What is shock
life-threatening, generalised form of acute circulatory failure with inadequate oxygen delivery to, and consequently oxygen utilisation by, the cells
Shock defined by:
Low BP
Tissue hypoperfusion
raised serum lactate
Equations
BP = CO x Resistance to Blood flow
CO = SV X HR
What is shock essentially
Ischaemia on global scale - circulatory failure of whole body
What is hypovolaemic shock
induced by a low fluid volume of blood. A loss of around 20% of total blood volume can be enough to induce hypovolaemic shock
2 types of hypovolaemic shock
- Non-haemorrhagic: the loss of fluid volume isn’t from bleeding e.g. dehydration, burns
- Haemorrhagic: loss of blood volume through ruptured blood vessels (i.e. loss of blood volume from bleeding) - e.g. GI bleeding, trauma, peri/post-operative
What does hypovolaemia lead to
- Total volume filling of heart goes down > SV goes down > decreased CO > decreased BP
- When CO goes down > epi and norepinephrine, ADH, Ang II are released > cause vasoconstriction of BVs
What does vasoconsctriction of BVs do?
increases vascular resistance and heart rate, and in turn, this increases cardiac output. These combined effects increase blood pressure.
Indicator of hypovolaemic shock
Decreased mived venous oxygen (MVO2)
What type of shock is hypovolaemic shock
Cold - BF also provides heat to the tissues, when it’s down, the skin starts to feel cool and clammy
S + S of hypovolaemic shock
- Cold and clammy skin
- Confusion and drowsiness
- Increased sympathetic tone
- Tachycardia or bradycardia: depending on stage
Initially narrow pulse pressure and weak pulse until there is compensation, and then again when there is failure of compensation
What is cardiogenic shock
shock related to pathology of the heart, which prevents it from pumping enough blood to the tissues
Causes of cardiogenic shock
- Acute MI - most common cause
- Pericardial effusion
- Cardiac tamponade
- arrhytmias
- Pulmonary embolus
- Pneumothorax
Signs of cardiogenic shock
- HF
- Raise JVP
- Pulmonary oedema
Cardiogenic shock pathophysiology
Same as hypovolaemic
Body release vasoconstrictors to increase vascular resistance to maintain BP
MVO2 down
Reduction in CO leads to lowered BF - Cold shock
Distributive shock
- There is typically leakiness of blood vessels and an excessive amount of arteriole vasodilation.
- If arterioles dilate, vascular resistance to blood flow goes down, so blood pressure goes down, leading to less perfusion and distribution of blood to organs and tissues.
What happens in septic shock
- Endotoxins on pathogens (gram - usually) cause cascade leading to lowered perfusion - damage endothelial cells releasing vasodilators
- Activate complement > activate mast cells + IM cell prod inflam cytokines > causes release of Platelet activating factor and ROS > Damage endothelial cells and increase vascular permeability so vesssels more leaky
What do endothelial cells also express in septic shock?
- Procoagulant - TF - these combined with decrease of anti-coags leads to increase in coag + clotting - further blockages and adds to perfusion
MVO2 and type of shock septic shock is
Warm due to increase in flow to peripheral BVs
MVO2 normal
S + S of septic shock
- Warm and flushed skin
- Pyrexia and rigors
- Nausea and vomiting
- Bounding pulse
What happens in an anaphylactic shock
- An allergic reaction that causes dangerously low blood pressure.
- Massive release of histamine and other vasoactive mediators causes hemodynamic collapse.
S + S of anaphylactic shock
- Warm and flushed skin
- Itching
- Sweating
- May be breathlessness and wheeze
- Cyanosis
- Low BP
- Tachycardia
What happens in neurogenic shock
The nervous system gets damaged and can’t control the body’s blood pressure.
e.g. spinal cord injury, epidural or spinal anaesthesia
Anaemia + Cytotoxic shock
- Anaemic shockNot enough oxygen being carried in blood
- Cytotoxic shockCells are poisoned
