28. Shock Flashcards
What is clinical shock?
This is an acute circulatory failure - with inadequate or inappropriately distributed tissue perfusion resulting in cellular hypoxia
How can tissue perfusion be adequately maintained?
Via maintenance of cardiac output and blood pressure
CO - 5l/min
Systolic BP - 120mmHg
MAP - 10mmHg
What can cause a drop in blood pressure sufficient to cause shock?
BP = CO x systemic vascular resistance
SO a drop in blood pressure leading to shock can be caused by a low cardiac output or a low vascular resistance
Why might there be a low CO?
CO = HR x SV
A low heart rate may be due to inhibition of autonomic system (perception of threat)
A low stroke volume (more common) due to reduced preload or due to reduced myocardial contractility
What factors can lead to a reduced myocardial contractility?
Cardiac disease
Hypoxia/hypercapnia
pH or electrolyte disturbance
Drugs e.g. beta blockers, calcium channel blockers
Why is it important to maintain systemic vascular resistance?
Explain this
Need to maintain adequate resistance to ensure an adequate distribution of the blood
If the resistance to just one organ falls then the blood will take this route i.e. the path of less resistance
SO the blood supply to all the other organs will fall
SO must maintain the level of resistance and pressure in all the systemic arteries i.e. the systemic vascular resistance
Which hormones act to maintain systemic vascular resistance?
Angiotensin 2 - acts on receptors of the endothelium to mediate constriction of the vascular muscle
Noradrenaline released from the nerves that innervate the smooth muscle to cause their constriction
SO angiotensin works on the lumen and noradrenalin works on the outside
What happens when the body goes into shock (moderate and severe)?
When in moderate shock, compensation will occur (compensated shock) and the circulation will return back to normal
BUT if the shock is too severe, the body cannot compensate and will move into decompensated shock
This means that no matter what you do, you cannot raise the blood pressure enough to maintain tissue and organ perfusion and the person will most likely die
What are the four classifications of shock?
Give the most common examples of each
Obstructive shock - physical obstruction causing failure of cardiac output e.g. pulmonary embolism
Distributive shock - loss of vasoconstriction leading to a failure of vascular resistance maintenance e.g. sepsis
Hypovolemic shock - where you have bled and lost too much blood so there is not enough circulating blood so that even if you were to increase the heart rate, preload cannot increase e.g. haemorrhage
Cardiogenic shock - failure of the heart to pump efficiently and supply blood to the body e.g. myocardial infarction/heart failure
How does hypovolemic shock present?
SO generally due to haemorrhage - major blood loss
Body tries to compensate for this by shutting down circulation to the skin - greyish pallor to the skin, cold and clammy skin, slow capillary refill
Low blood pressure
Tachycardia
Oliguria - there will be a massive release of ADH as don’t want to lose any more water through the urine (already lost so much from the bleed)
How does cardiogenic shock present?
Most of these patients have an AMI so present with chest pain, shortness of breath, nausea, vomiting
How does distributive shock present?
Low BP Tachycardia Fever Chills Rigors Fatigue Nausea Vomiting Difficulty breathing Anxiety COnfusion
How does obstructive shock present?
Generally due to tension pneumothorax Tachycardia Anxiety Chest pain Breath sounds are absent on affected hemiothorax Trachea deviates away from affected side
How much blood loss is life threatening?
Total body water is 45 litres
Total blood volume is 4.5-5 litres
Acute loss of greater than 40% of blood volume i.e. greater than 2 litres is immediately life threatening
Describe and explain the immediate compensatory response to haemorrhage
Works within seconds to minutes
The loss of blood results in a drop in blood pressure which is detected by baroreceptors
These then compensate by increasing sympathetic output to increase heart rate and contractility
The vasomotor centre in the medulla also signals to the hypothalamus to release ADH to reduce urine flow and sodium excretion