Monday LObs Flashcards
(83 cards)
What is a thrombus composed of?
Leukocytes, Erythrocytes and Platelets within a Fibrin Mesh.
Discuss Verchow’s Triad, an explanation of its 3 sections, and its relevance in diagnosing DVT. Include a diagram
V’s Triad consists of 3 factors that are critically important in the development of venous thrombosis:
- Venous stasis
Venous stasis can occur as a result of anything that slows or obstructs the flow of venous blood. This results in an increase in viscosity and the formation of microthrombi, which are not washed away by fluid movement.
- Activation of blood coagulation
A hypercoagulable state can occur due to a biochemical imbalance between circulating factors. This may result from an increase in circulating tissue activation factor, combined with a decrease in circulating plasma antithrombin and fibrinolysins.
- Venous Damage
Endothelial (intimal) damage in the blood vessel may be intrinsic or secondary to external trauma. It may result from accidental injury or surgical insult.
Draw the 6 possible Fates of Thrombi
PIC 601
What is a Baker’s Cyst?
A Baker’s cyst, also known as a popliteal cyst, is a type of fluid collection behind the knee.
The synovial sac of the knee joint can, under certain circumstances, produce a posterior bulge, into the popliteal space, the space behind the knee.
It is now being increasingly recognised that a Baker’s (popliteal) cyst, ruptured or otherwise, may simulate deep vein thrombosis.
What is a Homer’s sign test?
Homan’s sign test is a physical examination procedure that is used to test for Deep Vein Thrombosis (DVT).
In performing this test the patient will need to actively extend his knee.
Once the knee is extended the examiner raises the patient’s straight leg to 10 degrees, then passively and abruptly dorsiflexes the foot and squeezes the calf with the other hand.
Deep calf pain and tenderness may indicate presence of DVT.
Draw the flow chart of Wells Score and diagnostic tests, “Could Pat Butcher Try Some Superb Cornish Pasties in an Alternative Past?”
DVT Infographic
In the context of testing, define the following:
Sensitivity
Specificity
PPV
NPV
Sensitivity is the ability of a test to correctly identify patients with a disease.
Specificity: the ability of a test to correctly identify people without the disease.
The positive and negative predictive values (PPV and NPV) are the proportions of positive and negative results in statistics and diagnostic tests that are true positive and true negative results.
What is the difference between Proximal and Distal DVT?
Proximal DVT: Located in the popliteal, femoral, or iliac veins.
Isolated Distal DVT is confined to the calf veins (peroneal, posterior, anterior tibial, and muscular veins)
What does a D-Dimer test do?
Measures the level of D-Dimer (a protein fragment hat’s made when a blood clot dissolves in your body) in your blood.
Has high sensitivity and low specificity = Many false positives.
Can therefore rule out DVT, but not confirm it.
How and why does Venous Thromboses frequently present in the lower extremity veins?
In the absence of rhythmic contraction of the leg muscles, as in walking or moving, blood flow in the veins slows and even stops in some areas, predisposing patients to thrombosis.
Studies have shown that low flow sites, such as the soleal sinuses, behind venous valve pockets, and at venous confluences, are at most risk for the development of venous thrombi. Most of these locations begin in the calf.
As many as 1/3 of untreated symptomatic calf vein DVT extend to the proximal veins. Although calf vein thrombi are rare sources of clinically significant pulmonary embolism (PE), the incidence of PE with untreated proximal thrombi is 29-50%.
Define Haemostasis, and outline its three stages.
Pic 603
Name three methods in which the endothelium of blood vessels inhibits haemostasis during healthy blood flow
- Nitrous Oxide and PGI2 (Prostacyclin)
Both are chemicals released by the endothelium to inactivate platelets, and thereby inhibit their binding to the endothelial lining.
- Heparin Sulfate
Glycosaminoglycan protein - bound to plasma membrane - that binds and activates A.T.III (Anti-Thrombin III), which degrades clotting factors II, IX and X.
- Thrombomodullin
Receptor for Thrombin - Thrombin activates Protein C - which degrades clotting factors V, and VIII
Describe the mechanism of Vascular Spasm
- When injured, endothelial cells in the blood vessels secrete Endothelin. This binds to Type 2 G protein ETB receptors in the smooth muscle to initiate contraction (like NE from Vasomotor centre)
- Myogenic mechanism of smooth muscle cells - in which they contract in response to mechanical trauma
- Nociceptors in blood vessels are stimulated by inflammatory mediators and mechanical trauma to stimulate pain and enact a contractile muscular response.
Give an outline of Platelet Plug formation
- vWF (von Wildebronn’s Factor) is secreted by injured endothelial cells
- Injury to endothelial cells inhibits secretion of NO and PGI2, and inhibits upkeep of Thrombomodullin/Heparin Sulfate, meaning platelets can freely bind to collagen with the help of vWF.
- Platelets bind to vWF using their Gp1b receptors, to release TxA2, ADP and Seratonin, which encourages platelet coagulation to vWF. Platelets bind to each other via fibrinogen and GpIIb/IIIa.
- The released chemicals stimulate further contraction of the smooth muscle, enhancing the vascular spasm effect and starting a +feedback loop of platelet aggregation.
Draw the overall Coagulation Cascade and Fibrolysis Map, as well as which factors require Ca+ or Vitamin K to function.
Factors requiring Ca+: II, VII-XI, XIII
Factors requiring Vit K:
II, VII, IX, X, Protein C, Protein S
(diSCo 1972)
Factor XIII is also activated by Factor II as a Fibrin Stabilising factor.
Explain Haemophilias a, b and c through factor deficiencies
PIC 604
Describe the effects of a PE in terms of pulmonary infarction and ischemia
PIC 605
Describe the effects of a PE in terms of v/q mismatch
PIC 606
Describe the effects of a PE upon the cardiovascular system
Pic 607
What would you see on the ABGs for a patient with PE?
ABG: Most commonly shows hypoxemia and hypocapnea (respiratory
alkalosis) due to hyperventilation:
• type 1 respiratory failure
• ↓PaO2 and ↓PaCO2
What would you find on an ECG for someone with PE?
ECG is often normal, often used to rule out Myocardial Infarction and Pericarditis
Common findings include:
1. Sinus Tachycardia
2. Inverted T waves
3. S1Q3S3 (see picture)
What would you expect to find on a CXR for someone with PE?
CXR is neither sensitive
nor specific for confirming PE, mainly useful to rule out other conditions in DDx e.g. pneumonia,
pneumothorax.
Chest radiographic signs include:
• Fleischner sign: enlarged pulmonary artery (20%)
• Hampton hump: peripheral wedge of airspace opacity and implies lung
infarction (20%)
• Westermark sign: regional oligaemia and highest positive predictive value
(10%)
What is Oligaemia?
Just another goddamn word for Hypovolemia
What is a pneumothorax?
A Collapsed Lung
