chapter 9 - defibrillation

Question 1

what is the mechanism of defibrillation?

Answer 1

passage of an electrical current of sufficient magnitude across the myocardium to depolarise a critical mass of cardiac muscle simultaneously, enabling the natural pacemaker tissue to resume control.

Question 2

what are the three features of a defibrillator?

Answer 2

a power source capable of providing dc
a capacitor that can be charged to a pre-determined energy level
two electrodes which are placed on the patients chest, either side of the heart, across which the capacitor is discharged

Question 3

what influences the delivered current?

Answer 3

transthoracic impedence i.e. the electrical resistance

Question 4

how do biphasic defibrillators overcome transthoracic impedance?

Answer 4

they measure the transthoracic impedance, and adjust the energy delivered to compensate

Question 5

what two factors can effect how well the defibrillator pads are applied?

Answer 5

hair

trans patches already present

Question 6

what are the optimal positions for the defibrillator pads in VF/VT?

Answer 6

one electrode to the right of the upper sternum below the clavicle
apical electrode at the apex of the heart (left mid axillary line, at level v6)

Question 7

where should defibrillator pads be placed if a patient has an ICD?

Answer 7

10-15cm away from the ICD

Question 8

at which distance should O2 be taken away from the patient whilst delivery a shock?

Answer 8

1m

Question 9

which energy range should the first shock be?

Answer 9

120-150J

Question 10

what is synchronised cardioversion?

Answer 10

where the shock given is synchronised to the R wave of the ECG, given in atrial or ventricular tachyarythmias