Shock Flashcards
Define shock
A term used to describe the situation when there is insufficient blood supply to the tissues, to meet their demands.
4 main shock classes
Cardiogenic
Hypovolaemic
Obstructive
Distributive/normovolaemic
Define features of cardiogenic shock
The heart is unable to maintain an adequate blood pressure. This could be due to failure of the heart as a pump (myocardial damage or deterioration), severe alterations in rhythm such that contraction is not co-ordinated, or a mechanical defect (valve damage allowing blood to flow the wrong way)
Define features of hypovolaemic shock
There is a decrease in circulatory volume. This could be due to diminished blood volume, loss of whole blood, loss of plasma, loss of extracellular fluid
Define features of obstructive shock
There could be an inability of the heart to fill adequately, or obstruction to outflow from the heart (valve damage, aortic stenosis etc.)
Define features of distributive shock
Loss of sympathetic vasomotor tone (damage to the CVS centre in the medulla or damage to the sympathetic outflow)
Presence of vasodilator substances in the blood (e.g. histamine)
Shunting of vascular fluid to interstitial spaces
Arterio-venous shunting
Failure of the cells to use oxygen (e.g. poison)
Main causes of loss of vessel tone in distributive shock?
A loss of sympathetic-mediated vasomotor tone
The presence of vasodilator substances in the circulation
Consequence of prolonged and severe hypotension
3 common forms of distributive shock?
Anaphylactic
Neurogenic
Septic
Physiology of anaphylactic shock?
Massive vasodilation
Pooling of blood in the peripheral vessels
Increased capillary permeability
Treatment of anaphylactic shock
Adrenaline (constrict blood vessels and relax airways)
Antihistamines
Corticosteroids
Oxygen
S/S of septic shock
Fever Vasodilation Hyperventilation Altered cerebral blood flow Raised WCC Warm + flushed skin
4 stages of shock
INITIAL STAGE – perfusion is decreased but not enough to cause serious effects.
COMPENSATORY – perfusion is reduced, but mechanisms are able to maintain BP and tissue perfusion sufficiently to prevent cell damage.
PROGRESSIVE stage or stage of DECOMPENSATED shock – BP starts to fall, blood flow to the heart and brain becomes impaired, capillary permeability is increased, fluid leaves the capillaries, blood flow becomes sluggish and body cells and their enzyme systems are damaged.
IRREVERSIBLE stage – even if the blood volume is restored and vital signs stabilise, death ensues
What is a sympathetic mediated response to shock?
Due to baroreceptor reflex, sympathetic and medullary activity increase –>
Tachycardia
Increase cardiac contractility
Vasoconstriction
AIM: Prioritise blood perfusion to essential areas
What are the mechanisms in place to restore blood volume in shock?
Fluid absorption from interstitial spaces
Na and H2O preservation at kidneys
Compensatory mechanisms are..
SHORT TERM
In severe shock, or if the compensatory mechanisms continue for an extended period, the vascular system ______
In severe shock, or if the compensatory mechanisms continue for an extended period, the vascular system FAILS
There is relaxation of arterioles and venules with a consequent fall in peripheral resistance and hence M.A.P. Venous pooling of the blood occurs.
DUE TO local factors > sympathetic tone
S/S of shock
THIRST
COLD and CLAMMY ( sympathetic mediated)
PALE SKIN AND MM (in haemorrhage)
INCREASE HR
REDUCE URINE OUTPUT
RESTLESS –> COMA
Complications of shock?
ARDS: Due to increases pulmonary capillary permeability = stiff lung with imparied gas exchange
GI Ulceration: Due to vasoconstriction of blood vessels to the mucosa. Can lead to bleed ulcers and haemorrhage
DIC: formation of small clots in the microcirculation.
RENAL DAMAGE
MULTIPLE ORGAN FAILURE
DIC?
Disseminated Intravascular Coagulation
Treatment of shock
FLUIDS
First line: Saline
Then colloids (plasma expanders e.g. albumin and dextrans)
In cardiogenic shock, don’t overload the heart with fluid excess
VASOACTIVE DRUGS
Alpha stimulation –> Vasoconstriction
Beta1 stimulation –> Increased HR and contractility
Beta2 stimulation: Vasodilation of skeletal muscle bed and relaxation of bronchiole
Nitrates: Vessel dilation
