2- Haemodynamic Disorders Flashcards
What causes fluid to move into tissue
Capillary Hydrostatic Pressure - pushing OUT of vessel
• Plasma Oncotic Pressure - pulling IN to vessel
This is the pressure exerted by plasma protein
• Tissue Hydrostatic Pressure - pushing IN to vessel
What causes 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 facilitates movement of fluid into the
interstitium
• Lymphatic Obstruction
MOST COMMON - lymphoedema - breast cancer treatment - damage the lymph vessels leading to build up of fluid
Filariasis can cause massive lymphatic obstruction
What is pulmonary oedema
Cause: Raised hydrostatic pressure in the pulmonary capillary bed
• Most Common Cause of this: Left Ventricular Failure
increased pressure in the left atrium 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
• You can also get Non-Cardiogenic Pulmonary Odema caused by increased permeability
This is known as ARDS (Acute Respiratory Distress Syndrome) Commonly seen in injecting drug users
Most Common causes of ARDS: Sepsis, Shock and Trauma
• Can be chronic or acute
• MAIN SYMPTOM: DYSPNOEA
• Dyspnoea is worse when they lie flat because of the movement of fluid (this is
called orthopnoea)
• Fluid collection in alveolar spaces predisposes to bacterial infection in the lung
(pneumonia)
What are 4 types of cerebral oedema
- Vasogenic - physical breakdown of blood-brain barrier
Causes: Trauma and Tumours (by releasing factors which break down
barriers) - Cytotoxic - derangement of sodium-potassium membrane pump
Common in ischaemic strokes
Increase in sodium within cells encourages water to be taken up Causes intracellular oedema - Osmotic - reduction in plasma osmolality
Cause: SIADH (Syndrome of Inappropriate ADH secretion) SIADH is commonly caused by SMALL CELL LUNG CARCINOMA ADH release –> more water reabsorbed –> decrease in plasma osmolality - 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 (NOT blood plasma) moves into the interstitial space
What does cerebral oedema cause
Cerebral oedema contributes to a rise in intracranial pressure (ICP)
• High ICP can lead to brain herniation (squeezing of the brain across a structure
within the skull) and death
• Leads to confusion, nausea and vomiting
• Strategies to reduce ICP: raise head, inducing dehydration with drugs, surgical
decompression
What is osmolarity and osmololity
OsmolaRity = number of solute particles per LITRE OsmolaLity = number of solute particles per KILOGRAM
What is generalised oedema
Severe Generalised Oedema = Anasarca
• It is the widespread accumulation of fluid in subcutaneous tissues and serous cavities
• Same causes of localised oedema cause generalised oedema
• Common Causes:
Left Ventricular Failure - dependent oedema (accumulated in areas affected by gravity)
Nephrotic Syndrome - fluid accumulates in all parts of the body
• Consequences of Oedema in peripheral setting:
Impaired wound healing
Patients with generalised oedema are more prone to getting cellulitis
How does heart failure cause oedema
Mechanism of Heart Failure causing Oedema:
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 can happen to a thrombus
- Propagation
Thrombus gets BIGGER - accumulates more fibrin and takes up a larger portion of the vessel - Embolisation
Dislodges and travels to distant site - Dissolution
Thrombus is destroyed by fibrinolytics (can be endogenous or given as a
drug) - Organisation and Recanalisation
As a result of the thrombus, there is inflammation Thrombus becomes fibrotic and remodels
Lumen appears again allowing blood flow
What is thrombosis and what causes it
Abnormal blood clot formation in the circulatory system.
• Vessel Wall Injury
Physical Damage to Endothelium - exposes ECM and activated blood clotting cascade
Endothelial Dysfunction - endothelium isn’t working normally so causes alteration in the formation of pro- coagulants and anti-coagulants
• Stasis (alteration to blood flow)
Normal Blood Flow - laminar - platelets
are usually found in the centre of the vessel and is not exposed to endothelium - less chance of thrombosis
Stasis - loss or normal flow - platelets are exposed to the endothelium - more likely to form a clot
Stasis can also cause thrombosis by changing the dilution of blood clotting factors
• Hypercoagulability
Primary - Genetic Disorder - patients are more likely to form blood clots Most common hypercoagulability disorder in UK - Factor V Leiden Secondary - Acquired - risk factors for developing thrombosis - obesity, neoplasia, oral contraceptive pill
Describe cardiac thrombosis
STASIS is the main way that thromboses form
EXAMPLE: 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
Describe arterial thrombosis
Almost always related to vessel wall injury
• Vessel wall injury is often caused by atherosclerotic plaques
• Stenosis = narrowing of the artery by the thrombus
• Stenosis causes ischaemia of the tissue supplied by the artery
• Occlusion = complete blockage of the artery by the thrombus
• Occlusion causes infarction of the tissue supplied by the artery
Describe venous thrombosis
KEY FACTORS: Stasis and Hypercoagulability • Risk Factors: Age Obesity Malignancy Immobility Oral Contraceptive Pill • Most form in DEEP VEINS (DVT) • 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.
What are embolisms made from
Most emboli are fragments of dislodged thrombus (thromboemboli) • Rarer types of embolic material: Fat Air Amniotic Fluid Tumour
What are the types of thromboembolism
Venous Thromboembolism
• Most originate in Deep Veins (e.g. DVT)
• Most Significant Consequence - pulmonary (thrombo)embolism
Pulmonary Embolism
Consequence depends on the size of the embolus and where it gets lodged.
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
• 30% of patients with PE die from it
• Risk of death INCREASES with time taken to make the diagnosis
Arterial Thromboemboli
• Most originate in CAROTID ARTERIES
• Most likely to affect cerebral arteries - causing STROKE
Cardiac Thromboemboli
• 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
Describe haemorrhage
CAUSES:
Trauma
Intrinsic disease of the vessel
• Haemorrhage can be external or enclosed within a tissue
• Haematoma = a localised mass of extravasated blood that is relatively or
completely confined within an organ or tissue
• Haemorrhages are classified based on size:
1-2mm = petechiae
>3mm = purpura
1-2cm = ecchymoses
Large accumulations in body cavities (e.g. haemothorax)
• The result of a haemorrhage depends on:
Volume and rate of haemorrhage
Site
• 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
• Formation of a solid haematoma within the cranial cavity can be FATAL by causing a RISE IN INTRACRANIAL PRESSURE and TONSILLAR HERNIATION NOTE: Tonsillar Herniation - pushing the cerebellar tonsils through the foramen magnum possibly causing compression of the lower brain stem
• Chronic Low Grade Haemorrhage
May present with iron deficiency anaemia EXAMPLE: bleeding from colonic carcinoma
What are the 5 types of shock
- Hypovolaemic
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
By increasing HR you try to maintain regular CO - Cardiogenic
Due to IMPAIRED CARDIAC FUNCTION
CAUSES include: Acute MI, Cardiac Tamponade
Cardiac Tamponade - accumulation of fluid in the pericardium resulting in compression of the heart
Heart isn’t working properly so SV is REDUCED leading to shock - Septic
Result of INFLAMMATORY RESPONSE CAUSE: Vasodilation
Reduced SVR –> Reduced MAP - Anaphylactic
Result of IgE MEDIATED HYPERSENSITIVITY Similar to Septic Shock
CAUSES: Vasodilation, Increased Permeability Reduced SVR –> Reduced MAP - Neurogenic
RARE
Normally happens after trauma
Result of INJURY TO THE SYMPATHETIC PATHWAYS
CAUSES: loss of vasomotor tone - causes widespread vasodilation and reduced SVR
Also in neurogenic shock, you’ve disrupted the sympathetic pathways so you won’t be able to become tachycardic to increase cardiac output
What is shock
Occurs when tissue perfusion is insufficient to meet metabolic requirements.
• Characterised by HYPOTENSION
• Prolonged hypotension causes circulatory collapse leading to ischaemia of
multiple organs
• Most Vulnerable Organs: Kidneys, Bowel, Brain, Lungs, Heart
What is infarction
Tissue necrosis due to ischaemia.
• Most due to obstruction of an artery
• Some may occur due to venous obstruction
• More rarely occurs due to vasospasm and compression
• Red Infarcts - haemorrhagic - affects organs with a dual blood supply - generally
caused by venous blood supply
• White Infarcts - anaemic - affects solid organs which have one blood supply
• Infarcts heal by REPAIR
• Although structural integrity is maintained, there is some permanent loss of
functional tissue
What are Factors influencing development of infarction:
• Nature of Blood Supply
Lung and Liver = Dual Circulation
Kidney and Spleen = End Organs (single blood supply)
If there is an obstruction in the lung or liver, they can use other vessels to supply the tissue.
Kidney and spleen are more susceptible to infarction
• Rate of Development of Occlusion
If the occlusion develops slowly, there could be enough time for Collateral
Vessels to form and provide an alternate blood supply
• Vulnerability to Hypoxia
EXAMPLE: neurones are very susceptible to hypoxia, fibroblasts aren’t
• Oxygen content of the blood
EXAMPLE: patients who have anaemia and chronic heart failure will have reduced levels of oxygen in their blood - more prone to developing infarctions
Scribe myocardial infarction
Looks like a wedge shape - apex of the wedge is where the occlusion occurred TWO Types of MI:
Transmural Infarction
• Entire wall is affected
• Occurs when there has been
complete blockage of a vessel and complete cessation of the blood supply
Subendocardial Infarction
• Some myocardial tissue underneath the endocardium has been affected by infarction
• Caused by drop in blood oxygen content or rapid drop in blood supply (e.g. due to blood loss)
Describe small bowel infarction
RED INFARCT
• Surgical emergency
• Patients present with severe lactic acidosis
Describe atherosclerosis
Complex chronic disease - underlying cause of most vascular diseases
• Focal intimal accumulation of lipids and fibrous tissue associated with smooth
muscle proliferation
• Affects medium and large vessels
• Develops from fatty streak into plaque within the intima
What is the process of atherosclerosis?
- Endothelial damage
- Macrophage infiltration - macrophages release cytokines
- Cytokines recruit LDLs
- LDLs become oxidised
- Oxidised LDLs are pro-inflammatory and drive progression of plaque
- Smooth muscle cells migrate from the tunica media to the lesion
- Smooth muscle cells deposit a collagen rich matrix that forms a protective
fibrous cap
What are 2 types of plaque?
Stable Plaque Less inflammation Well developed thick fibrous caps Slow growing Less likely to rupture • Unstable Plaque More inflammation Lipid rich necrotic core Thin fibrous cap MORE LIKELY TO RUPTURE
What can hypokalaemia cause
Shock. It is hypokalaemia (low blood potassium), not hyperkalaemia (high blood potassium), that usually causes shock.
