Anaesthesiology - Shock Management

Question 1

Shock

Definition

Answer 1

inadequate oxygen delivery (DO2) to meet cellular metabolic demands

□ Oxygen delivery (DO2) = CO × CaO2

□ Oxygen content (CaO2) = Hb × SaO2 × 1.34(4) + PaO2 × 0.027(5)

Question 2

Stages of shock

Answer 2

□ Pre-shock (compensated shock): compensatory changes to ↓tissue perfusion
→ Features: tachycardia, modest Δs in BP, ↓urine output, mild-moderate ↑lactate/BE

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

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

Question 3

Define the tolerance of different tissue to hypoxia

Answer 3

□ Fibroblasts/epidermis/skeletal muscles (hours)
□ Myocardium, hepatocytes, renal (30min-2h)
□ Neurones (3-5min)

Question 4

Define classes of shock

Answer 4

Low cardiac output types:
* Hypovolemic shock
* Cardiogenic shock
* Obstructive shock

Low peripheral resistance types/ Distributive shocks:
* Septic/ SIRS-related shock
* Neurogenic shock
* Anaphylatic shock

Question 5

Features of shocks with low cardiac output e.g. hypovolemic shock

Answer 5

Signs:
 Hypotension with narrow BP (↑DBP due to reflex vasoconstricton; ↓pulse pressure due to ↓CO)
 Compensatory tachycardia and tachypnoea
 Cold, clammy and cyanotic skin
 Weak peripheral pulses

Features of ↓perfusion
 Hyperlactataemia and lactic acidosis
 Oliguria
 Mental status changes

Question 6

Obstructive shock

Cause
Features

Answer 6

Cause: Due to impeded LV filling → ↓CO
- pulmonary vascular (eg. massive PE),
- mechanical (eg. tension pneumothorax, tamponade)

Features:
- Beck’s triad: low blood pressure, distension of the jugular veins, and muffled or diminished heart sounds
- NO signs of ↑preload/↓preload

Question 7

Cardiogenic shock

Cause
Features

Answer 7

Due to cardiac pump failure → ↓CO

Causes:
□ Cardiomyopathic: MI, ADHF from DCMP, myocarditis, drug-induced
□ Arrhythmogenic: AF, AFlu, SVT, VT, VF, 3oHB
□ Mechanical: severe or acute VHD, septal or ventricular aneurysm rupture

Clinically recognized by features of pulmonary oedema and ↑preload
□ Forward failure: pallor, peripheral cyanosis, cold extremities, delayed capillary refill, oliguria, altered consciousness
□ Backward failure: dyspnoea, wheeze, cough with pink frothy sputum, cyanosis, basal crackles, displaced apex, gallop
□ Distended neck veins
□ ↑CVP >12mmHg on PAWP monitoring

Question 8

Neurogenic shock

Cause
Features

Answer 8

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

Causes: TBI, SCI, neuro-axial anaesthesia

Clinically recognized by
□ Paradoxically slow HR due to loss of SN control
□ Compatible Hx of CNS injury

Question 9

Anaphylactic shock

Cause
Features

Answer 9

Due to severe type I hypersensitivity reaction

Causes: food, medications, insect bites/stings

Clinically recognized by anaphylactic S/S
□ Severe bronchospasm and angioedema
□ Urticaria, widespread flushing and pruritus

Question 10

Septic shock

Cause
Features

Answer 10

Due to systemic inflammatory response syndrome (SIRS)→ vasodilatation

Causes: infectious vs non-infectious (eg. pancreatitis, burns, amniotic fluid/fat/air embolism)

Clinically recognized by
→ S/S of inf’n/infl’n, Fever or hypothermia
→ Vasopressor requirement to maintain MABP ≥65mmHg
→ Serum lactate >2mmol/L
→ No hypovolaemia

Question 11

Features of distributive shock

Answer 11

Clinically characterized by features of ↑CO
 Hypotension with wide BP (↓DBP due to peripheral vasodilatation; ↑pulse pressure due to ↓afterload)
 Compensatory tachycardia and tachypnoea
 Warm peripheries
 Bounding peripheral pulses

Features of hypoperfusion
 Hyperlactataemia and lactic acidosis
 Oliguria
 Mental status changes

Question 12

General approach to circulatory collapse

Answer 12

Assess and secure Airway: Airway management, RSI

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

Assess and secure Circulation
- Optimize preload by volume resuscitation ± vasopressors (adrenaline, noradrenaline) when there is insufficient preload (eg. ↓CVP, dry mucosa, ↓skin turgor)
- Optimize afterload by vasodilators and intra-aortic balloon pump (IABP) in cardiogenic shock only
- Optimize contractility by inotrope (dobutamine) or antiarrhythmics (if in arrhythmia) in cardiogenic shock only
- Optimize Hb by RBC transfusion to keep Hb 7-9mg/dL (10 if IHD)
- Optimize MABP by vasopressors esp in distributive shock

Question 13

First line investigations for shock

Answer 13

Clinical evaluation for type of shock and aetiology

Clinical monitoring: BP/P, UO, fluid balance charts, cardiac monitor

Early investigations:
- ECG: arrhythmia, ST changes (ischaemia, pericarditis), low-voltage (pericardial effusion, S1Q3T3/RV strain (PE)
- 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
- Cardiac enzymes/BNP: myocardial infarction (may be cause or result to shock)
- Clotting + D-dimer: ↑PT/INR (haemorrhagic shock, septic APR), ↑D-dimer (PE, DIC)
- CXR: pneumonia, pneumothorax, pulmonary oedema, widened mediastinum (obstructive shock), aortic dissection…
- POCUS: cardiac pathologies, pneumothorax, pleural effusion, ascites, DVT…
- ± pulmonary artery catheterization: determine CVP when dx uncertain

Question 13

Outline the division of total body water

Answer 13

Total body water (TBW) = 60% (M), 50-55% (F) of BW (~40L in 65kg male)

Intracellular fluid (ICF) = 60% TBW = 24L = 35% BW

Extracellular fluid (ECF) = 40% TBW = 16L = 25% BW
→ Intravascular fluid(plasma) = 1/4 of ECF = ~4L
→ Interstitial fluid = 3/4 of ECF = ~12L

Question 14

Outline framework for fluid therapy

Answer 14

Basal requirement:** maintenance fluid therapy** (indicated whenever NPO)
→ ‘4-2-1 rule’: 4mL/kg/h for first 10kg + 2mL/kg/h for next 10kg + 1mL/kg/h for every 10kg afterwards

Additional requirement for **preexisting and ongoing loss **
→ Poor intake due to pain/cachexia
→ GI loss due to ↑output (vomiting, diarrhoea) and ↓absorption (eg. LB obstruction, paralytic ileus)
→ Bleeding
→ 3rd space loss, eg. in sepsis, inflammation
→ Fasting before IVF replacement

Question 15

Define the two types of fluid therapy

Answer 15

Crystalloid: solutions of crystalline solids in water
Isotonic solutions: contain electrolytes, similar composition to plasma, equilibrated to extracellular compartment only
- Normal saline (NS, 0.9% NaCl): usual 1st line, cheap, but risk of inducing hyperchloremic acidosis
- Balanced solution (eg. Hartmann’s solution or Ringer’s lactate)

Glucose-containing: hypotonic but contains glucose for energy, equilibrated to total body water
- 5% dextrose solution (D5)

Colloid: suspensions of high molecular weight particles, Equilibrated to intravascular fluid only for volume resuscitation
- Eg. gelofusine (gelatin-derived), dextrans, hetastarch

Question 16

Compare the choice of fluids in fluid therapy

Answer 16

Crystalloid vs colloid: replace intravascular or extravascular volume?
→ Colloid for rapid restoration of intravascular volume, eg. bleeding
→ Crystalloid for correction of extravascular volume
→ For surgical patients, usually extravascular deficit > intravascular deficit

Buffered crystalloid vs isotonic saline: risk of hyperchloremic acidosis w/ massive NS infusion, consider Ringer’s lactate if ↑↑risk of hyperchloremic acidosis

Rate of replacement: Replace in small amounts and reassess (eg. 500mL/2h and reassess) unless emergency

Risk: fluid overload in elderly, congestive HF, chronic RF or post-op patients

Question 17

Blood transfusion

Indications
Considerations
Types of transfusion
Risks of transfusion

Answer 17

Indication: Hb <7g/dL, Symptom of anaemia severe

Consider age and co-morbidities of patient
- Low threshold if age >80y, underlying IHD, in shock w/ active bleeding
- High threshold if young, low baseline Hb, after curative cancer surgery

Types:
Whole blood: plasma and all elements of blood for volume resuscitation
Packed cells: blood with plasma (FFP), platelets (PLT concentrate) removed for correcting anemia only

Risks of transfusion:
→ ABO incompatibility (1/6000)
→ Allergic: febrile reaction (3%) (FNHTR), urticaria (1%), anaphylaxis (1/150,000)
→ ARDS (<1/10000)
→ Immunosuppression
→ Infections: hepatitis (1/150-1/5k), AIDS (1/200k), CMV, EBV, bacterial infection
→ Massive transfusion risks (>10 units): hypothermia, coagulopathy (haemodilution), hyperK, citrate toxicity (hypoCa, cardiac dysfx), metabolic alkalosis

Question 18

List causes of hypovolemic shock

Answer 18

□ Haemorrhagic: trauma, GI bleed, intra-op/post-op bleed, retroperitoneal bleed, ruptured ectopic pregnancy, post-partum haemorrhage, uterine or vaginal haemorrhage, spontaneous haemorrhage due to bleeding diathesis

□ Non-haemorrhagic: GI losses (eg. diarrhoea, vomiting), skin losses (eg. burns, heatstroke), renal losses (eg. osmotic diuresis, adrenal insufficiency), 3rd space losses (eg. post-op, IO, pancreatitis)

Question 19

Hypovolemic shock

Classes of severity

Answer 19

Question 20

Hypovolemic shock

Management

Answer 20

Airway, Breathing: High flow O2 with BVM w/ reservoir

Circulation:
→ Obtain large bore IV access (14/16G at antecubital vein)
→ Give rapid fluid challenge over 5-10min: 500mL (or 1000mL) of crystalloid solution (balanced or NS)
→ Reassess BP/P for every 5min, repeat fluid challenge if unresponsive
→ Consider RBC transfusion depending on Hb if haemorrhagic shock

Monitoring: Take blood for CBC, RFT, clotting, T/S, Foley’s catheter for UO, ABG for oxygenation, CVP monitoring if Hx of cardiac failure

Question 21

Cardiogenic shock management

Answer 21

□ Sit patient upright

□ High flow (15L/min) O2 with BVM with reservoir to keep SpO2 >94%

□ Optimize cardiac workload by
→ Inotropes (eg. IV dobutamine) if adequate filling pressure
→ Fluid resuscitation ± vasopressors if low filling pressure

□ Investigations and treatment for underlying cause should be done concurrently
→ RFT for any fluid/electrolytes abnormalities
→ ECG for any arrhythmias and MI
→ CXR for cardiac abnormalities and pulmonary oedema
→ ABG for acid-base abnormalities
→ Cardiac enzymes for MI
→ Echocardiogram if indicated

□ ACLS should be activated in cases of arrhythmogenic causes

Question 22

Septic shock

Prognostic score

Answer 22

qSOFA score: used in out-of-ICU setting for quick recognition of sepsis with worse outcome
□ Criteria: RR>22/min, sBP <100mmHg, altered GCS
□ Significance: 0= mortality <1%; 1 = mortality 2-3%, ≥2 = mortality ≥10%

Question 23

Septic shock

Clinical sequalae

Answer 23

CVS: septic shock with high CO and vasodilatation

Lungs: ARDS with non-cardiogenic pulmonary oedema → T1RF and ↓lung compliance

Kidneys: acute tubular necrosis affecting PCTs esp., causing low UO and hematuria

Blood: DIC with thrombocytopenia

GI (GI bleeding, ileus), liver (jaundice), brain (septic encephalopathy), PNS (critical illness polyneuropathy)

Question 24

Septic shock

Management

Answer 24

**Infection source control: **
- Identify + eradicate source asap
- IV broad-spectrum Abx asap ≤1h

Volume resuscitation:
- ≥ 30mL/kg IV crystalloids within first 3h of hypoperfusion
- Additional fluid guided by haemodynamic status
- Balanced crystalloid ± albumin (Do NOT use starch-based colloids, a/w ↑renal failure w/o survival benefit)

Vasopressors:
- Initial target MABP at 65mmHg (Higher BP targets increases AF risk, beneficial only if chronic HTN)
- Norepinephrine ± vasopressin or epinephrine (Dopamine a/w more arrhythmias)

Adjuncts:
- PEEP or BiPAP for ventilation
- Nutritional protocol: early enteral feeding
- Serum lactate as marker to guide resuscitation
- Glucose control to prevent hyperglycemia (a/w higher mortality)
- (Renal replacement therapy not used in sepsis-AKI unless indicated)

Question 25

Anaphylatic shock

Causes

Clinical features

Answer 25

Causes:
□ Idiopathic
□ Allergens (IgE-dependent): food (peanut, shellfish, milk, egg, strawberry), insect stings, drugs (antibiotics, biologics,), latex, food additives, semen (rare)
□ IgE-independent triggers: exercise, NSAIDs, radiocontrast agents, alcohol, cold, heat

Clinical features:
□ Respiratory compromise: dyspnoea, wheezes, bronchospasm, stridor, hypoxaemia, angioedema, nasal congestion, hoarseness
□ Shock: collapse, syncope, incontinence, ↓BP, tachycardia, dizziness
□ Skin/mucosal symptoms: generalized urticaria, pruritus, flushing, periorbital oedema, angioedema
□ GI symptoms: nausea, vomiting, diarrhoea, cramping abdominal pain

Question 26

Anaphylatic shock

Treatment

Answer 26

0.5mg (0.01mg/kg) IM epinephrine 1:1000, IV epinephrine if refractory

Airway: Immeidate intubation vs angioedema/ bronchospasm

Breathing: 100% O2

Circulation:
- Place pt in recumbent position and elevate the feet to restore intravascular volume
- Secure IV access and give rapid fluid challenge (1-2L IV NS)

Drug therapy:
→ Antihistamines: chlorphenamine 10-20mg slowly IV or IM
→ Steroids: hydrocortisone 200mg slowly IV or IM
→ Bronchodilators: salbutamol 2.5-5.0mg nebulized or 0.25mg IV
→ IV glucagon for those on β-blocker

Ix: Plasma mast cell tryptase, pulse oximetry, BP/P, ABG ± UO, CVP if severe hypotension