Shock is a state of acute
hypotension, which results in reduced perfusion and therefore oxygenation of
tissues
Stages of
shock
Compensated
shock
Nonprogressive
Sympathetic
responses of the body are able to maintain blood pressure at reasonable levels.
This
compensation prevents further deterioration of the circulatory system.
Increased
absorption of fluids from the gastrointestinal tract and interstitial fluid.
Formation
of angiotensin – vasoconstriction retention of water and salt
Release
of antidiuretic hormone, (vasopressin) - conserves water, vasoconstrictor
Progressive
shock
In
progressive shock the severity of the condition deteriorates.
Myocardium
is hypoperfused - cardiac output will drop - viscous downward spiral
Reduced
blood circulation to the gut -
gram-negative bacteria in the gut die and break up – endotoxins - toxic
to the heart muscle - further depress the activity of the myocardium.
Eventually
there will be hypoperfusion of the vasomotor centre in the medulla – loss
of sympathetic responses
When a
person is in progressive shock it is essential to treat the condition before
the shock becomes irreversible. The progressive phase is the last window of
opportunity for curative treatment.
Irreversible
shock
A person
in irreversible shock is still alive, but will go on to shortly die from shock.
Active
treatment may increase cardiac output and blood pressure for a period of time, but
the person will still go on to die from shock.
Treat
shock before this stage is reached.
The
Golden Hour`
`The
Golden Hour` - patients who have
experienced shock for more than one hour are likely to die.
In cases
of trauma, most patients could be saved if we could stop the bleeding, treat
injuries and restore blood pressure within one hour.
`Golden
Hour` of course begins at the time of trauma.
Physiological
response
Blood
pressure = Cardiac output x Peripheral resistance
Cardiac
output = Stroke volume x Heart rate
Frank – Starling law
When a
baroreceptor is stretched it is stimulated and produces nerve impulses.
Sensory
nerves travel from the baroreceptors to the medulla
Here they
influence the activity of the vasomotor and cardiac centres
Impulses
from the baroreceptors inhibit the sympathetic outflow from these centres
When blood
pressure falls there is a reduced firing rate from the baroreceptors
Reduced
inhibitory effect on the sympathetic outflow
This
results in increased sympathetic outflow from the medulla
Clinical
features of shock
Increased
sympathetic activity
Arterial
vasoconstriction
Constriction
- particularly at the level of the arterioles.
Reduced
volumes of blood perfusing peripheries – pallor
Venous
vasoconstriction
Will
increase venous blood pressure and help to maintain essential venous return.
Tachycardia
Clammy
Cold sweat
- in response to sympathetic stimulation.
Thirst
Hypovolaemia
Increase in
blood concentration – osmolarity
Thirst
centre in hypothalamus is also stimulated by a reduction in blood volume or
drop in blood pressure.
Coronary
and cerebral circulation
Sympathetic
response does not cause significant vasoconstriction in the coronary and
cerebral blood vessels.
Significant
hypoperfusion of the brain and myocardium does not occur until systolic blood
pressure drops significantly, probably to about 70 mmHg.
Respiratory
effects
Anaerobic
metabolism - accumulation of carbon
dioxide
Hypoxia
- increased respiratory rates.
Effects
on other body tissues
Skin,
gut and kidneys have a reduced blood supply
Renal
failure
Ischaemia
of the bowel - production of lactic acid
Systemic
acidosis
Liver -
patchy areas of necrosis
Clinical forms of shock
Cardiogenic
shock
Myocardial
infarction
Severe
heart valve dysfunction
Cardiomyopathy
Dysrhythmias
Hypovolaemic
shock
Haemorrhage
Burns
Dehydration
Septic
shock
Allergic shock
Neurogenic
shock
Obstructive
shock
Psychogenic
shock
Vaso-vagal
syncope
Management
principles
Usual priorities of care e.g. keep airway patent - use of suction as required.
Treatment
of underlying disorder
Oxygen
therapy
Continuous
cardiac monitoring
Adequate
intravenous access - crystalline, colloidal and blood based fluids
Urinary
catheter - hourly volumes of urine
Aim is
to maintain tissue perfusion - vasoconstricting drugs may increase blood
pressure by reducing vasoconstriction
Nurse in
physiologically desirable position.
Give drugs to
increase cardiac activity e.g. inotropes, monitor for effects/side effects.
Care of
intravenous infusions.
Care of
administration of plasma expanders and/or blood.
Care of
central venous pressure line and recordings.
Strict
recording of fluid balance.
Maintain
optimum temperature to support blood pressure.
Blood gases.
Give curative
or prophylactic antibiotics.
Full range of
psychological and family support.
Shock
and children
6
months - 500 mls of blood
1 year -
750 mls
2 years
– 1 litre
10 years
- 2 litres
No
progressive development of Hypotension
Children
are able to compensate extensively
Once
blood volumes drop to a certain level death ensues rapidly
Young
adults are much better compensators than older adults