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
How does VTE prophylaxis change in obesity?
difficult to dose in obese patients
- european guidelines state high risk (>55, BMI >55, prior VTE, venous disease, OSA, hypercoagulability or pul HTN) an elevated dose of LMWH is recommended 3000-4000 anti-10a international units
this is increased to 4000-6000 in obese patients
What happens with DVT prophylaxis in major orthopaedic surgery?
Post total knee or hip
- 10-14 days of thromboprophylaxis
- LMWH is the drug of choice and in CHEST guidelines is to continue for 35 days rather than 10-14.
- ongoing studies into direct oral anticoagulants for prolonged prophylaxis.
- LMWH >aspirin but quality of evidence is low
What are some high risk bleeding surgeries? How does anticoagulation post op change?
Urologic surgery Pacemaker or implantable defib colonic polyp resection >1-2cm Vascular organ (kidney, liver, spleen) Bowel resection Major surgery (joint, cancer, reconstructive) Cardiac, intracranial or spinal surgery
therapeutic LMWH should be resumed 48-72hrs post
- for discussion with surgeon
generally warfarin can be resumed 12-24hrs post op
What is the perioperative management of DOACs?
- should be ceased 2-3 half lives prior to surgery with low risk and 4-5half lives prior to high risk surgeries
(longer in renal impairment)
dabigatran mainly renally excreted therefore testing TCT to show it is normal is a cheap easy way to monitor absence of this drug
DOACs can be recommenced once bleeding risk is low (d1 post low risk procedures and day 2-3 post high risk)
What sort of anticoagulation should be used in liver disease?
Considerations:
- platelet count, increased risk of GI bleeding, factor production reduced
- aPTT and INR correlate poorly with bleeding complications
thrombocytopenia
- may be due to platelet production or increased clearance
- other causes:
chemo - more prone to bleed
HIT - prothrombotic
