7.4 Pulmonary Embolism, Pulmonary Hypertension & Transport Respiratory Meds

Pulmonary Embolism, Pulmonary Hypertension & Transport Respiratory Meds

Pulmonary vascular emergencies present unique hemodynamic and ventilatory challenges during critical care transport. Understanding the pathophysiology of right ventricular (RV) failure, systemic thrombolysis, pulmonary vasodilator transport protocols, and specialized respiratory pharmacotherapy is critical for the critical care paramedic.

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Pulmonary Embolism (PE): Risk Stratification

Pulmonary Embolism occurs when an embolus (most commonly thrombus originating from deep vein thrombosis of the lower extremities) occludes the pulmonary arterial circulation.

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Right Ventricular Strain Diagnostics

Acute pulmonary artery occlusion increases Right Ventricular afterload. The thin-walled RV dilates, fails, and impairs left ventricular filling through interventricular dependence.

Acute Pulmonary Artery Occlusion
              │
              ▼
      Abrupt Rise in PVR
              │
              ▼
  Acute RV Dilation & Wall Stress
              │
      ┌───────┴───────┐
      ▼               ▼
RV Myocardial   Interventricular Septal Shift
  Ischemia       (Bulges into Left Ventricle)
 (Troponin+)          │
                      ▼
           Reduced LV Preload & Stroke Volume
                      │
                      ▼
             Cardiogenic Shock

1. Electrocardiogram (ECG) Manifestations

• Sinus Tachycardia: Most common arrhythmia present.
• S1Q3T3 Pattern: Deep S wave in Lead I, prominent Q wave in Lead III, inverted T wave in Lead III (specific for acute RV strain, found in $\sim 20%$ of cases).
• Right Bundle Branch Block (RBBB): New complete or incomplete RBBB.
• Right Axis Deviation: Mean QRS axis $> +90^\circ$.
• T-Wave Inversions: Inverted T waves in precordial leads V1–V4 and inferior leads II, III, aVF.

2. Echocardiography & Biomarkers

• McConnell's Sign: Distinctive echocardiographic pattern showing hypokinesis of the RV free wall with normal wall motion at the RV apex.
• RV/LV Diameter Ratio: $\text{RV/LV ratio} > 0.9$ or $> 1.0$ indicates acute RV enlargement.
• D-Shaped Left Ventricle: Paradoxical bowing of the interventricular septum into the LV cavity during systole and diastole.
• Cardiac Troponin I/T: Indicates RV microvascular myocardial ischemia.
• B-type Natriuretic Peptide (BNP / NT-proBNP): Elevated secondary to acute RV wall stretch.

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Critical Care Management of Massive PE

1. Systemic Thrombolytic Therapy

Thrombolysis rapidly dissolves clot mass, reduces pulmonary vascular resistance, and restores RV function in Massive PE.

• Standard Alteplase (tPA) Protocol: $100 \text{ mg}$ IV infusion over 2 hours.
• Cardiac Arrest / Extreme Instability Protocol: $50 \text{ mg}$ IV push over 2 minutes (may repeat once in 15 minutes).
• Absolute Contraindications to Thrombolysis:
  1. Prior hemorrhagic stroke or stroke of unknown origin at any time.
  2. Ischemic stroke within the preceding 6 months.
  3. Central nervous system neoplasm or structural vascular lesion.
  4. Recent major trauma, surgery, or head injury within preceding 3 weeks.
  5. Active internal bleeding (excluding menses).

2. Anticoagulation Protocol

• Unfractionated Heparin (UFH) is the preferred agent during transport due to its rapid onset, short half-life ($60-90 \text{ minutes}$), and full reversibility with Protamine Sulfate ($1 \text{ mg}$ protamine per $100 \text{ units}$ heparin).
• Dosing: IV bolus $80 \text{ units/kg}$ followed by continuous infusion at $18 \text{ units/kg/hr}$, titrated to target aPTT of 60–80 seconds ($1.5 - 2.5 \times$ control).

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Resuscitation Hazards in Acute RV Failure

Managing acute right heart failure in PE requires strict fluid restriction and specific vasopressor choices:

The Fluid Bolus Trap!

• AVOID AGGRESSIVE FLUID BOLUSES: The thin-walled right ventricle is extremely volume-sensitive. Fluid boluses over-stretch the RV, worsen RV ischemia, shift the septum further into the LV, and decrease cardiac output!
• Fluid Rule: If hypovolemic, give no more than a single cautious challenge of $250-500 \text{ mL}$ isotonic fluid.

Inotrope & Vasopressor Selection

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Pulmonary Arterial Hypertension (PAH) Transport Rules

Pulmonary Arterial Hypertension (PAH) is defined by a mean Pulmonary Artery Pressure ($\text{mPAP}$) $> 20 \text{ mmHg}$ at rest with pulmonary vascular resistance ($\text{PVR}$) $> 2 \text{ Wood units}$.

Continuous Targeted Pulmonary Vasodilator Therapies

Patients with severe PAH are maintained on continuous targeted pulmonary vasodilator infusions or inhalations:

• Prostacyclins: Inhaled Epoprostenol (Flolan / Veletri), Treprostinil (Remodulin / Tyvaso), Continuous IV Epoprostenol.
• Inhaled Nitric Oxide (iNO): Selective pulmonary vasodilator gas administered via specialized transport delivery systems ($20-40 \text{ ppm}$).

THE CRITICAL MANDATE: NEVER INTERRUPT PROSTACYCLIN INFUSIONS

• Half-Life Alert: Intravenous Epoprostenol has an extremely short half-life of 3 to 6 minutes!
• Rebound Hypertensive Crisis: Abrupt interruption of epoprostenol or treprostinil (due to depleted pump battery, line kink, or empty syringe) triggers catastrophic, fatal rebound pulmonary vasoconstriction, acute RV collapse, and immediate cardiac arrest.
• Transport Precautions:
  1. Transport with a dedicated backup infusion pump loaded and running in parallel.
  2. Prepare a backup syringe of epoprostenol/treprostinil prior to departure.
  3. Maintain dedicated IV lines (NEVER flush or co-infuse other medications through a prostacyclin line!).

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Transport Respiratory Pharmacotherapy

Inhaled Mucolytics & Hypertonic Saline

• Hypertonic Saline ($3%$ or $7%$): Nebulized to induce osmotic draw of water into airways, rehydrating thick mucus in cystic fibrosis or bronchiectasis.
• Acetylcysteine (Mucomyst): $3-5 \text{ mL}$ of $10%$ or $20%$ solution nebulized to break disulfide bonds in mucoproteins. Caution: Can trigger acute bronchospasm; always co-administer with an inhaled beta-agonist (e.g., albuterol).

Racemic Epinephrine

• Dose: $0.5 \text{ mL}$ of $2.25%$ solution diluted in $3 \text{ mL}$ normal saline via nebulizer.
• Mechanism: Alpha-1 agonist stimulation induces mucosal vasoconstriction, dramatically reducing upper airway edema in post-extubation stridor and croup.

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