AMP 18: Defibrillation

Question 1

Name 8 reported extra-cardiac causes for Vfib in dogs and cats

Answer 1

• shock
• hypoxemia
• electrolyte disorders
• acid-base disorders
• electrical shock
• excessive sympathetic tone
• hypothermia
• drug reactions

Question 2

List factors within or outside of the clinicians control that affect impedance to current during defibrillation

Answer 2

Within clinician’s control:
* paddle size
* quality of contact between tissue and paddles
* amount of air inchest (give shock and end-exhalation!)
Outside of clinician’s control:
* absolute amount of air and tissue in the chest
* chest width

Question 3

Do defibrillators use a direct (DC) or alternating current (AC(?

Answer 3

• direct current

Question 4

List safety precautions that should be taken to prevent accidental shocking of personnel during defibrillation

Answer 4

• patient should be on a nonconducting surface (E.g., rubber mat)
• no one is touching the patient
• contact gel should not extend beyond the surface of the pad
• warning shout “clear” with sufficient time for personnel to step away
• operator must visually verify that everyone is clear before giving shock

Question 5

What are risk factors for accidental patient burning during defibrillation

Answer 5

• poor contact –> arcing of electrical current
• isopropyl alcohol used

Question 6

How commonly does a shockable rhythm occur in in-hospital CPA in dogs and cats?

Answer 6

28% in dogs, 16% in cats (Kass, Haskins, Survival following CPR in dogs and cats, 1992 JVECC)

Question 7

Fill the gaps:

Survival rates decrease by ——- for each minute the ventricles fibrillate and thus survival approaches zero after —— min of ventricular fibrillation

Answer 7

Survival rates decrease by 7-10% for each minute the ventricles fibrillate and thus survival approaches zero after 10-12 min of ventricular fibrillation

Question 8

List the steps of External defibrillation

Answer 8

Question 8

What is “fine ventricular fibrillation”?

Answer 8

form of ventricular fibrillation where the undulations of the baseline are so small that it appears similar to asystole on the ECG

Question 9

List the steps of internal defibrillation

Answer 9

Question 10

When attempting cardioversion of VT or SVT, at what phase of the cardiac cycle should the shock occur?

Answer 10

R or S wave

Question 11

At what phase during the cardiac cycle could attempted cardioversion cause ventricular fibrillation?

Answer 11

during the repolarization process, i.e., during the T wave

Question 12

When attempting cardioversion of SVT or VT, what energy setting should be used?

Answer 12

for VT half of the energy setting used for defibrillation (i.e., 1-2 J/kg)
for SVT less energy is usually required for successful cardioversion (0.5-1 J/kg)

Question 13

At what energy dose has defibrillation shown to injury dogs or be lethal in dogs

Answer 13

• injury starts as low as 10 J/kg (median dose required for injury 30 J/kg)
• median lethal dose 470 J/kg

Data from experiments using monophasic defibrillators march 19 9.50am

Question 14

What energy dose should be used for internal defibrillation in veterinary patients?

Answer 14

10% of the external dose - about 0.2 -0.5J/kg

Question 15

List drugs that have been shown to increase the defibrillation threshold (i.e., lead to requirement of higher dose for successful defibrillation)

Answer 15

• amiodarone
• lidocaine
• mexiletine

Sotalol and beta-blockers decrease the threshold

less important in biphasic defibrillators though