Shock Flashcards
Define shock.
Shock is present when the BP or circulation BV is reduced to a level where tissue oxygenation is inadequate leading to cellular hypoxia + irreversible tissue injury
What 3 humoral control mechanisms exist for circulating blood?
- RAAS
- Aldosterone
- ADH
What 3 neural control mechanisms exist for circulating blood?
- Carotid + aortic baroreceptors
- Medullary cardiac + vasomotor centres
- PNS
How does the RAAS system control circulation blood?
- Decreased NaCl, BP or ECV
- Glomerulus granule cells in kidney secrete renin
- Renin converts angiotensinogen (liver) to angiotensin I
- ACE (lungs) converts angiotensin I to angiotensin II
- Angiotensin II has many effects to increase BP + BV
What effects does aldosterone have?
- Stimulates kidney to add Na+ channels
- More Na+ reabsorbed into EC space
- H2O follows osmotically
- Increased H2O back into EC space
What effects does ADH have?
- Stimulates the addition of aquaporins into the collecting tubule membrane in the kidneys
- Increased H2O back into EC space
What effects does angiotensin II have?
- Stimulates adrenal cortex to produce aldosterone
- Stimulates ADH secretion
- Stimulates thirst in brain to increase fluid intake
- Arterial smooth muscle activated to constrict to increase BP
What are baroreceptors? When do they fire?
Mechanoreceptors for pressure than fire with each heart beat so reduced BP will reduce firing and vice versa
How does the baroreceptor reflex work?
- Increased BP is detected by aortic arch + carotid sinus baroreceptors
- Increased firing of CN IX + X afferents
- Cardiac + vasomotor centers in medulla detect this
- Increased firing of CN X efferent -> decreased HR
- Decreased firing of sympathetic nerves -> negative inotropy/chronotropy
- Decreasing firing to vessels -> vasodilation
How can you work out the mean arterial blood pressure?
1/3 (SBP - DBP) + DBP
What is the average mean arterial blood pressure in the autoregulatory range?
~90
What are the 3 different types of shock?
- Vasodilatory
- Cardiogenic
- Hypovolaemic
What are the 3 causes of vasodilatory shock?
- Anaphylaxis
- Neurogenic (NOT spinal)
- Septic
How is septic shock caused?
Inflammatory mediators causes SIRS -> vasodilation + increased vascular permeability
What can cause cardiogenic shock?
Myocardial damage
Arrhythmias
Extrinsic compression (pericardial disease)
Outflow obstruction
What is Starling’s law?
The force of contraction of the cardiac muscle depends on its initial length i.e. heart pumps out blood that is returned to it or blood that it allows to return to it
What is the definition of hypotension?
SBP < 90mmHg or 20mmHg below patients normal
What are the pitfalls of the definitions of hypotension?
May not know patients normal BP
Young + previously fit
Elderly
Drugs
Why can mean arterial blood pressure be useful?
Good index of tissue perfusion
What are the mechanisms of shock?
C: inadequate Circulating volume
P: failure of pump (Pressure)
R: damage to control of Resistance
What are the 3 problems that can occur with preload i.e. capacitance?
- Hypovolaemia
- Vasodilatation
- Heart failure
Why do autoregulation mechanisms exist in the body?
To maintain blood flow and perfusion of tissues in the autoregulatory range
For each type of shock there exists 3 aspects, what are these?
- Prime problem
- Compensatory changes
- Clinical consequences
What occurs in shock due to inadequate circulating volume with reference to the 3 aspects of shock?
- Prime problem: inadequate volume + fall in CO (P)
- Compensation: increased R + tachycardia (but CO falls)
- Consequences: hypotension which clinically will cause:
- Cold/clammy peripheries
- Tachycardia
- Thready pulse
- Prolonged cap refill
- Empty veins
What occurs in shock due to pump/pressure failure with reference to the 3 aspects of shock?
- Prime problem: fall in CO (P)
- Compensation: increased R + tachycardia which causes further problem due to increased capacitance (C)
- Clinical consequence:
- Cold/clammy peripheries
- Tachycardia (maybe)
- Thready pulse
- Prolonged cap refill
- Raised JVP (maybe)
- Peripheral oedema
- Hepatomegaly
- Bi-basal crackles
What occurs in shock due to vasodilatation (R control damaged) with reference to the 3 aspects of shock?
- Prime problem: vasodilation (R) + hypotension
- Compensation: tachycardia + CO (P) rise
- Clinical consequence:
- Warm/dry peripheries
- Tachycardia
- Short cap refill
- Bounding pulse
What signs of shock present as a result of poor tissue perfusion?
Lactic acidosis
Oliguria
Altered conciousness
What signs of shock present as a result of compensation?
Fight/flight response
Tachypnoea (blow CO2 off)
Renal response (e.g. UO)
What is the pneumonic to remember how to initially assess and manage shock?
A: airway with O2 therapy
B: breathing with ventilatory assessment/assistance
C: circulation with fluid resuscitation
D: disability
E: exposure, environment + other examination
What would you do first to initially assess and manage shock?
Deal with airway compromise
Give high flow O2
What would you do second to initially assess and manage shock?
Do RR
Inspect, palpate, percuss + auscultate
What would you do third to initially assess and manage shock?
Assess peripheral perfusion (are peripheries cool/clammy or warm/dry?) Do pulse (volume/rate) IV access (blood, which tests?) Fluid challenge (if hypotension exists)
What would you do fourth to initially assess and manage shock?
Assess conscious level with AVPU in acute environment + look at pupils
What would you do fifth to initially assess and manage shock?
Investigate causes e.g. revealed bleeding, concealed bleeding, peripheral oedema etc.
What are the causes of hypovolaemia?
- Intravascular: blood (revealed or concealed)
2. Extravascular: evaporation, GI losses or polyuria
What is transcellular fluid?
That which lies in epithelial lined spaces having passed through the lining
What are the different causes for pump failure?
- Intrinsic: muscle, conductive tissue or valves
2. Extrinsic: obstruction, compression or blood supply
