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
