Shock Flashcards
Define shock
When the blood pressure or circulating blood volume is reduced to a level where tissue oxygenation is inadequate leading to cellular hyypoxia and irreversible tissue injury
What are the categories of shock?
Vasodilation
Cardiogenic (pump failure)
Hypovolaemic
What humoral factors are involved in control of BP?
RAAS: Renin, Angiotensin II, Aldosterone
ADH
What neural factors control BP?
Baroreceptor reflex (receptors found in aortic arch and carotid sinus)
Medullary cardiac and vasomotor centres (involved in baroreceptor and chemoreceptor reflexes)
Peripheral nervous system
What is hypovolaemic shock and how might a patient present?
Hypotension due to inadequate volume causing a fall in cardiac output
Patient may present with cold/ clammy peripheries, tachycardia (compensatory), prolonged capillary refill time (vasoconstriction increases resistance as a compensatory mechanism) and empty veins
What is classified as vasodilatory shock?
Anaphylaxis
Neurogenic
Septic (caused by inflammatory mediators/ SIRS)
What is classified as cardiogenic shock?
Myocardial damage
Arrhythmias
Extrinsic compression (pericardial disease)
Outflow obstruction
How does Angiotensin II act to increase BP?
- Hypothalamus - increases thirst to increase fluid intake
- Adrenal cortex - secretes Aldosterone
- Arteries - vasoconstriction
How does Aldosterone act to increase BP?
Increases sodium and water reabsorption in the kidneys by binding to mineralocorticoid receptors in principal cells in the late DCT and cortical collecting tubule.
Mineralocorticoid receptors bind to the cell nucleus and increase production of ENaC and Na+/K+ ATPase.
How does Renin act to increase BP?
Conversion of Angiotensinogen (from the liver) into Angiotensin I (which is then converted into its active form, Angiotensin II, by ACE)
How does ADH act to increase BP?
Insertion of aquaporin channels in the late DCT and cortical collecting tubule to increase water permeability (and therefore increase reabsorption)
How does the baroreceptor reflex respond to changes in BP?
Reduced BP = reduced firing (of parasympathetic afferents)
Increased BP = increased firing
Increased BP = CN IX and X fibres send signals to medullary cardiac and vasomotor centres which consequently reduced firing of sympathetic efferents to the heart muscle (negative inotropy and chronotropy) and vessels (vasodilation) and increases firing of parasympathetic (vagal) efferents to decrease HR
What is classified as hypotension?
Either a systolic of <90mmHg or of 20mmHg below the patient’s normal [may not know patients normal]
What is cardiogenic shock and how might a patient present?
Problem caused by a fall in cardiac output (due to pump failure)
Patient may present with cold/ clammy peripheries, tachycardia (compensatory), prolonged capillary refill time (compensatory - vasoconstriction increases resistance), raised JVP, peripheral oedema, hepatomegaly, bi-basal crackles
What is vasodilatory shock and how might a patient present?
Vasodilation causing hypotension
Compensate with tachycardia and cardiac output rises
Patient may present with warm/ dry peripheries, tachycardia, short capillary refill time, bounding pulse
