Pathophysiology - Hypovolaemic shock

Question 1

What is the definition of hypovolaemia?

Answer 1

The loss of at least 20% of the circulating blood volume

Question 2

What is the formula for oxygen delivery?

Answer 2

O2 delivery = Blood flow * [Hb] * O2 saturation

Question 3

What are the causes of volume contraction (loss of fluid)?

Answer 3

GI losses - diarrhoea, vomiting

Bleeding - trauma, surgery, childbirth

GU losses - diabetes, high output renal failure

Skin and respiratory losses - burns, trauma, sweat

Surgical drains

Question 4

Why does loss of fluid matter?

Answer 4

Lost fluid => loss of blood => reduced venous pressure => reduced cardiac output

also, loss of blood loss of Hb => decreased O2 delivery

Question 5

What is the formula for mean arterial pressure?

Answer 5

Mean arterial pressure = cardiac output * total peripheral resistance

Question 6

What are some of the symptoms resulting from fluid depletion?

Answer 6

Fatigue

Thirst

• due to chances in ECF volume possible

Question 7

Describe the four phases of response in hypovolaemic shock

Answer 7

CNS ischaemic response

Non-progressive shock = recovers from shock

Progressive shock = deterioration

Irreversible shock = “downward spiral”

Question 8

Describe the phsyiological process of non-progressive shock

Answer 8

Baroreceptors => SNS => increased HR + vasoconstriction => increased BP

Chemoreceptors =>

• increase SNS in response to decreased 02
• decrease PNS in response to decreased O2
• vasoconstriction due to hypoxia

Renin-angiotensin system activated

Faster absorption in GI tract => increase BP

CNS ischaemic response => rapid sympathetic response

Question 9

Where are the baroreceptors located?

Answer 9

Baroreceptors (pressure receptors) are located in:

• carotid sinus
• atria
• aortic arch

Question 10

Where are the chemoreceptors located?

Answer 10

Aortic arch

Carotid body

Question 11

Which two nerves control the parasympathetic activity of the heart?

Answer 11

Vagus nerve

Glossopharyngeal nerve

Question 12

Which three things do chemoreceptors response to?

Answer 12

Decrease O2

Increased CO2

Decreased pH

Question 13

Describe the phsyiological process of progressive shock

Answer 13

Cardiac depression

• lack of nutrients and O2 at myocardium causes an already hypoxic heart deteriorate further
• vasomotor centre fails
• release of lactate in cells due to reduced tissue perfusion, as well as thrombosis in small vessels
• leaky vessels due to prolonged hypoxia => …=> tissue necrosis

Despite this, patients can still be saved although probably suffer tissue and organ damage

Question 14

Describe the phsyiological process of non-reversible shock

Answer 14

Myocardium deterioration is extensive and no turning back

Irreversible clotting and tissue necrosis

Question 15

What can large amounts of endotoxin cause?

Answer 15

Septic Shock

• low cardiac output (& low peripheral resistance)
• blood vessel injury, thrombosis, DIC
• Acute respiratory distress syndrome

Question 16

What is Disseminated Intravascular Coagulation?

Answer 16

Pathological release of procoagulant in the circulation

Widespread activation

Formation of fibrin clots

Thrombotic occlusion of small and midsized vessels

Systemic formation of fibrin results from:

• increased generation of thrombin
• suppresion of physiologic anticoagulantion mechanisms
• impaired fibrolysis => delayed removal of fibrin