1. Human impedance variability and defibrillator test protocol
January 29-February 1, 2003
Human impedance variability and defibrillator test protocol
Why 50 Ω loads are not enough to test modern defibrillators

2. Defibrillators: life saving
January 29-February 1, 2003
Defibrillators: life saving
Convert certain heart arrhythmias to normal
Convert v-fib back to normal
Have to work first time, every time.
Batteries may not be fully charged or faulty
Charging circuits may be faulty, may not deliver enough energy
Must deliver proper energy to account for differing patient sizes/impedances
Hospitals are required to determine their own testing protocol and frequencies based on manufacture recommendations and prior equipment testing and failue history.
Other reasons to test include:
FDA/Ministries of Health guidelines
International and National standards
Manufacturers specifications
Joint Commission oversight of a hospital’s own medical device manufacturing plan

3. Current vs. energy Current—not energy—defibrillates.
January 29-February 1, 2003
Current vs. energy
Current—not energy—defibrillates.
Successful defibrillation requires enough current be delivered to the heart muscle during the shock.
Must transit through the chest/thorax and the impedance it represents.
Body mass, skin resistance, tissue type and amount all play a part in the chest/thorax impedance presented to the charge delivered by the defibrillator.

4. Transthoracic impedance
January 29-February 1, 2003
Transthoracic impedance
Transthoracic impedance = the body’s resistance to current flow
Human impedance variability has been shown to vary from 25 ohms to 180 ohms1
Energy in respect to impedance is the determining factor to successful defibrillation—not energy alone.
Impedance is the natural dynamic resistance to defibrillation or other inductive electrical occurances applied to the body by an outside appliance or force.
Some people have naturally higher impedance than others.
You can’t tell if someone has high impedance simply by looking at him or her.

5. Transthoracic impedance (cont.)
January 29-February 1, 2003
Transthoracic impedance (cont.)
Just a few known causes of differing impedances in human beings include:
Body mass
Age
Disease
Skin resistance
Tissue type and amount

6. Transthoracic impedance (cont.)
January 29-February 1, 2003
Transthoracic impedance (cont.)
Successful defibrillation requires sufficient current to the heart muscle.
Defibrillation current is affected by transthoracic impedance
Modern (biphasic) defibrillators measure impedance and adjust energy delivery accordingly
“Humans exhibit a wide range of transthoracic impedance, and defibrillators compensate for this range of impedance in different ways.”
-- McDaniel, Garret, Burke and Arzbaecher2

7. Schematic and formula EH = I2 x RH x Time (Watt Seconds or Joules)
January 29-February 1, 2003
Schematic and formula
Current decreases as thoracic impedance (resistance) increases
EH = I2 x RH x Time
(Watt Seconds or Joules)
Defibrillator

8. How defibrillators account for human impedance variability
January 29-February 1, 2003
How defibrillators account for human impedance variability
Monophasic (older) defibrillators
Current flows only one direction  impedance not measured

9. How defibrillators account for human impedance variability (cont.)
January 29-February 1, 2003
How defibrillators account for human impedance variability (cont.)
Biphasic (modern) defibrillators
Current flows first in one direction, then reverses and flows in opposite direction.
Impedance measured and energy delivery is adjusted internally based on energy setting or (for AEDs) arryhthmia.
Smart defibrillators not only deliver the specified power selected by the user but also determine the patient’s specific input impedance and delivers the specified power based on each individual patient’s impedance.
Lowe energy is used in biphasic waveforms.

10. Biphasic waveforms Q: Are all biphasic waveforms alike?
January 29-February 1, 2003
Biphasic waveforms
Q: Are all biphasic waveforms alike?
A: No. There are different biphasic waveforms based on different manufacturer’s specifications.
Rectilinear Biphasic (ZOLL)
Smart Biphasic
(Philips)
Different waveforms perform differently, depending on their shape, duration, voltage, current, and response to impedance.
Different biphasic waveforms are designed to work at different energies.
Pulsed Biphasic
(Schiller)

11. Clinical impedance examples
January 29-February 1, 2003
Clinical impedance examples
Low impedance (50 Ω)
A 360-joule biphasic defibrillator delivers more current than required, exposing patient to potentially harmful high-peak currents
Average impedance (75 Ω)
A 360-joule biphasic defibrillator and a 200-joule rectilinear defibrillator may be equally effective
High impedance (> 100 Ω)
A 200-joule rectilinear shock delivers a higher average current than a 360-joule biphasic defibrillator shock, therefore making it more effective at lower energy levels.

12. Impedance and defibrillation outcomes
January 29-February 1, 2003
Impedance and defibrillation outcomes
Too little or too much is no good
Too much peak current during shock can injure the heart
It’s the peak current (not energy) that can injure the heart
 It is imperative the current delivered to the heart is matched to the individual impedance of each patient and not just the delivered energy.
The incorporation of varying human impedances is important with respect to patient safety and the successful outcome of each defibrillation attempt.

13. Load testing: accounting for impedance variability
January 29-February 1, 2003
Load testing: accounting for impedance variability
Q: Are 50 Ω test loads enough to ensure output conditions of modern-day defibrillators?
Do all of your hospital’s patients have the same input impedance? No!
A: Testing beyond the 50 Ω load is necessary to ensure defibrillator inventory performance of modern defibrillators
Based on varying patient input impedance and manufacture delivered power characteristics it is important to know how your defibrillator inventory is performing based on current defibrillator protocol.
Only by testing with more than just a 50 Ω load can you know how your fleet is truly performing.

14. Load testing: accounting for impedance variability (cont.)
January 29-February 1, 2003
Load testing: accounting for impedance variability (cont.)
Q: What loads are recommended?
A: Section of the IEC standard3 and AAMI DF80 standards4 require defibrillators to be tested on different resistance loads of 25, 50, 75, 100, 125, 150 and 175 ohms to ensure proper current is delivered to patients with different impedances.

15. When to test with other loads
January 29-February 1, 2003
When to test with other loads
Each hospital’s equipment history should be considered.
Standard protocol recommends multiple impedance tested on incoming inspection and after a repair to charging circuit or applied parts.
May also be helpful when troubleshooting “failed to deliver energy” complaints.

16. January 29-February 1, 2003
The 7010 solution
Designed to facilitate load testing for modern defibrillator technology quality assurance and standards compliance
Selectable loads
25 Ω
50 Ω
75 Ω
100 Ω
125 Ω
150 Ω
175 Ω
200 Ω
The only device available today capable of testing beyond 175 ohms for extreme impedance conditions.
Impulse 7010 Selectable Load Accessory

17. January 29-February 1, 2003
References
American Heart Association. Guidelines 2000 for Cardiopulmonary Resuscitation and Emergency Care. Circulation Supplement. 2000; 102:8
McDaniel W.C., Garrett, M, Burke M.C., Arzbaecher R, Comparison of the Efficacy of Two Biphasic Waveform Defibrillators in a Model of Simulated Higher Impedance Patients, Engineering in Medicine and Biology Soceity, Proceedings of the 25th Annual International Conference of the IEEE. Volume I, issue 17-21, Sept Page(s) Vol. I
IEC Medical Electrical Equipment Part 2-4: Particular Requirements for the Safety of Cardiac Defibrillators, Section 6.8.3
ANSI/AAMI DF80:2003 Medical electrical equipment—Part 2-4: Particular Requirements for the Safety of Cardiac Defibrillators (Including Automated External Defibrillators)

18. References (cont.) Want to know more? Check these out:
January 29-February 1, 2003
References (cont.)
Want to know more? Check these out:
Mittal S, Ayati S, Stein KM, Knight BP, Morady F, Schwartzman D, et al. Comparison of a novel rectilinear biphasic waveform with a damped sine wave monophasic waveform for transthoracic ventricular defibrillation. ZOLL Investigators. J Am Coll Cardiol 1999; 34:
Schneider T, Martens PR, Paschen H, Kuisma M, Wolcke B, Gliner BE, et al. Multicenter, randomized, controlled trial of 150-J biphasic shocks compared with 200- to 360-J monophasic shocks in the resuscitation of out-of-hospital cardiac arrest victims. Optimized Response to Cardiac Arrest (ORCA) Investigators. Circulation 2000; 102:
Mittal S, Ayati S, Stein KM, Schwartzman D, Cavlovich D, Tchou PJ, et al. Transthoracic cardioversion of atrial fibrillation: comparison of rectilinear biphasic versus damped sine wave monophasic shocks. Circulation 2000; 101:
Walker RG, Melnick SB, Chapman FW, Walcott GP, Schmitt PW, Ideker RE. Comparison of six clinically used external defibrillators in swine. Resuscitation 2003; 57:
Niemann JT, Walker RG, Rosborough JP. Ischemically Induced Ventricular Fibrillation (VF): A Comparison of Fixed and Escalating Energy Defibrillation. Acad Emerg Med 2003; 10: 454.

19. January 29-February 1, 2003
Questions?
For more information on the Impulse 7010 solution for variable impedance testing, contact Fluke Biomedical today.
Fluke Biomedical
Toll free: (800)
Direct: (440)
Fax: (440)
How can you as a biomed best determine the proper output characteristics of your defibrillator inventory? Is a one-size fits all patient impedance good enough or should you be considering all of your patients?