Acute circulatory failure / Shock Flashcards
What is shock?
Shock is an acute circulatory failure with inadequate or inappropriately distributed tissue perfusion which is insufficient to meet cellular metabolic needs.
Medical shock is a life-threatening emergency
What are the different types of shock?
- Hypovolaemic
- Cardiogenic
- Obstructive
- Distributive
- septic
- anaphylactic
- neurogenic
What is hypovolaemic shock?
- most common type of shock
- based on insufficient circulating volume
- primary cause = loss of fluid from circulation
- most often ‘haemorrhagic shock’
- causes: internal bleeding, traumatic bleeding, high output fistulae, dehydration or severe burns
What are signs of hypovolaemic shock?
- anxiety
- altered mental state (due to reduced cerebral perfusion + subsequent hypoxia)
- compensatory tachycardia
- compensatory tachypnoea
- hypotension
- rapid, weak, thready pulse
- fatigue
- thirst
- slow cap refill due to compensatory peripheral vasoconstriction
- cold, clammy skin
What is cardiogenic shock?
- caused by failure of heart to pump effectively
- can be due to damage to heart muscle
- most often from a large myocardial infarction
- other causes of cardiogenic shock include arrhythmias, cardiomyopathy, congestive cardiac failure (CCF) or cardiac valve problems
What are the signs of cardiogenic shock?
similar to hypovolaemic shock but with:
- raised JVP
- pulsus alternans
- gallop rhythm
- pulmonary oedema
- basal crackles
What is obstructive shock?
Caused by obstruction in blood flow which impedes circulation. In each of the following, venous return to the heart is impaired or prevented:
- cardiac tamponade - accumulation of fluid in pericardial space which impairs venous return (it is a pericardial effusion which causes haemodynamic compromise)
- pulmonary embolism - thromboembolism of the vessel of the lungs impairs venous return
- tension pneumothorax - inc intrathoracic pressure impairs venous return
What are the signs of obstructive shock?
similar to hypovolaemic shock but with:
- raised JVP
- pulses paradoxus in case of tamponade
Distributive shock is similar to hypovolaemic shock in that there is insufficient intravascular volume of blood. However, this type of shock is due to peripheral dilatation of blood vessels which acts to diminish systemic vascular resistance, compared to other types of shock which impair cardiac output.
What is septic shock and its clinical signs?
- due to systemic infection resulting in vasodilatation + hence hypotension
- signs are similar to hypovolaemic shock except in first stages where there is:
- pyrexia w/ rigors
- systemic vasodilatation
- warm + sweaty skin (due to vasodilatation)
- increased levels of neutrophils
What is anaphylactic shock?
- due to severe anaphylactic rxn to allergen/antigen/drug/foreign protein
- causing release of histamine
- this causes widespread dilatation
- leading to hypotension + inc cap permeability
What are the signs of anaphylactic shock?
- dyspnoea due to bronchospasm
- systemic vasodilatation
- warm skin
- hypotension
- urticaria
- oedema of face + larynx
- angio-oedema
What is neurogenic shock?
- rare form of shock
- occurs due to trauma to spinal cord or post-spinal surgery
- results in sudden loss of autonomic + motor reflexes below injury level
- hence, without stimulation by sympathetic nervous system, vessels relax -> resulting in vasodilatation -> hypotension
What are signs of neurogenic shock?
- as with hypovolaemic shock
- but in high spinal injuries may also be accompanied by profound bradycardia due to loss of cardiac accelerating nerve fibres from sympathetic nervous system at t1-t4
How do history and examination help indicate the cause of shock?
The history and clinical examination will often indicate the cause of shock.
For instance, following trauma a hypotensive patient may be shocked because of massive blood loss (hypovolaemic), tension pneumothorax or cardiac tamponade (obstructive), spinal cord injury (neurogenic) or a drug reaction (anaphylactic).
There are slight differences in clinical signs and their timings depending on the cause of shock.
How might central venous pressure measurement help indicate the cause of shock?
- CVP is related to right ventricle end-diastolic pressure
- RVEDP depends on circulating blood vol, venous tone, intrathoracic pressure + right ventricular function
- CVP measured by inserting catheter into SVC + connecting to manometer
- if CVP low -> hypovolaemia or distributive shock
- if CVP high -> obstructive or cardiogenic shock
- isolated readings are of limited value
- a trend of CVP readings should be used in conjunction w/ other parameters
