L19 - Haemodynamic shock Flashcards
define haemodynamic shock
An acute condition of inadequate blood flow throughout the body caused by a fall in blood pressure
NOTE - this fall in BP can be due to a fall in CO or a fall in TPR beyond the capacity of the heart to cope
MABP = CO X TPR
Shock due to a fall in CO can fall into one of four subtypes. What are they and define each
hypovolaemic shock - reduced blood volume due to poor venous return (due to haemorrhage)
Cardiogenic shock - This is when the ventricles cannot empty properly due to the pump function of the heart failing
Mechanical shock - The ventricles cannot adequately fill due to a physical obstruction
Distributive shock - Due to a profound vasodilation (decrease in TPR)
Remember to use the following calculations to justify your points in questions. Complete the following
a) MaBP = CO X TPR
b) CO = ?
c) MaBP = SV X HR X TPR
d) MaBP = diastolic pressure + 1/3 pulse pressure
CO = SV X HR
What are two of the three major causes of cardiogenic shock?
Following MI (damage to the left ventricle)/serious arrythmias/Acute worsening heart failure
What is the first signs of shock?
A dramatic drop in ARTERIAL BP
What are some specific signs that would suggest a cardiogenic shock?
oliguria (reduced urine production) due to poor kidney perfusion/normal or elevated CVP (JVP)
What is cardiac arrest?
An unresponsiveness associated with a lack of pulse. The heart has stopped OR ceased to pump effectively (this is basically the most severe form of shock)
explain the difference between cardiac arrest and MI (heart attack)
A heart attack is when one of the coronary arteries becomes blocked. The heart muscle is robbed of its vital blood supply and, if left untreated, will begin to die because it is not getting enough oxygen. A cardiac arrest is when a person’s heart stops pumping blood around their body and they stop breathing normally.
What are the three things that you need to do when someone goes into cardiac arrest?
Chest compressions and ventilation/defibrillation/adrenaline
Name two common causes of mechanical shock
cardiac tamponade (can be from trauma/pericarditits etc.)/pulmonary embolism
what are some signs that indicate that a massive PE is causing the mechanical shock?
pulmonary artery pressure is high/LA pressure is low/ dyspnoea (heavy and laboured breathing) and chest pain/CVP is high
Above what % of reduction in our total blood volume are we likely to see signs of shock?
20-30% = some signs
above 30% = serious shock response
Briefly explain the compensatory mechanism to haemorrhage
Haemorrhage->venous pressure drops (detected by baroceptors) -> SV drops -> CO drops -> Sympathetic stimulation increases HR and force of contraction -> venoconstriction and other peripheral vasoconstriction occurs to balance out the drop in CO to maintain MaBP
think about your equations
Explain the phenomenon ‘internal transfusion’ which we see in patients undergoing hypovolaemic shock
Loss of blood volume means the starling forces change -> fluid moves into the capilaries from the interstitial space due to the reduced plasma hydrostatic pressure in the capillaries
What are some specific signs of hypovolaemic shock?
Tachycardia/weak pulse/pale skin/cold extremities (due to peripheral vasoconstriction)/LOW CVP
Other than haemorrhage what else can cause hypovolaemic shock?
Severe burns/severe diarrhoea or vomiting cuasing excess loss of Na+ and thus causing severe dehydration
Compensatory mechanisms work to a point in hypovolaemic shock but what is the complication that can occur once this mechanism reaches its threshold?
Danger of decompensation
What is decompensation?
Peripheral vasoconstriction has happened too much (originally it was trying to rectify MaBP). It has caused damage of tissues due to hypoxia. Eventually the tissues release so many vasodilators that these surpasses the vasconstriction mechanism of the SNS and causes a widespread vasodilation -> TPR falls -> MaBP falls -> VITAL organs no longer perfused -> multi-system organ failure
What are the long term responses to hypovolaemic shock/hypovolaemia (short term is activation of SNS)?
activation of renin-angiotensin system/ADH release (say anti-diuretic hormone in exam)
The other category of shock is shock due to a fall in peripheral resistance (due to excessive vasodilation). This category is called ‘distributive shock’, name the 2 major types
Toxic (septic) shock/ anaphylactic shock
Name two major causes of cardiac arrest
Asystole (loss of electrical and mechanical activity/ Pulseless electrical activity - electrical activity but no pulse/ Ventricular fibrillation (unco-ordinated electrical actvity so we’re not getting a pulse)
What is the most common cause of cardiac arrest?
VF (can be following MI/electrolyte imbalance/arrythmias)
Explain septic shock
Wide spread inlfammatory response causes profound vasodilation (overrides sympathetic response) -> dramatic fall in TPR -> Impaired perfusion of vital organs -> hypercoagulability of blood also can also cause ischaemia of the extremities in later stages-> capillaries also become leaky after a time which can exacerbate the situation by reducing CO
Describe a classical presentation of septic shock
Patient is tachycardic (SYM response) with warm, red extremities initially due to vasodilation (drops MaBP) BUT then in later stages we see localise hypoperfusions cuasing cold extremities becasue of increasing hypercoagulability of the blood in sepsis response
Explain anaphylactic shock
Severe allergic reaction (anaphylaxis) -> mast cells release histamine -> widespread vasodilation (drops MaBP) overcomes SYM response -> impaired perfusion of vital organs -> mediators also cause bronchoconstriction inappropriatey causing a difficulty breathing
Describe a patient in classical anaphylactic shock
Patient has collapsed with difficulty breathing/tachycardic/red,warm extremities
What is the immediate treatment for someone in anaphylactic shock?
adrenaline - stimulates vasoconstriction at alpha 1 adrenoceptors (Gq)
What is the treatment for a cardiac tamponade
pericardiocentesis - needle up through the xiphoid process of sthe sternum then 45 degrees towards the head
What is needed urgently for someone in hypovolaemic shock?
A blood transfusion
What is a cardiac tamponade (form of mechanical shock) and describe the classical presentation
blood or fluid build up in the pericardial space restricts filling of the heart. High CVP (and thus JVP), low arterial BP
Describe the presentation of a pulmonary embolism
High CVP (JVP), shock, chest pain
