Pulmonary embolus 

Types

• massive PE is defined as acute PE with obstructive shock or SBP <90 mmHg
• submassive PE is acute PE without systemic hypotension (SBP ≥90 mm Hg) but with either RV dysfunction or myocardial necrosis
• those with none of the above severe features are non-massive or low risk PEs

Common clinical features of pulmonary embolism

• New or worsening breathlessness, particularly if it was sudden in onset
• Tachypnoea (respiratory rate of 20 breaths or more per minute)
• Chest pain, which may be pleuritic, or retrosternal and angina-like
• Tachycardia (heart rate > 100 beats per minute)
• Haemoptysis
• Syncope
• Hypotension (systolic blood pressure < 90 mmHg)
• Crepitations

RISK FACTORS

Major (relative risk 5-20) – SLOMMP

• Surgery – major abdominal/pelvic, hip/knee replacements, post ICU
• Lower limb problems – #, varicose veins
• Obstetrics – late pregnancy, C/S, puerperium
• Malignancy – abdominal/pelvic, advanced/metastatic
• Mobility – hospitalization, institutional care
• Previous VTE

Moderate risk factors (odds radio 2–9)

• Knee arthroscopy
• Central venous lines
• Chemotherapy
• Congestive heart failure or respiratory failure
• Oestrogens – OCP, HRT

• Stroke
• Pregnancy and puerperium
• Previous VTE
• Thrombophilia

Weak risk factors (odds ratio <2)

• Bed rest >3 days
• Immobility due to sitting (eg. travel)
• Increasing age
• Laparoscopic surgery
• Obesity
• Varicose veins

Thrombophillias

• Factor V Leiden mutation
• Prothombin gene mutation
• Hyperhomocysteinaemia
• Antiphospholipid antibody syndrome
• Deficiency of antithrombin III, protein C or protein S
• High concentrations of factor VIII or XI
• Increased lipoprotein (a) -> test in those < 50years with recurrent or a strong FHx

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INVESTIGATIONS

PERC rule

• Aged <50 years
• Pulse <100 beats per minute
• SaO2 ≥95%
• No haemoptysis
• No oestrogen use
• No surgery or trauma requiring hospitalisation within four weeks
• No prior venous thromboembolism
• No unilateral leg swelling

The PERC rule validation study included patients who presented with a primary complaint of shortness of breath or chest pain, and it is reasonable to use it for either of these symptoms. The PERC rule has not been validated for people with:

• active cancer, thrombophilia or a strong family history of thrombophilia
• transient tachycardia or beta-blocker use that may mask tachycardia
• leg amputations
• morbid obesity (leg swelling not easily determined)
• baseline hypoxaemia when oximetry reading <95% is longstanding.

If the patient’s PERC score is >0, then an enzyme-linked immunosorbent assay (ELISA)-type D-dimer is recommended

• goal = confirm diagnosis + assess severity
• normal compliance and peak pressures on ventilator
• increased PACO2 -> ETCO2 to gradient
• hypoxaemia
• ECG:
  • mostly normal
  • sinus tachycardia
  • SI, QIII, TIII 
  • non specific ST changes or TWI in anterior leads (right heart strain)
  • right axis deviation
  • s wave (I and aVL) > 1.5mm
  • Q wave in III and aVF
  • p pulmonale
  • RBBB

• CXR:
  • rules out other pathology, focal oligaemia, wedge density (pulmonary infarction)
• ABG:
  • reduced PaO2 in keeping with size of PE, metabolic acidosis with circulatory collapse, respiratory alkalosis
• D-Dimer:
  • reassuring if negative to exclude PE, use in conjunction with clinical probability
• TNT:
  • elevation is associated with adverse outcome even in normotensive patients, also associated with haemodynamic instability in patients with non-massive PE
• BNP and NT-terminal BNP:
  • if low correlates well with uneventful course
• CTPA
  • as good as pulmonary angiography (gold standard), can calculate RV/LV ratio (>0.9) = severe
• ECHO:
  • RV dialation, paradoxical septal motion towards the LV, TR, RVF, PHT or PA thrombus on TOE,
• US:
  • leg veins (not as accurate as initially thought -> have low threshold to re-scan)
• V/Q scan:
  • only really used now when CT is contraindicated (normal scan, low, intermediate and high probability with various criteria)

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Management

Resuscitation

    B – Correct Hypoxia on presentation – Supplemental Oxygen, High Flow, intubation. Avoid Positive Pressure Ventilation (BiPap, CPAP, Mechanical Ventilation) if possible – Positive pressure may worsen right heart strain/, (Avoid intubation if possible, Intubation and ventilation is challenging to manage in Pulmonary Embolism)

    C – Correct Hypotension (target >90 mmHg). Small fluid challenges (e.g. 250 ml aliquots) are preferred to avoid further RV strain. Consider Norepinephrine for refractory Hypotension (rather than alpha agonists)

• MASSIVE
  • haemodynamically unstable -> thrombolyse/embolectomy
• SUB-MASSIVE
  • haemodynamically stable with evidence of RV dysfunction -> strongly consider thrombolysis/embolectomy but need to balance risk of bleeding
• NON-MASSIVE
  • haemodynamically stable with normal RV function -> anticoagulation

Anticoagulation

• LMWH
  • dalteparin 200 U/kg, up to 18,000 U daily or 100 U/kg, up to 9000 U twice daily; or 
  • enoxaparin 1.5 mg/kg daily or 1 mg/kg twice daily.
  • Twice-daily dosing is preferred if the risk of bleeding or thrombus extension is high (eg older age, obesity, malignancy)
  • If creatinine clearance is <30 mL/min, dose adjustment is required.
• Warfarin
  • After the initial treatment period with LMWH
  • warfarin is usually used for continued anticoagulation
  • target INR : 2.0–3.0
  • minimum of 3 months
• Duration
  • PE + definite provoking risk factor (recent major surgery) the risk of recurrence is generally low, and 3–6 months of anticoagulant treatment is sufficient.
  • unprovoked PE the recurrence risk is higher, and long term anticoagulation may be indicated.