8.3 Venous Thromboembolism, Anticoagulation & Pressure Injury Prevention

8.3 Venous Thromboembolism, Anticoagulation & Pressure Injury Prevention

Quick Answer: Venous Thromboembolism (comprising Deep Vein Thrombosis and Pulmonary Embolism) and Pressure Injuries represent high-frequency preventable complications in hospitalized, immobilized patients. VTE arises from Virchow's Triad (endothelial damage, venous stasis, hypercoagulability). DVT manifests with unilateral calf swelling, warmth, and erythema, while PE causes sudden dyspnea, pleuritic chest pain, and hypoxemia. Unfractionated heparin is monitored via aPTT (antidote: Protamine Sulfate), and Warfarin via PT/INR (antidote: Vitamin K1). Pressure injuries occur when external pressure exceeds 32 mmHg capillary closing pressure over bony prominences; prevention demands 2-hourly repositioning using a 30-degree lateral tilt, heel floating, moisture barrier creams, and Braden Scale risk monitoring.

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Pathophysiology of Venous Thromboembolism: Virchow's Triad

Venous Thromboembolism (VTE) encompasses Deep Vein Thrombosis (DVT) and its fatal sequela, Pulmonary Embolism (PE). In 1856, Rudolf Virchow articulated the three physiological abnormalities that predispose to intravascular thrombus formation, known collectively as Virchow's Triad:

                               VIRCHOW'S TRIAD
                                      |
        +-----------------------------+-----------------------------+
        |                             |                             |
        v                             v                             v
  ENDOTHELIAL INJURY            VENOUS STASIS               HYPERCOAGULABILITY
        |                             |                             |
 * Vascular trauma & fractures  * Prolonged bed rest & coma   * Malignancy & sepsis
 * Major orthopedic surgery     * Orthopedic casts & traction * Pregnancy & puerperium
 * Indwelling central lines     * Paralysis / Hemiplegia      * Oral contraceptives/HRT
 * Endothelial shear & smoking  * Long-haul travel (>4 hours) * Inherited thrombophilias

1. Endothelial Injury: Mechanical, chemical, or inflammatory disruption of the vascular intimal lining exposes subendothelial collagen and tissue factor. Platelets adhere, activate, and initiate the intrinsic and extrinsic coagulation cascades. Primary clinical drivers include major orthopaedic surgery (total hip or knee arthroplasty), pelvic fractures, intravenous catheter trauma, and severe sepsis.
2. Venous Stasis: Impairment of normal venous blood velocity allows activated clotting factors to accumulate locally and prevents clearance by circulating hepatic inhibitors. Venous blood pooling is precipitated by prolonged bed rest ($>72\text{ hours}$), general anesthesia, immobility following stroke, congestive heart failure, and extended travel in cramped postures.
3. Hypercoagulability: Pathological alterations in biochemical constituents of blood shifting the homeostatic balance toward thrombosis. Acquired drivers include active malignancy (release of tumor procoagulants), pregnancy and the immediate postpartum period, exogenous estrogen therapy (oral contraceptives, hormone replacement therapy), nephrotic syndrome, and dehydration. Congenital states include Factor V Leiden mutation, Prothrombin gene mutation, and deficiencies of Protein C, Protein S, or Antithrombin III.

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Deep Vein Thrombosis (DVT): Clinical Assessment and Diagnostic Pearls

Deep Vein Thrombosis typically originates in the deep veins of the calf (peroneal, posterior tibial) and extends proximally into the popliteal, femoral, and iliac veins. Proximal DVT carries a dramatically higher risk of pulmonary embolization.

Clinical Manifestations

• Unilateral Leg Edema: Marked difference in lower limb circumference (a difference $>3\text{ cm}$ measured 10 cm below the tibial tuberosity is clinically significant).
• Localized Tenderness and Calf Pain: Deep, aching heaviness or throbbing exacerbated by weight-bearing.
• Erythema and Local Warmth: Cutaneous vasodilation overlying the inflamed, obstructed venous channel.
• Superficial Venous Engorgement: Visible distension of collateral superficial veins.

[!CAUTION] Clinical Pearl: The Inefficacy and Dangers of Homan's Sign Homan's sign—eliciting calf pain upon abrupt passive dorsiflexion of the patient's foot with the knee extended—was historically taught as a diagnostic sign of DVT. In modern nursing practice, performing Homan's sign is strictly contraindicated! It has exceptionally poor sensitivity ($<35%$) and specificity, but more critically, vigorous physical dorsiflexion or deep calf kneading exerts mechanical shearing forces that can dislodge a friable, non-adherent thrombus, converting a localized peripheral DVT into a lethal, migrating pulmonary embolus.

Diagnostic Modalities

• Compression Duplex Ultrasound: The gold-standard, non-invasive imaging modality. Inability to compress the vein lumen under direct transducer pressure confirms the presence of an intraluminal thrombus.
• D-Dimer Assay: A fibrin degradation product released during endogenous fibrinolysis. A negative D-dimer ($<500\text{ ng/mL}$) has a high negative predictive value, safely ruling out DVT in low-risk individuals. A positive test is non-specific (elevated in infection, trauma, surgery, and pregnancy) and requires confirmatory ultrasound.

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Pulmonary Embolism (PE): The Acute Cardiopulmonary Emergency

Pulmonary Embolism arises when a venous thrombus (predominantly from the iliofemoral system) detaches, travels through the inferior vena cava, traverses the right cardiac chambers, and impacts within the pulmonary arterial circulation.

Pathophysiological Cascade

Arterial obstruction creates an area of ventilated lung that is unperfused (alveolar dead space), producing severe ventilation-perfusion ($V/Q$) mismatch, profound arterial hypoxemia, and reflex bronchoconstriction. Massive saddle emboli occlude $>50%$ of the pulmonary vascular bed, causing an abrupt rise in pulmonary vascular resistance, acute right ventricular failure (cor pulmonale), cardiogenic shock, and sudden cardiac arrest.

Clinical Presentation

• Sudden-Onset Dyspnea: The single most common symptom, occurring abruptly at rest.
• Pleuritic Chest Pain: Sharp, stabbing thoracic pain exacerbated by inspiration or coughing, indicating peripheral pulmonary infarction.
• Tachypnea and Tachycardia: Respiratory rate $>20\text{ breaths/min}$ and heart rate $>100\text{ bpm}$.
• Hemoptysis: Coughing up blood-tinged or frank bloody sputum.
• Signs of Massive PE: Syncope, profound hypotension (systolic BP $<90\text{ mmHg}$), cool clammy skin, elevated jugular venous distension, cyanosis, and acute cardiovascular collapse.

Immediate Emergency Nursing Actions

1. Positioning: Instantly elevate the head of the bed to high-Fowler's position to maximize thoracic excursion and ease breathing.
2. Oxygen Therapy: Administer supplemental high-flow oxygen via non-rebreather mask to maintain $\text{SpO}_2 \ge 95%$.
3. Call Rapid Response / Notify Physician: Summon emergency medical assistance immediately.
4. Diagnostic Preparation: Obtain stat 12-lead ECG (evaluating for sinus tachycardia or the classic $S_1Q_3T_3$ right heart strain pattern) and arterial blood gases (revealing acute hypoxemia and respiratory alkalosis).
5. Establish Large-Bore IV Access: Prepare for emergent systemic anticoagulation (IV heparin bolus) or thrombolytic therapy (Alteplase/rtPA) in hemodynamically unstable massive PE.

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VTE Prevention: Mechanical versus Pharmacological Prophylaxis

Every hospitalized adult must undergo structured VTE risk assessment upon admission (e.g., using the Caprini or Wells risk models).

1. Mechanical Prophylaxis

• Early and Frequent Ambulation: The single most effective physiological intervention; activates the "calf muscle pump" to propel venous blood toward the heart.
• Graduated Compression Stockings (TED Hose): Exert a graduated pressure gradient (highest at the ankle [18 mmHg], reducing proximally to 14 mmHg at the calf and 8 mmHg at the thigh) to augment deep venous return velocity. The nurse must measure leg circumference accurately, inspect skin beneath stockings daily, and remove them for 30 minutes each shift for hygiene.
  • Contraindication: Severe peripheral arterial occlusive disease (ankle-brachial index $<0.8$), acute massive leg edema, local leg gangrene, or active dermatitis.
• Intermittent Pneumatic Compression (IPC) Devices: Inflatable cuffs applied to calves that intermittently inflate to 35–55 mmHg to simulate normal walking. Strictly contraindicated on any limb with a known or suspected active DVT due to embolization danger.

2. Pharmacological Prophylaxis

Administered to moderate- and high-risk surgical and medical inpatients:

• Low Molecular Weight Heparin (LMWH): Enoxaparin 40 mg subcutaneously once daily (or 30 mg SC q12h post-orthopedic surgery). First-line agent due to high bioavailability and predictable dose-response.
• Unfractionated Heparin (UFH): 5,000 units subcutaneously every 8 to 12 hours. Preferred in patients with severe renal failure (creatinine clearance $<30\text{ mL/min}$) because it is cleared hepatically rather than renally.

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Therapeutic Anticoagulation: Laboratory Monitoring and Reversal Pharmacology

When acute VTE is established, therapeutic-dose anticoagulation arrests thrombus propagation and allows endogenous fibrinolysis to dissolve the clot.

Critical Nursing Anticoagulation Protocols

• Heparin-Induced Thrombocytopenia (HIT): A life-threatening immune complication mediated by antibodies against platelet factor 4 (PF4)-heparin complexes, causing paradoxical wide-scale arterial and venous thrombosis with marked thrombocytopenia. The nurse must monitor platelet counts every 2 to 3 days. A $\ge 50%$ drop in platelet count from baseline (typically between days 5 and 10 of heparin therapy) mandates immediate cessation of all heparin products and switching to an alternative non-heparin anticoagulant (such as argatroban or fondaparinux).
• Warfarin "Bridging" Therapy: Warfarin requires 3 to 5 days to achieve therapeutic anticoagulation because pre-existing circulating clotting factors must decay. Furthermore, warfarin initially depletes Protein C (a natural anticoagulant with a short 6-hour half-life) before depleting procoagulant factors, creating a transient prothrombotic state. Therefore, parenteral heparin or enoxaparin must be co-administered with warfarin for a minimum of 5 days AND until the INR is $\ge 2.0$ for at least 24 consecutive hours before discontinuing heparin.
• Bleeding Precautions: Institute bleeding precautions for all anticoagulated patients: use a soft-bristle toothbrush, electric razor, avoid intramuscular injections, apply firm pressure to venipuncture sites for $\ge 5$ minutes, monitor stools for melena, check urine for hematuria, and educate patients to maintain consistent dietary intake of vitamin K-rich foods (spinach, cabbage, broccoli).

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Pressure Injury Etiology & Capillary Closing Pressure

A Pressure Injury (previously referred to as pressure ulcer, decubitus ulcer, or bedsore) is localized damage to the skin and underlying soft tissue, usually over a bony prominence, resulting from intense, prolonged mechanical pressure or pressure in combination with shear.

The Pathophysiological Threshold: 32 mmHg

Normal microcirculatory arteriolar capillary closing pressure averages 32 mmHg (with venous capillary pressure averaging 12 mmHg). When external compressive pressure exerted between a rigid external surface (mattress, wheelchair) and internal skeletal bony prominences exceeds 32 mmHg, capillary lumens collapse completely:

1. Microvascular Occlusion: Local blood flow halts, depriving soft tissues of oxygen and vital cellular nutrients.
2. Metabolic Waste Accumulation: Anaerobic metabolism ensues, accumulating toxic lactic acid and metabolic by-products, causing local vasodilation and interstitial edema.
3. Ischemia-Reperfusion and Necrosis: If pressure is unrelieved, irreversible cellular ischemia develops. Tissue necrosis characteristically begins at the deep muscle-bone interface (the "tip of the iceberg" phenomenon) where compressive stresses are highest, extending outward toward the epidermis.
4. Friction and Shearing Forces: Friction strips the protective stratum corneum. Shear occurs when the skeleton slides downward (e.g., when the head of the bed is elevated $>30^\circ$) while the superficial skin remains stationary against sheets. This stretches and angulates microvessels, producing deep fascial tears and accelerated ischemia.

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Standardized Risk Stratification: The Braden Scale

The Braden Scale for Predicting Pressure Sore Risk is the universally validated clinical risk assessment tool utilized in nursing practice. It evaluates six physiological and environmental subscales:

                               BRADEN SCALE DOMAINS
                                        |
        +--------------+----------------+----------------+--------------+
        |              |                |                |              |
        v              v                v                v              v
 Sensory Perception  Moisture        Activity         Mobility       Nutrition
 (Score 1-4)       (Score 1-4)     (Score 1-4)      (Score 1-4)    (Score 1-4)
                                                                        +
                                                                Friction & Shear
                                                                  (Score 1-3)

1. Sensory Perception (1 to 4): Ability to respond meaningfully to pressure-related discomfort.
2. Moisture (1 to 4): Degree to which skin is exposed to moisture (sweat, urine, wound exudate).
3. Activity (1 to 4): Degree of physical activity (bedfast to walks frequently).
4. Mobility (1 to 4): Ability to change and control body position independently.
5. Nutrition (1 to 4): Usual food intake pattern and nutritional status.
6. Friction and Shear (1 to 3): Amount of assistance required during movement and degree of sliding.

Scoring Interpretation

Total scores range from 6 to 23. Lower scores indicate higher vulnerability:

• $\le 9$: Very High Risk
• 10 to 12: High Risk
• 13 to 14: Moderate Risk
• 15 to 18: Mild Risk / At Risk
• 19 to 23: Generally No Risk

Clinical Standard: Perform Braden scoring within 2 hours of hospital admission, upon any significant clinical status change, and at least once daily in medical-surgical units (every shift in intensive care units).

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Pressure Injury Staging (NPIAP / EPUAP Framework)

Pressure injuries are staged according to the depth of anatomical tissue destruction using the National Pressure Injury Advisory Panel (NPIAP) staging system:

1. Stage 1 Pressure Injury: Non-Blanchable Erythema of Intact Skin

• Features: Intact skin with a localized area of non-blanchable erythema (does not turn white when gentle fingertip pressure is applied). May be preceded by changes in skin temperature (warmth or coolness), tissue consistency (firm or boggy), or localized pain.
• Assessment in Darkly Pigmented Skin: In dark skin tones, blanching may not be visible; the area may present with persistent red, blue, or purple hues, edema, induration, and distinct local warmth or tenderness compared to surrounding skin.

2. Stage 2 Pressure Injury: Partial-Thickness Skin Loss with Exposed Dermis

• Features: Shallow open ulcer with a viable, moist, pink or red wound bed without slough, eschar, or granulation tissue. Adipose (fat) and deeper tissues are not visible.
• Also presents commonly as an intact or open/ruptured serum-filled blister.
• Exclusions: This stage should not be used to describe moisture-associated skin damage (MASD), incontinence-associated dermatitis (IAD), skin tears, or tape burns.

3. Stage 3 Pressure Injury: Full-Thickness Skin Loss

• Features: Full-thickness loss of skin in which subcutaneous adipose (fat) is visible in the ulcer bed. Granulation tissue and epibole (rolled wound edges) are frequently present. Slough and/or eschar may be visible, but do not obscure the depth of tissue loss.
• Undermining and tunneling may occur.
• Critical Boundary: Fascia, muscle, tendon, ligament, cartilage, and bone are NOT exposed or directly palpable.

4. Stage 4 Pressure Injury: Full-Thickness Skin and Tissue Loss

• Features: Extensive tissue destruction with exposed or directly palpable fascia, muscle, tendon, ligament, cartilage, or bone. Slough and/or eschar may be visible.
• Epibole, deep undermining, and extensive sinus tracts/tunneling are common.
• Carries an imminent risk of systemic sepsis and acute/chronic osteomyelitis.

5. Unstageable Pressure Injury: Obscured Full-Thickness Skin and Tissue Loss

• Features: Full-thickness tissue loss in which the actual depth and base of the ulcer cannot be confirmed because it is completely obscured by slough (yellow, tan, gray, green, or brown) or eschar (tan, brown, or black) in the wound bed.
• Clinical Management: Until enough slough and eschar are removed (debrided) to expose the wound base, the true stage cannot be determined (it will be either Stage 3 or Stage 4).
• Exception: Stable eschar on the heel (dry, adherent, intact, without erythema or fluctuance) acts as the body's natural anatomical cover and should NOT be softened or debrided.

6. Deep Tissue Pressure Injury (DTPI): Persistent Non-Blanchable Deep Red, Maroon, or Purple Discoloration

• Features: Intact or non-intact skin with localized, persistent non-blanchable deep red, maroon, or purple discoloration, or epidermal separation revealing a dark wound bed or blood-filled blister.
• Results from intense, deep muscle-bone interface mechanical shearing forces. The injury may rapidly evolve to reveal the actual extent of full-thickness tissue destruction or may resolve without tissue loss.

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Evidence-Based Nursing Prevention and Skin Preservation Protocols

Preventing pressure injury requires systematic, uninterrupted implementation of pressure redistribution and skin preservation protocols:

1. The 2-Hourly Repositioning Schedule and 30-Degree Lateral Tilt

• Repositioning Interval: Turn bedbound patients at least every 2 hours around-the-clock (every 1 hour for chair-bound patients).
• The 30-Degree Lateral Tilt: When positioning patients on their side, place them at a 30-degree lateral incline, supported by pillows along the back and between the legs. Avoid full 90-degree lateral side-lying positions, which place direct, crushing perpendicular weight on the greater trochanters and lateral malleoli.
• Head-of-Bed Elevation: Keep the head of the bed elevated at $\le 30\text{ degrees}$ (unless medically contraindicated for aspiration risk or enteral feeding) to minimize gravitational sliding and destructive sacral shear forces.

2. Heel Offloading (Floating Heels) and Support Surfaces

• Heel Offloading: Heels represent the second most common site of pressure injury. Suspend and "float" the heels completely off the mattress surface by placing a pillow or positioning bolster longitudinally beneath the lower calves. Avoid placing pillows directly under the Achilles tendon or popliteal fossa.
• Dynamic Support Surfaces: Provide pressure-relieving foam mattresses or dynamic alternating-pressure air mattresses for high-risk patients (Braden score $\le 12$) to cycle microvascular interface pressures.

3. Moisture Control and Skin Barrier Management

• Cleanse skin immediately after episodes of incontinence using lukewarm water and mild, pH-balanced cleansing foams (avoid harsh, alkaline bar soaps).
• Pat skin dry gently; avoid abrasive rubbing.
• Apply silicone-based moisture barrier creams or zinc oxide barrier ointments over the perineum and buttocks to shield skin from caustic urine and digestive enzymes.
• Never massage reddened bony prominences: Massaging erythematous skin shears and ruptures fragile underlying capillary networks, accelerating tissue necrosis.

4. Nutritional Optimization for Tissue Viability

• Ensure high-protein dietary intake (1.25 to 1.5 grams of protein per kilogram of body weight per day) to maintain positive nitrogen balance and support tissue repair.
• Provide oral nutritional supplements enriched with Vitamin C (cofactor for collagen synthesis), Zinc (essential for protein synthesis and re-epithelialization), and generous oral/enteral fluid intake to maintain adequate tissue hydration and skin turgor.