Haemodynamic disorders Flashcards
What are the three forces involved in oedema?
- capillary hydrostatic pressure
- plasma oncotic pressure
- tissue hydrostatic pressure
What are the causes of oedema?
- Increased Capillary Hydrostatic Pressure
E.g. venous obstruction, congestive cardiac failure - Decreases Capillary Oncotic Pressure
E.g. nephrotic syndrome (loss of proteins through leaky kidneys), cirrhosis, malnutrition - Inflammation
Increased vascular permeability - Lymphatic Obstruction
Lymphoedema - breast cancer treatment
Filariasis can cause massive lymphatic obstruction
What is pulmonary oedema?
What is the cause?
What is the most common pathology?
Cause: Raised hydrostatic pressure in the pulmonary capillary bed
Most common pathology: Left ventricular failure causing increased pressure in the left atrium. This causes back pressure into the capillaries. This pushes water into the interstitial space. Fluid accumulates in the interstitial space and then spills over into the alveolar spaces. This is Cardiogenic Pulmonary Oedema
What are the symptoms of pulmonary oedema?
- Dyspnoea (worse when they lie flat - orthopnoea)
- Fluid collection in alveolar spaces predisposes to bacterial infection in the lung (pneumonia)
What are the four types of cerebral oedema and their causes?
1) Vasogenic - physical breakdown of blood-brain barrier
Causes: trauma and tumours (by releasing factors which break down barriers)
2) Cytotoxic - derangement of sodium-potassium membrane pump
Increase in sodium within cells encourages water to be taken up
Causes intracellular oedema
Common in ischaemic strokes
3) Osmotic - reduction in plasma osmolality
Cause: SIADH (Syndrome of Inappropriate ADH secretion)
SIADH is commonly caused by small lung cell carcinoma
4) Interstitial - breakdown of CSF-brain barrier
Cause: Obstructive Hydrocephalus (abnormal accumulation of cerebrospinal fluid in the brain - due to blockage in flow of CSF)
CSF moves into the interstitial space
Osmolality vs osmolarity
OsmolaRity = number of solute particles per LITRE
OsmolaLity = number of solute particles per KILOGRAM
What is generalised oedema?
severe generalised oedema is anasarca
widespread accumulation of fluid in subcutaneous tissues and serous cavities (pitting)
What are the causes of generalised oedema?
Left Ventricular Failure - dependent oedema (accumulated in areas affected by gravity)
Nephrotic Syndrome - fluid accumulates in all parts of the body (causes reduced albumin)
Hepatic failure (causes reduced albumin so colloid pressure reduced)
How does heart failure cause oedema?
renin
- Low Renal Blood Flow
- Release of Renin from kidneys
- Formation of angiotensin II
- Release of aldosterone from adrenal gland
- Absorption of sodium and water from kidneys
- Generalised oedema
What are the consequences of cerebral oedema?
leads to high intracranial pressure and so higher risk of brain herniation and death
to reduce this raise head, induce dehydration and surgical decompression
Which three things lead to the formation of a thrombus?
Virchow’s triad:
- change in blood flow (stasis) as during stasis platelets are exposed to endothelium and more likely to clot. Stasis an also cause thrombosis by changing the dilution of blood clotting factors.
- change in endothelium e.g. damage or endothelium dysfunction
- change to blood constituents e.g. hypercoagulability caused by genetics or acquired disorders
Cardiac thrombosis
E.g. due to Atrial Fibrilation
Left Atrial Thrombosis is usually related to atrial fibrillation
Left Ventricular Thrombosis is usually related to prior myocardial infarction
Most important complication: Systemic Embolisation
Arterial thrombosis
Almost always related to vessel wall injury - often caused by atherosclerotic plaques
If artery narrows - ischaemia
occlusion - infarction
Venous thrombosis
Key factors: Stasis and Hypercoagulability
Most form in deep veins
Most important complication: Pulmonary Embolism
What is an embolism?
A detached intravascular solid, liquid or gaseous mass that is carried by the blood to a site distant from its point of origin. Most are thromboemboli but can be air, fat, amniotic fluid or a tumour
Venous Thromboembolism
Most originate in Deep Veins
Most Significant Consequence - pulmonary (thrombo)embolism
Pulmonary embolism and how do the consequences differ depending on where it gets lodged and its size?
Emboli lodging in a major pulmonary artery can cause instantaneous death
If it gets lodged at the bifurcation of one pulmonary artery into two, it is called a saddle embolus
Emboli lodging in medium sized arteries present with breathlessness
Small emboli lodging in small arteries cause non-specific symptoms - e.g. dizziness, chest pain, breathlessness
Risk of death increases with time taken to make the diagnosis
Cardiac thromboemboli
How does the location of lodging affect the outcome?
Most originate on the left side of the heart
May lodge in:
Cerebral Artery - STROKE
Mesenteric Artery - BOWEL INFARCTION
Lower Limb Artery - ACUTE LOWER LIMB ISCHAEMIA
What is are the causes of haemorrhages and what does the outcome depend on?
Causes:
- Trauma
- Intrinsic disease of the vessel
The result of a haemorrhage depends on:
- Volume and rate of haemorrhage
- Site
What does the rupturing of a large and small vessel result in?
Rupture of a major vessel causes acute haemorrhage with risk of:
- Hypovolaemia
- Shock
- Death
Rupture of a small vessel can still be fatal if it occurs at a vital site - e.g. brainstem haemorrhage
What is the effect of a solid haematoma in the cranial cavity?
Formation of a solid haematoma within the cranial cavity can be fatal by causing a rise in intracranial pressure and tonsillar herniation
What is shock and the most vulnerable organs?
Occurs when tissue perfusion is insufficient to meet metabolic requirements. Caused by pump failure or peripheral circulation failure.
Hypotension - circulatory collapse leading to ischaemia of multiple organs. Initially reversible.
Most Vulnerable Organs: Kidneys, Bowel, Brain, Lungs, Heart
What are the five types of shock?
- hypovolaemic
- cardiogenic
- septic
- anaphylactic
- neurogenic
Hypovolaemic shock: causes and mechanism
Most commonly due to loss of volume
Causes include: Trauma, Haemorrhage
Low blood volume –> Low SV –> Reduced CO –> Reduced MAP
Body tries to compensate with tachycardia
