Operating instructions

LIFEPAK 500 Automated External Defibrillator Operating Instructions A-1
©1996–2003 Medtronic Physio-Control Corp.
Shock Advisory System
Appendixes
OVERVIEW OF THE SHOCK ADVISORY SYSTEM
The Shock Advisory System (SAS) is an ECG analysis system built into the LIFEPAK 500 AED that
advises the operator if it detects a shockable or nonshockable rhythm. This system makes it possible
for individuals not trained to interpret ECG rhythms to provide potentially-lifesaving therapy to victims of
ventricular fibrillation or pulseless ventricular tachycardia. The Shock Advisory System contains the
following features:
• Electrode contact determination
• Automated interpretation of the ECG
• Operator control of shock therapy
• Continuous Patient Surveillance System
• Motion detection
Electrode Contact Determination
The patient's transthoracic impedance is measured through the defibrillation electrodes. If the baseline
impedance is higher than a maximum limit, it is determined that the electrodes are not in sufficient
contact with the patient or not properly connected to the AED. ECG analysis and shock delivery are
inhibited. The operator is advised to connect electrodes any time electrode contact is inadequate. If you
continue to get a
CONNECT ELECTRODES message, remove electrodes and make sure skin is clean and
dry. Shave excessive hair and apply a new set of electrodes.
Automated Interpretation of the ECG
The Shock Advisory System is designed to recommend a shock if it detects the following:
• Ventricular fibrillation — with a peak-to-peak amplitude of at least 0.08 mV
• Ventricular tachycardia — defined as having a heart rate of at least 120 beats per minute, QRS
width of at least 0.16 seconds, and no apparent P waves.
Pacemaker pulses may prevent advisement of an appropriate shock, regardless of the patient’s
underlying rhythm. The Shock Advisory System is designed to recommend no shock for all other ECG
rhythms, including asystole, pulseless electrical activity, idioventricular rhythms, bradycardia,
supraventricular tachycardias, and normal sinus rhythms.
ECG analysis is performed on consecutive 2.7-second segments of ECG. The analysis of two out of
three consecutive segments must agree before a decision (
SHOCK ADVISED or NO SHOCK ADVISED) is
made.
The LIFEPAK 500 AED’s SAS performance for adult and pediatric ECGs is summarized in the following
tables.
Table A-1 LIFEPAK 500 AED SAS Performance Table for Adult ECGs
Rhythm Class
ECG Test
1
Sample Size
Performance Goal
2, 3
Observed Performance
Sensitivity or Specificity [LCL]
4
Shockable:
coarse VF
168 >90% sensitivity 100.0% [98.6%]
Shockable:
shockable VT
65 >75% sensitivity 84.6% [77.3%]
Nonshockable:
NSR
144 >99% specificity
for NSR (AHA)
100.0% [98.4%]
Nonshockable:
asystole
43 >95% specificity 100.0% [94.8%]
Nonshockable:
all other rhythms
531 >95% specificity 95.7% [94.3%]