Shock

Question 1

What are the four main classes of shock?

Answer 1

Cardiogenic, hypovolaemic, obstructive and distributive.

Question 2

Describe the underlying cause of cardiogenic shock?

Answer 2

Heart fails to pump adequately, the CO falls despite normal or elevated blood volume. Usually due to MI but can be due to arrhythmias. Preload and afterload are increased, so is central venous pressure.

Question 3

Describe the underlying cause of hypovolaemic shock

Answer 3

Acute loss of 15-20% blood volume. At 15-20% blood loss CO falls but MABP is maintained, however at 35-45% loss both CO and MABP fall to zero = death.

Question 4

What is the underlying cause of obstructive shock?

Answer 4

Shock that results from mechanical obstruction of blood flow through veins, heart and lungs. Can be caused by PE (most common) aortic aneurysm, cardiac tamponade etc. Results in elevated right heart pressure = signs of RHF

Question 5

What is the underlying cause of distributive/normovolaemic shock?

Answer 5

Loss of BV tone, enlargement of vascular compartment and fluid shifts away from heart and central circulation. The loss of blood vessel tone is cause by loss of sympathetic mediated vasomotor tone or vasodilators.

Question 6

What are the three common forms of distributive shock?

Answer 6

Anaphylactic, neurogenic and septic shock.

Question 7

What is anaphylactic shock and what is it cause by?

Answer 7

• Characterised by massive vasodilation, pooling of blood in peripheral vessels and increased capillary permeability.
• Due to immunological mediation reaction where vasodilators like histamine is released into blood, accompanied by laryngeal oedema. Usually presents with abdo cramps, burning skin, itching, coughing, wheezing and a drop in BP.

Question 8

What is septic shock due to?

Answer 8

Disseminated infection and release of inflammatory mediator into systemic circulation. Can result in release of histamine, kinins and prostaglandins.

Question 9

What is neurogenic shock caused by?

Answer 9

Defect in vasomotor centre in brainstem or sympathetic outflow to blood vessels.

Question 10

What can cause a transient form of neurogenic shock?

Answer 10

Emotional distress = fainting.

Question 11

Describe the stages of shock

Answer 11

Initial stage, compensatory stage, progressive stage and irreverable stage.

Question 12

What occurs in the initial stage?

Answer 12

Perfusion is decreased but not enough to cause serious effects.

Question 13

What occurs in compensatory stage?

Answer 13

Perfusion is reduced but mechanisms are able to maintain BP and tissue perfusion sufficiently to prevent cell damage.

Question 14

What occurs in the progressive stage of shock?

Answer 14

BP falls, blood flow to heart and brain is impaired, capillary permeability is increased so fluid leaves the capillaries. Blood flow becomes sluggish. Cells and enzymes are damaged.

Question 15

What occurs in the irreversible stage?

Answer 15

Even if blood volume is restored and vital signs stabilise - death occurs anyways

Question 16

What occurs if the compensatory mechanisms are extended for a period of time.

Answer 16

• Local factors controlling vascular tone override the sympathetic effect and the smooth muscle relaxes. This results in a fall of MABP

Question 17

Describe the cellular changes that occur with low tissue perfusion

Answer 17

Low oxygen causes cells to work anaerobically, producing lactic acid, results in NaCl accumulation. The cells swell making the membrane more permeable. Mitochondrial function is impaired leading to cell damage and lysis. Lysis causes release of cytokines.

Question 18

What are the signs and symptoms of shock?

Answer 18

Thirst - due to decreased blood volume.
Skin and body temperature - cold and clammy skin due to SNS.

Pulse and pressures - increased in HR but weak pulses.

Urine output - decreases.

Sensorium - apprehensive and restlessness is common

Question 19

What are some of the complications of shock?

Answer 19

• Shock lung - respiratory failure due to decreased lung perfusion and ischaemic.
• GI ulceration - Due to decreased blood flow to mucosa
• Disseminated intravascular coagulation - Small clots in microcirculation.
• Renal damage - Acute tubular necrosis resulting in poor urine output.
• Multiple organ failure

Question 20

What is the treatment of shock?

Answer 20

Directed towards controlling improving tissue perfusion. Vasoactive drugs can be used as they can constrict or dilate blood vessels.

In hypovolaemic shock you want to restore blood volume via fluid (saline = 1st line), blood, plasma expanders or dextran’s (care because may cause anaphylaxis.

In cardiogenic shock increasing blood volume may cause worsening of situation but nitrites can be used.