Acute Circulatory Failure/Shock Flashcards

1
Q

What is shock?

A

Shock is an acute circulatory failure with inadequate or inappropriately distributed tissue perfusion which is insufficient to meet cellular metabolic needs.

Medical shock is a life-threatening emergency

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2
Q

What are the different types of shock?

A
  • Hypovolaemic
  • Cardiogenic
  • Obstructive
  • Distributive
    • septic
    • anaphylactic
    • neurogenic
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3
Q

What is hypovolaemic shock?

A
  • most common type of shock
  • based on insufficient circulating volume
  • primary cause = loss of fluid from circulation
  • most often ‘haemorrhagic shock’
  • causes: internal bleeding, traumatic bleeding, high output fistulae, dehydration or severe burns
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4
Q

What are signs of hypovolaemic shock?

A
  • anxiety
  • altered mental state (due to reduced cerebral perfusion + subsequent hypoxia)
  • compensatory tachycardia
  • compensatory tachypnoea
  • hypotension
  • rapid, weak, thready pulse
  • fatigue
  • thirst
  • slow cap refill due to compensatory peripheral vasoconstriction
  • cold, clammy skin
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5
Q

What is cardiogenic shock?

A
  • caused by failure of heart to pump effectively
  • can be due to damage to heart muscle
  • most often from a large myocardial infarction
  • other causes of cardiogenic shock include arrhythmias, cardiomyopathy, congestive cardiac failure (CCF) or cardiac valve problems
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6
Q

What are the signs of cardiogenic shock?

A

similar to hypovolaemic shock but with:

  • raised JVP
  • pulsus alternans
  • gallop rhythm
  • pulmonary oedema
  • basal crackles
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7
Q

What is obstructive shock?

A

Caused by obstruction in blood flow which impedes circulation. In each of the following, venous return to the heart is impaired or prevented:

  • cardiac tamponade - accumulation of fluid in pericardial space which impairs venous return (it is a pericardial effusion which causes haemodynamic compromise)
  • pulmonary embolism - thromboembolism of the vessel of the lungs impairs venous return
  • tension pneumothorax - inc intrathoracic pressure impairs venous return
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8
Q

What are the signs of obstructive shock?

A

similar to hypovolaemic shock but with:

  • raised JVP
  • pulses paradoxus in case of tamponade
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9
Q

Distributive shock is similar to hypovolaemic shock in that there is insufficient intravascular volume of blood. However, this type of shock is due to peripheral dilatation of blood vessels which acts to diminish systemic vascular resistance, compared to other types of shock which impair cardiac output.

What is septic shock and its clinical signs?

A
  • due to systemic infection resulting in vasodilatation + hence hypotension
  • signs are similar to hypovolaemic shock except in first stages where there is:
    • pyrexia w/ rigors
    • systemic vasodilatation
    • warm + sweaty skin (due to vasodilatation)
    • increased levels of neutrophils
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10
Q

What is anaphylactic shock?

A
  • due to severe anaphylactic rxn to allergen/antigen/drug/foreign protein
  • causing release of histamine
  • this causes widespread dilatation
  • leading to hypotension + inc cap permeability
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11
Q

What are the signs of anaphylactic shock?

A
  • dyspnoea due to bronchospasm
  • systemic vasodilatation
  • warm skin
  • hypotension
  • urticaria
  • oedema of face + larynx
  • angio-oedema
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12
Q

What is neurogenic shock?

A
  • rare form of shock
  • occurs due to trauma to spinal cord or post-spinal surgery
  • results in sudden loss of autonomic + motor reflexes below injury level
  • hence, without stimulation by sympathetic nervous system, vessels relax -> resulting in vasodilatation -> hypotension
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13
Q

What are signs of neurogenic shock?

A
  • as with hypovolaemic shock
  • but in high spinal injuries may also be accompanied by profound bradycardia due to loss of cardiac accelerating nerve fibres from sympathetic nervous system at t1-t4
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14
Q

How might central venous pressure measurement help indicate the cause of shock?

A
  • CVP is related to right ventricle end-diastolic pressure
  • RVEDP depends on circulating blood vol, venous tone, intrathoracic pressure + right ventricular function
  • CVP measured by inserting catheter into SVC + connecting to manometer
  • if CVP low -> hypovolaemia or distributive shock
  • if CVP high -> obstructive or cardiogenic shock
  • isolated readings are of limited value
  • a trend of CVP readings should be used in conjunction w/ other parameters
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15
Q

Clearly the underlying cause of the patients sepsis needs to be identified and treated and the patient supported regardless of the cause or severity. If however any of the red flags are present the ‘sepsis six’ should be started straight away.

What is the ‘sepsis six’?

A
  1. Administer oxygen: Aim to keep saturations > 94% (88-92% if at risk of CO2 retention e.g. COPD)
  2. Take blood cultures
  3. Give broad spectrum antibiotics
  4. Give intravenous fluid challenges: NICE recommend a bolus of 500ml crystalloid over less than 15 minutes
  5. Measure serum lactate
  6. Measure accurate hourly urine output
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16
Q

What are volume expanders and why are they necessary?

A
  • volume replacement is necessary in hypovolaemic shock
  • also in anaphylactic + septic shock where there is vasodilatation, sequestration of blood and loss of circulating volume secondary to capillary leakage
  • the choice of fluid depends on clinical situation:
    • whole blood
    • colloid solutions
    • crystalloid solutions
17
Q

What is the difference between colloid and crystalloid solutions?

A

Colloidal sollutions contain larger insoluble molecules, used to replace fluid in hypovolaemic pts and to maintain blood vol. Useful in acute blood loss before whole blood becomes available, and for vol replacement in anaphylactic + septic shock. They act by maintaining high colloid osmotic pressure to produce a greater and more sustained increase in plasma volume than crystalloid solutions. Eg. gelofusin

Crystalloid solutions are aqueous of mineral salts/water soluble molecules, useful to provide rapid plasma volume expansion. Saline common. Ringer’s lactate (5% dextrose) is indicated for large vol replacement if pt at risk of hypoglycaemia or hypernatraemia. They quickly redistribute into interstitial fluid. However, large volumes carry risk of pulm oedema so best avoided. Freq used for vol replacement in d+v, and sometimes with burns. Once blood vol restored, consider inotropic drug.

18
Q

What are possible complications of tranfusions?

A
  • febrile non-haemolytic transfusion rxn
  • bacterial infection
  • viral infection
  • transfusion-related acute lung injury
  • volume overload
  • acute haemolytic reaction