5-Shock Flashcards
Define shock
An acute condition of inadequate blood flow throughout the body
What is the formula for mean arterial pressure, with regard to diastolic and pulse pressure?
Mean arterial BP = Diastolic pressure X 1/3 pulse pressure
Define cardiogenic shock
Sudden failure of the heart to pump sufficient volume of blood
What are the causes of cardiogenic shock?
Damage to the left ventricle after an MI
Acute worsening of heart failure
Serious arrhythmias
Describe the events of cardiogenic shock
The heart fills but doesn’t pump effectively
Drop in arterial blood pressure
Poor tissue perfusion
Poor coronary perfusion exacerbates problem, poor kidney perfusion reduces urine production (oliguria)
What happens to central venous pressure in cardiogenic shock?
CVP is normal or raised
Define mechanical shock
Failure of the heart to fill due to a physical obstruction
What causes mechanical shock?
Pulmonary embolism
Cardiac tamponade
What side of the heart does mechanical shock due to cardiac tamponade affect?
Both
What effect does mechanical shock have on central venous pressure?
CVP is high
What effect does mechanical shock have on arterial blood pressure?
Low arterial BP
Describe how a pulmonary embolism can cause mechanical shock
Part of a DVT breaks off, travels through venous system
Pumped out of heart via pulmonary artery till it reaches the lungs, causing partial blockage
Pulmonary artery pressure increases
Right ventricle cannot empty
Central venous pressure high
Decreased return of blood to the left heart
Limited filling and low pressure in left heart
Arterial BP low
SHOCK!
Define hypovolaemic shock
Heart failure due to acute loss of blood volume
What causes hypovolaemic shock?
Haemorrhage
Severe burns
Severe diarrhoea/vomiting/loss of Na
What are the signs of hypovolaemic shock?
Tachycardia
Weak pulse
Pale
Cold and clammy extremities
What happens to central venous pressure in hypovolaemic shock?
CVP decreases
What happens to arterial pressure in hypovolaemic shock?
Arterial pressure decreases
What happens to cardiac output in hypovolaemic shock and why?
Cardiac output decreases due to starlings law, heart fibres are stretched less before contraction so do not contract as hard
Describe how the body compensates for hypovolaemic shock
Increased sympathetic stimulation Tachycardia Increased force of contraction Peripheral vasoconstriction Venoconstriction Movement of fluid into capillaries as increased TPR reduces capillary hydrostatic pressure
What are the dangers of decompensation in hypovolaemic shock and why does it occur?
Occurs as compensatory vasoconstriction causes tissue damage due to hypoxia, so vasodilators released.
Decreases TPR and BP falls dramatically, failure to perfuse organs
What are they body’s long term responses to hypovolaemic shock?
Activation of RAAS and ADH
Define distributive shock
Blood volume remains constant but circulating volume increases due to decreased TPR
Define toxic/septic shock
Persisting hypotension requiring treatment to maintain blood pressure despite fluid resuscitation
Describe the series of events that lead to septic shock
Endotoxins released by circulating bacteria
Excessive inflammatory response and profound vasodilation
Dramatic fall in TPR
Fall in arterial pressure
Capillaries become leaky due to reduced blood volume
Increased coagulation and vital organ hypoperfusion
What effects does septic shock have on arterial pressure?
Arterial BP reduced
What is the body’s response to septic shock?
Increased sympathetic output- vasoconstrictor effects overridden by mediators of vasodilation
Increased heart rate
Increased stroke volume
Define anaphylactic shock
A severe allergic reaction resulting in poor perfusion to organs
Describe the events that lead to anaphylactic shock
Histamine released from mast cells
Vasodilatory effect
Fall in TPR
Dramatic drop in arterial pressure
Increased sympathetic response, but increased cardiac output can’t compensate for the vasodilation
Impaired organ perfusion, bronchoconstriction and laryngeal oedema causing difficultly breathing
What are the signs of anaphylactic shock?
Collapse
Difficulty breathing
Rapid heart rate
Warm red extremities
How do you treat anaphylactic shock and why does it work?
Treat with adrenaline
Causes vasoconstriction via actions at a1 adrenoreceptors
