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2025 Part Twos > Truama - Shock, resuscitation > Flashcards

Truama - Shock, resuscitation Flashcards

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1
Q

What is the definition of shock?

A

Inadequate delivery of oxygenated blood to tissues, resulting in cellular hypoxia

‘Supply cannot meet demand.’

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2
Q

What determines the basis of shock?

A

Cardiac output

CO = SV x HR

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3
Q

What is the formula for stroke volume (SV)?

A

SV = Preload + contractility - after load (a.k.a EDV - ESV)

EDV = End Diastolic Volume, ESV = End Systolic Volume

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4
Q

What is the formula for blood pressure (BP)?

A

BP = CO x TPR

CO = Cardiac Output, TPR = Total Peripheral Resistance

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5
Q

What are the classifications of shock?

A
  • Hypovolaemic/Haemorrhagic Shock
  • Cardiogenic Shock
  • Cardiac compressive (e.g. cardiac tamponade)
  • Obstructive Shock (e.g. Mediastinal compression)
  • Distributive Shock
  • Neurogenic Shock
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6
Q

What causes hypovolaemic shock?

A

Decreased intravascular volume, causing significant reduction in pressure and flow

Characterised by significantly reduced filling pressures.

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7
Q

How is cardiac output maintained initially in hypovolaemic shock?

A

By tachycardia (compensatory)

Increased peripheral and splenic resistance, and myocardial contractility also help maintain BP.

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8
Q

What are the earliest signs of haemorrhagic shock?

A
  • Anxiety
  • Increased respiratory rate (RR)
  • Narrowed pulse pressure
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9
Q

At what class of blood loss is tachycardia typically seen?

A

Class 2, 30% blood loss

Hypotension is a later sign (class 3).

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10
Q

Which patient populations should be approached with caution in shock?

A
  • Young people
  • Elderly

Young people can compensate before they tank out; elderly do not have physiological reserve.

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11
Q

What caution should be taken with beta-blockers in shock?

A

They may impair compensatory mechanisms.

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12
Q

What is Class 1 shock characterized by?

A

15% blood volume loss, <750ml blood loss, HR <100, BP normal, pulse pressure normal, RR 14-20

Class 1 shock indicates minimal physiological changes.

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13
Q

What is the blood volume loss percentage for Class 2 shock?

A

30% blood volume loss

Class 2 shock corresponds to 750-1500ml blood loss.

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14
Q

What heart rate (HR) is associated with Class 2 shock?

A

HR >100

This indicates a compensatory tachycardia in response to decreased blood volume.

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15
Q

What are the vital signs for Class 3 shock?

A

HR >120, BP Decreased, Pulse pressure Narrowed, RR 30-40

Class 3 shock indicates significant physiological compromise.

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16
Q

Class 4 shock is characterized by blood volume loss greater than _______.

A

> 40% blood volume loss

Class 4 shock indicates severe hemorrhagic shock with major physiological derangements.

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17
Q

What is the blood loss range for Class 3 shock?

A

2000ml blood loss

This level of blood loss leads to critical changes in vital signs.

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18
Q

What respiratory rate (RR) is typical for Class 4 shock?

A

RR >35

Elevated respiratory rate indicates significant distress and compensatory mechanisms.

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19
Q

In Class 4 shock, what happens to the blood pressure (BP)?

A

BP Decreased

This reflects the body’s inability to maintain perfusion due to severe volume loss.

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20
Q

What is the pulse pressure status in Class 3 shock?

A

Pulse pressure Narrowed

A narrowed pulse pressure is indicative of decreased stroke volume and compromised hemodynamics.

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21
Q

What is the heart rate (HR) threshold for Class 4 shock?

A

HR >140

This indicates a critical compensatory response to extreme hypovolemia.

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22
Q

What is cardiogenic shock?

A

Pump failure

Cardiogenic shock occurs when the heart fails to produce adequate cardiac output even when end-diastolic volume is normal.

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23
Q

What happens in cardiogenic shock?

A

There is volume (blood), but heart can’t pump = pump failure

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24
Q

What are the causes of cardiogenic shock related to stroke volume?

A
  • Increase afterload
  • Reduced contractility

Causes include pulmonary embolism, air embolus, ARDS, aortic stenosis, calcification of systemic arteries, and stiffening of arterial walls.

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25
What can reduce myocardial contractility?
* Dysrhythmias * Myocardial ischaemia from hypotension * High levels of catecholamines * Inflammatory mediators ## Footnote Normal resting cardiac output may not increase to meet demands, such as in heart failure or due to medications like beta blockers.
26
What is cardiac compressive shock?
No preload ## Footnote External forces compress thin-walled chambers of the heart and great veins, causing impaired diastolic filling.
27
What causes reduced preload in cardiac compressive shock?
* Cardiac tamponade * Tension pneumothorax * Positive pressure ventilation with high tidal volume * Elevated diaphragm * Abdominal compartment syndrome
28
What characterizes distributive (inflammatory) shock?
Dilation of capacitance reservoirs in response to endotoxins or prolonged hypovolaemic shock
29
What does distributive shock cause?
* Peripheral pooling of blood * Failure of energy production * Severe lactic acidosis
30
What is neurogenic shock?
Loss of alpha-adrenergic tone, causing vasodilation and reduced peripheral vascular resistance
31
How is neurogenic shock diagnosed?
Diagnosis of exclusion!
32
What is obstructive shock?
Intravascular obstruction causes undue burden on heart, decreasing venous return and causing hypotension
33
What are the causes of obstructive shock?
* Pulmonary embolism * Air embolus * ARDS * Aortic stenosis * Obstruction of microcirculation due to hypertensive disease and chronic hypertension
34
What is the formula for measuring flow in the context of shock?
Flow = Pressure/resistance (Ohm’s law)
35
What should be the focus when measuring shock?
Focus on flow rather than pressure
36
What is the effect of most drugs that increase pressure in shock?
They do so by increasing resistance, thus reducing flow
37
What determines cardiac output according to Starling's Law?
Pre-load, Contractility of heart, After-load ## Footnote Pre-load is the volume entering the heart, contractility refers to the strength of heart contractions, and after-load is the resistance against which the heart must pump.
38
What is the relationship between pre-load and cardiac output?
Greater pre-load results in greater cardiac output ## Footnote This is due to the stretching of myocardial fibers leading to increased contractility, known as the Frank-Starling principle.
39
What can increase contractility of the heart?
Inotropic agents ## Footnote These agents enhance the strength of the heart's contractions.
40
How is after-load defined?
Wall tension in left ventricular ejection ## Footnote It is determined by systolic pressure and left ventricular radius, which is related to end-diastolic volume.
41
What is the best indirect measure of flow?
Urine output ## Footnote It reflects kidney perfusion and overall circulatory status.
42
What does a GCS score indicate?
Brain function ## Footnote A higher GCS indicates better neurological function and can reflect cerebral perfusion.
43
What does a central venous pressure of less than 4 cm water indicate?
Venous system empty and pre-load reduced ## Footnote This suggests that the heart may not be receiving enough blood to pump effectively.
44
What is the normal range for central venous pressure?
4-12 cm water ## Footnote Values outside this range indicate potential issues with fluid status or heart function.
45
What does elevated central venous pressure suggest?
Increased pre-load due to overfilling or pump failure ## Footnote This can indicate conditions like cardiogenic shock.
46
What is the primary cause of systemic arterial hypotension and central venous hypotension?
Hypovolaemia ## Footnote This condition indicates a deficit in blood volume.
47
What is indicated by high central venous pressure and low arterial pressure?
Shock more likely due to pump failure ## Footnote This scenario suggests that the heart is unable to effectively pump blood.
48
How can systemic arterial pressure be measured?
Indirectly with BP cuff, directly with arterial line ## Footnote Both methods are used to assess blood pressure and circulatory status.
49
What is unique about the right-sided circulation?
It is a valveless system ## Footnote This means that the cardiac output of the right heart flows without valves, affecting pressure dynamics.
50
How can pulmonary artery pressure be measured?
By occluding a catheter placed in the pulmonary artery and measuring back pressure ## Footnote This method allows for assessment of pressures within the right heart and lungs.
51
What technique can be used to measure cardiac output in the pulmonary artery?
Thermodilution ## Footnote This technique involves injecting a known volume of cold fluid and measuring temperature changes to calculate cardiac output.
52
Fill in the blank: After-load is determined by systolic pressure and ______.
Left ventricular radius ## Footnote The left ventricular radius is related to the volume of blood in the heart at the end of diastole.
53
What is the best way to measure the impact of shock?
At the cellular level, best measured by blood gas ## Footnote This measurement provides insight into the adequacy of oxygen delivery to cells.
54
What is shock defined as?
Adequate delivery of oxygenated blood to cells, resulting in cellular hypoxia ## Footnote Understanding this definition is crucial for assessing shock.
55
What should be checked to evaluate shock?
At the cellular level ## Footnote This emphasizes the importance of cellular assessment in shock management.
56
What are the key measurements taken in blood gas analysis?
* PaCO2 * PaO2 * pH * Base excess * Lactate ## Footnote Each of these measurements provides specific information about respiratory and metabolic status.
57
What does PaCO2 measure?
Alveolar ventilation ## Footnote A normal PaCO2 indicates adequate ventilation in the body.
58
What does PaO2 represent?
Partial pressure of O2 ## Footnote However, it does not indicate the delivery rate of oxygen to tissues.
59
What should be evaluated to assess oxygen utilization?
Metabolic activity of cells by looking at pH and base excess ## Footnote These factors provide insights into how effectively cells are using oxygen.
60
What can lactate levels indicate in shock evaluation?
May lag behind but can be measured ## Footnote Elevated lactate levels can indicate tissue hypoxia and metabolic distress.
61
What does DCR stand for?
Damage Control Resuscitation
62
What are the key principles of Damage Control Resuscitation?
* Haemostatic resuscitation * Permissive hypotension (as indicated) * Rapid definitive control of bleeding via Damage Control Surgery
63
Where does the Damage Control Resuscitation process begin and continue?
It begins pre-hospital and continues through ED, operating theatre and ICU
64
What is the typical blood product resuscitation ratio for haemostatic resuscitation?
1:1:1 or 2:1:1
65
What fluids should be limited during haemostatic resuscitation?
Crystalloid fluids
66
What complications can arise from aggressive fluid resuscitation?
* Oedema * Compartment syndrome * Acute lung injury (ARDS) * Dilutional coagulopathy * Clot disruption risk of ongoing bleeding
67
What triggers the activation of massive transfusion protocol (MTP)?
Expected or actual haemorrhagic shock, e.g., ongoing haemodynamic instability after 2-4 RBC unit transfusion
68
What is the recommended approach to haemostatic resuscitation?
* Balanced ratio of blood products: 2:1:1 * Tranexamic acid * Cryoprecipitate
69
What is the lethal triad that needs proactive correction during haemostatic resuscitation?
* Hypothermia * Metabolic acidosis * Coagulopathy
70
How can hypothermia be prevented during haemostatic resuscitation?
* Use warmed fluids (e.g., Level 1 Fluid Warmer) * Bair Hugger or warm blankets * Minimise exposure * Increase ambient temperature * Continuous temperature monitoring
71
Why is it important to manage metabolic acidosis during haemostatic resuscitation?
pH strongly affects activity of Factors V, VIIa, and X, and acidosis inhibits thrombin generation.
72
What cardiovascular effects can occur with acidosis (pH <7.2)?
* Decreased contractility and CO * Vasodilatation and hypotension * Bradycardia * Increased dysrhythmias
73
What FFP to PRBC ratios are now used in haemostatic resuscitation?
1:1 or 2:3
74
What is the role of cryoprecipitate in haemostatic resuscitation?
Provides an additional option for Factor replacement for a lower volume of fluid
75
Is rFVIIa used in trauma and how is it classified?
Used off label and anecdotally
76
What is the definition of Permissive Hypotension?
Limited or low volume replacement intended to maintain minimum adequate organ perfusion, rather than aiming for restoration of 'normal' blood pressure.
77
What is the rationale for Permissive Hypotension?
It avoids disruption of blood clot with higher blood pressures and worsening bleeding before definitive haemostasis is achieved.
78
What is the target blood pressure in Permissive Hypotension?
Accept a lower blood pressure to avoid exsanguination, but enough to maintain organ perfusion. Common values used are: * SBP >70 * MAP 65
79
Is low blood pressure the target in Permissive Hypotension?
No, low blood pressure is not the target but a compromise in the ED setting prior to haemorrhage control.
80
What are the cautious considerations for using Permissive Hypotension?
Not widely accepted and not appropriate for confirmed or suspected severe head injury.
81
Why is higher blood pressure required in patients with severe head injury?
Higher BP is required to prevent secondary hypoxic brain injury.
82
What variability should be considered in perfusion pressures among patients?
Perfusion pressures are variable among patients, particularly in the elderly with chronic hypertension.

2025 Part Twos (43 decks)

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