Shock

Question 1

What is haemodynamic shock?

Answer 1

Acute circulatory failure that leads to inadequate oxygen intake that results in cellular dysfunction, which can be irreversible and lead to end-organ dysfunction if there is a delay in treatment.

Question 2

What determines haemodynamic regulation?

Answer 2

Vascular resistance
Blood pressure
Circulating volume

Question 3

Which systems are involved in haemodynamic regulation?

Answer 3

Cardiovascular system
Renal system through RAAS activation
Neural control, through communication with baroreceptors
-> These collectively form the neurohormonal communication to maintain adequate blood supply to individual organs.

Question 4

Where are the aortic baroreceptors located?

Answer 4

In the carotid sinus and the aortic arch, to rapidly adjust heart rate. They become activated due to high BP, they send signals via the vagus nerve and synapse in the nucleus tractus solitaris in the medulla to transmit to the nucleus ambiguus, which provides parasympathetic outflow to decrease cardiac activity and inhibits sympathetic outflow.

Question 5

What is the role of the baroreceptors reflex?

Answer 5

Regulate acute short-term fluctuations of cardiac pressure due to posture, exercise or emotions.

Question 6

Where are the cardiopulmonary receptors located?

Answer 6

Low pressure areas of the heart in the right atria, right ventricle, pulmonary artery and pulmonary veins.

Question 7

What is the role of the cardiopulmonary receptors?

Answer 7

They respond to changes in pressure, due to:
A receptors which detect pressure during atrial contraction
B receptors which detect pressure during atrial diastole when filling occurs

Question 8

How do cardiopulmonary receptors act?

Answer 8

They are low pressure baroreceptors which reduce firing of the vagus nerve when there is a greater volume of blood to the cardiopulmonary centre in the medulla via the nucleus tractus solitaris to the nucleus tragus. This will stimulate greater sympathetic activity through catecholeamines because high volume of blood will stimulate greater cardiac output to increase circulation, and this increases blood flow to the kidneys for more excretion of water and Na+.

Vagus nerve also acts on the hypothalamus to reduce the secretion of ADH, for decreased water absorption.

Question 9

What is the role of atrial natriuretic peptide?

Answer 9

Produced when atria are under stretch to cause vasodilation of the renal arterioles to decrease the water and Na+ reabsorption.

Question 10

What is natriuresis?

Answer 10

Increased excretion of sodium in the urine.

Question 11

What increases natriuresis?

Answer 11

Atrial natriuretic peptide (ANP)
Ventricular natriuretic peptide (VNP)
Calcitonin

Question 12

What decrease natriuresis?

Answer 12

Aldosterone, which promotes after and sodium reabsorption.

Question 13

What are the causes of shock?

Answer 13

Shock is broadly categorised into three categories:
Hypovolemia
Cardiogenic pump failure
Loss of systemic resistance

Question 14

What is hypovolemic shock?

Answer 14

Loss of intravascular volume circulating in the body which may be due to:
->Haemorrhage via trauma
->Non-haemorrhagic due to excessive dehydration, diarrhoea/vomiting, burns, hyperglycaemia

Baroreceptors respond to this fall in pressure by increasing sympathetic activity from the cardiovascular centre for increasing cardiac output, however hypotension cannot be corrected because of low fluid.

Question 15

What is the presentation of hypovolemic shock?

Answer 15

Cool and clammy skin with prolonged capillary refill time and a weak pulse. Tachycardia, tachypnoea, oliguria and empty veins are important features, with neurological disturbances like anxiety and confusion.

Question 16

What is pump failure?

Answer 16

Cardiogenic shock which occurs typically due to obstruction to the heart from pericardial tamponade or myocardial infarction which prevents the circulation of blood around the body.

It is divided into systolic and diastolic dysfunction.

Question 17

What is the physiological response of the body to Cardiogenic shock?

Answer 17

Baroreceptors respond to low pressure by increasing sympathetic activity from the centre to increase heart rate and lead to tachycardia. Blood pressure will rise as more sodium and water is retained by the kidneys, however the dysfunction in the heart means it cannot pump the blood it is receiving, therefore it will dilate.

Question 17

How does systolic dysfunction of the heart present?

Answer 17

Disrupts ejection of blood from the heart, causing decreased stroke volume and cardiac output.

Question 18

What is the presentation of cardiogenic shock?

Answer 18

Raised JVP, sweating and pallor.
Cold clammy peripheries with increased capillary refill time and tachycardia with oliguria.

Question 18

How does diastolic dysfunction of the heart present?

Answer 18

Disrupts filling of the heart, causing pulmonary oedema, hypoxia and decreased oxygen supply.

Question 19

What is distributive shock

Answer 19

Lack of resistance to blood flow leads to vasodilation which causes a drop in blood pressure, which can occur due to:
Sepsis
Neurogenic damage that causes systemic vasodilation
Pancreatitis
Transfusion reaction
Liver failure

Question 20

How does septic shock occur?

Answer 20

Endotoxins from gram negative bacteria present in the bloodstream stimulate production of inflammatory mediators that increase vascular permeability cause systemic vasodilation. There is increased action of the complement pathway for clotting in the microvasculature.

It leads to systemic inflammatory response and despite fluid resuscitation, there is persistent hypotension.

Question 21

What is systemic inflammatory response?

Answer 21

Severe response of the body that means 2 out of 4 criteria are met where:
Temperature is above 38 degrees or below 36 degrees
Heart rate is over 90bpm
Respiratory rate is greater than 20
WBC count is higher or lower than the normal range

Question 22

What are the causes of septic inflammatory response?

Answer 22

Sepsis
Burns
Pancreatitis
Trauma

Question 23

How does early septic shock present?

Answer 23

Bounding pulse with warm, dry peripheries, with fast capillary refill time and tachycardia.

Question 24

How does late septic shock present?

Answer 24

Reduced cardiac output, cold and clammy peripheries

Question 25

What is the most common sites of septic shock?

Answer 25

Chest
Abdomen
Genitourinary tract

Question 26

How does anaphylactic shock present?

Answer 26

Type 1 hypersensitivity reaction mediated by IgE due to ingestion of allergen which results in increased capillary permeability which causes distributive shock.

Question 27

What are the characteristic signs of anaphylactic shock?

Answer 27

Hoarseness of voice and stridor
Tachycardia and tachypnoea, hypotension
Skin flushing and abdominal pain.

Question 28

What is neurogenic shock?

Answer 28

Distributive shock where there is damage to the spinal cord below the level of T6 that causes loss of sympathetic tone to the thoracic tone, resulting in decreased heart rate and cardiac output.

Question 29

What are the clinical features of neurogenic shock?

Answer 29

Hypotension, Bradycardia, Temperature dysregulaton and Dry skin.
There may be flaccid paralysis and anaesthesia and loss of bladder and bowel control.

Question 30

What is obstructive shock?

Answer 30

Systemic hypoperfusion due high after load or anatomical restriction in the flow of blood in heart due to:

Pulmonary embolism
Collapse pneumothorax pressing against the heart
Constrictive pericarditis or cardiac tamponade
Aortic stenosis

Question 31

How does obstructive shock present?

Answer 31

Tachycardia
Hypotension
Chest pain due to ischaemia
Tachypnea to compensate

Question 32

What are the stage of shock?

Answer 32

Initial stage
Compensatory stage
Progressive stage
Refractory stage

Question 33

What is the initial stage of shock?

Answer 33

The drop in tissue oxygen saturation results in anaerobic metabolism, and there is a buildup in lactic acid buildup due to liver dysfunction.

Question 34

What is the compensatory stage of shock?

Answer 34

Maintenance of blood pressure via vasoconstriction: Arterial baroreceptors increase firing of the vagus nerve on the nucleus traguus to increase sympathetic firing from the cardiovascular centre, and the vagus nerve will stimulate the posterior pituitary gland to increase ADH secretion. There will be an increase in cardiac output and RAAS activation, resulting in increase in blood volume and tachycardia, with blood being redirected to the vital organs.

Decreased perfusion to the lungs means a drop in blood oxygen saturation for gas exchange, so hyperventilation occurs.

Question 35

What is the progressive stage of shock?

Answer 35

When the compensatory stage has failed, it cannot be maintenances, therefore there is a reduction in cardiac output and increased capillary permeability, resulting in loss of proteins and fluids into the interstitial space, resulting in oedema, which further decreases loss of blood volume. Heart cells of the electrical conduction system begin to die and there is alveolar collapse which causes pulmonary oedema. Liver dysfunction can lead to uncontrolled bleeding in the body.

Question 36

What is the refractory stage of shock?

Answer 36

Final stage of shock where there is poor tissue perfusion that leads to cerebral ischaemia and widespread organ failure, where recovery is unlikely.

Question 37

What are clinical signs of shock?

Answer 37

Renal window with decreased urine output less than 0.5 ml/kg/h
Neurologic window where there is altered mental state and consciousness
Peripheral window where skin is cold and clammy

Question 38

How is shock diagnosed?

Answer 38

Blood pressure below 90mmhg
Mean arterial pressure lesser than 65mmhg or it decreases by 40mmHg from the baseline
Tachycardia
Hyperventilation
Temperature
Mixed venous oxygen saturation
-> These factors depend on the type of shock and stage of shock

Question 39

What is SvO2?

Answer 39

The amount of oxygen bound to haemoglobin in the blood returning to the right side of the heart, which is indicative of how much oxygen of left over by the tissues. It indicates oxygen transport which is lowered in septic shock,

Question 40

How is shock assessed?

Answer 40

Assessment of:
Ventilatory effort
Peripheral perfusion and pulses
Level of alertness and blood sugar
Exposure and environment

Question 41

How is shock managed?

Answer 41

Identify the cause of impaired tissue perfusion and correct it
Increase intravascular volume with isotonic crystalline fluids
Drug therapy and vasopressors

Question 42

How is cardiogenic shock managed?

Answer 42

Vasodilators
Thrombolysis
Revascularisations
Intra-aortic ballon pump

Question 43

How is septic shock managed?

Answer 43

Replace fluids and antibiotics