Chapter 9: Defibrillation

Question 1

How quickly after onset of VF or pulseless VT does cerebral hypoxic injury begin?

Answer 1

Within 3 minutes

Question 2

In absence of bystander CPR, how much does mortality rate increase for every minute between collapse and attempted defibrillation?

Answer 2

7-10%

Question 3

Do short interruptions in chest compressions (to assess rhythm and give rescue breaths) impact success of defibrillation?

Answer 3

1. Yes!
2. Associated with myocardial dysfunction
3. Reduced survival
4. Pre-shock pause should also be minimised

Question 4

When bystander CPR is given, how much does mortality rate increase for every minute between collapse and attempted defibrillation?

Answer 4

3-4%

Question 5

What features do defibrillators have in common?

Answer 5

1. Power source capable of providing DC
2. Capacitor that can be charged to pre-determined level
3. 2 electrodes placed on patients chest

Question 6

How is successful defibrillation defined?

Answer 6

1. Absence of VF/pVT 5s after shock delivery
2. Ultimate goal is ROSC

Question 7

What factors impact defibrillation success?

Answer 7

1. Transthoracic impedance:
   - good contact with pads
   - clean and dry area
   - shave off hair
2. Electrode position - best to be over area in fibrillation

Question 8

What other electrode positions are acceptable for defibrillation?

Answer 8

1. Antero-posterior - left precordium and inf. to left scapula
2. Postero-lateral - mid axillary line and inf. to right scapula
3. Bi-axillary:
   Patients with implantable pacemakers/defib’s - must place 10-15cm away from these

Question 9

What should you do first CPR or defibrillation?

Answer 9

1. If unwitnessed -Begin CPR immediately while defib is being set up

Once defibrillator on, dont delay, attempt ASAP

Question 10

What should you do if a cardiac arrest is witnessed (and VF/pVT)?

Answer 10

1. Confirm rhythm
2. Give 3 successive shocks
3. Check for rhythm, pulse and signs of ROSC

Question 11

What shock energy should be used?

Answer 11

First at minimum of 150J

Based on manufacturers guidance - if don’t know then maximum shock energy for all

Generally 200J

Question 12

What safety checks are key when defibrillating?

Answer 12

1. Ensure no-one is touching the body
2. Wipe water away from patient chest before
3. Don’t hold IV infusion equipment or patients trolley during delivery
4. Oxygen safety

Question 13

How should oxygen be used safely during defibrillation?

Answer 13

1. Take off any mask or nasal cannula and place >1m away
2. Can leave ventilation bag connected to tracheal tube or supraglottic airway
3. If pt on ventilator - leave ventilator tubing unless preventing CPR > ventilation bag and switch off ventilator

Patients in critical care unit may be dependent of PEEP so try leave connected to ventilator

Question 14

How is defibrillation modified in children?

Answer 14

1. >8 yo - same as adult
2. 1-8 yo - special paediatric electrodes or can use adult but ensure don’t overlap
3. < 1 can use AED if no other option

Question 15

What is the shock synchronised with in synchronised cardioversion?

Answer 15

1. R wave
2. This avoids relative refractory period
3. Minimises risk of inducing VF

VF/pVT don’t require this

Question 16

If synchronised cardioversion fails, what should you do?

Answer 16

1. Choose a different lead
2. Adjust amplitude

Question 17

Can implantable ICD’s give a shock?

Answer 17

1. Yes
2. At 40 or 80J
3. No warning
4. Number of shocks depends on the device

Can deactivate defibrillation capability by placing ring magnet over ICD - doesn’t disable pacemaker

Question 18

Should you defibrillate a patient if they have an ICD?

Answer 18

1. Yes
2. If the ICD has not delivered a shock or if it has failed to terminate the arrhythmia

Question 19

What is the maximum energy needed for internal defibrillators?

Answer 19

1. 50J
2. Typically deliver between 10-20J