Cardiology JC011: Low BP / Fast Pulse + No BP / No Pulse: Shock And Fluid Balance, Basic Life Support And Resuscitation

Question 1

Determinants of Oxygen delivery

Answer 1

1. Oxygen content of blood —> CaO2
2. Ability to deliver oxygenated blood around the body —> CO

CaO2:
[(Hb x SaO2 x 1.34) / 100] + (pO2 x 0.0027)
—> 1.34 ml of O2 can be carried by 1g of fully saturated Hb
—> only 0.0027 ml of O2 dissolved in plasma for each kPa of O2 partial pressure
—> Hb can carry O2 more efficiently

SaO2 vs CaO2 vs PaO2:
SaO2: % saturation of Hb with O2
CaO2: actual amount of O2
PaO2: indicator of lungs’ ability to exchange gases with atmosphere

Question 2

Oxygen Delivery (DO2)

Answer 2

DO2 = CO x CaO2

CO = HR x SV

Question 3

Shock

Answer 3

Inadequate oxygen delivery to meet cellular metabolic demands
—> ∵ low CaO2 / low CO

• may be caused by failure of >=1 factors

Question 4

Pathophysiology

Answer 4

Impaired Oxygen delivery
—> Hypoxia
—> Anaerobic metabolism (inefficient energy production)
—> Acidosis (***Lactate)
—> Cell death

Question 5

***Classification of Shock

Answer 5

1. Hypovolaemic
   - Haemorrhage
   - Burns
   - Dehydration
2. Cardiogenic (pump failure)
   - MI
3. Distributive
   - Vasodilatation
   - Myocardial depression
4. Others
   - Obstructive
   - Adrenocortical insufficiency
   - Neurogenic (spinal cord injury)

Question 6

1. Hypovolaemic shock

Answer 6

***Volume failure

Result of IV blood volume depletion

• haemorrhage
• vomiting
• diarrhoea
• dehydration
• evaporation during major operations

Effect:
1. **↓ Preload —> ↓ SV
2. ↓ CO, BP, LV filling pressure (usually after decompensation)
3. ↑ Systemic Vascular Resistance (from vasoconstriction), ↑ HR
—> **sympathetic compensatory response to ↓ BP
—> avoid analgesic / anaesthetics that ↓ sympathetic response!!!

Question 7

2. Cardiogenic shock

Answer 7

***Pump failure

↓ Blood flow due to intrinsic defect in cardiac function

• Muscles: HF
• Valves: Stenotic, Incompetent

Effect:

1. ↓ Contractility —> ↓ SV
2. ***↑ LV filling pressure (backward failure) —> with / without Pulmonary edema
3. ↑ SVR, ↑ HR —> sympathetic compensatory response to ↓ BP

—> ↑ SVR can be detrimental ∵ ↑ afterload make heart work even harder
—> ↑ HR can ↓ perfusion time of myocardium during diastole

Question 8

3. Distributive shock

Answer 8

***Normal Heart, Normal Blood volume

Peripheral vascular dilation —> ↓ SVR —> ***Apparent hypovolaemia

• sepsis
• anaphylaxis
• adrenal insufficiency
• neurogenic (SNS damaged in spinal cord esp. neck)

Effect:
1. ↑ CO but perfusion of vital organs (e.g. brain, kidney) is compromised ∵ ↓ BP
—> body loses ability to ***distribute blood properly

2. Low to Normal LV filling pressure
3. Warm peripheries (later become cold), Bounding pulses (↑ SBP ∵ ↑ CO + ↓ DBP ∵ vasodilation)
   —> Low BP

Question 9

4. Obstructive shock

Answer 9

Mechanical obstruction to ***cardiac filling

Consider ***Cardiac tamponade

• ***JVP / CVP high
• BP low
• ***Pulsus paradoxus

Other causes:

• Tension pneumothorax
• Massive pulmonary embolus

Question 10

***Treatment of Shock

Answer 10

1. Identify cause
2. Treat appropriately
3. Restore oxygen delivery
4. Basic life support

Hypovolaemic:

• ***IV fluid / blood
• Vasopressors (only short term effect) —> will still eventually decompensate —> cardiac arrest

Cardiogenic:
- **Vasodilators / **Inotropes (more short term) —> ↓ backward failure —> ↓ Stretch of heart (Starling curve)

Sepsis:

• IV fluid + ***Vasopressors (Adrenaline: direct antagonist of histamine)
• Eradication of infective focus, Give antiobiotics

Question 11

Basic life support

Answer 11

1. Recognition of Cardiac arrest
   - **unconscious
   - **absent / abnormal breathing
   - healthcare provider can check for pulse for ***<10s, no pulse —> assume cardiac arrest
2. Shout for help
3. AED
   - ∵ most cardiac arrest related to ***VF (definitive treatment: AED)
4. CPR
   - 30 compressions + 2 breaths
   - 2 finger breadths above Xiphisternum
   - open up airway: ***Head tilt, Chin lift, Jaw thrust
   - use AED as soon as available
5. Drug therapy
   - IV / IO access
   - **Epinephrine 1mg every 3-5 mins
   - **Amiodarone / ***Lidocaine for refractory VF / pVT
6. Consider advanced airway
   - Quantitative waveform capnography —> measure CO2 concentration in expired gas

Question 12

Recognition of Cardiac arrest

Answer 12

Diagnosis: Clinical

1. ***Loss of consciousness
2. Absent major pulse
   - assume cardiac arrest if patient suddenly **collapse / unresponsive + **breathing abnormally
   - do not take >=10s to check for pulse —> start chest compressions immediately

Question 13

Opening airway

Answer 13

1. Head tilt
2. Chin lift
3. Jaw thrust

Beware suspected cervical spine injury

Question 14

Breathing / Not breathing

Answer 14

If breathing:

1. Recovery position
   - allow patient to breathe more easily
   - regurgitate gastric content less likely to obstruct airway
2. Call for help

If NOT breathing:
Start chest compression
- Press down sternum 5-6 cm, release fully
- ***100-120 / min
- compression and release should take equal amount of time
- compression only CPR: continuously give compressions —> stop ONLY if patient shows signs of regaining consciousness AND breathe normally

Question 15

Expired air ventilation

Answer 15

• Occlude patient’s nose
• Maintain chin lift
• Normal full deep breath
• Ensure good mouth to mouth seal
• ***Compression : Ventilation = 30:2
• Blow steadily (1s) until ***visible chest rise + watch chest rise
• Allow chest to fall

Substitute:

• Laerdal mask
• Laryngeal mask
• Self-inflating bag

Question 16

Post-cardiac arrest care

Answer 16

1. Optimise **Cardiopulmonary function + **Vital organ perfusion after ROSC (Return of Spontaneous Circulation)
2. Transport to appropriate hospital / ICU / CCU
3. Identify + Treat ACS / other reversible causes
4. Control temperature (***hypothermia) to optimise neurologic recovery
5. Anticipate, treat, prevent ***multiple organ dysfunction

Question 17

Case 1: motorcyclist hit lamppost

• unconscious (GCS 7/15)
• weak, rapid pulse
• stridor (supraglottic obstruction, occur on inspiration)

(Wheeze: Infraglottic obstruction, occur on expiration)

Answer 17

1. Airway
   - neck stabilisation + intubate
2. Breathing
   - ventilate (ambu bag, high conc. O2)
3. Circulation
   - 14G IV cannula x2 (L arm + L saphenous vein)
   - draw 10 ml blood for cross-match

Reassess:

• BP 60/40
• Pulse 150
• GCS 7
• R femoral fracture
• Pelvic fracture
• R chest injury

Why still hypotensive + tachycardic?
- Cardiogenic problem?
- Preload problem?
—> Likely to be Hypovolaemia

Treatment:
- IV colloid solution

• 1000 ml (fluid warmer) immediately
  —> ***leg raise alternative quick way to assess volume
  —> after leg raise BP↑ and HR↓ —> indicative of Hypovolaemia
• Assess + Repeat

Initial improvement then deterioration

• ↓ SaO2
• ↑ Airway pressure
• ↓ Air entry R side

DDx:

• Further bleeding
• Tension pneumothorax
• Cardiac tamponade

CXR shows Tension pneumothorax (mediastinum pushed to other side)
—> Chest drainage

Question 18

Case 2: 69 male 48 hours after surgery for aortic aneurysectomy
- epidural local anaesthetic infusion —> good analgesia

Pre-op co-morbidities:

• stable angina
• hypertension: well controlled
• non-insulin dependent DM
• smoker: mild COPD

Presentation:

• pale
• sweaty
• conscious but slightly confused
• Pulse 130 but irregular
• BP 90/50 (low considering patient’s HT history)

Answer 18

1. Airway
   - clear
2. Breathing
   - slightly tachypnea, O2 therapy given (nasal)
3. Circulation
   - IV cannula inserted
4. Resuscitation trolley sent for

DDx:

1. Arrhythmia
   - ECG shows AF
   - secondary to MI? (peak time for post-op incidence) / Ischaemia?
2. Hypotension
   - could be secondary to arrhythmia / excessive sympathetic block from epidural (but usually not tachycardic) / surgical bleeding
3. LA toxicity
   - causes bradyarrhythmia

CXR —> shows pulmonary edema, ↑ CTR —> HF
—> Can conclude Cardiogenic shock / Pump failure

Pathophysiology of Cardiogenic shock from AF:
- Loss of atrial contraction
—> ↓ LV filling

- Fast HR in presence of ischaemic heart disease
—> myocardial supply demand imbalance
—> exacerbation of ischaemia
—> ↓ myocardial contractility
—> ↑ LV pressure
—> ↑ lung pressure
—> pulmonary edema

Treatment:

1. Cardioversion (if unstable haemodynamics)
2. Antiarrhythmic drugs (if stable) —> Amiodarone
3. May require inotropic support
   * **Excessive IV fluids will exacerbate the condition!!!