and stroke
Caprini score model
- type of surgery
- validated in plastic/reconstructive surgery
based on score determines level of prophylaxis
- very low (nothing)
- low (mechanical preferably intermittent pneumatic compression)
- mod (LMWH or mechanical with stockings/IPC)
- high (LMWH plus mechanical with stockings/IPC)
- high risk cancer surgery (prolonged duration 4 weeks prophylaxis)
if high ris and clexane/heparin CI then use fondaprinux or aspirin low dose
major ortho surg carries significant risk and difficult to determine exact risk
