Shock Flashcards
What is shock?
“Shock is an inadequate delivery of oxygen and nutritive substances to the tissues within the body”
-impaired blood flow
Causes of shock:
Haemorrhage Myocardial infarction Asphyxiation Anaphylaxis (hypersensitivity reaction) Medications that reduce heart function/BP Spinal injuries Infection Burns
What causes shock?
- Reduction in circulatory volume
- Failure of an effective pump (heart)
- Lack of blood vessel tone and an enlarged vascular component & lack of blood flow
What are the types of shock?
Hypovolaemic
Cardiogenic
Vascular
Neurogenic
What is Hypovolaemic shock?
This is when a loss of IV volume occurs.
Can be caused by haemorrhage, dehydration, plasma loss from being burnt and sever D&V
What is cardiogenic shock?
This is where the heart fails to pump
Caused by myocardial infarction, pulmonary embolus and medications that cause heart rate/BP disturbances
What is vascular shock?
Where there is a loss of vascular tone
Caused by septic shock, toxic shock and anaphylaxis
What is neurogenic shock?
A loss of vascular tone due to lack of neurological control
Caused by a severe emotional experience, head injury or a spinal injury
Tissue fluid during shock
All types of shock eventually result in impaired tissue perfusion. Good tissue perfusion is due to arterial blood pressure being maintained.
Tissue fluid maintains homeostasis by bringing O2 and nutrients to the cell and removing CO2 and other waste products of metabolism.
Tissue perfusion during shock
In hypovolaemic shock the reduced blood flow reduces perfusion of the tissues (cuts down movement of tissue fluid)
Perfusion causes fall in amount of nutrients reaching the tissue cells and the accumulation of toxic waste may cause death of cells.
What are the three variables that affect blood pressure?
Cardiac output
Peripheral resistance
Blood volume
What is cardiac output?
“Amount of blood that the heart pumps out per minute.”
STROKE VOLUME x HEART RATE
(Stroke volume = amount of blood that the left ventricle pumps out during each contraction.)
What is peripheral resistance?
“The force created by the friction between the blood and walls of blood vessels.”
Greater the PR is the greater the Blood Pressure is.
Vasoconstriction increases PR
Vasodilation decreases PR
Neurones in the Vasomotor centre in medulla regulates the diameter of arterioles.
What are signs and symptoms of shock?
Altered consciousness Increased respiratory rate/hyperventilation Thirst Decreased urine output Increased heart rate (Tachycardia) Cold and clammy Decreased BP Weak or rapid pulse
How does the autonomic response respond to shock?
- Baroreceptors detect a fall in BP (RECEPTOR)
- Vasomotor centre in medulla &a cardiac centre in medulla (CONTROLLER)
- Vasoconstriction leads to increased PR / increased heart rate (EFFECTOR)
- BP increases
What are the components of the responses to shock?
Renin-angiotensin-aldosterone system
Anti-diuretic hormone (ADH)
(Also includes adrenaline and nor-adrenaline which enhance sympathetic effects)
What is the Renin-Angiotensin-Aldosterone System?
It is the main way in which the body responds to changes in blood volume and pressure. When BP falls renin-secreting cells in the kidney are stimulated to secrete renin.
What does renin do?
Converts angiotensinogen into angiotensin 1
Angiotensin 1 is then converted into angiotensin 2 (causes vasoconstriction of efferent arteriolar which causes an ⬆️ in pressure and increases filtration rate in kidney tubules)
Angiotensin 2 also stimulates thirst
What are the roles of ADH and Aldosterone (two hormones) ?
Both play a key role in fluid balance and have more long term effects in BP control.
Aldosterone - enables target cells in kidney tubules to become more permeable to sodium ions which are then reabsorbed back into blood = ⬆️ water absorption (water follows sodium ions via osmosis) = increased blood volume & ⬆️ BP.
Role of ADH in conserving fluid to restore blood vol and BP
- Fall in blood pressure detected by baroreceptors
- Hypothalamus receives nerve impulses
- ADH secretion increases in hypothalamus
- ADH released from posterior pituitary gland which caused an increase in water reabsorption
- Blood volume and BP increases
What are the consequences of shock for cell function?
Lack of O2 avail to cells means CO2 builds up and energy production falls. Anaerobic cell respiration causes a build up in lactic acid and eventually no ATP can be produced.
Lack of energy = cell dysfunction and cell membrane permeability alters.
Lysosomes release enzymes which destroy cell integrity and causes the cell to die (if cell membrane is destroyed cellular changes are irreversible)
What happens if homeostasis isn’t restored during shock?
Shock will progress and can cause multiple organ system failure. Heart rate slows, BP falls and the heart no longer pumps blood = death.
What are the stages of shock?
Depends on the amount of blood volume lost.
Stage one 0-15%
Stage four 40%+
Depends on individual circumstances and patient.
What are the consequences of uncompensated shock?
HYPOXIA
- lack of O2
- Cellular metabolism switches to anaerobic pathways (no O2)
- lactic acid builds up
- acidosis occurs which damages capillaries which become more permeable and leak more fluid
- blood pressure and tissue perfusion drops more
- the accumulation of waste products causes vasodilation which causes blood pressure to drop even further
- organs become ischaemic = organ failure
What causes reduced output of urine during shock?
Increased activity of renin angiotensin aldosterone system and increased secretion of antidiuretic hormone (ADH)
What happens when systems cannot compensate for shock?
Homeostasis is not restored and shock will progress causing multiple organ system failure. Heart rate slows, BP falls and heart no longer pumps blood.
