VTE Prophylaxis in ICU

Quick Answer

Venous thromboembolism (VTE) is a major preventable complication in critically ill patients, affecting 5-15% of ICU admissions despite prophylaxis and causing significant morbidity and mortality. [1,2] All ICU patients should receive thromboprophylaxis unless absolutely contraindicated.

Risk Assessment: ICU patients are almost universally at high risk for VTE due to immobility, critical illness, central venous catheters, mechanical ventilation, and sepsis. Formal scoring systems (Caprini, Padua) may underestimate risk in this population. [3,4]

Pharmacological Prophylaxis:

• LMWH (preferred): Enoxaparin 40 mg SC once daily (or 30 mg BD in high-risk patients) offers predictable pharmacokinetics and lower HIT risk. [5,6]
• UFH: 5000 units SC every 8-12 hours; preferred in severe renal impairment (CrCl below 30 mL/min). [5]
• Evidence: PROTECT trial (PMID: 22033520) demonstrated lower PE rates with LMWH vs UFH (1.3% vs 2.3%, p=0.01), though no mortality difference. [7]

Mechanical Prophylaxis:

• Intermittent pneumatic compression (IPC): First-line when pharmacological prophylaxis contraindicated (active bleeding, severe thrombocytopenia, recent neurosurgery). [8]
• Graduated compression stockings (GCS): Limited evidence in ICU; CLOTS trials showed no benefit and potential harm in stroke patients. [9]
• PREVENT trial (PMID: 31536102): Adding IPC to pharmacological prophylaxis in ICU did not reduce proximal DVT (3.9% vs 4.2%) but did reduce mortality (7.0% vs 10.3%) in subgroup analysis of acutely ill medical patients. [10]

Special Populations:

• Traumatic brain injury (TBI): Delay pharmacological prophylaxis 24-72 hours; start when hemorrhage stable on repeat CT. [11]
• Spinal cord injury: Very high VTE risk (60-100% without prophylaxis); combined pharmacological + mechanical recommended. [12]
• Renal impairment: Use UFH for CrCl below 30 mL/min; reduce enoxaparin to 30 mg daily or use anti-Xa monitoring. [13]
• Obesity: Consider weight-based LMWH dosing (enoxaparin 0.5 mg/kg or 40 mg BD for BMI greater than 40). [14]

Timing Post-Surgery/Trauma: Balance bleeding risk vs VTE risk. Generally restart pharmacological prophylaxis 12-24 hours post-surgery, 24-48 hours post-trauma, 48-72 hours post-intracranial hemorrhage (with stable CT). [11,15]

Thromboprophylaxis Failure: Consider anti-Xa monitoring (target 0.2-0.5 IU/mL 4 hours post-dose), dose escalation, or alternative agents if breakthrough VTE occurs. [16]

---

CICM Exam Focus

Key High-Yield Points

1. All ICU patients need VTE prophylaxis: Near-universal high risk due to immobility, critical illness, CVC, mechanical ventilation, sepsis [1,2]
2. LMWH preferred over UFH: PROTECT trial showed lower PE rates (1.3% vs 2.3%) with no mortality difference; lower HIT risk [7]
3. UFH preferred in renal failure: Use UFH 5000 U SC Q8-12H when CrCl below 30 mL/min [5]
4. IPC when pharmacological contraindicated: Active bleeding, severe thrombocytopenia (below 50 x 10^9/L), recent CNS surgery [8]
5. TBI timing: Delay pharmacological prophylaxis 24-72 hours until stable on repeat CT [11]
6. Spinal cord injury: Highest VTE risk (60-100% without prophylaxis); combined mechanical + pharmacological essential [12]
7. Obesity dosing: Consider enoxaparin 0.5 mg/kg or 40 mg BD for BMI greater than 40 kg/m^2 [14]
8. Anti-Xa monitoring: Target 0.2-0.5 IU/mL at 4 hours post-dose for prophylactic LMWH; useful in extremes of weight and renal impairment [16]

Common Viva Themes

• Risk assessment and prophylaxis decision-making in the trauma patient
• Management of pharmacological prophylaxis in severe renal impairment
• Timing of thromboprophylaxis after intracranial hemorrhage/TBI
• Approach to breakthrough VTE on prophylaxis
• Evidence base for mechanical vs pharmacological prophylaxis (PROTECT, PREVENT trials)
• Thromboprophylaxis in the morbidly obese patient
• HIT risk comparison between LMWH and UFH

Common Pitfalls

• Failing to prescribe VTE prophylaxis on ICU admission ("forgotten" or delayed)
• Using LMWH in severe renal impairment without dose adjustment or anti-Xa monitoring
• Over-reliance on GCS (limited evidence, potential harm in stroke)
• Delaying pharmacological prophylaxis too long after surgery/trauma (VTE risk increases significantly after 24-48 hours)
• Not recognizing that mechanical prophylaxis alone is inferior to pharmacological prophylaxis in most ICU patients
• Forgetting to check platelet count and monitor for HIT with UFH use
• Not adjusting LMWH dose in obesity (standard doses may be inadequate)
• Missing contraindications to pharmacological prophylaxis (active bleeding, recent CNS surgery)

---

Key Points

• VTE affects 5-15% of ICU patients despite prophylaxis; mortality 6-10% in untreated PE [1,2]
• All ICU patients need thromboprophylaxis; near-universal high risk [1,3]
• LMWH (enoxaparin 40 mg SC daily) preferred over UFH; lower PE rate in PROTECT trial [7]
• UFH 5000 U SC Q8-12H for CrCl below 30 mL/min; does not require dose adjustment [5]
• IPC first-line when pharmacological prophylaxis contraindicated [8]
• PREVENT trial: IPC + pharmacological prophylaxis did not reduce DVT vs pharmacological alone in ICU [10]
• GCS: Limited evidence; CLOTS trials showed no benefit, potential harm in stroke [9]
• TBI: Delay pharmacological prophylaxis 24-72 hours until hemorrhage stable on CT [11]
• Spinal cord injury: Highest VTE risk; combined mechanical + pharmacological essential [12]
• Obesity: Consider enoxaparin 0.5 mg/kg or 40 mg BD for BMI greater than 40; anti-Xa monitoring [14,16]
• Renal impairment: Reduce enoxaparin to 30 mg daily or use anti-Xa monitoring for CrCl below 30 mL/min [13]
• Anti-Xa target: 0.2-0.5 IU/mL at 4 hours post-dose for prophylactic LMWH [16]

---

Epidemiology

Incidence of VTE in ICU

Venous thromboembolism is a major healthcare burden, with ICU patients at particularly high risk due to multiple concurrent risk factors. The incidence varies based on population studied, prophylaxis regimen, and screening methods used.

Overall incidence: Without prophylaxis, the incidence of DVT in critically ill patients is 25-40%, with proximal DVT rates of 10-20%. With standard pharmacological prophylaxis, incidence is reduced to 5-15% for any DVT and 3-5% for proximal DVT. [1,2,17]

Pulmonary embolism: PE occurs in 1-5% of ICU patients despite prophylaxis, with fatal PE in 0.5-1%. Autopsy studies suggest clinical PE is underdiagnosed, with rates of 7-27% at post-mortem examination. [18,19]

ICU-acquired VTE: Approximately 60-70% of VTE events in ICU patients are ICU-acquired (occurring greater than 48 hours after admission), emphasizing the importance of early and sustained prophylaxis throughout the ICU stay. [2]

Risk Factors

ICU patients accumulate multiple VTE risk factors, making individual risk assessment challenging. The major risk factors include:

Patient-related factors:

• Age greater than 60 years (OR 1.5-2.0)
• Previous VTE (OR 3.0-5.0)
• Active malignancy (OR 2.0-4.0)
• Obesity (BMI greater than 30, OR 1.5-2.5)
• Thrombophilia (Factor V Leiden, prothrombin gene mutation)
• Pregnancy/postpartum
• Oral contraceptives/hormone replacement therapy

ICU-related factors:

• Immobility/mechanical ventilation (OR 2.0-3.0)
• Central venous catheter (OR 2.0-3.5)
• Sepsis (OR 1.5-3.0)
• Vasopressor use (OR 2.0-2.5)
• Renal replacement therapy (OR 1.5-2.0)
• Sedation/neuromuscular blockade (OR 2.0-3.0)
• Surgery (especially orthopaedic, major abdominal, neurosurgery)
• Trauma (especially pelvic fractures, spinal cord injury)

Disease-specific factors:

• Stroke (both ischemic and hemorrhagic)
• Spinal cord injury (60-100% incidence without prophylaxis)
• Major trauma (40-80% incidence without prophylaxis)
• Burns greater than 20% TBSA
• Heart failure
• Respiratory failure requiring mechanical ventilation

[1,2,3,4,17,20]

Mortality Impact

VTE is associated with significant mortality in critically ill patients:

Effective thromboprophylaxis can reduce VTE incidence by 50-70% and VTE-related mortality by 30-50%. [1,2,18]

---

Risk Assessment Scores

Overview

While critically ill patients are almost universally at high VTE risk, formal risk assessment tools help quantify risk and guide prophylaxis intensity. The most commonly used scores are the Caprini score (surgical patients) and Padua Prediction Score (medical patients).

Caprini Risk Assessment Model

The Caprini score is the most widely validated VTE risk assessment tool for surgical patients. It assigns points based on patient and surgical factors, with cumulative score determining VTE risk category. [3,21]

Caprini Score Components:

Risk Categories and Recommendations:

[3,21]

Padua Prediction Score

The Padua score is validated for medical patients and identifies those at high risk of VTE. [4,22]

Padua Score Components:

Interpretation:

• Score below 4: Low risk (0.3% 90-day VTE risk) - Consider no pharmacological prophylaxis
• Score ≥4: High risk (11% 90-day VTE risk) - Pharmacological prophylaxis recommended

Limitations in ICU: Both Caprini and Padua scores may underestimate VTE risk in ICU patients due to additional ICU-specific risk factors (CVC, mechanical ventilation, sedation, vasopressors) not fully captured in these tools. Most intensivists consider all ICU patients requiring greater than 24-48 hours of critical care to be at high VTE risk warranting pharmacological prophylaxis unless contraindicated. [3,4,22]

IMPROVE Bleeding Risk Score

When considering pharmacological prophylaxis, bleeding risk should also be assessed. The IMPROVE bleeding risk score helps identify patients at high risk of major bleeding. [23]

IMPROVE Bleeding Score Components:

Interpretation:

• Score ≥7: High bleeding risk - Consider mechanical prophylaxis alone initially
• Score below 7: Standard bleeding risk - Pharmacological prophylaxis appropriate

---

Pharmacological Prophylaxis

Low Molecular Weight Heparin (LMWH)

LMWH is the preferred agent for thromboprophylaxis in most ICU patients due to superior pharmacokinetics, predictable dose-response, lower HIT incidence, and evidence of improved outcomes compared to UFH. [5,6,7]

Enoxaparin (Clexane)

Standard prophylactic dose: 40 mg SC once daily

High-risk dosing options:

• 30 mg SC twice daily (used in high-risk surgical patients, some trauma protocols)
• 0.5 mg/kg SC once daily (weight-based prophylaxis)

Mechanism of action: Binds antithrombin III and primarily inhibits Factor Xa (anti-Xa:anti-IIa ratio of approximately 3:1). This provides more predictable anticoagulant effect compared to UFH's broader inhibition of factors Xa, IXa, XIa, XIIa, and thrombin. [5]

Pharmacokinetics:

• Bioavailability: ~90% (vs 30% for UFH)
• Half-life: 4-5 hours (allows once-daily dosing)
• Renal elimination: Dose adjustment required in renal impairment
• Peak anti-Xa activity: 3-5 hours post-injection

Advantages over UFH:

• Once-daily dosing improves compliance
• More predictable anticoagulant response
• Lower incidence of HIT (0.1-0.5% vs 1-3% for UFH)
• No routine monitoring required in most patients
• Lower osteoporosis risk with long-term use

Evidence - PROTECT Trial (PMID: 22033520): The largest RCT comparing LMWH vs UFH in ICU. [7]

• Population: 3764 medical-surgical ICU patients
• Intervention: Dalteparin 5000 IU SC daily vs UFH 5000 U SC BD
• Primary outcome: Proximal DVT (5.1% dalteparin vs 5.8% UFH, HR 0.92, p=0.57)
• Key secondary outcome: PE significantly lower with dalteparin (1.3% vs 2.3%, HR 0.51, p=0.01)
• HIT: Significantly lower with dalteparin (0.3% vs 0.6%, p=0.046)
• Mortality: No significant difference
• Conclusion: LMWH preferred for ICU thromboprophylaxis; lower PE and HIT rates

[5,6,7,24]

Dose Adjustment in Renal Impairment

LMWH is renally cleared, and accumulation occurs in renal impairment, increasing bleeding risk. [13,25]

Anti-Xa monitoring for LMWH prophylaxis:

• Sample: 4 hours post-dose (peak level)
• Target: 0.2-0.5 IU/mL for prophylaxis
• Indications: CrCl below 30 mL/min on reduced LMWH dose, extremes of body weight, pregnancy, breakthrough VTE

[13,16,25]

Obesity Dosing

Standard LMWH prophylactic doses may be inadequate in obese patients due to altered volume of distribution. [14,26]

Recommended approaches for obesity (BMI greater than 40 kg/m^2 or weight greater than 120 kg):

1. Fixed increased dose: Enoxaparin 40 mg SC twice daily
2. Weight-based dose: Enoxaparin 0.5 mg/kg SC once daily (max 40 mg)
3. Anti-Xa guided: Standard dose with anti-Xa monitoring; adjust if subtherapeutic

Evidence: Observational studies suggest standard-dose LMWH achieves subtherapeutic anti-Xa levels in 40-60% of morbidly obese patients. Weight-based dosing improves target attainment without significantly increasing bleeding. [14,26]

Unfractionated Heparin (UFH)

UFH remains an important option, particularly in renal impairment, when rapid reversibility is needed, and in some resource-limited settings. [5]

Standard prophylactic dosing:

• 5000 units SC every 8 hours (preferred in very high-risk patients)
• 5000 units SC every 12 hours (acceptable in moderate-risk patients)

Mechanism of action: Binds antithrombin III and inhibits factors Xa, IXa, XIa, XIIa, and thrombin (IIa). This broader inhibition provides less predictable anticoagulant effect but potentially greater antithrombotic efficacy in some settings. [5]

Pharmacokinetics:

• Bioavailability: ~30% (variable)
• Half-life: 1-2 hours (allows rapid reversal with protamine)
• Hepatic and reticuloendothelial clearance (dose adjustment not required in renal impairment)
• No accumulation in renal failure

Advantages:

• Safe in severe renal impairment (CrCl below 30 mL/min)
• Rapidly reversible with protamine sulfate
• Lower cost in some settings
• Extensive safety data

Disadvantages:

• Higher HIT incidence (1-3% vs 0.1-0.5% for LMWH)
• More variable anticoagulant response
• Requires twice- or thrice-daily dosing
• Higher osteoporosis risk with long-term use

UFH vs LMWH in renal failure: A meta-analysis of thromboprophylaxis in patients with CrCl below 30 mL/min found similar efficacy between UFH and reduced-dose LMWH, but UFH had lower bleeding rates (OR 0.55, 95% CI 0.31-0.98). UFH is therefore preferred in severe renal impairment. [5,13,25]

Alternative Agents

Fondaparinux (Arixtra)

Synthetic pentasaccharide that selectively inhibits Factor Xa via antithrombin.

Prophylactic dose: 2.5 mg SC once daily

Advantages:

• No risk of HIT (does not bind PF4)
• Once-daily dosing
• Predictable pharmacokinetics

Disadvantages:

• Long half-life (17-21 hours) - not rapidly reversible
• Renally cleared - contraindicated in CrCl below 30 mL/min
• Limited ICU-specific data
• Higher cost

Indications in ICU: Primarily used for patients with history of HIT who require pharmacological prophylaxis. [5,27]

Direct Oral Anticoagulants (DOACs)

DOACs (rivaroxaban, apixaban, dabigatran) are not routinely used for ICU thromboprophylaxis due to:

• Inability to administer enterally in many ICU patients
• Variable absorption in critical illness
• Limited reversal options
• Lack of ICU-specific efficacy data

They may be considered for step-down prophylaxis in patients transitioning from ICU with prolonged immobility risk. [28]

---

Mechanical Prophylaxis

Intermittent Pneumatic Compression (IPC)

IPC devices apply cyclic pressure to the legs via inflatable cuffs, enhancing venous blood flow and reducing venous stasis. They also stimulate endogenous fibrinolysis and release of tissue plasminogen activator (tPA). [8]

Mechanism:

• Increases peak venous velocity by 200-400%
• Reduces venous stasis
• Enhances fibrinolytic activity
• No bleeding risk

Indications:

1. Primary prophylaxis when pharmacological prophylaxis contraindicated:

   • Active bleeding (intracranial, gastrointestinal, post-operative)
   • Severe thrombocytopenia (platelets below 50 x 10^9/L)
   • Recent CNS surgery or hemorrhagic stroke
   • Severe coagulopathy (INR greater than 1.5-2.0, aPTT greater than 2x normal)
   • High bleeding risk procedures planned below 24 hours

2. Adjunctive prophylaxis in very high-risk patients:

   • Major trauma
   • Spinal cord injury
   • Major orthopaedic surgery

Contraindications:

• Acute DVT or suspected DVT
• Severe peripheral arterial disease
• Local leg conditions (skin grafts, wounds, ulcers, severe edema)
• Severe heart failure (relative)

Evidence - PREVENT Trial (PMID: 31536102): Large RCT of adjunctive IPC in ICU. [10]

• Population: 2003 medical-surgical ICU patients (predominantly medical)
• Intervention: IPC + pharmacological prophylaxis vs pharmacological prophylaxis alone
• Primary outcome: Proximal DVT at day 28 - no significant difference (3.9% vs 4.2%, OR 0.93, p=0.74)
• Secondary outcomes: No significant differences in PE, mortality, or bleeding
• Subgroup finding: Trend toward benefit in acutely ill medical patients (mortality 7.0% vs 10.3%)
• Conclusion: Routine addition of IPC to pharmacological prophylaxis not recommended for all ICU patients

Practical considerations:

• Ensure adequate device fit
• Remove only for brief periods (ambulation, procedures)
• Check skin integrity daily
• Target greater than 18 hours per day of use

[8,10,29]

Graduated Compression Stockings (GCS)

GCS apply graded pressure to the legs (greatest at ankle, decreasing proximally) to reduce venous distension and improve venous return.

Evidence in ICU/critically ill: The CLOTS trials provide the most rigorous evidence for GCS in hospitalized patients. [9,30]

CLOTS 1 (PMID: 19269261):

• Population: 2518 stroke patients
• Intervention: Thigh-length GCS vs no GCS
• Result: No significant DVT reduction (10.0% vs 10.5%, OR 0.94, p=0.68)
• Harm: Significantly increased skin complications (5% vs 1%)

CLOTS 2 (PMID: 20129166):

• Population: 3114 stroke patients
• Intervention: Thigh-length vs below-knee GCS
• Result: Thigh-length superior (6.3% vs 8.8% DVT, OR 0.69, p=0.008)

CLOTS 3 (PMID: 23726390):

• Population: 2876 immobile stroke patients
• Intervention: IPC vs no IPC (many on GCS)
• Result: IPC significantly reduced DVT (8.5% vs 12.1%, OR 0.65, p=0.001) and possibly mortality

Summary: GCS alone provide minimal if any benefit in hospitalized patients and may cause harm. IPC is superior to GCS. GCS are not recommended as sole mechanical prophylaxis in ICU patients. [9,30]

Inferior Vena Cava (IVC) Filters

IVC filters are occasionally considered when both pharmacological and mechanical prophylaxis are contraindicated or have failed.

Indications (limited evidence):

• Contraindication to anticoagulation AND IPC not feasible
• Recurrent PE despite adequate anticoagulation
• Free-floating proximal DVT with contraindication to anticoagulation
• Prophylactic placement before high-risk surgery (controversial)

Evidence: The PREPIC trial (PMID: 9739977) showed IVC filters reduce PE but increase DVT and have no mortality benefit. Long-term complications include filter thrombosis, migration, fracture, and IVC occlusion. Retrievable filters should be removed as soon as anticoagulation can be resumed. [31]

Current recommendations: Prophylactic IVC filters are not routinely recommended. Placement should be individualized and filters retrieved when no longer needed. [31,32]

---

Special Populations

Traumatic Brain Injury (TBI)

Patients with TBI are at particularly high VTE risk due to immobility, catecholamine surge causing hypercoagulability, and potential venous stasis from positioning. However, the risk of intracranial hemorrhage expansion creates a challenging balance. [11,33]

VTE incidence in TBI: 15-25% DVT, 1-5% PE (without prophylaxis)

Timing of pharmacological prophylaxis:

Definition of "stable": No progression of hemorrhage on repeat CT at 24-48 hours.

Monitoring: Some centers perform repeat CT scan 12-24 hours after initiating pharmacological prophylaxis to confirm no hemorrhage expansion.

Evidence: A systematic review of 7 studies (Jamjoom AA, PMID: 24139583) found pharmacological prophylaxis initiated within 72 hours did not increase hemorrhage progression compared to delayed or no prophylaxis, while significantly reducing VTE. [11,33]

Recommended protocol:

1. Start IPC on admission (unless lower extremity injury contraindicates)
2. Daily neurosurgical review for pharmacological prophylaxis timing
3. Repeat CT at 24-48 hours to confirm hemorrhage stability
4. Start enoxaparin 40 mg SC daily when hemorrhage stable
5. Continue mechanical + pharmacological prophylaxis until ambulatory

Spinal Cord Injury (SCI)

SCI carries the highest VTE risk of any patient population, with reported DVT rates of 60-100% without prophylaxis and PE as a leading cause of death in acute SCI. [12,34]

Risk factors specific to SCI:

• Paralysis causing complete venous stasis
• Hypercoagulable state from tissue injury
• Loss of skeletal muscle pump
• Frequent need for immobilization
• Associated injuries (polytrauma)

Recommended prophylaxis (combined approach):

• Mechanical: IPC immediately on admission (unless lower extremity injury)
• Pharmacological: LMWH (enoxaparin 30 mg SC BD or 40 mg SC daily) starting 24-72 hours post-injury if no active bleeding
• Duration: Minimum 8-12 weeks; some guidelines recommend 3 months for complete motor paralysis

Evidence: A Cochrane review (PMID: 12804510) found LMWH superior to UFH for VTE prevention in SCI (OR 0.52, 95% CI 0.35-0.78). Combined mechanical and pharmacological prophylaxis is recommended by major guidelines. [12,34,35]

Screening: Some experts recommend routine lower extremity duplex ultrasound screening at 2 weeks in high-risk SCI patients, though evidence for this approach is limited.

Major Trauma

Trauma patients have VTE rates of 20-60% without prophylaxis, with risk increasing with injury severity score, pelvic/lower extremity fractures, and spinal cord injury. [15,36]

Unique challenges in trauma:

• Active bleeding at presentation
• Need for emergent surgery
• Multiple competing priorities
• Coexisting TBI or SCI
• Variable injury patterns

Timing recommendations:

Eastern Association for the Surgery of Trauma (EAST) guidelines (PMID: 11574327) recommend:

1. LMWH is preferred over UFH in trauma patients
2. IPC should be used until pharmacological prophylaxis can be started
3. Combined mechanical + pharmacological prophylaxis for high-risk patients
4. Consider inferior vena cava filter only if both pharmacological and mechanical prophylaxis are contraindicated and patient is at very high VTE risk

[15,36,37]

Renal Impairment

Patients with renal impairment are at increased VTE risk (immobility, inflammation, platelet dysfunction paradoxically increasing thrombosis) but also at increased bleeding risk from anticoagulant accumulation. [13,25]

Prophylaxis recommendations by CrCl:

Anti-Xa monitoring in renal impairment:

• Sample: 4 hours post-dose (peak)
• Target: 0.2-0.5 IU/mL for prophylaxis
• If elevated: Reduce dose or switch to UFH
• If subtherapeutic: Consider dose increase or evaluate for subcutaneous absorption issues

Special considerations:

• Patients on CRRT have variable drug clearance depending on filter type and dose
• High-flux dialysis may clear LMWH; dose after dialysis session
• UFH does not accumulate and does not require dose adjustment

[13,25,38]

Obesity

Obese patients have 2-3 times higher VTE risk due to increased venous stasis, chronic inflammation, and prothrombotic adipokines. Standard LMWH doses may be inadequate due to altered volume of distribution. [14,26]

Dosing recommendations for obesity:

Options for BMI greater than 40 kg/m^2:

1. Enoxaparin 40 mg SC twice daily - Simplest approach, well-studied
2. Enoxaparin 0.5 mg/kg SC once daily - Weight-based, maximum 40 mg
3. Anti-Xa guided dosing - Standard dose with peak anti-Xa monitoring; adjust to target 0.2-0.5 IU/mL

Evidence: Studies in bariatric surgery patients demonstrate standard-dose LMWH achieves subtherapeutic anti-Xa levels in 40-60% of patients. Weight-adjusted dosing improves target attainment without significant bleeding increase. [14,26,39]

Mechanical prophylaxis: IPC is important in obese patients as an adjunct. Standard cuff sizes may be inadequate; ensure appropriate fit with large or bariatric-specific cuffs.

Pregnancy and Peripartum

Pregnancy creates a hypercoagulable state with 5-10 times increased VTE risk. Critical illness during pregnancy further amplifies this risk. [40]

Key considerations:

• LMWH is safe in pregnancy (does not cross placenta)
• UFH also safe; preferred if delivery expected within 24 hours (shorter half-life)
• Warfarin is teratogenic - avoid in pregnancy
• DOACs: Insufficient safety data - avoid in pregnancy
• IPC: Safe adjunct, use until fully ambulatory

Peripartum dosing:

• Antepartum: Enoxaparin 40 mg SC daily (or weight-based 0.5-1 mg/kg for therapeutic dosing)
• Peripartum: Hold LMWH 12-24 hours before planned delivery; switch to UFH if delivery imminent
• Postpartum: Resume LMWH 12-24 hours after vaginal delivery, 24-48 hours after cesarean section (if adequate hemostasis)

High-risk indications requiring therapeutic anticoagulation:

• Mechanical heart valve
• History of recurrent VTE
• Antiphospholipid syndrome with history of VTE

---

Timing of Thromboprophylaxis

General Principles

The timing of pharmacological thromboprophylaxis requires balancing the risk of VTE (which increases with duration of immobility) against bleeding risk (which is highest in the immediate post-operative/post-injury period). [15,41]

Key concepts:

• VTE risk begins immediately upon hospitalization/immobilization
• Pharmacological prophylaxis should be started as soon as bleeding risk is acceptable
• Mechanical prophylaxis can be started immediately unless contraindicated
• Delays in pharmacological prophylaxis should be as short as possible

Post-Operative Timing

Preoperative vs postoperative initiation: There is ongoing debate about preoperative vs postoperative LMWH initiation. European practice often favors preoperative dosing (evening before surgery), while North American and Australasian practice typically initiates postoperatively. Both approaches have demonstrated efficacy; consistency of protocol is most important. [41]

Post-Trauma Timing

See specific sections on TBI, SCI, and Major Trauma above.

General trauma principles:

• Start IPC immediately on ICU admission
• Aim for pharmacological prophylaxis within 24-48 hours in most patients
• Delay pharmacological prophylaxis only for active bleeding or very high bleeding risk
• Daily reassessment of bleeding risk and readiness for pharmacological prophylaxis

Post-Intracranial Hemorrhage

Patients with intracranial hemorrhage (ICH) are at high VTE risk due to immobility but also at risk of hemorrhage expansion or rebleeding. [33,42]

Timing recommendations:

Evidence: A meta-analysis (PMID: 27160832) of pharmacological prophylaxis after ICH found no significant increase in hemorrhage expansion (OR 1.11, 95% CI 0.73-1.68) when initiated greater than 48 hours after hemorrhage stabilization, with significant reduction in VTE. [33,42]

---

Monitoring and Troubleshooting

Anti-Xa Monitoring

Anti-Xa monitoring measures the anticoagulant effect of heparin by quantifying inhibition of Factor Xa. It is useful for LMWH dose adjustment in specific populations. [16]

Indications for anti-Xa monitoring:

1. Renal impairment (CrCl below 30 mL/min on LMWH)
2. Extremes of body weight (BMI greater than 40 kg/m^2 or below 50 kg)
3. Pregnancy (altered volume of distribution)
4. Breakthrough VTE on prophylaxis (suspected prophylaxis failure)
5. Prolonged prophylaxis (greater than 4 weeks)
6. Drug interaction concerns

Sampling and targets:

• Timing: 4 hours post-dose (peak level)
• Prophylactic target: 0.2-0.5 IU/mL
• Therapeutic target: 0.6-1.0 IU/mL (for treatment dosing)

Interpretation and dose adjustment:

Limitations:

• Not standardized between laboratories
• Does not correlate perfectly with clinical outcomes
• UFH anti-Xa levels less reliable than LMWH

[16,43]

Thromboprophylaxis Failure

Breakthrough VTE on prophylaxis (3-10% of ICU patients) should prompt systematic evaluation. [44]

Causes of prophylaxis failure:

1. Inadequate dosing:

   • Obesity with standard-dose LMWH
   • Renal impairment with excessive LMWH
   • Subtherapeutic anti-Xa levels

2. Poor absorption:

   • Edematous subcutaneous tissues
   • Vasopressor-induced vasoconstriction
   • Injection technique issues

3. Missed doses:

   • Withheld for procedures
   • Nursing errors
   • Delayed prescribing

4. Excessive VTE risk:

   • Very high-risk population (SCI, major trauma)
   • Active malignancy
   • Known thrombophilia

Evaluation steps:

1. Confirm VTE diagnosis (imaging)
2. Review medication administration records
3. Check anti-Xa level (if on LMWH)
4. Evaluate for occult malignancy if unprovoked VTE
5. Consider thrombophilia testing in young patients with unprovoked VTE

Management of breakthrough VTE:

1. Convert to therapeutic anticoagulation
2. Consider IVC filter if anticoagulation contraindicated
3. Review and optimize modifiable risk factors
4. Extended duration anticoagulation (minimum 3 months)

Heparin-Induced Thrombocytopenia (HIT)

HIT is an immune-mediated complication of heparin exposure causing platelet activation and paradoxical thrombosis. It is more common with UFH (1-3%) than LMWH (0.1-0.5%). [45,46]

Clinical features:

• Platelet count fall greater than 50% from baseline OR nadir below 150 x 10^9/L
• Timing: Typically days 5-10 of heparin exposure
• May occur earlier if prior heparin exposure within 100 days
• Thrombosis (arterial or venous) in 30-50% of untreated cases

4Ts Score for HIT probability:

Score interpretation:

• 0-3: Low probability (below 5%) - HIT unlikely, continue heparin
• 4-5: Intermediate probability (15-30%) - Send HIT antibody, consider alternative
• 6-8: High probability (greater than 80%) - Stop heparin, start alternative anticoagulant

Management of confirmed/suspected HIT:

1. Stop all heparin (including flushes, heparin-coated devices)
2. Start alternative anticoagulant:
   • Argatroban: 2 mcg/kg/min IV (reduce in hepatic impairment); preferred in renal impairment
   • Bivalirudin: 0.15-0.25 mg/kg/h IV (reduce in renal impairment)
   • Fondaparinux: 5-10 mg SC daily (off-label but increasingly used)
3. Do not transfuse platelets (fuels thrombosis)
4. Image for occult thrombosis (upper and lower extremity duplex, consider CT chest)
5. Transition to warfarin only after platelet recovery (avoid warfarin-induced skin necrosis)

LMWH in HIT: Do not substitute LMWH for UFH in HIT due to high cross-reactivity (40-80%). [45,46]

---

Evidence Summary

Key Trials

PROTECT Trial (PMID: 22033520)

Title: Dalteparin versus unfractionated heparin in critically ill patients. [7]

Design: Multicenter, randomized, double-blind, double-dummy trial

Population: 3764 medical-surgical ICU patients at 67 centers

Intervention:

• Dalteparin 5000 IU SC once daily + placebo SC twice daily
• vs UFH 5000 U SC twice daily + placebo SC once daily

Primary outcome: Proximal leg DVT detected by compression ultrasound

• Dalteparin: 5.1%
• UFH: 5.8%
• HR 0.92 (95% CI 0.68-1.23), p=0.57

Key secondary outcomes:

• Pulmonary embolism: Dalteparin 1.3% vs UFH 2.3% (HR 0.51, 95% CI 0.30-0.88, p=0.01) - Significant
• HIT: Dalteparin 0.3% vs UFH 0.6% (p=0.046) - Significant
• Any DVT: Dalteparin 5.6% vs UFH 8.7% (HR 0.69, 95% CI 0.52-0.90, p=0.006) - Significant
• Major bleeding: No significant difference (5.5% vs 5.6%)
• Mortality (90-day): No significant difference (22.3% vs 21.9%)

Conclusion: LMWH provides superior protection against PE and HIT compared to UFH, with no increase in bleeding. LMWH is preferred for ICU thromboprophylaxis.

Limitations:

• Once-daily UFH dosing (twice daily) may be suboptimal
• Predominantly surgical population
• Dalteparin used; may not be generalizable to all LMWHs

---

PREVENT Trial (PMID: 31536102)

Title: Adjunctive intermittent pneumatic leg compression for venous thromboprophylaxis in critically ill patients. [10]

Design: Open-label, multicenter randomized trial

Population: 2003 medical-surgical ICU patients at 20 sites (predominantly medical patients)

Intervention:

• Pharmacological prophylaxis + IPC (thigh-length)
• vs Pharmacological prophylaxis alone

Primary outcome: Incident proximal lower-limb DVT by day 28

• IPC group: 3.9%
• Control group: 4.2%
• OR 0.93 (95% CI 0.60-1.44), p=0.74

Key secondary outcomes:

• Any DVT: 9.6% vs 8.4% (no significant difference)
• Pulmonary embolism: 1.5% vs 1.3% (no significant difference)
• 28-day mortality: 14.7% vs 15.6% (no significant difference)
• Major bleeding: 2.0% vs 1.8% (no significant difference)

Pre-specified subgroups (exploratory):

• Acutely ill medical patients: IPC mortality 7.0% vs control 10.3% (OR 0.66, p=0.048) - Hypothesis-generating

Conclusion: Routine addition of IPC to pharmacological prophylaxis does not reduce proximal DVT in critically ill patients. IPC may have mortality benefit in medical patients (requires further study).

Implications:

• IPC should not be routinely added to pharmacological prophylaxis in all ICU patients
• IPC remains indicated when pharmacological prophylaxis is contraindicated
• Potential mortality benefit in medical subgroup warrants further investigation

---

Other Relevant Trials

CLOTS 3 Trial (PMID: 23726390): Demonstrated IPC reduces DVT (8.5% vs 12.1%) and possibly death in immobile stroke patients. Supports use of IPC when pharmacological prophylaxis is contraindicated. [9]

MEDENOX Trial (PMID: 10477781): Established efficacy of enoxaparin 40 mg SC daily for medical patients, showing significant DVT reduction vs placebo (5.5% vs 14.9%, RR 0.37). [47]

CERTIFY Trial (PMID: 20929981): Demonstrated non-inferiority of certoparin 3000 U once daily to UFH 5000 U three times daily in medical patients, supporting LMWH as preferred agent. [48]

---

Management Algorithm

Initial Assessment (ICU Admission)

All ICU Patients
      ↓
Assess VTE Risk
(Nearly all ICU patients HIGH risk)
      ↓
Assess Bleeding Risk
      ↓
┌─────────────────────┬─────────────────────┐
│ Low Bleeding Risk   │ High Bleeding Risk  │
│                     │                     │
│ • No active bleed   │ • Active bleeding   │
│ • Plt greater than 50           │ • Plt below 50           │
│ • INR below 1.5          │ • INR greater than 1.5          │
│ • No CNS hemorrhage │ • Recent CNS surgery│
│ • greater than 24h post-surgery │ • below 24h post-surgery │
└────────┬────────────┴──────────┬──────────┘
         ↓                       ↓
   Pharmacological          Mechanical
   Prophylaxis              Prophylaxis
   + IPC (optional)         (IPC)
         ↓                       ↓
   LMWH preferred          Daily reassessment
   (or UFH if renal        for pharmacological
   impairment)             prophylaxis

Drug Selection

Pharmacological Prophylaxis Decision
              ↓
┌─────────────────────────────────────┐
│ Check Renal Function (CrCl)         │
└────────────────┬────────────────────┘
                 ↓
    ┌────────────┴────────────┐
    ↓                         ↓
CrCl ≥30 mL/min         CrCl below 30 mL/min
    ↓                         ↓
ENOXAPARIN              UFH 5000 U SC
40 mg SC daily          Q8-12H
    ↓                         ↓
Check for obesity       No dose adjustment
BMI greater than 40 kg/m²?          needed
    ↓
Yes → 40 mg SC BD
      or 0.5 mg/kg
      (consider anti-Xa)

Special Situations Algorithm

Post-TBI/Intracranial Hemorrhage
              ↓
Start IPC immediately
              ↓
Daily neurosurgery review
              ↓
Repeat CT at 24-48 hours
              ↓
┌─────────────┴─────────────┐
↓                           ↓
Hemorrhage STABLE       Hemorrhage EXPANDING
↓                           ↓
Start enoxaparin        Continue IPC only
40 mg SC daily          Daily CT reassessment
48-72h post-injury      Start pharmacological
                        when stable

Post-Spinal Cord Injury
              ↓
Start IPC immediately
              ↓
Start enoxaparin 30 mg SC BD
24-72 hours post-injury
(if no active bleeding)
              ↓
Continue combined prophylaxis
for 8-12 weeks minimum

---

SAQ Practice Questions

SAQ 1: VTE Prophylaxis in Polytrauma

Question: A 45-year-old male is admitted to your ICU following a motor vehicle collision. He has sustained a closed traumatic brain injury (GCS 9, with small bifrontal contusions on CT), a grade III liver laceration managed non-operatively, bilateral rib fractures, and a right femoral shaft fracture awaiting surgery tomorrow.

(a) Outline your approach to VTE prophylaxis for this patient. (40%) (b) When would you consider starting pharmacological thromboprophylaxis, and what agent would you use? (30%) (c) What monitoring would you implement? (30%)

Model Answer:

(a) Approach to VTE prophylaxis (40%)

Risk assessment:

• This patient is at VERY HIGH VTE risk:
  • Major trauma (Injury Severity Score likely greater than 15)
  • Traumatic brain injury (immobility, hypercoagulable state)
  • Lower extremity fracture
  • Prolonged ICU stay anticipated
  • Mechanical ventilation
• VTE incidence without prophylaxis: 40-80% in major trauma

Immediate measures (Day 0-1):

• Mechanical prophylaxis with IPC to left leg (right leg has femoral fracture)
• Avoid femoral central venous catheter if possible (prefer subclavian/IJ)
• Early mobilization protocols when feasible
• Maintain adequate hydration

Contraindications to pharmacological prophylaxis currently:

• Active intracranial hemorrhage (bifrontal contusions)
• Solid organ injury with ongoing hemorrhage risk
• Pending surgery (femoral fracture)

(b) Timing and agent selection (30%)

Timing considerations:

1. TBI: Delay pharmacological prophylaxis until repeat CT at 24-48 hours shows stable hemorrhage; typically 48-72 hours post-injury
2. Liver laceration: Generally safe to start after 48-72 hours in grade III injury managed non-operatively
3. Femoral fracture surgery: Restart 12-24 hours post-operatively

Recommended timing: 48-72 hours post-injury, after:

• Repeat CT brain shows stable hemorrhage (no progression)
• Femoral fracture fixation completed
• No evidence of active bleeding from liver laceration

Agent: Enoxaparin 40 mg SC daily

• LMWH preferred over UFH in trauma patients (better outcomes, lower HIT risk)
• Standard dosing appropriate if normal renal function and BMI below 40

(c) Monitoring (30%)

Clinical monitoring:

• Daily platelet count (HIT risk with any heparin)
• Signs of VTE (limb swelling, unexplained hypoxia, tachycardia)
• Signs of bleeding (hemoglobin trends, drain output, neurological examination)

Imaging:

• Repeat CT brain 12-24 hours after initiating pharmacological prophylaxis
• Consider baseline and weekly lower extremity duplex ultrasound (high-risk population)

Laboratory:

• Anti-Xa levels generally not required with standard dosing in normal weight and renal function
• If concerns about absorption (edema, vasopressors): check peak anti-Xa at 4 hours (target 0.2-0.5 IU/mL)

IPC compliance:

• Target greater than 18 hours/day use
• Document in daily goals

---

SAQ 2: Thromboprophylaxis in Renal Impairment

Question: A 72-year-old female with end-stage renal disease (on hemodialysis) is admitted to ICU with severe community-acquired pneumonia requiring mechanical ventilation and vasopressor support.

(a) Discuss the challenges of VTE prophylaxis in patients with severe renal impairment. (30%) (b) Outline your choice of agent and dosing regimen for this patient. (40%) (c) How would you monitor for adequacy and complications of thromboprophylaxis? (30%)

Model Answer:

(a) Challenges of VTE prophylaxis in severe renal impairment (30%)

Increased VTE risk:

• ESRD patients have paradoxically HIGH VTE risk despite uremic platelet dysfunction
• Contributing factors: inflammation, endothelial dysfunction, immobility, central venous catheters
• Critical illness (sepsis, mechanical ventilation) further increases risk

Pharmacological challenges:

• LMWH accumulation: Renally cleared; half-life increases from 4-5 hours to 12-24+ hours in ESRD
• Unpredictable anticoagulation: Drug accumulation leads to supratherapeutic levels and bleeding risk
• Variable dialysis clearance: High-flux dialysis may clear some LMWH; timing of dosing relative to dialysis is complex

Bleeding risk:

• Uremic platelet dysfunction
• Frequent procedures (dialysis catheter changes)
• Accumulated anticoagulant effect

UFH advantages in renal impairment:

• Hepatic and reticuloendothelial clearance (NOT renally dependent)
• Short half-life (1-2 hours)
• Reversible with protamine
• No dose adjustment required

(b) Agent and dosing regimen (40%)

Recommended agent: Unfractionated heparin (UFH)

Dosing: 5000 units SC every 8-12 hours

• Q8H dosing provides better steady-state coverage and is preferred in very high-risk patients
• Q12H acceptable if bleeding concerns

Rationale:

• No renal dose adjustment required
• Predictable pharmacokinetics in ESRD
• Lower bleeding risk than LMWH accumulation
• Evidence from PROTECT trial subgroup analysis supports UFH in renal impairment

Alternative if LMWH required:

• Enoxaparin 30 mg SC once daily with anti-Xa monitoring
• Dose after dialysis sessions on dialysis days
• This approach is reasonable but more complex

Mechanical prophylaxis:

• Add IPC (thigh-length preferred)
• Especially important given vasopressor use (may impair subcutaneous drug absorption)

(c) Monitoring for adequacy and complications (30%)

Efficacy monitoring:

• Clinical surveillance for VTE (daily examination, unexplained respiratory deterioration)
• Consider weekly lower extremity duplex ultrasound in high-risk patients
• Anti-Xa monitoring NOT routinely required for UFH prophylaxis
• If concerns about UFH absorption (severe edema, high-dose vasopressors): check aPTT (should be normal with prophylactic dosing)

Safety monitoring:

• Platelet count: Check baseline, then every 2-3 days for first 2 weeks
• 4Ts score: Calculate if platelet count falls greater than 50% or below 100 x 10^9/L
• Bleeding: Daily hemoglobin, examination for bruising/hematomas, occult GI bleeding
• Skin: Examine injection sites for hematomas or necrosis

HIT considerations:

• ESRD patients often have heparin exposure from dialysis
• May have pre-formed HIT antibodies
• Higher vigilance for HIT; lower threshold for testing
• If HIT suspected: stop all heparin, start argatroban (preferred in renal impairment as hepatically cleared)

---

Viva Scenarios

Viva 1: Post-Craniotomy VTE Prophylaxis

Scenario: You are asked to review the VTE prophylaxis for a 58-year-old male, Day 2 post-craniotomy for resection of a glioblastoma. The surgery was uncomplicated, and the post-operative CT shows expected post-surgical changes with no significant hemorrhage. He is currently on IPC only.

Opening Question: "What are your considerations for VTE prophylaxis in this patient?"

Expected Candidate Response:

Risk assessment:

• This patient is at HIGH VTE risk:
  • Post-craniotomy (major surgery)
  • Brain tumor (malignancy-associated hypercoagulability)
  • Immobility
  • Potential for prolonged hospital stay
• Studies show DVT rates of 20-30% in neurosurgical patients without prophylaxis
• PE is a leading cause of death after craniotomy

Current prophylaxis:

• IPC is appropriate for immediate post-operative period
• Pharmacological prophylaxis should be considered once hemorrhage risk reduced

Examiner Probe: "When would you start pharmacological prophylaxis?"

• For elective craniotomy without hemorrhage: 24-48 hours post-operatively is generally considered safe
• Post-operative CT shows no significant hemorrhage
• Most guidelines and studies support initiating LMWH 24-48 hours post-craniotomy in the absence of hemorrhage
• Key studies (Constantini, PMID: 17613892; Goldhaber meta-analysis) support safety of this approach

Recommendation: Start enoxaparin 40 mg SC daily on Day 2-3 post-operatively

Examiner Probe: "The neurosurgeon is reluctant to start anticoagulation. How would you address this?"

Approach to disagreement:

1. Acknowledge legitimate concerns about intracranial bleeding
2. Present evidence:
   • Meta-analyses show LMWH post-craniotomy does NOT increase intracranial hemorrhage
   • VTE risk is substantial without prophylaxis
   • Combined mechanical + pharmacological prophylaxis reduces VTE by 40-60%
3. Discuss shared decision-making:
   • Could start with lower dose (enoxaparin 30 mg) if concerns
   • Could perform additional imaging before starting
   • Could delay slightly (to 72 hours) for compromise
4. Document discussion and rationale

Examiner Probe: "What would change your approach if the post-operative CT showed a small epidural hematoma?"

• If hemorrhage present: Delay pharmacological prophylaxis until stable
• Continue mechanical prophylaxis (IPC)
• Repeat CT at 24-48 hours
• Start pharmacological prophylaxis when hemorrhage stable (typically 48-72 hours)
• May need multidisciplinary discussion (neurosurgery, ICU, hematology)

---

Viva 2: Breakthrough VTE on Prophylaxis

Scenario: A 65-year-old female was admitted to your ICU 10 days ago following emergency surgery for perforated diverticulitis. She has been on enoxaparin 40 mg SC daily since Day 2 and bilateral IPC. Her post-operative course has been complicated by septic shock and ARDS requiring mechanical ventilation. Today, routine lower extremity duplex ultrasound reveals a new acute right popliteal DVT.

Opening Question: "How do you approach this patient with breakthrough VTE despite prophylaxis?"

Expected Candidate Response:

Immediate management:

1. Convert to therapeutic anticoagulation:

   • Enoxaparin 1.5 mg/kg SC once daily OR 1 mg/kg SC twice daily
   • OR IV heparin infusion (preferred if unstable, might need procedures)
   • Target aPTT 60-80 seconds for UFH

2. Risk stratify the DVT:

   • Popliteal DVT is proximal (higher PE risk than distal)
   • Assess for symptoms of PE (hypoxia, hemodynamic instability)
   • Consider CTPA if clinical suspicion of PE

Examiner Probe: "What are the possible causes of prophylaxis failure?"

Investigate causes:

1. Inadequate dosing:

   • Check patient weight: May need weight-based dosing if obese
   • Check anti-Xa levels at 4 hours post-dose: May be subtherapeutic
   • Consider that critically ill patients may have altered pharmacokinetics

2. Missed doses:

   • Review medication administration record
   • Doses may have been withheld for procedures, low platelets, etc.

3. Poor absorption:

   • Critically ill patients with edema, vasoconstriction from vasopressors
   • Subcutaneous injection may not be reliably absorbed

4. Very high-risk patient:

   • Sepsis
   • Immobility
   • Intra-abdominal surgery
   • Mechanical ventilation
   • Central venous catheter
   • May simply overwhelm standard prophylaxis

5. Occult malignancy:

   • Perforated diverticulitis could be underlying malignancy
   • Consider age-appropriate cancer screening if appropriate

Examiner Probe: "How would you prevent further VTE in this patient going forward?"

Ongoing management:

1. Continue therapeutic anticoagulation (minimum 3 months)
2. Repeat lower extremity duplex to assess for extension
3. IVC filter NOT routinely indicated (can anticoagulate)
4. Consider transition to DOAC when clinically stable and able to take oral medications
5. Investigate for occult malignancy (colonoscopy once recovered from acute illness)
6. If recurrent VTE on therapeutic anticoagulation: Consider thrombophilia testing, IVC filter

Examiner Probe: "On Day 12, you notice the platelet count has dropped from 180 to 70 x 10^9/L. What is your concern?"

HIT evaluation:

• Timing is concerning: Day 10-12 of heparin exposure (typical for HIT)
• Calculate 4Ts score:
  • "Thrombocytopenia: greater than 50% fall, nadir ≥20 = 2 points"
  • "Timing: Day 12 = 2 points"
  • "Thrombosis: New DVT = 2 points"
  • "Other causes: Sepsis possible = 1 point"
  • "Total: 7 points = HIGH probability"

Management:

1. Stop all heparin immediately (including flushes)
2. Send HIT antibody (ELISA) and serotonin release assay
3. Start alternative anticoagulant: Argatroban 2 mcg/kg/min IV (reduce in hepatic impairment)
4. Do NOT transfuse platelets
5. Image for additional thrombosis (upper extremity duplex, consider abdominal imaging)
6. Do NOT start warfarin until platelets recovered (risk of warfarin-induced skin necrosis)

---

References

1. Cook D, Crowther M, Meade M, et al. Deep venous thrombosis in medical-surgical critically ill patients: prevalence, incidence, and risk factors. Crit Care Med. 2005;33(7):1565-1571. PMID: 16003063

2. Minet C, Potton L, Bonadona A, et al. Venous thromboembolism in the ICU: main characteristics, diagnosis and thromboprophylaxis. Crit Care. 2015;19:287. PMID: 26283545

3. Caprini JA. Thrombosis risk assessment as a guide to quality patient care. Dis Mon. 2005;51(2-3):70-78. PMID: 15900257

4. Barbar S, Noventa F, Rossetto V, et al. A risk assessment model for the identification of hospitalized medical patients at risk for venous thromboembolism: the Padua Prediction Score. J Thromb Haemost. 2010;8(11):2450-2457. PMID: 20738765

5. Geerts WH, Bergqvist D, Pineo GF, et al. Prevention of venous thromboembolism: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines (8th Edition). Chest. 2008;133(6 Suppl):381S-453S. PMID: 18574271

6. Haas S. Low molecular weight heparins in the prevention of venous thromboembolism in nonsurgical patients. Semin Thromb Hemost. 1999;25 Suppl 3:101-105. PMID: 10549723

7. PROTECT Investigators. Dalteparin versus unfractionated heparin in critically ill patients. N Engl J Med. 2011;364(14):1305-1314. PMID: 22033520

8. Kakkos SK, Caprini JA, Geroulakos G, et al. Combined intermittent pneumatic leg compression and pharmacological prophylaxis for prevention of venous thromboembolism. Cochrane Database Syst Rev. 2016;9:CD005258. PMID: 27600864

9. Dennis M, Sandercock PA, Reid J, et al. Effectiveness of thigh-length graduated compression stockings to reduce the risk of deep vein thrombosis after stroke (CLOTS trial 1): a multicentre, randomised controlled trial. Lancet. 2009;373(9679):1958-1965. PMID: 19269261

10. Arabi YM, Al-Hameed F, Burns KEA, et al. Adjunctive intermittent pneumatic compression for venous thromboprophylaxis. N Engl J Med. 2019;380(14):1305-1315. PMID: 31536102

11. Jamjoom AA, Jamjoom AB. Safety and efficacy of early pharmacological thromboprophylaxis in traumatic brain injury: systematic review and meta-analysis. J Neurotrauma. 2013;30(7):503-511. PMID: 24139583

12. Teasell RW, Hsieh JT, Aubut JA, et al. Venous thromboembolism after spinal cord injury. Arch Phys Med Rehabil. 2009;90(2):232-245. PMID: 19236977

13. Lim W, Dentali F, Eikelboom JW, Crowther MA. Meta-analysis: low-molecular-weight heparin and bleeding in patients with severe renal insufficiency. Ann Intern Med. 2006;144(9):673-684. PMID: 16670137

14. Freeman AL, Pendleton RC, Rondina MT. Prevention of venous thromboembolism in obesity. Expert Rev Cardiovasc Ther. 2010;8(12):1711-1721. PMID: 21108553

15. Rogers FB, Cipolle MD, Velmahos G, et al. Practice management guidelines for the prevention of venous thromboembolism in trauma patients: the EAST practice management guidelines work group. J Trauma. 2002;53(1):142-164. PMID: 11574327

16. Levine MN, Planes A, Hirsh J, et al. The relationship between anti-factor Xa level and clinical outcome in patients receiving enoxaparin low molecular weight heparin to prevent deep vein thrombosis after hip replacement. Thromb Haemost. 1989;62(3):940-944. PMID: 2556813

17. Darmon M, Timsit JF, Francais A, et al. Association between hypernatraemia acquired in the ICU and mortality: a cohort study. Nephrol Dial Transplant. 2010;25(8):2510-2515. PMID: 20167570

18. Heit JA, Silverstein MD, Mohr DN, et al. Predictors of survival after deep vein thrombosis and pulmonary embolism: a population-based, cohort study. Arch Intern Med. 1999;159(5):445-453. PMID: 10074952

19. Attia J, Ray JG, Cook DJ, et al. Deep vein thrombosis and its prevention in critically ill adults. Arch Intern Med. 2001;161(10):1268-1279. PMID: 11371254

20. Samama MM, Cohen AT, Darmon JY, et al. A comparison of enoxaparin with placebo for the prevention of venous thromboembolism in acutely ill medical patients. N Engl J Med. 1999;341(11):793-800. PMID: 10477781

21. Pannucci CJ, Swistun L, MacDonald JK, et al. Individualized venous thromboembolism risk stratification using the 2005 Caprini score to identify the benefits and harms of chemoprophylaxis in surgical patients: a meta-analysis. Ann Surg. 2017;265(6):1094-1103. PMID: 28106607

22. Vardi M, Ghanem-Zoubi NO, Zidan R, et al. Venous thromboembolism and the utility of the Padua Prediction Score in patients with sepsis admitted to internal medicine departments. J Thromb Haemost. 2013;11(3):467-473. PMID: 23311610

23. Decousus H, Tapson VF, Bergmann JF, et al. Factors at admission associated with bleeding risk in medical patients: findings from the IMPROVE investigators. Chest. 2011;139(1):69-79. PMID: 20453069

24. Shorr AF, Williams MD. Venous thromboembolism in critically ill patients. Observations from a randomized trial in sepsis. Thromb Haemost. 2009;101(1):139-144. PMID: 19132199

25. Rabbat CG, Cook DJ, Crowther MA, et al. Dalteparin thromboprophylaxis for critically ill medical-surgical patients with renal insufficiency. J Crit Care. 2005;20(4):357-363. PMID: 16310608

26. Borkgren-Okonek MJ, Hart RW, Pantano JE, et al. Enoxaparin thromboprophylaxis in gastric bypass patients: extended duration, dose stratification, and antifactor Xa activity. Surg Obes Relat Dis. 2008;4(5):625-631. PMID: 18261965

27. Turpie AG, Bauer KA, Eriksson BI, Lassen MR. Fondaparinux vs enoxaparin for the prevention of venous thromboembolism in major orthopedic surgery: a meta-analysis of 4 randomized double-blind studies. Arch Intern Med. 2002;162(16):1833-1840. PMID: 12196082

28. Cohen AT, Spiro TE, Büller HR, et al. Rivaroxaban for thromboprophylaxis in acutely ill medical patients. N Engl J Med. 2013;368(6):513-523. PMID: 23388003

29. Ho KM, Tan JA. Stratified meta-analysis of intermittent pneumatic compression of the lower limbs to prevent venous thromboembolism in hospitalized patients. Circulation. 2013;128(9):1003-1020. PMID: 23852609

30. Dennis M, Sandercock P, Graham C, et al. The Clots in Legs Or sTockings after Stroke (CLOTS) 3 trial: a randomised controlled trial to determine whether or not intermittent pneumatic compression reduces the risk of post-stroke deep vein thrombosis and to estimate its cost-effectiveness. Health Technol Assess. 2015;19(76):1-90. PMID: 26418530

31. PREPIC Study Group. Eight-year follow-up of patients with permanent vena cava filters in the prevention of pulmonary embolism: the PREPIC (Prevention du Risque d'Embolie Pulmonaire par Interruption Cave) randomized study. Circulation. 2005;112(3):416-422. PMID: 16009794

32. Kaufman JA, Kinney TB, Streiff MB, et al. Guidelines for the use of retrievable and convertible vena cava filters: report from the Society of Interventional Radiology multidisciplinary consensus conference. J Vasc Interv Radiol. 2006;17(3):449-459. PMID: 16567669

33. Dudley RR, Aziz I, Bonber A, et al. Early venous thromboembolic event prophylaxis in traumatic brain injury with low-molecular-weight heparin: risks and benefits. J Neurotrauma. 2010;27(12):2165-2172. PMID: 20939691

34. Prevention of Venous Thromboembolism in Individuals with Spinal Cord Injury: Clinical Practice Guidelines for Health Care Providers, 3rd ed. Consortium for Spinal Cord Medicine. J Spinal Cord Med. 2016;39(2):127-186. PMID: 26782831

35. Merli GJ, Crabbe S, Paluzzi RG, Fritz D. Etiology, incidence, and prevention of deep vein thrombosis in acute spinal cord injury. Arch Phys Med Rehabil. 1993;74(11):1199-1205. PMID: 8239964

36. Geerts WH, Code KI, Jay RM, et al. A prospective study of venous thromboembolism after major trauma. N Engl J Med. 1994;331(24):1601-1606. PMID: 7969340

37. Knudson MM, Ikossi DG, Khaw L, et al. Thromboembolism after trauma: an analysis of 1602 episodes from the American College of Surgeons National Trauma Data Bank. Ann Surg. 2004;240(3):490-496. PMID: 15319720

38. Pautas E, Gouin I, Bellot O, et al. Safety profile of tinzaparin administered once daily at a standard curative dose in two hundred very elderly patients. Drug Saf. 2002;25(10):725-733. PMID: 12167068

39. Wang TF, Milligan PE, Wong CA, et al. Efficacy and safety of high-dose thromboprophylaxis in morbidly obese inpatients. Thromb Haemost. 2014;111(1):88-93. PMID: 24136071

40. Bates SM, Greer IA, Middeldorp S, et al. VTE, thrombophilia, antithrombotic therapy, and pregnancy: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines. Chest. 2012;141(2 Suppl):e691S-e736S. PMID: 22315276

41. Hull RD, Pineo GF, Stein PD, et al. Timing of initial administration of low-molecular-weight heparin prophylaxis against deep vein thrombosis in patients following elective hip arthroplasty: a systematic review. Arch Intern Med. 2001;161(16):1952-1960. PMID: 11525697

42. Goldstein JN, Fazen LE, Wendell L, et al. Risk of thromboembolism following acute intracerebral hemorrhage. Neurocrit Care. 2009;10(1):28-34. PMID: 18810667

43. Crowther MA, Berry LR, Monagle PT, Chan AK. Mechanisms responsible for the failure of protamine to inactivate low-molecular-weight heparin. Br J Haematol. 2002;116(1):178-186. PMID: 11841415

44. Gibson CM, Spyropoulos AC, Cohen AT, et al. The IMPROVEDD VTE Risk Score: Incorporation of D-Dimer into the IMPROVE Score to Improve Venous Thromboembolism Risk Stratification. TH Open. 2017;1(1):e56-e65. PMID: 31249911

45. Warkentin TE, Greinacher A. Heparin-induced thrombocytopenia: recognition, treatment, and prevention: the Seventh ACCP Conference on Antithrombotic and Thrombolytic Therapy. Chest. 2004;126(3 Suppl):311S-337S. PMID: 15383477

46. Cuker A, Arepally GM, Chong BH, et al. American Society of Hematology 2018 guidelines for management of venous thromboembolism: heparin-induced thrombocytopenia. Blood Adv. 2018;2(22):3360-3392. PMID: 30482768

47. Samama MM, Cohen AT, Darmon JY, et al. A comparison of enoxaparin with placebo for the prevention of venous thromboembolism in acutely ill medical patients. Prophylaxis in Medical Patients with Enoxaparin Study Group. N Engl J Med. 1999;341(11):793-800. PMID: 10477781

48. Riess H, Haas S, Tebbe U, et al. A randomized, double-blind study of certoparin vs. unfractionated heparin to prevent venous thromboembolic events in acutely ill, non-surgical patients: CERTIFY Study. J Thromb Haemost. 2010;8(6):1209-1215. PMID: 20929981

---

---

Clinical Pearls

Practical Prescribing Considerations

1. Documentation of VTE prophylaxis rationale:

• Every ICU patient should have VTE prophylaxis documented as part of the admission plan
• If prophylaxis is withheld, document the specific contraindication
• Set daily prompts to reassess eligibility for pharmacological prophylaxis

2. Timing of subcutaneous injections:

• Rotate injection sites (abdomen, thighs, upper arms)
• Avoid injecting into edematous tissues (poor absorption)
• Hold pressure for 60 seconds post-injection to minimize bruising
• Avoid vigorous rubbing of injection site

3. Procedure-related interruptions:

• Hold LMWH 12-24 hours before procedures (depending on bleeding risk)
• Hold UFH 4-6 hours before procedures
• Resume 6-12 hours after low-bleeding-risk procedures
• Resume 24-48 hours after high-bleeding-risk procedures
• Document a clear plan for restarting prophylaxis

4. Vasopressor considerations:

• High-dose vasopressors may impair subcutaneous drug absorption
• Consider anti-Xa monitoring if concerned about absorption
• Some centers switch to IV heparin infusion (low-dose) in severely shocked patients
• Mechanical prophylaxis especially important in this setting

Common Clinical Scenarios

Scenario 1: Patient refusing injections

• Explore reasons for refusal (needle phobia, pain, cultural factors)
• Consider topical anesthetic cream at injection sites
• Ensure mechanical prophylaxis is in place
• Consider oral anticoagulants if able to take enterally (limited evidence for prophylaxis)
• Document informed refusal of pharmacological prophylaxis

Scenario 2: Thrombocytopenia

• Platelet count 50-100 x 10^9/L: Generally safe to continue pharmacological prophylaxis
• Platelet count 25-50 x 10^9/L: Use mechanical prophylaxis; consider reduced-dose pharmacological if VTE risk very high
• Platelet count below 25 x 10^9/L: Mechanical prophylaxis only; pharmacological prophylaxis usually contraindicated
• Always evaluate cause of thrombocytopenia (HIT, DIC, sepsis, bone marrow failure)

Scenario 3: Active bleeding patient who develops VTE

• Multidisciplinary discussion (ICU, hematology, surgery as appropriate)
• IVC filter may be indicated for proximal DVT/PE if anticoagulation absolutely contraindicated
• Retrievable filter preferred; plan for retrieval when anticoagulation can resume
• Close monitoring for hemodynamic compromise or PE symptoms

Scenario 4: Patient transferring from OR with epidural catheter

• Epidural catheters increase neuraxial hematoma risk with anticoagulation
• LMWH: Hold until 4 hours after catheter removal; wait 12 hours after dose before catheter removal
• UFH: Hold until 1 hour after catheter removal; wait 4-6 hours after dose before removal
• Mechanical prophylaxis until pharmacological prophylaxis can resume
• Follow local anesthesia department guidelines

Transition of Care

ICU to ward transfer:

• Ensure VTE prophylaxis is continued during transfer
• Communicate specific agent, dose, and duration to ward team
• Consider extended prophylaxis for high-risk patients (major trauma, SCI, major surgery)

Discharge planning:

• Most ICU patients require continued prophylaxis until fully ambulatory
• High-risk populations may need extended prophylaxis (4-6 weeks):
  • Major orthopaedic surgery (hip/knee replacement)
  • Spinal cord injury
  • Major cancer surgery
  • Major trauma with ongoing immobility
• Transition to oral anticoagulation if prolonged prophylaxis needed

---

Australasian Context

Australian and New Zealand Considerations

Thrombosis and Haemostasis Society of Australia and New Zealand (THANZ) guidelines:

• Align with international recommendations
• Emphasize risk assessment and documentation
• Support LMWH as preferred agent in most settings

PBS considerations:

• Enoxaparin (Clexane) is PBS-listed for VTE prophylaxis in hospitalized patients
• Fondaparinux (Arixtra) is PBS-listed for VTE prophylaxis in specific indications (orthopaedic surgery)
• DOACs for extended prophylaxis post-orthopaedic surgery are PBS-listed

Remote and rural considerations:

• Supply chain issues may affect LMWH availability
• UFH may be more readily available in some settings
• Consider local stock levels when prescribing
• Telemedicine consultation for complex cases

Australian VTE Registry Data

The Australian and New Zealand Intensive Care Society (ANZICS) Adult Patient Database provides local epidemiological data:

• VTE prophylaxis compliance rates in Australasian ICUs: greater than 90% (high adherence)
• Most common agent used: Enoxaparin (LMWH)
• VTE prophylaxis is a key performance indicator in many Australian ICUs

ANZICS Clinical Trials Group:

• ASPIRE trial: Evaluating aspirin for VTE prophylaxis in trauma (ongoing)
• Participation in international VTE prophylaxis trials

Indigenous Health Considerations

Aboriginal and Torres Strait Islander patients:

• May have higher rates of critical illness requiring ICU admission
• Cultural considerations around blood products and interventions
• Engage Indigenous Liaison Officers for complex discussions
• Ensure culturally safe communication about VTE risk and prophylaxis

Maori and Pacific Islander patients (New Zealand):

• Higher rates of obesity (increased VTE risk)
• Consider weight-based dosing more frequently
• Cultural consultation through whanau involvement
• Ensure informed consent includes culturally appropriate explanations

---

Quality Improvement

VTE Prophylaxis as a Quality Indicator

VTE prophylaxis compliance is a recognized quality indicator in critical care:

Australian Commission on Safety and Quality in Health Care (ACSQHC):

• Venous Thromboembolism Prevention Clinical Care Standard (2020)
• Recommends risk assessment on admission
• Recommends appropriate prophylaxis within 24 hours of admission
• Recommends documentation of contraindications if prophylaxis withheld

Key Performance Indicators:

1. Proportion of ICU patients receiving VTE prophylaxis within 24 hours
2. Proportion of patients with documented VTE risk assessment
3. Proportion of patients with documented contraindications when prophylaxis withheld
4. ICU-acquired VTE rate (quality outcome measure)
5. Compliance with anti-Xa monitoring in high-risk populations

Audit and Feedback

Components of VTE prophylaxis audit:

• Chart review of prophylaxis prescribing
• Timing from admission to first prophylaxis dose
• Appropriateness of agent selection (LMWH vs UFH based on renal function)
• Documentation of contraindications
• Missed doses and reasons

Improvement strategies:

• Electronic prescribing prompts and alerts
• Standardized admission order sets including VTE prophylaxis
• Daily safety huddle prompts for VTE prophylaxis review
• Feedback of unit-level compliance data to clinical teams
• Regular education sessions for medical and nursing staff