JC 11 (Surgery) - Shock

Question 1

Define Shock

Answer 1

state of cellular and tissue hypoxia due to reduced O2 delivery, increased O2 consumption or inadequate O2 utilization

inadequate oxygen delivery (DO2) to meet cellular metabolic demands

Question 2

3 methods to assess for tissue hypoperfusion clinically

Answer 2

o Skin: Decreased capillary refill/ Cool and pale skin
o Renal: Decreased urine output < 0.5 mL/kg/hr
o CNS: Anxiety/ Lethargy/ Confusion

Question 3

Equations for oxygen delivery and oxygen content

Answer 3

□ Oxygen delivery (DO2) = CO × CaO2

□ Oxygen content (CaO2) = Hb × SaO2 × 1.34 + PaO2 × 0.027

Question 4

Hypotension is a pre-requisite to shock
True or False, explain

Answer 4

Circulatory failure may not present as occult hypotension

o Patients in the early stages of shock can be normotensive or hypertensive
o Patients who have hypotension does NOT necessarily have shock:
chronic hypotension, drug-induced hypotension, autonomic dysfunction, vasovagal syncope and peripheral artery disease

Question 5

Define absolute, relative and orthostatic hypotension

Answer 5

• Absolute = SBP < 90 mmHg (OR) MAP < 65 mmHg
• Relative = Reduction in SBP > 40 mmHg from baseline
• Orthostatic = Reduction in SBP > 20 mmHg (OR) DBP > 10 mmHg on standing

Question 6

Stages of shock

Answer 6

□ Pre-shock: compensated shock to tissue hypoperfusion
→ tachycardia, modest increase BP, low urine output, mild lactate

□ Shock: compensatory changes overwhelmed
→ Low BP and S/S of tissue hypoperfusion, eg. oliguria, cold and clammy skin

□ End-organ dysfunction: multiorgan failure and death
→ acute renal failure, severe hypotension, mental obtundation and coma

Question 7

4 severities of hypovolemic shock and associated volume blood loss

Answer 7

Question 8

Compare the HR, BP and RR response in 4 severities of shock

Answer 8

Question 9

List all assessments for severity of shock

Answer 9

1. Volume of blood loss
2. HR
3. BP
4. RR
5. Mental status
6. Capillary refill
7. Bowel sounds
8. Urine output

Question 10

Compare the Mental status between 4 severities of shock

Answer 10

Question 11

Compare capillary refill time, bowel sounds and urine output for 4 severities of shock

Answer 11

Question 12

4 classes of shock

Answer 12

Hypovolemic

Cardiogenic

Obstructive

Distributive: Sepsis, anaphylaxis, Neurogenic

Question 13

Causes of hypovolemic shock

Answer 13

Causes:

haemorrhagic

• trauma, GI bleed

non-haemorrhagic

• excessive vomiting and diarrhea,
• skin burns,
• 3rd space loss,
• dehydration

Question 14

Causes of cardiogenic shock

Answer 14

Causes:

1. cardiomyopathic (eg. MI, severe dilated cardiomyopathy, myocarditis),
2. arrhythmogenic,
3. mechanical (eg. severe valvular heart disease, ruptured LV aneurysm, atrial myxoma)

Question 15

Causes of obstructive shock

Answer 15

 Cardiac tamponade
 Pulmonary embolism
 Tension pneumothorax

Question 16

Causes of distributive shock

Answer 16

Sepsis

Anaphylaxis: severe systemic allergic reaction to an antigen precipitated by abrupt release of chemical mediators in a previously sensitized patient

Neurogenic: traumatic brain injury or spinal cord injury, Interruption of autonomic pathways leading to loss of sympathetic tone and unopposed vagal tone

Question 17

Compare anaphylaxis reaction to anaphylactoid reaction

Answer 17

Anaphylaxis refers severe systemic allergic reaction to an antigen precipitated by abrupt release of chemical mediators in a previously sensitized patient

Anaphylactoid reaction refers to direct histamine release from mast cells without need for prior sensitization

Question 18

Common causes of anaphylactic shock

Answer 18

Common causes for anaphylactic shock
o Drugs: Penicillin/ Aspirin/ NSAIDs/ Colloids/ TCM
o Food: Peanuts/ Egg/ Shellfish
o Venoms: Bees/ Wasp/ Hornets
o Environment: Latex/ Dust/ Pollen grains
o Infections: EBV/ HBV/ Coxsackie virus/ Parasites

Question 19

Pathophysiology of hypovolemic shock

Answer 19

Pathophysiology - Intravascular blood volume depletion
↓ Preload (e.g. due to blood loss)
↓ SV (Frank-Starling curve: Decrease preload = Decrease stroke volume)
↓ CO, BP and LV filling pressure
↑ Sympathetic compensation to increase HR and Total Peripheral resistance

>> Increase HR

>> Increase Systemic vascular resistance

>> Decrease JVP

Question 20

Pathophysiology of cardiogenic shock

Answer 20

Pathophysiology
↓ Blood flow to heart due to intrinsic cardiac function deficit
↓ Contractility
↓ SV + Increase LV filling pressure (Backward failure - pulmonary edema)
↓ CO
↑ Sympathetic compensation to increase HR and Total Peripheral resistance

Increase HR, Systemic vascular resistance, JVP

Question 21

Pathophysiology of obstructive shock

Triad of symptoms

Answer 21

Mechanical obstruction to cardiac filling > Low LV filling > ↓CO and BP + Backward failure of right heart (Increase JVP)

Beck’s triad of cardiac tamponade
• Hypotension (Low BP)
• Distended neck veins (High CVP)
• Muffled heart sounds

Question 22

Pathophysiology of Distributive shock

Answer 22

Peripheral vascular dilatation > Increase CO (opposite to hypovolemic and cardiogenic shock), but perfusion of vital organ remains compromised as the body lose ability to distribute blood properly

1. Hypotension with wide BP (↓DBP due to peripheral vasodilatation)
2. Compensatory tachycardia and tachypnoea
3. Warm peripheries
4. Bounding peripheral pulses
5. Features of hypoperfusion
    Hyperlactataemia and lactic acidosis
    Oliguria
    Mental status changes

>> Increase HR (except neurogenic shock with low HR)

>> Decrease systemic vascular resistance

>> Decrease JVP

Question 23

Pathophysiology of Neurogenic shock

Answer 23

Neurogenic shock
Due to interruption of neurogenic vasomotor control → inappropriate ↓HR, ↓SVR

>> Paradoxically slow HR due to loss of SN control
>> Decrease systemic vascular resistance

>> Decrease JVP

Question 24

Features of anaphylactic shock

Answer 24

Due to severe type I hypersensitivity reaction

Anaphylactic S/S
□ Severe bronchospasm and angioedema
□ Urticaria, widespread flushing and pruritus

Question 25

Airway protective measures

Answer 25

→ Airway management measures as required: Head-tilt, chin lift, jaw thrust (for suspected C-spine injury), remove foreign bodies…etc → Rapid sequence intubation

Question 26

Breathing protective measures

Answer 26

→ High flow O2 (15L/min) using face-mask and reservoir for ALL pt → Mechanical ventilation if intractable hypoxaemia/hypercapnia, resp distress or ↓consciousness

Question 27

Circulation protective measures 1. Hypovolemia (2) 2. Cardiogenic (3) 3. Distributive (3))

Answer 27

Hypovolemia: * Optimize preload by **_volume resuscitation ± short-term vasopressors_** (adrenaline, noradrenaline) * Secure **_large-bore IV access_** (14-18G) Cardiogenic * Optimize afterload by **_vasodilators and intra-aortic balloon pump_** (IABP) * Optimize contractility by **_inotrope (dobutamine) or antiarrhythmics_** (if in arrhythmia) * Optimize Hb by **_RBC transfusion_** to keep Hb 7-9mg/dL Distributive * As above * + Optimize MABP by **_vasopressors_** * + eradicate infective focus

Question 28

First-line monitoring for suspected shock

Answer 28

Clinical evaluation for type of shock and aetiology Clinical monitoring: BP/P, UO, fluid balance charts, cardiac monitor

Question 29

First-line tests/ investigations for suspected shock with rationale (7)

Answer 29

Cardiogenic: **ECG, Cardiac enzymes/BNP** **CBC**/D: anaemia w/ bleeding (haemorrhagic shock), ↑eosinophil (anaphylaxis), ↑/↓WBC (sepsis or stress response), ↓PLT (bleeding tendency) **L/RFT:** ↑U/Cr (shock-induced AKI), ↑ALT/AST (shock liver), electrolyte disturbance, dehydration (hypovolemia) **V/ABG + lactate:** lactic acidosis (poor tissue perfusion), assess need for ventilation **Clotting + D-dimer:** ↑PT/INR (haemorrhagic shock, septic APR), ↑D-dimer (PE, DIC) * *CXR:** pneumonia, pneumothorax, pulmonary oedema, widened mediastinum (obstructive shock) , aortic dissection...

Question 30

Acute management of Cardiac arrest

Answer 30

1. CPR with 30:2 compression -ventilation ratio 2. Shock for Ventricular defibrillation 3. Adrenaline (or amiodarone/ Lidocaine for refractory) 4. Airway: ET tube or supraglottic advanced airway 5. Monitor return of spontaneous circulation: Pulse, BP, ECG

Question 31

Acute assessment of hypovolemia

Answer 31

Straight leg raise if unsure of hypovolemic shock * If BP goes up \> hypovolemic shock Fluid challenge: 100-500mL of fluid infusion to see If BP goes up

Question 32

Acronym for causes of traumatic cardiac arrest

Answer 32

HOTT Hypovolemia Oxygen Tension pneumothroax Tamponade