Part of the ICU Emergencies Hub — browse every related guide in one place.
Virchow's triad identifies the three conditions that predispose to venous thrombus formation — understanding these explains both why certain patients are at high risk and why specific prophylaxis interventions work:
1. Venous stasis (slow blood flow): Immobility, bed rest, prolonged travel, paralysis, venous insufficiency. Slow-moving blood allows clotting factors to accumulate locally rather than being washed through the circulation. Prophylaxis: ambulation, elevation, sequential compression devices (SCDs).
2. Endothelial injury (damage to the vessel wall): Surgery (especially orthopedic and pelvic surgery), trauma, central line insertion, IV drug use. Damaged endothelium exposes subendothelial collagen and initiates the clotting cascade. Prophylaxis: atraumatic technique with venipuncture and catheter care, minimize endothelial trauma.
3. Hypercoagulability (increased clotting tendency): Malignancy (cancer cells release procoagulant substances), pregnancy, oral contraceptives, hereditary thrombophilia (Factor V Leiden, antiphospholipid syndrome), dehydration, obesity, sepsis, HIT (heparin-induced thrombocytopenia). Prophylaxis: anticoagulant medications (heparin, LMWH, direct oral anticoagulants).
| Risk Category | Examples |
|---|---|
| High risk | Hip or knee replacement surgery, hip fracture repair, major trauma, spinal cord injury, malignancy with active treatment, prior DVT/PE history |
| Moderate risk | Major abdominal/pelvic surgery, prolonged immobility (>3 days), heart failure exacerbation, acute infectious illness requiring hospitalization, pregnancy/postpartum |
| Low risk | Minor surgery (<30 minutes), ambulatory patients, minor illness without immobility |
Classic DVT presentation: unilateral lower extremity swelling, warmth, redness, and tenderness — particularly in the calf or thigh. However: up to 50% of DVTs are asymptomatic. Homan's sign (calf pain with passive dorsiflexion) was historically taught but has poor sensitivity and specificity and is no longer recommended as a diagnostic test.
Upper extremity DVT: less common; associated with central line placement, thoracic outlet syndrome, or effort thrombosis (Paget-Schroetter syndrome). Presents with arm swelling, heaviness, pain, or visible venous engorgement. PICC-associated DVT is among the most common hospital-acquired DVTs.
PE occurs when a venous thrombus (most commonly from the deep veins of the legs or pelvis) breaks free and occludes part of the pulmonary arterial circulation. The clinical presentation ranges from asymptomatic (small PE with minimal impact on perfusion) to massive PE with cardiogenic shock and cardiac arrest.
Classic PE symptoms: Sudden onset dyspnea (most common symptom), pleuritic chest pain (sharp, worse with deep breathing or coughing), tachycardia, tachypnea, hypoxia (new oxygen requirement or worsening SpO2), anxiety and sense of impending doom, hemoptysis (blood-tinged sputum — less common). Massive PE adds: hypotension, syncope, right heart strain signs on EKG (S1Q3T3, new RBBB, sinus tachycardia), distended neck veins.
Notify the provider immediately for any patient with sudden onset dyspnea, unexplained tachycardia, or new hypoxia — particularly in a patient with risk factors for VTE. PE is diagnosed by CT pulmonary angiography (CTPA) — the gold standard. D-dimer is a sensitive but non-specific screening test (elevated in PE, but also in sepsis, trauma, malignancy, pregnancy).
Pharmacological prophylaxis: Unfractionated heparin (UFH) 5,000 units SQ q8-12h; or LMWH (enoxaparin 40 mg SQ daily or 30 mg BID depending on risk). Hold prophylaxis if platelet count drops significantly (check for HIT), active bleeding, or spinal/epidural procedure within 12–24 hours. Document administration times — gaps in prophylaxis coverage are gaps in protection.
Mechanical prophylaxis: Sequential compression devices (SCDs/pneumatic compression devices) inflate and deflate sequentially to simulate the calf muscle pump and prevent stasis. Apply to the lower extremities while the patient is in bed (not during ambulation). Remove for skin assessment, wound care, and ambulation. Never apply over active DVT sites. Graduated compression stockings (TED stockings) provide a lower level of prophylaxis — appropriate adjunct, not a substitute for SCDs in high-risk patients.
Early ambulation: The single most effective non-pharmacological VTE prevention intervention. Ambulate patients as early as medically safe after surgery or acute illness. "Up to the chair" is not ambulation — walking is required to activate the calf muscle pump. Document ambulation distance and patient tolerance.
| Agent | Monitoring | Key Nursing Considerations |
|---|---|---|
| Heparin IV infusion | aPTT every 6 hours until therapeutic; daily once stable. Platelet count every 2–3 days (HIT monitoring) | Therapeutic aPTT: typically 60–100 seconds (institution-specific); adjust per weight-based protocol. Reversal: protamine sulfate. Watch for HIT: platelet drop 30–50% on days 5–10 of heparin exposure |
| Enoxaparin (Lovenox) | Anti-Xa level for therapeutic dosing in renal impairment, obesity, pregnancy | Dose-reduce in renal impairment (CrCl <30); do not give if CrCl <15. Rotate injection sites in abdomen; do not expel air bubble before injection. Reversal: partial with protamine |
| Warfarin (Coumadin) | INR daily until therapeutic (2.0–3.0 for most indications); weekly once stable | Multiple drug and food interactions (especially vitamin K-rich foods). Teach consistent vitamin K intake rather than avoidance. Reversal: vitamin K (slow) or FFP/4-factor PCC (urgent). Bridging with heparin/LMWH until INR therapeutic |
| DOACs (rivaroxaban, apixaban, dabigatran) | Routine monitoring not required; check renal function at initiation and periodically | Do not crush dabigatran capsules. Reversal agents: idarucizumab (dabigatran) or andexanet alfa (rivaroxaban/apixaban). Avoid in severe renal impairment |
Related guides: Vital signs | Chest tube care | Shock types | Blood transfusion
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