Pathogenesis
Virchow's Triad
1. Venous stasis
2. Hypercoagulability
3. Endothelial damage
Starts as platelet nidus at valves
- thrombogenic materials elaborated by platelets
- leads to development of fibrin thrombus
- thrombus grows
Thrombus may
- detach as embolus
- be completely dissolved / recanalise
- organise with valve incompetence
Risk factors
1. Patient
Previous DVT
Increasing Age
Obesity
Varicose veins
Immobility
Pregnancy
OCP / HRT
Smokers
Inherited Thrombophilia
Paralysis
Malignancy
Recent MI
2. Disease / Surgery
Trauma or surgery
Malignancy
Infection
Risk Groups
High Risk
Family history
Past History DVT/PE
OCP / Pregnancy / HRT
OT to pelvis & hip
Obesity
Hypercoagulable state
Varicose veins
Moderate Risk
Major surgery in age > 40
Major medical illness
Any large surgical procedure
Obese
Low Risk
Minor surgery < 30 min
Immediate mobilization
Rates without Prophylaxis
DVT rates without prophylaxis
- THR 50-70%
- TKR 50%
PE rates without prophylaxis
- asymptomatic PE 10 - 20%
- symptomatic PE 2%
- fatal PE 0.1 - 0.2%
Timing
DVT
- peak Day 3
- 80% of DVT occur during inpatient stay
- can occur as late as day 40
PE
- 50% fatal PE's > 3/52 i.e. occur at home
Fatal PE & Theory of Propagation
Calf DVT
- calf DVT has 20% chance of propagation
- ? PE less likely
Proximal thrombi
- are at greatest risk of embolism
- 50% chance PE
Screening DVT
Issue
- should all high risk patients get regular ultrasound?
- i.e early diagnosis and treatment to avoid PE
Problem
- 80% PE without clinical evidence DVT
- 2/3 patients with fatal PE die in 30min
Effect
PE leads to hypoxaemia from
- VQ mismatch
- Right Heart Failure
Diagnosis DVT
1. Clinical
- inaccurate
- non specific & non sensitive
- 50% patients with DVT have no clinical signs
- 50% with suggestive clinical signs have negative venogram
2. Venography
Gold standard
- sensitivity & specificity >95%
- outlines entire deep venous system of leg
Disadvantage
- invasive
- expensive
- 5% can't cannulate foot
- requires expertise
- risk of inducing DVT 1%
- contrast reaction 0.02%
- doesn't visualise pelvic veins
3. Duplex Ultrasound Scanning
Real-time US combined with colour imaging
- veins visualised
- femoral & popliteal veins visualised
- presence of lumen, compressibility & flow assessed
- sensitivity & specificity for proximal thrombi 95%+
- sensitivity only 70% calf DVT
Advantage
- non-invasive
- rapid & inexpensive
- use only above the knee
Disadvantage
- poor test if poor equipment & inexperienced user
Results
Schellong et al J Thromb Haemost 2007
- VENUS study
- compared venography to compression ultrasound in same patient
- 1100 orthopedic patients on oral anticoagulant
- venography rate of DVT was 19%
- ultrasound rate of DVT was 11.5%
- US sensitivity 31% specificity 98%
Diagnosis Pulmonary Embolus
Clinical
- unhelpful
- symptoms & signs non-specific
D Dimer
- always raised post op
- useful in low risk patient
- negative D dimer in this group excludes DVT
ECG
- usually sinus tachycardia
- right heart strain - S1 Q3 T3 (20%)
CXR
- usually normal
- exclude pneumonia
ABG's
- sensitive but not specific
- hypoxemia / hypocapnia / respiratory alkalosis
VQ Scan
Te99 labelled Albumin spheres trapped in capillaries / Xenon33 Gas in alveoli
- both detected by scintiscan
- compared with each other for mismatch
Advantage
- non-invasive
Disadvantage
- results not always clear-cut
- intermediate and high risk
- require further investigation
- low probability - 2% risk PE
CT Pulmonary Angiogram
Advantage
- definitive
Disadvantage
- difficult & expensive
- risk of contrast reactions
MRI
Useful for pelvic DVT
- patient with entire leg swollen
- negative ultrasound
- particularly post THR / pelvic / acetabular surgery
Management
DVT / PE
Established DVT & PE
- treat with anticoagulation
- prevent further clot propagation / embolisation
- allows fibrinolytic system to act unopposed
- does not directly dissolve thrombus
Calf DVT
- treatment debatable
- risk PE low but not zero
- 20% propagation rate
- usually treat for 3 months
- can give aspirin and repeat US in 7 - 10 days
Screening for Thrombophilia
Protein C / Protein S deficiency
Anti-thrombin 3 deficiency
Factor 5 Liaden (activated protein C / APC)
Lupus anticoagulant
Cardiolipin
Prophylaxis
Can be divided into
- mechanical prophylaxis & chemoprophylaxis
- preoperative, intraoperative, & postoperative
Mechanical
Early mobilisation
TEDS
Sequential Compression Devices
Foot pumps
Chemoprophylaxis
LMWH / Heparin / Warfarin / Aspirin / Oral Factor X inhibitors
Preoperative
Screen for high-risk groups
- obesity
- Family Hx
- previous DVT/ PE
- varicose veins
- yypercoagulable states
- OCP / HRT / smoking
Stop smoking & HRT
Preoperative clinic to encourage exercises & post-op regimen (education)
- admit day of surgery
Keep well-hydrated
Intraoperative
Regional anaesthesia
Planes et al JBJS Br 1991
- RCT of GA v Spinal with enoxeparin in patients with THR
- 6% proximal DCT in each group
- 0% distal DCT in GA group v 5% rate distal DVT in spinal group
- enoxeparin 40 mg sc day before GA
Intraoperative mechanical prophylaxis
- compression on other leg
Consider
Tourniquet
- cuff width at least 30% diameter of leg
- tapered low-pressure cuff if possible
- minimal tourniquet time
Minimal tissue damage & bleeding
- activates coagulation cascade
Avoid extremes of flexion for long periods
Avoid extrinsic pressure to limb
- care of position & extrinsic pressure to other leg
Postoperative
1. Early mobilisation
2. Early chemoprophylaxis
3. Early mechanical prophylaxis
- TEDS
- foot-pumps & Sequential Compression Devices
- applied in OT
- until mobile
Check calves daily for tenderness & swelling
Spinal surgery
FDA
- does not approve chemoprophylaxis for any spinal procedure
Epidurals
Epidural haematoma
- most often on removal of epidural
- 1:2 000 without chemoprophyaxis
- 3: 1 000 with Clexane
- not within 24 hours of insertion or removal