CAM201 Lecture Notes - Lecture 7: Positive Feedback, Blood Transfusion, Pulmonary Embolism
Learning Objectives
• Define shock
• Classify and define the major types of shock
• Compare and contrast the mechanisms/pathophysiology between the major types of shock
• Explain the short, intermediate and long term compensatory mechanisms for maintaining
blood pressure in the context of shock
Pressure Determines and Enables Blood Flow
• Systemic flow is the entire output of the heart (CO)
• This is calculated using Ohm's law
• If we assume that Right atrial pressure = 0mmHg, rearrange equation:
o Mean Art Pressure = CO X TPR
• What determines CO?
o Mean Art Pressure = HR X SV X TPR
Recap
We can regulate systemic blood pressure through one of the following mechanisms
What Happens When Blood Pressure Drops?
find more resources at oneclass.com
find more resources at oneclass.com
Hypotension and Hypoperfusion
• Perfusion can be decreased locally or globally in the body
• A local perfusion defect is due to localised vessel occlusion
o E.G stroke or myocardial infarction
• A global perfusion reduction is due to a reduction in the perfusion pressure (i.e systolic
pressure) and affects all tissues/organs and can lead to shock
o Compensatory mechanisms ensure that vital organs are protected
o Existence of local blood vessels disease can make tissues less tolerant to a drop in
perfusion
• E.g If BP falls in an individual with coronary vessel disease they will experience
myocardial ischaemia at a higher BP than a healthy individual and therefore be
more susceptible to BP fluctuations
What is Shock?
• In general shock = hypotension = inadequate blood flow through the body resulting in
insufficient O2 and nutrient delivery to cells
• Its difficult to define shock because its not a single disease. In general you can think of shock as
cardiovascular collapse
• Even the CVS system itself - (the heart musculature wall of the blood vessels, vasomotor
system and other circulatory parts) begins to deteriorate, so the shock, once begun, is prone
to getting worse
o i.e shock is self-sustaining and progressive
What is the Progression of Shock?
Stage 1 = Non-progressive shock
• Also called compensated, meaning the person recovers
• Bodies compensatory mechanisms kick in to maintain SBP and perfusion
Stage 2 = Progressive shock
• Characterised by a positive-feedback cycle that feeds into sustained deterioration of
cardiovascular function
• Can be reversed if treated quickly and appropriately
find more resources at oneclass.com
find more resources at oneclass.com
• If untreated progresses to stage 3
Stage 3 = Irreversible shock
• Also called decompensated shock and involves multi-organ damage
• There is no therapy adequate to save the patients life
o Even is therapy appears to restore SBP (e.g fluid replacement) the CVS continues to
degrade progressively leading to death.
Classification of Shock
1. Hypovolaemic Shock
• Due to decreased circulating blood volume (e.g haemorrhage) and is characterised by a
reduction in diastolic filling pressures
2. Cardiogenic Shock
• Due to cardiac pump failure related to loss of myocardial contractility/function or
structural/mechanical failure of the heart (e.g infarction) characterised by increased diastolic
filling pressures and volumes
3. Obstructive Shock
• Due to obstruction of flow (e.g pulmonary embolus) in the cardiovascular unit and
characterised by either impairment of diastolic filling or excessive afterload
4. Distributive Shock
• Due to a loss of vasomotor control (e.g septic shock) resulting arterial /venous dilation and
characterised by increased cardiac output and decreased peripheral resistance
Some diseases like septic shock can have elements from each of the types of shock above
Hypovolaemic Shock
Two Main Types
1. Haemorrhagic
• Due to large blood loss from body
• Ruptured spleen
• Blunt trauma injury
Or
1. Non-haemorrhagic
• Loss of total body water (severe dehydration from diarrhoea or vomiting)
• Redistribution from vascular to extravascular space (pancreatitis)
Frank-Starling
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Systemic flow is the entire output of the heart (co: this is calculated using ohm"s law. If we assume that right atrial pressure = 0mmhg, rearrange equation: mean art pressure = co x tpr, what determines co, mean art pressure = hr x sv x tpr. We can regulate systemic blood pressure through one of the following mechanisms. In general shock = hypotension = inadequate blood flow through the body resulting in insufficient o2 and nutrient delivery to cells. Its difficult to define shock because its not a single disease. Stage 1 = non-progressive shock: also called compensated, meaning the person recovers, bodies compensatory mechanisms kick in to maintain sbp and perfusion. Stage 2 = progressive shock: characterised by a positive-feedback cycle that feeds into sustained deterioration of cardiovascular function, can be reversed if treated quickly and appropriately. Some diseases like septic shock can have elements from each of the types of shock above.
