Pulmonary embolism

What are the different types of pulmonary embolism?

Blood clot (thrombus) → >90%

Fat globule (fat embolism)

Bubble of air/gas (gas embolism)

Foreign material (tumour cells or bacteria)

virchows triad 

What can cause hypercoagulability? 

• Thrombophilia

• Pregnancy (post-partum)

• Infection/sepsis

• Autoimmune disease

• Dehydration

• Post surgery/trauma

What can cause vascular damage?

• Injury/trauma

• Catheter

• Venepuncture

• Atherosclerosis

What can cause circulatory problems?

• Immobility

• Venous obstruction

• Varicose veins

• Low heart rate

• Atrial fibrillation

• Congenital conditions

Risk factors for Pulmonary embolism

THROMBOSIS

Trauma or history of travel
Hospitalization and hormones
Relatives, family history
Old age
Malignancy
long Bone fractures
Obesity and obstetrics
Sand Smoking
Immobilization
other Sickness (nephrotic syndrome)

What does pulmonary embolism mechanical obstruction lead to?

Reduced perfusion V/Q>1 (in the affected area) → Blood get re-directed V/Q<1 (in other areas of lungs) → Results in low pO2 (hypoxaemia)→ hyperventilation→ hypocapnia→ respiratory alkalosis

What does pulmonary embolism inflammatory response lead to?

Endothelial injury → endothelin→ pulmonary oedema→ Pleural effusion→crackles/rales

How does pleural effusion affect the heart?

mechanical obstruction + inflammatory response → pulmonary A hypertension →

Increase RV afterload will cause:

• Increased venous pressure→ Jugular vein distension

• Septum gets pushed→ septal dyskinesia→ affecting LV

• Eventually reduce LV preload→ Reduced CO→ Reduced BP→ Syncope

•  Increased HR to correct reduced Bp

• Low LV preload→ reduced coronary  circulation→ Ischemia → MI 

Signs of pulmonary embolism

• tachypnoea

• rales/crackles

• tachycardia

• change in heart sounds

Symptoms of pulmonary embolism

• dyspnoea

• pleuratic chest pain

• cough

• haemoptosis

What are the different classifications of pulmonary embolism?

Time:

• Acute: Immediately after obstruction

• Subacute: within days or weeks after obstruction

• Chronic: Over many years, development of pulmonary hypertension (chronic
  thromboembolic pulmonary hypertension, CTEPH)

hemodynamic stability:

• Hemodynamically unstable PE: present with hypotension → high risk

• Hemodynamically stable PE: may be associated right ventricular strain → risk if RV strain

How can you diagnose a pulmonary embolism?

• Computed Tomography Pulmonary Angiogram (CTPA)

• D-Dimer test: if presence of D-Dimer in blood = there is a clot but don’t know where

• Ventilation perfusion scan

→ Air circulation: breathe in radioactive gas and the machine scan the air flow

→ Blood circulation: Radioactive albumin injected into a vein and the machine scans the lungs as blood flows through them

Wells criteria to diagnose pulmonary embolism (using signs)

If score >1, PE likely
If score<1, PE unlikely

General/ immediate treatment of pulmonary embolism

• Oxygen supplementation

• IV Fluids (restoring perfusion if unstable)

• Vasopressor support (if unstable

• Stabilise airway with intubation and mechanical ventilation (if necessary)

How does fibrinolysis happen?

1. Tissue plasminogen activator (tPA) is released from endothelial cells (stimulated by thrombin)

2. tPA cleaves plasminogen → plasmin

3. plasmin cleaves fibrin → releases D-dimer + fibrinogen

How does a clot form?

vWF activates platelets → release ADP, seratonin, thromboxane A2

activate GPIIb/IIIa receptor →platelet can bind to fibrinogen

→ platelet plug → activate clotting factors (extrinsic + intrinsic): prothrombin → thrombin → cleaves fibrinogen → fibrin

** requires Ca2+ and K+

How do we prevent coagulation?

endothelial cells secrete:

NO + prostaglandins → inhibit platalets

heparin sulphate → activate anti thrombin III → inhibit clotting factors

thrombomodulin → modulates thrombin → activates protein C → binds to protein S → inhibit clotting factors

What anticoagulant drugs can we use to prevent clot formation?

Warafin + heparin

• Vitamin K antagonist → inhibit vit k

• inhibits factor II, VII, IX, X

• also inhibits Protein C so we need more heparin (natural anticoagulant)

Direct oral anticoagulants

• inhibit thrombin/prothrombin

• Some inhibit factor Xa

what pathway does INR test?

extrinsic pathway 

time taken for blood to clot compared to normal time

what test tests for intrinsic pathway?

aPTT test

How do you treat blood clots?

Thrombolytic agents: tPA activator, Streptokinase/urokinase → lyse existing blood clot

Inferior vena cava filters: prevent clots entering the heart and Pulmonary A

Percutaneous pulmonary embolus mechanical
thrombectomy: surgical removal of the emboli