Basic Science

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