This Week’s EMCQs – Week 4

QUESTION 1

There are two types of Defibrillators available in most of the Emergency Departments in Australasia – Monophasic Defibrillator and/or Biphasic Defibrillator.

Which one of the following statements is TRUE regarding defibrillators?

A: Monophasic Defibrillators are more effective than Biphasic Defibrillator.

B: Monophasic defibrillator has a lessor risk of damaging the heart muscle

C: ARC guideline recommends no more than 200 Joules for Biphasic Defibrillator.

D: ARC guideline recommends 360 Joules for Monophasic Defibrillator

A: Monophasic Defibrillators are more effective than Biphasic Defibrillator.

B: Monophasic defibrillator has a lessor risk of damaging the heart muscle

C: ARC guideline recommends no more than 200 Joules for Biphasic Defibrillator.

D: ARC guideline recommends 360 Joules for Monophasic Defibrillator (Correct answer)

Commentary

What is the difference between Monophasic and Biphasic Defibrillator?

Availability

Monophasic Defibrillator: Monophasic defibrillators are less popular in the current context.

Biphasic Defibrillator: Biphasic defibrillation is more common nowadays and used for implantable as well as external defibrillators.

Adjustment for Patient Impedance

Monophasic Defibrillator: Monophasic defibrillator is not able to adjust the current according to the resistance exerted by the patient’s body.

Biphasic Defibrillator: Biphasic defibrillators are capable of changing the current as per the patient’s impedance hence known to be more effective. Different manufacturers have used this functionality to produce different types of biphasic defibrillators.

Strength of the Current

Monophasic Defibrillator: Monophasic defibrillator uses a fixed current to deliver 360J energy to terminate cardiac arrhythmias.

Biphasic Defibrillator: In contrast, biphasic defibrillators can manually or automatically adjust the strength of the current, and it uses lesser strength than monophasic defibrillators.

Overall Effectively

Monophasic Defibrillator: Monophasic defibrillators are less efficient.

Biphasic Defibrillator: In contrast, biphasic defibrillators are more efficient.

Risk of Damaging Heart Muscles

Monophasic Defibrillator: Monophasic defibrillator has a greater risk of damaging the heart muscle as it delivers a greater current.

Biphasic Defibrillator: Biphasic defibrillator uses a smaller current and hence the damage is minimized.

The Australian and New Zealand Committee on Resuscitation (ANZCOR) make the following recommendations:

  1. A defibrillation shock is delivered as soon as a defibrillator is available.
  1. Paddles or pads are placed on the exposed chest in an anterior-lateral position or an anterior-posterior position.
  1. In patients with an ICD or a permanent pacemaker the defibrillator pad/paddle is placed on the chest wall ideally at least 8 cm from the generator position.
  1. Self-adhesive defibrillation pads are used for defibrillation.
  1. Biphasic waveforms are used for defibrillation.
  1. For Monophasic waveforms: the initial energy level for adults is set at maximum (usually 360 Joules) for all shocks.
  1. For Biphasic waveforms: the default energy level for adults is set at 200J for all shocks. Other energy levels may be used providing there is relevant clinical data for a specific defibrillator that suggests that an alternative energy level provides adequate shock success (e.g. Usually greater than 90%).
  1. If the first shock is not successful and the defibrillator is capable of delivering shocks of higher energy, it is reasonable to increase the energy to the maximum available for subsequent shocks.
  1. A single shock strategy is used in patients in cardiac arrest requiring defibrillation for VF or pulseless VT.
  1. The use of AEDs to facilitate early defibrillation in hospitals is reasonable, but services that introduce AEDs must be aware of the possible adverse impact of interruptions to CPR, especially in non-shockable rhythms.

QUESTION 2

A 23-year-old girl had flu like symptoms for few days while visiting north of Queensland. She participated in diving activity during her visit to the Great Barrier Reef. She developed tinnitus after she completed that activity.

During her return flight to her home town, she experiences sudden onset of worsening tinnitus, vertigo, nausea and vomiting with loss of hearing in her left ear.

Which one of the following is the most likely diagnosis?

A: BPPV

B: Flight related infection

C: Dysbarism

D: Decompression illness

A: BPPV

B: Flight related infection

C: Dysbarism (Correct answer)

D: Decompression illness

Commentary

This lady most likely has suffered from Inner Ear barotrauma that worsened during her flights.

Dysbarism has different type of presentation that include:

  • Middle ear barotrauma
  • Inner ear barotrauma
  • External ear barotrauma
  • Sinus barotrauma

Reference: Textbook of adult emergency medicine, Cameron P et al, 4th edition. Page 923.