Physiology 8 Flashcards
Shock?
Abnormality of circulatory system resulting in inadequate tissue perfusion and oxygenation
What does shock lead to? How? (4)
* Cellular failure
How…
* Inadequate tissue perfusion
* Inadequate tissue oxygenation
* Anaerobic metabolism
* Accumulation of metabolic waste products
Adequate tissue perfusion depends on? (2)
Adequate blood pressure and adequate cardiac output
What 3 factors affect SV?
* Preload (venous return)
* Myocardial contractility
* Afterload
What causes hypovolaemic shock? (6)
* Loss of blood volume
* Decreased Venous Return
* Decreased End Diastolic Volume
* Decreased Stroke Volume
* Decreased Cardiac Output and Decreased blood pressure
* Inadequate Tissue Perfusion
What is preload (and thus SV) dependent on?
Myocardial fibre lengths which are dependent on EDV
Cardiogenic shock? Causes?
* Sustained hypotension caused by decreased cardiac contractility (problem with pump)
* Massive MI or arrhythmia
Explain the process of development of cardiogenic shock (4)
* Decreased Cardiac Contractility
* Decreased Stroke Volume
* Decreased Cardiac Output & Decreased blood pressure
* Inadequate Tissue Perfusion
What does sympathetic stimulation do to Frank-Starling curve? Parasympathetic? Cardiogenic shock?
* Shifts to left - higher SV at given EDV * Shifts to right - lower SV at given EDV * In cardiogenic shock extreme shift to right since pump no longer functioning
Explain process of development of obstructive shock e.g. from tension pneumothorax? (6)
* Increased intrathoracic pressure
* Decreased Venous Return
* Decreased End Diastolic Volume
* Decreased Stroke Volume
* Decreased Cardiac Output and Decreased blood pressure
* Inadequate Tissue Perfusion
What are different types of shock? (4) What causes these?
* Hypovolaemic e.g. hemorrhagic, non-hemorrhagic
* Cardiogenic: e.g. acute myocardial infarction
* Obstructive: e.g. cardiac temponade, tension pneumothorax, pulmonary embolism, severe aortic stenosis
* Distributive: neurogenic e.g. spinal cord injury, or Vasoactive e.g. septic shock, anaphylactic shock
Explain the process of development of neurogenic shock (5) What kind of shock is neurogenic shock?
* Loss of Sympathetic Tone
* Massive Venous & Arterial Vasodilatation
* Decreased Venous Return & Decreased SVR (TPR)
* Decreased Cardiac Output & Decreased blood pressure
* Inadequate Tissue Perfusion
* Type - distributive shock
What is sympathetic tone?
Continuous low-level sympathetic stimulation resulting in continuous release of noradrenaline
Explain the process of development of vasoactive shock (5) What is vasoactive shock also known as?
* Release of Vasoactive Mediators
* Massive Venous & Arterial Vasodilatation - also Increased Capillary Permeability
* Decreased Venous Return & decreased SVR (TPR)
* Decreased Cardiac Output & decreased blood pressure
* Inadequate Tissue Perfusion Septic shock, anaphylactic shock
How is intravascular blood volume lost in vasoactive shock?
Blood leaks from capillaries
What is the treatment for shock? (7)
* ABCDE approach
* High flow oxygen
* Volume replacement (if patient losing volume - NOT in cardiogenic shock)
* Inotropes for cardiogenic shock
* Immediate chest drain for tension pneumothorax
* Adrenaline for anaphylactic shock
* Vassopressors for septic shock
Why are inotropes used to treat cardiogenic shock?
Increase cardiac contractility
What are causes of hypovolaemic shock? (2)
Haemorrhagic and non-haemorrrhagic
* Haemorrhage e.g. trauma, surgery, GI haemorrhage
* Vomiting, diarrhoea, excessive sweating
How does haemorrhage lead to hypovolaemic shock?
* Decrease in blood volume
* Causes decreased CO
* Circulatory shock due to decreased MABP
How does non-hemorrhagic hypovolaemia lead to hypovolaemic shock?
* Decrease in ECFV including plasma volume
* Decreased blood volume
* Causes decreased CO
* Circulatory shock due to decreased MABP
In hemorrhagic shock, how long can body maintain blood pressure?
Compensatory mechanisms can maintain blood pressure until >30% of blood volume is lost
Learn table illustrating different classifications of hemorrhagic shock
…
In hemorrhagic shock, what causes tachycardia? Small volume pulse? Cool peripheries?
* Increased HR via baroreceptor reflex
* Decreased SV causes small volume pulse
* Cool peripheries caused by decreased CO and increased systemic vascular resistance via baroreceptor reflex
Explain the process of hemorrhagic shock (5)
* Increased HR (tachycardia) via baroreceptor reflex
* Decreased SV (small volume pulse)
* Cardiac output decreased
* Increased systemic vascular resistance via baroreceptor reflex
* Decreased mean arterial blood pressure if >30% loss
Does cerebral blood flow change a lot in response to changes in MABP? Why? (2)
No
* As blood pressure increases, cerebral vessels constrict to restrict flow
* As blood pressure decreases, cerebral vessels dilate to increase flow
When will cerebral flow vary with MABP?
* If MABP <60, inadequate perfusion of brain
* If MABP >120, will increase cerebral blood flow
