Study Notes on Pulmonary Embolism

Overview of Pulmonary Embolism

  • Discusses signs, symptoms, risk factors, pathophysiology, investigations, diagnosis, treatment, and management.

Signs and Symptoms of Pulmonary Embolism

  • Common indicators include:

    • Dyspnea (difficulty breathing)

    • Chest pain (may vary in intensity)

    • Tachycardia (elevated heart rate)

    • Hypotension (low blood pressure)

    • Signs of Deep Vein Thrombosis (DVT), including:

    • Swollen legs

    • Pain in lower legs

Causes of Pulmonary Embolism

  • Majority of cases (90-95%) are due to thrombosis from deep veins (DVT).

    • Deep Vein Thrombosis mainly develops in lower limb veins, particularly:

    • External iliac vein

    • Femoral vein

    • Deep femoral vein

    • Popliteal vein

    • Posterior tibial vein

    • Less common sites include:

    • Right-sided heart chambers

    • Uterine veins

    • Great saphenous vein

Risk Factors for Pulmonary Embolism

  • Surgical procedures:

    • Major abdominal and pelvic surgeries

    • Orthopedic surgeries

  • Physiological changes:

    • Pregnancy (obstetric risk factor)

    • Cardiorespiratory issues (e.g., COPD, congestive heart failure)

  • Vascular conditions:

    • Varicose veins

    • Fractures

    • Malignant diseases

  • Age and lifestyle concerns:

    • Increasing age

    • Immobility (prolonged inactivity)

  • Thrombotic disorders:

    • Conditions that predispose to clot formation.

Pathophysiology of Pulmonary Embolism

  • Thrombus Definition:

    • A thrombus is a mass composed of clumped red blood cells, platelets, and fibrin.

  • Virchow's Triad:

    • Three components that lead to thrombus formation:

    • Abnormal blood flow (Venous stasis)

    • Hypercoagulability (thrombophilia)

    • Altered vessel wall (vessel wall injury): endothelial injury

  • Fates of a thrombus:

    • Possible outcomes include:

    • Resolution (disappearance of thrombus)

    • Propagation (growth of thrombus)

    • Embolism (thrombus detachment leading to obstruction)

    • Recanalization (formation of channels in the thrombus)

    • Organization (integration of thrombus into vessel walls)

Effects of Embolism on the Cardiovascular System

  • Impact on blood pressure and heart output:

    • Increased pulmonary vascular pressure, causing:

    • Backflow of blood to the right side of the heart

    • Elevated right ventricular pressure

    • Dilation of right ventricle leading to right-sided heart failure

    • Consequences:

    • Decreased stroke volume

    • Decreased cardiac output

    • Resulting in hypotension or low blood pressure

  • Compensation Mechanisms:

    • Detection of decreased cardiac output stimulates:

    • Sympathetic nervous system response

    • Increasing heart rate (tachycardia)

    • Attempted vasoconstriction to raise blood pressure, which may be ineffective.

Effects of Embolism on the Respiratory System

  • Ventilation vs. Perfusion (VQ Mismatch):

    • Obstruction leads to abnormal gas exchange.

    • Causes:

    • Inflammation and release of cytokines.

    • Bronchoconstriction, decreasing oxygen intake.

    • Results in:

    • Hypoxemia (low oxygen levels)

    • Hypocapnia (low carbon dioxide levels)

    • May lead to respiratory alkalosis, detectable via arterial blood gas test.

Investigations for Pulmonary Embolism

  • X-Ray:

    • Usually normal but can help exclude differential diagnoses (e.g., pneumonia, pneumothorax).

    • Possible findings in PE include:

    • Enlarged pulmonary artery

    • Wedge-shaped opacity (indicative of infarction)

    • Elevated hemidiaphragm

    • Pleural effusion

  • ECG:

    • Often normal but used to differentiate from myocardial infarction:

    • Common findings:

      • Sinus tachycardia (present in 50% of cases)

      • Right ventricular strain (inverted T-waves in leads V1 to V4)

      • S1Q3T3 pattern (deep S-wave in lead I, deep Q and T-waves in lead III)

  • CT Pulmonary Angiogram:

    • Considered the gold standard for PE detection.

  • VQ Perfusion Scan:

    • Less definitive than CT but provides additional information.

  • Bedside Echocardiogram:

    • Assess heart function and presence of thrombi.

  • D-Dimer Assay:

    • Used for assessing the propensity for thrombus formation and ruling out PE.