L19 - Haemodynamic shock

Question 1

define haemodynamic shock

Answer 1

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

Question 2

Shock due to a fall in CO can fall into one of four subtypes. What are they and define each

Answer 2

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)

Question 3

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

Answer 3

CO = SV X HR

Question 4

What are two of the three major causes of cardiogenic shock?

Answer 4

Following MI (damage to the left ventricle)/serious arrythmias/Acute worsening heart failure

Question 5

What is the first signs of shock?

Answer 5

A dramatic drop in ARTERIAL BP

Question 6

What are some specific signs that would suggest a cardiogenic shock?

Answer 6

oliguria (reduced urine production) due to poor kidney perfusion/normal or elevated CVP (JVP)

Question 7

What is cardiac arrest?

Answer 7

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)

Question 8

explain the difference between cardiac arrest and MI (heart attack)

Answer 8

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.

Question 9

What are the three things that you need to do when someone goes into cardiac arrest?

Answer 9

Chest compressions and ventilation/defibrillation/adrenaline

Question 10

Name two common causes of mechanical shock

Answer 10

cardiac tamponade (can be from trauma/pericarditits etc.)/pulmonary embolism

Question 11

what are some signs that indicate that a massive PE is causing the mechanical shock?

Answer 11

pulmonary artery pressure is high/LA pressure is low/ dyspnoea (heavy and laboured breathing) and chest pain/CVP is high

Question 12

Above what % of reduction in our total blood volume are we likely to see signs of shock?

Answer 12

20-30% = some signs

above 30% = serious shock response

Question 13

Briefly explain the compensatory mechanism to haemorrhage

Answer 13

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

Question 14

Explain the phenomenon ‘internal transfusion’ which we see in patients undergoing hypovolaemic shock

Answer 14

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

Question 15

What are some specific signs of hypovolaemic shock?

Answer 15

Tachycardia/weak pulse/pale skin/cold extremities (due to peripheral vasoconstriction)/LOW CVP

Question 16

Other than haemorrhage what else can cause hypovolaemic shock?

Answer 16

Severe burns/severe diarrhoea or vomiting cuasing excess loss of Na+ and thus causing severe dehydration

Question 17

Compensatory mechanisms work to a point in hypovolaemic shock but what is the complication that can occur once this mechanism reaches its threshold?

Answer 17

Danger of decompensation

Question 18

What is decompensation?

Answer 18

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

Question 19

What are the long term responses to hypovolaemic shock/hypovolaemia (short term is activation of SNS)?

Answer 19

activation of renin-angiotensin system/ADH release (say anti-diuretic hormone in exam)

Question 20

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

Answer 20

Toxic (septic) shock/ anaphylactic shock

Question 21

Name two major causes of cardiac arrest

Answer 21

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)

Question 22

What is the most common cause of cardiac arrest?

Answer 22

VF (can be following MI/electrolyte imbalance/arrythmias)

Question 23

Explain septic shock

Answer 23

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

Question 24

Describe a classical presentation of septic shock

Answer 24

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

Question 25

Explain anaphylactic shock

Answer 25

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

Question 26

Describe a patient in classical anaphylactic shock

Answer 26

Patient has collapsed with difficulty breathing/tachycardic/red,warm extremities

Question 27

What is the immediate treatment for someone in anaphylactic shock?

Answer 27

adrenaline - stimulates vasoconstriction at alpha 1 adrenoceptors (Gq)

Question 28

What is the treatment for a cardiac tamponade

Answer 28

pericardiocentesis - needle up through the xiphoid process of sthe sternum then 45 degrees towards the head

Question 29

What is needed urgently for someone in hypovolaemic shock?

Answer 29

A blood transfusion

Question 30

What is a cardiac tamponade (form of mechanical shock) and describe the classical presentation

Answer 30

blood or fluid build up in the pericardial space restricts filling of the heart. High CVP (and thus JVP), low arterial BP

Question 31

Describe the presentation of a pulmonary embolism

Answer 31

High CVP (JVP), shock, chest pain