Haemodynamic disorders Flashcards
What is oedema?
An abnormal increase in interstitial fluid
Under normal circustances, how does fluid leave the circulation at the arterial end?
Hydrostatic pressure > oncotic pressure
Under normal circustances, how does fluid leave the circulation at the venous end?
Oncotic pressure > hydrostatic pressure
What is the flow of interstitial fluid governed by?
- Hydrostatic and oncotic pressures
- Endothelial permeabillity
Name 5 aetiologies of oedema
- Increased hydrostatic pressure
- Heart failure results in increase in hydrostatic pressure (generalised oedema)
- Salt and H₂O retention
- Reduced cardiac output stimulates renin-angiotensin system which leads to sodium retention (generalised oedema)
- Reduced plasma oncotic pressure (reduced albumin)
- Plasma oncotic pressure is governed by [albumin]
- When [albumin] < 25g/L fluid leaves microcirculation
- Cause of generalised oedema
- Loss of protein (nephrotic syndrome, protein loos enteropathy)
- Inflammation
- Loss of protein rich fluid locally
- Lymphatic obstruction
- Localised oedema
- Non pitting protein rich oedema
- Obstruction by tumour, lymph node dissection, chronic inflammation
What is the difference between localised and generalised oedema?
LOCALISED = cerebral and pulmonary oedema
GENERALISED = fluid in serous cavities (pleural, pericardial, peritoneal) > 5L
What are the causes of localised oedema?
- Left heart failure
- Inflammation
- Venous hypertension
- Lymphatic obstruction
What are the causes of generalised oedema?
- Congestive heart failure
- Hypoproteinaemia (low protein content)
- Nutritional oedema
What happens during pulmonary oedema?
- Normally plasma oncotic pressure > hydrostatic pressure in pulmonary capillaries
- Left heart failure increases hydrostatic pressure in pulmonary capillary bed
- Fluid accumulates first in interstitial space and then eventually spills into alveolar spaces
What are the signs and symptoms of pulmonary oedema?
- Breathelessness (dyspnoea)
- Breathlessness typically worse on lying flat (orthopnoea)
- Fluid in alveolar spaces predisposese to bacterial infection in lung (pnuemonia)
What is thrombosis?
Abnormal blood clot formation in the circulatory system
According to Virchow’s Triad, what are the three causes of thrombosis?
- Endothelial injury (usually where vessels bifurcate)
- –> platelet activation
- Arteries have high rates of blood flow and hence are under high shear stress
- Stasis or turbulent blood flow
- –> endothelial injury
- Stasis = disruption of laminar blood flow and development of venous thrombi
- Turbulent = endothelial injury and formation of local pockets of stasis –> arterial and cardiac thrombi
- Blood hypercoagulability (can be genetic or acquired)
- Blood disorder
- Can be primary or secondary
- Primary = factor V mutation, protein C deficiency
- Secondary = multifactorial, obesity, cancer, stasis, advancing age, use of oral contraceptive pill
What is venous thrombosis caused by?
Usually stasis and hypercoagulability
TRUE OR FALSE:
Most venous thromboses form in deep leg veins
TRUE
E.g. deep venous thrombosis (DVT)
What is the most important potential complication of venous thrombosis?
Pulmonary embolism
What is arterial thrombosis caused by?
Almost always related to vessel wall injury caused by atherosclerotic plaques
What are the complications of arterial thrombosis?
- Narrowing (stenosis) of artery by thrombus causes ischaemia of the tissue supplied by the artery
- Complete blockage (occlusion) of artery causes infarction of the tissue supplied by the artery
What are the 4 fates of thrombi?
- Propagation
- Accumulation of further platelets and fibirin in a semi-occlusive thrombus
- Embolisation
- Thrombi dislodge and travel through circulation
- Dissolution
- Fibrinolysis in early thrombi
- Organisation and recanalisation
- Older thrombi enveloped by fibroblasts, endotheilal cells and smooth muscle cells
- Capillary channels develop within thrombus
What is the clinical significance of thrombosis?
Come to clinical attention when they:
- either obstruct arteries or veins
- when they embolism
What are emboli?
Abnormal material within the circulatory system that is carried in the blood to a site distant from its point of origin.
Most emobli are fragments of dislodged thrombus (thromboemboli)
Other rarer types include fat, air, amniotic fluid, tumour
What are infarcts?
Areas of ischaemic necrosis caused by occlusion
What is infarction most commonly caused by?
Thrombic or embolic vascular occlusion (though other causes need to be excluded)
What are the differences between red and white infarcts?
RED INFARCTS:
- Occur as a result of venous occlusion
- Occur in loose tissue (e.g. lungs)
- Occur in organs with dual circulation (e.g. lung, bowel)
- Can reperfuse a site of previous arterial occlusion
WHITE INFARCTS:
- Occurs as a result of arterial occlusion
- In dense/solid organs
TRUE OR FALSE:
Infarcts heal by repair meaning that both structural integrity and function are maintained
FALSE:
Although structural integrity is maintained, there is permanent loss of functional tissue
What are pulmonary emboli?
- Originate from deep vein thrombosis (lower extremities)
- Can range form silent to symptomatic and even lead to sudden death
What are systemic emboli?
- Arise in the arterial system
- Originate from:
- dislodged atheromatous
- thrombi from within heart
- Thrombi within the heart:
- due to cardiomyocyte death and thus no contractility
- due to atrial fibrillation
What is myocardial infarction caused by?
Most commonly coronary artery occlusion:
- Occlusive thrombus in coronary artery
- Acute plaque change/rupture
Can also be due to:
- Coronary artery vasospasm
- Emboli (from left atrium-atrial fibrillation)
- Vasculitis
- Haematological abnormalities (sickle cell disease)
What is a haemorrhage?
Extravasation of blood due to vessel rupture
What might a haemorrage be due to?
Trauma or an intrinsit disease of a vessel
Rupture of a major vessel causes accurate haemorrhage with risk of…?
Hypovolaemia, shock and death
What is shock?
Systemic hypotension due to reduced circulatory volume or reduced cardiac output
Name and describe 5 types of shock
- Cardiogenic shock
- When the heart isn’t working properly
- Numerous causes such as acute Mi, arrhythmias, cardiac tamponade etc.
- Hypovolaemic shock
- Loss of blood or plasma due to haemorrhage or fluid loss
- Septic shock
- An infection activates immune system
- Resultatn vasodilation and pooling of blood
- Neurogenic shock
- Loss of vascular tone
- Cord injury, anaesthetic medication
- Anaphylatic shock
- Allergic reaction
What is the cause of hypovolaemic shock?
- Fluid loss
- Start having symptoms when more than 1L of blood (20%) is lost
What is cardiogenic shock caused by?
- Heart cannot pump enough blood to meet body’s demands
- Caused by acute myocardial infarction
- High mortality rate
Outline the continuum from SIRS to septic shock
- Systemic inflammatory response syndrome (SIRS)
- 2 or more of either:
- Temperature >38 or <36°C
- Tachycardia
- High respiratory rate
- High WBC count
- 2 or more of either:
- Sepsis (SIRS + infection)
- Severe sepsis
- Septic shock
What is septic shock most commonly caused by?
Pathogen: gram positive bacteria
Endotoxins released by pathogens:
- activate complement pathway
- damage endothelial cells
- tumour necrosis factor
What are the general complications of a septic shock?
- Organ dysfunction and multi-organ failure
- Ischaemic tissue - lactic acidosis
- Acute tubular necrosis
