Abnormal increase in interstitial fluid
What three forces determine the movement of fluid between blood vessels and the interstitial space?
Capillary hydrostatic pressure
Plasma hydrostatic pressure
Plasma oncotic pressure
What are the four broad causes of oedema?
Increased capillary hydrostatic pressure Decreased plasma oncotic pressure (e.g. nephrotic syndrome) Inflammation Lymphatic Obstruction
What is a common cause of pulmonary oedema?
Increased plasma hydrostatic pressure in the pulmonary capillary bed
Left Ventricular Failure – build up of pressure in left atrium leading to back pressure into the capillaries – this pushes water into the tissues
This is cardiogenic pulmonary oedema
What is non-cardiogenic pulmonary oedema?
Caused by increased permeability
ARDS – Acute Respiratory Distress Syndrome
Often caused by Sepsis, Shock and Trauma
What are the four types of cerebral oedema?
Vasogenic – physical breakdown of the blood-brain barrier – commonly due to trauma or tumours
Interstitial – breakdown of the CSF-brain barrier – commonly due to obstruction of the flow of CSF (Obstructive Hydrocephalus)
Cytotoxic – derangement of the sodium-potassium pumps leads to a build up of intracellular sodium causing intracellular oedema (common with ischaemic strokes)
Osmotic – increase in plasma osmolality – commonly caused by Syndrome of inappropriate ADH secretion (SIADH) that is commonly caused by small cell lung cancer
What are the possible serious consequences of cerebral oedema?
Rise in intracranial pressure, which could cause herniation
What are two common causes of generalised oedema?
Left Ventricular Failure Nephrotic Syndrome
What is a consequence of oedema in a peripheral setting?
Impaired wound healing
What are the three main factors affecting thrombus formation?
Vessel Wall Injury
What is cardiac thrombosis caused by and what is an important complication?
Stasis – e.g. atrial fibrillation
Complication – systemic embolisation
What is arterial thrombosis caused by?
Vessel wall injury
What is venous thrombosis caused by and what is an important complication?
Stasis and Hypercoagulability Complication – pulmonary embolism
What are the four fates of a thrombus?
Propagation– thrombus accumulates fibrin and grows
Embolisation– thrombus dislodges and moves somewhere else
Dissolution– thrombus is dissolved by fibrinolytics
Organisation and Recanalisation– thrombus becomes fibrotic and is remodelled, lumen appears again allowing blood flow
Where do most arterial thromboemboli originate?
A localised mass of extravasated blood that is relatively or completely confined within an organ or tissue
What are the three classes of haemorrhage based on size?
Petechiae = 1-2mm Purpura = >3mm Ecchymoses = 1-2cm
What is shock characterised by?
What two equations are used to evaluate the effects of changes in various vascular factors?
MAP = CO x SVR CO = HR x SV
What are the five types of shock?
Cardiogenic Hypovolaemic Anaphylactic Neurogenic Septic
Describe each of the five types of shock and its causes and effects
Cardiogenic -impaired cardiac function, Causes include cardiac tamponade, Reduced SV
Hypovolaemic– loss of blood volume,
Causes include: trauma, haemorrhage Low SV leads to Low MAP Body tries to compensate with tachycardia
Anaphylactic– IgE mediated hypersensitivity, Causes vasodilation and increased permeability, Reduced SVR leads to Reducer MAP
Neurogenic– injury to sympathetic pathways, Normally happens after traum,a Widespread vasodilation and reduced SVR
Septic– result of inflammatory response, Causes vasodilation. Reduced SVR leads to Reduced MAP
Tissue necrosis due to unresolved ischaemia
What are the two types of infarct and how are they different?
Red – haemorrhagic – affects organs with a dual blood supply
White – anaemic – affects solid organs that have one blood supply
How can the rates of development of the occlusion affect the infarction?
If the occlusion develops slowly then there may be enough time for collateral vessels to form
What are the two types of myocardial infarction?
Transmural – across the whole wall of the heart
Subendocardial – just the layer under the endocardium
Describe the process of atherosclerosis.
1) Endothelial damage
2) Macrophage infiltration and release of cytokines
3) Cytokines recruit LDLs
4) LDLs become oxidised and hence become pro-inflammatory and drive progression of plaque
5) Smooth muscle cells migrate from the tunica media to the lesion and deposit a collagen-rich matrix, which forms a protective fibrous cap
What are the two types of atherosclerotic plaque and how are they different?
Stable – thick fibrous cap – less likely to rupture
Unstable – thinner fibrous cap – more likely to rupture