Deep Vein Thrombosis (DVT)

Deep vein thrombosis (DVT) is the formation of a thrombus within the deep venous system, DVT may be:

• Proximal DVT → popliteal, femoral, iliac veins
• Distal (calf) DVT → tibial, peroneal, muscular calf veins
• Upper extremity DVT
• Catheter-associated DVT
• Unusual-site thrombosis → mesenteric, portal, cerebral venous sinus thrombosis

Pathophysiology

Virchow Triad

1. Venous Stasis

2. Endothelial Injury

3. Hypercoagulability

Venous thrombi are:

• “Red thrombi”
• Rich in fibrin and RBCs

Risk Factors

Major Risk Factors

Inherited Thrombophilia

Acquired Hypercoagulable States

Clinical Features

Symptoms(50% of patients with acute DVT may lack specific signs or symptoms.)

Signs

Severe Forms

Phlegmasia Alba Dolens

• Massive DVT
• Pale swollen leg
• Arterial spasm

Phlegmasia Cerulea Dolens

• Massive iliofemoral thrombosis
• Cyanotic oedematous painful limb
• Venous gangrene risk

Medical emergency.

Post-Thrombotic Syndrome (PTS)

Chronic venous damage after DVT.

Features

• Chronic edema
• Pain
• Hyperpigmentation
• Venous eczema
• Ulcers

Diagnostic Approach

Step 1: Clinical Probability Assessment

Wells Score for DVT

Interpretation

This is now commonly used in guidelines with D-dimer algorithms.

Step 2: D-Dimer

D-dimer = fibrin degradation product.

Elevated In

• DVT
• PE
• Sepsis
• Pregnancy
• Surgery
• Cancer
• Elderly

Role

• Excellent negative predictive value
• Useful in low/intermediate risk

Age-Adjusted D-Dimer

Age × 10 ng/mL after age 50.

Example:
Age 70 → cutoff 700 ng/mL

Step 3: Compression Ultrasonography

First-line Investigation

Sensitivity:

• Excellent for proximal DVT
• Lower for distal DVT

Findings

• Noncompressible vein
• Intraluminal thrombus
• Absent flow
• Loss of phasicity

Compression Ultrasound Strategies

• patient supine in the frog-leg position, apply approximately 20 to 30 degrees of reverse Trendelenburg to increase venous distention. 
• If DVT studies are negative, repeat testing may be required in one to two weeks to rule out a propagating calf DVT further. 
• No convincing evidence that properly performed venous compression ultrasound dislodges clot

Simplified NICE-Based DVT Diagnostic Algorithm

Other Imaging

CT Venography

Useful for:

• Pelvic DVT
• Iliac thrombosis

MR Venography

Useful in:

• Pregnancy
• Contrast allergy

Contrast Venography

Gold standard historically.
Rarely used now.

Laboratory Evaluation

Baseline Tests

• CBC
• PT/INR
• aPTT
• Renal function
• Liver function

Thrombophilia Testing

Indications:

• Young patient
• Recurrent thrombosis
• Strong family history
• Unusual site thrombosis

Not routinely recommended during acute thrombosis.

Differential Diagnosis

Management

NICE guidelines strongly recommend anticoagulation for proximal DVT and PE, but isolated distal (calf) DVT management may be individualized because not all distal DVTs require immediate full anticoagulation.

1. Low Molecular Weight Heparin (LMWH)

• Enoxaparin
• Dalteparin

Advantages

• Predictable
• Less HIT
• No routine monitoring

Dose

Enoxaparin dose=1 mg/kg SC every 12 hours

Alternative:
1.5 mg/kg once daily.

Renal Failure

Dose adjustment needed.

2. Unfractionated Heparin (UFH)

Preferred in:

• Severe renal failure
• High bleeding risk
• Need for procedures

Monitoring

aPTT:Target:1.5–2.5 × control

3. Direct Oral Anticoagulants (DOACs) -outpatient treatment

• contraindicated in raised INR levels(liver disease use  low-molecular-weight heparin.)
• DOACs and LMWH should be avoided in patients with end-stage renal disease. 
• In patients with remarkable dyspepsia or any past medical history suggestive of gastrointestinal bleeding, VKA, and apixaban are the preferred treatments.
• It should be noted that DOCAs, eg, dabigatran, factor Xa inhibitors, eg, rivaroxaban, and selective factor Xa inhibitors, eg, edoxaban, might be associated with higher rates of gastrointestinal bleeding.

DOAC Dosing

Apixaban

10 mg twice daily for 7 days→5 mg twice daily

Rivaroxaban

15 mg twice daily for 21 days→20 mg once daily

4. Warfarin

Why Warfarin Is Not Started Alone in Acute DVT?

Warfarin initially lowers Protein C faster than procoagulant factors, creating a temporary hypercoagulable state.

Therefore:

• Warfarin must be overlapped with:LMWH/UFH/Fondaparinux

for at least:

• 5 days minimum AND
• Until INR is therapeutic for ≥24 hours (usually INR 2–3)

Indications Where Warfarin 

• Mechanical Heart Valves-DOACs are contraindicated. Warfarin is the standard anticoagulant.

• Antiphospholipid Syndrome (APS)

• Severe Renal Failure Particularly: CrCl <15 mL/min,Dialysis patients.Warfarin often preferred because many DOACs accumulate.

5.Fondaparinux 

Fondaparinux is almost completely renally excreted.

Major Indication

Heparin-induced thrombocytopenia,If the platelet count drops to less than 75,000, switch from heparin to fondaparinux, which is not associated with heparin-induced thrombocytopenia.

Duration of Anticoagulation

Cancer-Associated Thrombosis

Preferred: DOACs OR. LMWH

Higher recurrence risk.

DVT in Pregnancy

Preferred drug:LMWH

Avoid:

• Warfarin
• Most DOACs

Continue treatment:

• Throughout pregnancy
• 6 weeks postpartum

Catheter-Directed Thrombolysis

Indications

• Massive iliofemoral DVT
• Limb-threatening thrombosis
• Severe symptoms

Drugs:

• Alteplase
• Urokinase

Mechanical Thrombectomy

Used in:

• Extensive clot burden
• Severe symptoms
• Failed anticoagulation

Inferior Vena Cava (IVC) Filter

Indications

Complications:

• Filter thrombosis
• Migration
• Recurrent DVT

Compression Stockings

May reduce:

• Symptoms
• Edema

Role in PTS prevention controversial.

Ambulation

Early ambulation encouraged after anticoagulation initiation.

Avoid prolonged bed rest.

DVT Prophylaxis

1. Mechanical Prophylaxis

Reduces venous stasis mechanically.

Includes:

1. Intermittent pneumatic compression (IPC)-superior to GCS
2. Sequential compression devices (SCD)-Sequential inflation: Distal → proximal,Physiologic venous emptying
3. Graduated compression stockings (GCS)
4. Venous foot pumps
5. Early mobilization

Recommended Pressure Settings

Typical IPC pressures:

• Foot pump: 100–130 mmHg
• Calf IPC: 35–45 mmHg
• Thigh IPC: 45–55 mmHg

Cycle:

• Inflation: 10–15 sec
• Deflation: 45–60 sec

GRADUATED COMPRESSION STOCKINGS (GCS)

Definition

Elastic stockings that exert graded pressure:

• Highest at ankle
• Gradually decreases proximally

Typical gradient:

• Ankle: 18–20 mmHg
• Calf: lower
• Thigh: even lower

Pressure Gradient in GCS

Typical:

• 100% pressure at ankle
• 70% at calf
• 40% at thigh

This gradient promotes upward venous flow.

Contraindications to Mechanical Prophylaxis

• Severe peripheral arterial disease
• Acute limb ischemia
• Severe cellulitis
• Massive edema
• Severe dermatitis
• Severe Congestive Heart Failure with Pulmonary Edema(May increase venous return excessively.)
• Open wounds
• Acute DVT

Concern:

• Possible clot dislodgement
• PE risk

(Though some newer evidence suggests carefully monitored use may be acceptable after anticoagulation initiation.)

PREVENT Trial (NEJM 2019)

Compared:

• Pharmacologic prophylaxis alone vs Pharmacologic + IPC
• Finding:No significant reduction in proximal DVT with adjunct IPC.

Implication:

• IPC alone is useful when anticoagulation contraindicated.
• Routine addition to anticoagulation may provide limited additional benefit.

2. Pharmacological Prophylaxis

Uses anticoagulants.

Includes:

• Low molecular weight heparin (LMWH)( superior efficacy compared to UFH in medical and surgical critically ill patients.)
• Unfractionated heparin (UFH)
• Fondaparinux
• Direct oral anticoagulants (DOACs)

Contraindications to Pharmacologic Prophylaxis

DRUGS WITH DOSAGE

Renal Failure Dosing

LMWH accumulates in renal dysfunction.

CrCl <30 mL/min

Options:

• Dose reduction/Anti-Xa monitoring/Use UFH instead
• Platelet counts should be monitored regularly to detect the development of heparin-induced thrombocytopenia.
• Routine Anti-Xa monitoring is NOT required for LMWH.
• Anti-Xa is mainly used in obesity, renal failure, pregnancy, and ECMO.
• Peak Anti-Xa level is checked 4 hours after LMWH dose.
• Prophylactic LMWH target: 0.2–0.5 IU/mL.
• Therapeutic BID LMWH target: 0.6–1.0 IU/mL.
• Anti-Xa is often more reliable than aPTT in critically ill patients.
• UFH therapeutic Anti-Xa target is 0.3–0.7 IU/mL.

Obesity Dosing

Obesity increases VTE risk.

Standard prophylactic doses may be inadequate.

Some centers monitor anti-Xa levels.

Fondaparinux -2.5 mg SC once daily

Renal Adjustment

Contraindicated If:CrCl <30 mL/min

Direct oral anticoagulants (DOACs)

Common Risk Assessment Models

1. Padua Prediction Score (Medical Patients)

Used in hospitalized medical patients.

High Risk

Padua score ≥4

Major Components

2. Caprini Score (Surgical Patients)

Widely used in surgical patients.

Risk Categories

3. ICU-VTE Score (Most ICU-Specific)

Designed specifically for critically ill ICU patients.

ICU-VTE Score Components

Interpretation

Limitations

• Not universally used in all ICUs
• Most ICU patients still receive prophylaxis regardless of score

Most ICU Patients Automatically considered: Moderate-to-high VTE riskTherefore: Pharmacologic prophylaxis usually started unless contraindicated

For Bleeding Risk -IMPROVE Bleeding Risk Score

Interpretation

Duration of DVT/VTE Prophylaxis

• National Comprehensive Cancer Network (NCCN), the American Society of Clinical Oncology (ASCO), and an international consensus group do not recommend routine VTE prophylaxis in ambulatory patients with cancer, except for those at very high risk of VTE
• Warfarin can be used for DVT prophylaxis but is now less favored due to INR monitoring and delayed onset.
• Aspirin is increasingly used after orthopedic surgery in selected low-risk patients.
• Aspirin is less effective than anticoagulants for VTE prevention.
• Aspirin is NOT adequate standalone prophylaxis for most ICU patients.

REFERENCES

1. Helms J, Middeldorp S, Spyropoulos AC. Thromboprophylaxis in critical care. Intensive Care Med. 2023 Jan;49(1):75-78. doi: 10.1007/s00134-022-06850-7. Epub 2022 Aug 29. PMID: 36038712; PMCID: PMC9422935.
2. Jagiasi BG, Chhallani AA, Dixit SB, Kumar R, Pandit RA, Govil D, Prayag S, Zirpe KG, Mishra RC, Chanchalani G, Kapadia FN. Indian Society of Critical Care Medicine Consensus Statement for Prevention of Venous Thromboembolism in the Critical Care Unit. Indian J Crit Care Med. 2022 Oct;26(Suppl 2):S51-S65. doi: 10.5005/jp-journals-10071-24195. PMID: 36896363; PMCID: PMC9989869.
3. Waheed SM, Kudaravalli P, Hotwagner DT. Deep Venous Thrombosis. [Updated 2023 Jan 19]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2026 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK507708/
4. Badireddy M, Mudipalli VR. Deep Venous Thrombosis Prophylaxis. [Updated 2023 May 7]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2026 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK534865/