Cardiac Arrest: Reversible Causes

Question 1

What are the 8 reversible causes of cardiac arrest?

(4Hs and 4Ts)

Answer 1

H - Hypoxia
H - Hypothermia/hyperthermia
H - Hypovolaemia
H - Hypokalaemia/hyperkalaemia

T - cardiac Tamponade
T- Toxins
T - Thrombosis
T - Tension pneumothorax

Question 2

What is the most common non-cardiac cause of arrest?

Answer 2

Sustained hypoxia

Question 3

Causes of hypoxia?

Answer 3

• Airway obstruction (e.g. choking, soft tissue obstruction resulting from a reduced level of consciousness)
• Asthma
• Drowning
• Hanging
• Asphyxia

Question 4

Relevant investigations in the context of hypoxia?

Answer 4

1) Bedside: O2 sats, capnography, RR

2) ABG

Question 5

What are the management priorities for correcting hypoxia during resuscitation?

Answer 5

1) Assess the airway for causes of obstruction such as angioedema, vomit or foreign body

2) Initiate basic airway management to clear any obstructions and optimise oxygenation

3) Auscultate to check for breath sounds and air entry when ventilating, and listen for stridor which may indicate airway obstruction

4) Aim for a normal ventilation rate with the highest feasible oxygen concentration

Question 6

How can hypovolaemia cause cardiac arrest?

Answer 6

Blood volume, reduced by fluid loss causes a reduction in pressure and cardiac output until cardiac arrest occurs.

Question 7

What are some causes of hypovolaemia?

Answer 7

1) External blood loss (e.g. traumatic injuries, haematemesis)

2) Internal blood loss (e.g. ruptured aortic aneurysm, gastrointestinal bleeding)

3) Other causes of fluid loss (e.g. diarrhoea & vomiting, dehydration, renal disease)

Question 8

Relevant investigations in the context of hypovolaemia?

Answer 8

1) Hb/haematocrit: may be low

2) ABG

3) Focused Assessment with Sonography in Trauma (FAST): bedside ultrasound can be used to identify any internal bleeding

4) BP etc

Question 9

What are the management priorities for correcting hypovolemia during resuscitation?

Answer 9

1) A full secondary survey will identify any external bleeding and some internal causes (e.g. distended abdomen)

2) Catastrophic haemorrhage control (e.g. tourniquets, pelvic binders)

3) Blood transfusion

4) Fluid resuscitation

5) Oxygen therapy

Question 10

Define hypothermia

Answer 10

A core temp <35 degrees celsius:

• Mild: 32-35
• Mod: 30-32
• Severe: <30

Question 11

What is a potential cause of hypothermia?

Answer 11

Drowning

Question 12

Hypothermia affects which two main patient groups?

Answer 12

1) Winter sports participants

2) Urban poor (e.g those experiencing homelessness, drug and alcohol addiction and poor socioeconomic conditions)

Question 13

What are the relevant investigations in the context of hypothermia?

Answer 13

1) Core temp

2) ABG

3) FBC: may cause haematocrit to rise, thrombocytopenia

4) U&Es: hyperkalaemia (ndicative of cell necrosis)

5) Glucose: hypoglycaemia

6) Calcium

7) Magnesium

8) Coagulation profile: blood viscosity is reduced in hypothermia

Question 14

How can core temp be measured?

Answer 14

a) a tympanic in spontaneously breathing patients

b) oesophageal in patients with ET or supraglottic devices in situ.

Question 15

What is important to note about ABG results in hypothermia?

Answer 15

When interpreting a blood gas from a hypothermic patient, take into account that blood gas machines rewarm samples to 37°C.

These values can be corrected mathematically but are difficult to interpret. Therefore use uncorrected values to guide practice.

Question 16

What are the management priorities for correcting hypothermia during resuscitation?

Answer 16

1) Chest compression and ventilation rate should remain as per normothermic guidelines (120bpm and 12 ventilations per minute)

2) Aim for a normal CO2 on ABG (uncorrected)

3) If VF persists after 3 shocks, delay further shocks until the core temperature is >30°C

4) Reduced metabolism means drugs should be withheld if the core temperature is <30°C. Timing intervals should be doubled if the core temperature is 30-34°C (e.g. 6-10 minutes for adrenaline).

5) Rewarming should be performed with extracorporeal life support (ECLS) preferably with extracorporeal membrane oxygenation (ECMO) over cardiopulmonary bypass (CRB).

Question 17

Give some causes of hyperkalaemia

Answer 17

• Renal impairment
• Medications (e.g. ACE-inhibitors)
• Diabetic ketoacidosis
• Trauma
• Burns

Question 18

What are the management priorities for correcting hypo/hyperkalaemia during resuscitation?

Answer 18

1) 10ml calcium chloride 10% IV by rapid bolus injection

2) Give 10 units soluble insulin and 25g glucose IV by rapid injection to shift potassium into cells.

3) Monitor blood glucose: administer 10% glucose infusion guided by blood glucose to avoid hypoglycaemia.

4) Shift potassium into cells: give 50 mmol sodium bicarbonate (50 mL 8.4% solution) IV by rapid injection.

5) Consider dialysis for refractory hyperkalemia cardiac arrest to remove potassium from the body.

Question 19

What are some causes of a tension pneumothorax?

Answer 19

Traumatic: penetrating injuries to the chest (e.g. gunshot or stab wound), rib fractures

Medical: mechanical ventilation, asthma

Question 20

1st line investigation in tension pneumothorax?

Answer 20

CXR

Question 21

What are the management priorities for correcting tension pneumothorax during resuscitation?

Answer 21

1) Needle decompression: insert a large-bore cannula (e.g. orange 14G or grey 16G) into the 2nd intercostal space (above the 3rd rib), along the mid-clavicular line.

2) Subsequent decompressions should be placed laterally to the initial one – but a chest drain should be prioritised if the equipment is readily available.

3) Thoracostomy should be completed as soon as equipment and qualified staff are available, followed by a chest drain insertion to either 4th or 5th intercostal space at the anterior axillary line (with CXR to confirm correct placement and reinflation of the lung)

Question 22

What is cardiac tamponade?

Answer 22

Results from the presence of blood or fluid in the pericardial space (the sac around the heart). This limits the filling of the ventricles, reducing stroke volume and cardiac output, and causing cardiac arrest.

Question 23

Causes of cardiac tamponade?

Answer 23

1) Trauma to the chest/heart (e.g. penetrating injuries)

2) Ventricular wall rupture following a myocardial infarction

3) Metabolic causes (e.g. chronic kidney disease leading to an accumulation of toxins and fluid)

4) Infection of the pericardium (pericarditis)

Question 24

What are the relevant investigations in the context of cardiac tamponade?

Answer 24

1) Echo

2) ECG

3) CXR

4) CT imaging

Question 25

What are the 2 management options for correcting cardiac tamponade during resuscitation?

Answer 25

1) Pericardiocentesis

2) Resuscitative thoracotomy

Question 26

Give some causes of cardiac arrest as a result of toxins?

Answer 26

1) Medication overdose: e.g. tricyclic antidepressants, beta blockers and opioids

2) Illicit drug use (e.g. opiates or cocaine) can result in long QT and pulseless arrest

Question 27

Relevant investigations in the context of toxins?

Answer 27

1) U&Es

2) Core temp: drug overdose can result in hypo/hyperthermia

3) Assess pupils (e.g. upillary constriction in opioid overdose)

4) Collateral history

Question 28

How can thrombosis cause cardiac arrest?

Answer 28

A thrombus is a blood clot which can become dislodged and obstructs blood vessels (typically PE or (MI).