Disturbances in circulation Flashcards
Describe some aspects of haemorrhage…
Bleeding from a damaged vessel
- Often caused by trauma
- Vascular disease may predispose to
- Local high blood pressure may predispose to
- A diffuse haemorrhage may occur in coagulation disorders
What is diapedesis?
Loss of individual RBCs between endothelial cells
What is a haematoma?
A local accumulation of blood that is usually clotted
What is petechiae?
Pin-point haemorrhages
- usually capillary bleeds
What is ecchymoses?
Paint brush “splashed” haemorrhages over skin or mucous membranes
What are some local effects of haemorrhage?
The effect depends on location
- Space-occupying lesions
- Small haemorrhages
- Larger haematomas
What are the systemic affects of haemorrhage?
Depends on the severity and speed of onset
- Repeated minor blood loss may lead to iron deficiency
e. g. GIT ulcers
When is hypovolaemic shock likely?
When there is acute blood less of 30% or more
What happens if there is slower loss of 30% of total blood volume?
Compensation may be enough
- The body has its own compensatory mechanisms that come into play
Describe the three compensatory mechanisms…
Redistribution is a Rapid Response occurs within minutes
Restoring blood fluid volume is a medium term mechanism that occurs within hours
Replacing RBCs is a longer term mechanism that occurs within 5-14 days
Describe the Blood redistribution compensatory mechanism…
Some arterioles constrict to divert blood to vital organs
- Spleen contracts at the same time
Describe the Restoration of blood volume compensatory mechanism…
Extravascular fluid moves into the vascular system
- this helps to maintain blood pressure
- Causes Haemodilution
Takes 48 hours
- then you can estimate the blood loss by PCV
What level of PCV would you expect in a dog that has just lost 20% of its circulating blood volume?
Normal
- it has lost RBCs and fluid in the same ratio
What level of PCV would you expect in a dog that has lost 20% of its circulating blood volume 24 hours ago?
Low
- due to haemodilution
- the extravascular fluid has moved into the vascular system and diluted the blood
Describe the replacement of lost erythrocytes compensatory mechanism…
This is a bone marrow response
- Makes as many RBCs as it can
- Indicated by reticulocytes which are immature form of RBCs
What are haemorrhagic diatheses?
Haemorrhagic tendencies associated with:
- disorders of the blood clotting mechanism
- Vascular disease
What is purpura haemorrhagica? Describe it…
Horse vascular disease
- Haemorrhage and oedema
- Due to allergic reactions causing damage to arteriole epithelium
- Often due to previous strangles infection
Describe Vitamin C deficiency…
Vitamin C is a cofactor in collagen
- Results in weakness of connective tissues
- Haemorrhage from multiple vessels
- Delayed wound healing
- Tends to only be seen in species that can’t synthesise their own vitamin C e.g. guinea pigs
What is shock?
Failure of the circulatory system to adequately perfuse vital organs
- disparity between circulating blood volume and the size of the vascular space
What are the three categories of shock?
- Hypovolaemic
- Cardiogenic
- Vasculogenic (septic)
What is hypovolaemic shock…
- Decreased blood volume
- Loss of fluid by vascular compartment
e. g. sweating, diuresis
What is vasculogenic/ septic shock?
Septicaemia with gram -ve bacteria (endotoxaemia)
- Systemic vasodilation
Widespread endothelial cell damage
What is cardiogenic shock?
Decreased cardiac output
- acute severe myocardial failure
- improper diastolic filling
- improper systolic emptying
Blood sits stagnant and doesn’t circulate properly
What is irreversible shock?
When the body’s compensatory mechanisms are insufficient to sustain the patient
- inadequate tissue perfusion
- causes ischaemic injury to cells
What are the consequences of inadequate tissue perfusion?
Endothelial cells cause leaky vessels
- Vascular fluid lost
- RBCs sludge due to lack of vascular fluid
- Kidney and liver cell necrosis
- Heart arrythmias
- Brain damage/ loss of consciousness
What are the consequences of inadequate tissue perfusion?
Anaerobic metabolism
- build up of metabolites
- these metabolites exacerbate perpetuating failing C.O and worsen perfusion
= irreversible shock
What is Oedema?
Excessive accumulation of tissue fluid
How does oedema form?
When too much fluid forms
- Increased hydrostatic pressure
- Decreased colloid osmotic pressure
- Increased vascular permeability
OR
Not enough fluid is removed
- Impaired lymphatic drainage
What normally occurs in a blood vessel in terms of fluid regulation?
It is a balance between hydrostatic and osmotic pressures in blood vessels (starling’s law)
- some fluid moves out of vessels at the arterial end but is balanced by lymphatic drainage plus resorption (COP) of fluid at the venous end
Describe increased hydrostatic pressure…
Increased pressure in the capillaries
- determined by venous pressure
Local i.e. finger obstruction
OR
Systemic i.e. heart failure
Decreased COP…
Due to decreased production of albumin - decreased AA supply - severe chronic liver disease OR Increased loss of albumin - haemorrhage - inflammation - kidney - burns
Albumin in the most important osmotically active substance in the blood
- Little protein but there is plenty of it
ALWAYS SYSTEMIC
Impaired lymphatic drainage…
Causes LOCALISED oedema
- a.k.a lymphoedema
Can be external or internal obstruction
Increased vascular permeability…
Usually local
Most often results from inflammation
Increased endothelial leakiness
Loss of fluid, cells, protein into the tissues
- this results in a high protein fluid called exudate
What is transudate?
Fluid
- Low protein
- Doesn’t clot
- Few cells present
- Low specific gravity
- Clear/ straw coloured
What is exudate?
Fluid
- High total protein
- Clots
- High cellularity
- High specific gravity
- Turbid
Describe the gross appearance of oedema in an animal
- Body cavities contain free fluid
- Solid tissues are wet, heavy and enlarged
- Sub cut tissues
- distension
- swelling
- gravity dependent
- incised tissue may pour fluid
