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Workshop on EMS technology — Proceedings
SPECIAL CONTRIBUTION
Workshop on EMS Technology--- Proceedings George Podgorny, MD* -editor Mark B. Gausman, PE, BEEt -coeditor J. Steve Adler, BSEE, M B A t - coeditor Las Croabas, Puerto Rico March •976 Podgorny G, Gausman MB, Adler JS: Proceedings of workshop on EMS technology, Las Croabas, Puerto Rico, March 1976. JACEP 7:66-70, February 1978. emergency medical services, technology; cardiac defibrillation; monitoring; equipment and supplies; communications. INTRODUCTION An EMS technology workshop was sponsored by the American College of Emergency Physicians (ACEP) in conjunction with its Winter Symposium in Puerto Rico. The framework, organization support and agenda were developed jointly by ACEP, Physio-Control Corporation and Motorola Communications and Electronics, Incorporated. The workshop brought together physicians knowledgeable in EMS and technical representatives from the bioengineering discipline and industry. Specifically, the workshop was organized into four committees to discuss defibrillation, monitoring, communications and transportation.* The workshop produced some suggested guidelines and specifications for the functional and technical requirements of EMS equipment.
DEFIBRILLATION A defibrillator is an electrical device t h a t delivers to the heart the amount of electrical energy required for conversion of abnormal rhythm. Although there are many types of defibrillators, these discussions and recommendations were limited to portable and battery operated defibrillators. Physician control of equipment selection, its utilization, and training of its users is vital.
Paddle Type and Size Most manufacturers use stainless steel paddle electrodes because of their corrosion resistance, ease of maintenance and durability. The resistivity of the metal in the defibrillator paddle is relatively unimportant since the impedance is determined mostly by the gel and the intervening tissue. Corroded paddles or accumulated dry paste or gel on the paddles will decrease conductivity. All paddles should, therefore, be thoroughly cleansed after each use. 1) P a d d l e S u r f a c e : The surface of the paddle electrodes should be brushed, not polished. A brushed or roughened metal surface offers better electrodeelectrolyte surface contact enhancing conductivity. A minimum electrode surface area of 50 sq cm is recommended to minimize tissue damage and assure adequate contact area. *From the Section on Education ACEP, t Physio-Control Corporation, and $Motorola Communications and Electronics, Incorporated. Workshop held March 1976 in Las Croabas, Puerto Rico. Participants were: Transportation - - David Nelson, MD, Lewellyn Stringer, MD, David R. Boyd, MD, Garry Briese, Fred Hill and Don VanSiclaa; Communications - Terrence Carden, Jr., MD, John Farquhar, MD, J. Rybak, MD, and Steve Adler; Monitoring - - Patrick Lilja, MD, Robert
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J. Rathburn, MD, Marty Briter, RN, Greg Heib, PhD, Ed Heilman and Mark Gausman; Defibrillation - - Stan Zydlo, MD, Les Geddes, PhD, Karl G. Mangold, MD, John J. Cahill, MD and Stanley M. Seiffert. Address for reprints: Steve Adler, Distribution Manager, Advanced Systems, Motorola Communications and Electronics, Incorporated, 1303 East Algonquin Road, Schaumburg, Illinois 60196.
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2) P a d d l e Design: P a d d l e s should be designed to p r e v e n t a n y of the electrode surfaces from coming in contact with the operator. The operator should be able to e x e r t full pressure w i t h o u t b e n d i n g or breaki n g the paddle. The o u t p u t c i r c u i t should be charged from a control on the paddles. The paddles should each have a button for d e l i v e r i n g the defibrillation pulse. This will provide a margin of safety should a single button be a c c i d e n t a l l y pressed. The cable from the paddles to the defibrillator should be a t least five feet long when fully extended. 3) Paddle Electrolyte S o l u - , tion: M a n y of t h e d i f f e r e n t g e l s , pastes, c r e a m s a n d u l t r a s o n i c oils used between the p a t i e n t and defibr i l l a t o r paddles r e s u l t in u n n e c e s s a r y tissue damage and highly variable delivered energy levels.~, 2 Elect r o c a r d i o g r a p h y c r e a m g e n e r a l l y has a r e s i s t i v i t y of 300 to 400 ohm cm a n d is not recommended for use with defibrillators, a l t h o u g h some m a n u als state t h a t such compounds can be used for this purpose. ~ Only low resistivity electrolytes, such as saline soaked pads or low r e s i s t i v i t y gels, are desirable. The p a d d l e e l e c t r o d e s a n d t h e gel t o g e t h e r should not have more t h a n 5 ohms resistance. 3 Some gels a c t as a t e m p o r a r y DC block at the electrode gel interface and d e l a y recovery of monitoring. 4 The gel should allow recovery of m o n i t o r i n g w i t h i n five seconds. 5 4) Paddles Placement: A n i m a l studies have shown t h a t one of the electrodes placed over the apical a r e a is o p t i m a l for d e f i b r i l l a t i o n . 6 However, there exists no definite quant i t a t i v e d a t a on h u m a n s for placem e n t o f t h e s e c o n d p a d d l e . I t is suggested t h a t h i g h r i g h t a n t e r i o r l a t e r a l t h o r a x below the clavicle, left infra-scapular and r i g h t m i d - l a t e r a l thoracic p l a c e m e n t s have proven effective 7 (Figure). S t u d i e s to d e t e r m i n e p r o p e r paddle p l a c e m e n t for best i n t r a c a r diac c u r r e n t density are needed. One method of study would be to a l w a y s record paddle placement, patient weight, e n e r g y setting, prior medication, n u m b e r of a t t e m p t s , a n d results. Possibly, t h e c u r r e n t l y used m i d s t e r n a l and apical position is not best. When possible, the paddles should be spaced at l e a s t o n e - h a l f of the paddle d i a m e t e r apart. The elect r o l y t e gel s h o u l d n o t b r i d g e t h e space between the paddles. ~,3,s
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F i g . Suggested paddle placement for defibrillation. From Tacker. 7
Defibrillator Waveform Two g e n e r a l types of waveforms are now in use: d a m p e d s i n u s o i d a l (Edmark, Lown, Gurvich) and trapezoidal.6, 9-11 T h e r e a r e also v a r i a tions in m a x i m u m delivered energy. Most currently available damped sinusoidal waveform defibrillators deliver a m a x i m u m of 320 joules of energy into a 50 ohm resistor, while some t r a p e z o i d a l d e f i b r i l l a t o r s deliver 250 joules. The effectiveness of one d e f i b r i l l a t o r c o m p a r e d w i t h a n o t h e r should n o t be j u d g e d on the b a s i s o f w a v e f o r m or d e l i v e r e d energy alone since m a n y o t h e r factors are involved.6, ~-~3 The e n e r g y dose concept based on the p a t i e n t ' s w e i g h t m a y be useful in d e t e r m i n i n g the proper e n e r g y for defibrillation. However, a t the prese n t time the information conflicts as to w h a t t h e d o s a g e s h o u l d be. 14-17 Drugs, metabolic state, t e m p e r a t u r e , hypoxia, m y o c a r d i a l ischemia and infarction all m o d i f y t h e s t r e n g t h of c o u n t e r - s h o c k r e q u i r e d to defibrill a t e . 17 A l t h o u g h s o m e d r u g s a r e known to raise a n d others to lower the e n e r g y t h r e s h o l d required to defibrillate, the effects of drugs used in cardiac m a n a g e m e n t on the r e q u i r e d e n e r g y level are l a r g e l y u n q u a n t i rated. TM
Monitoring and Recording For EMS use, the portable batt e r y d e f i b r i l l a t o r s h o u l d also have m o n i t o r i n g capability.
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1) Oscilloscopic Display: Oscilloscopic d i s p l a y s are c u r r e n t l y available in so-called ~bouncing ball" and nonfade types. ~Bouncing ball" types of displays require closer observation and more frequent a d j u s t m e n t for int e n s i t y . H o w e v e r , t h e y m a y be lighter in w e i g h t and less expensive. Nonfade displays are e a s i e r to read in the v a r y i n g a m b i e n t light conditions e n c o u n t e r e d in E M S b u t are n o r m a l l y more expensive. It seems t h a t the nonfade d i s p l a y is becoming more common i n EMS. 2) Hard Copy Display: Most currently available battery-operated defibrillators w i t h a h a r d copy w r i t e r use the h e a t e d stylus. The t r a c i n g s provide good c o n t r a s t and detail. In the future, voltage-sensitive p a p e r recorders m a y become available w h i c h c a n r e d u c e p o w e r consumption and e l i m i n a t e the problems of s t y l u s b u r n o u t a n d b r e a k a g e . However, t h e i r tracirrgs m a y have poorer r e s o l u t i o n . P e r m a n e n t tracings should be k e p t and be available for l a t e r retrieval. 3) Magnetic Tape: These devices are l i g h t w e i g h t and can record ECG and voice simultaneously. However, the data are not immed i a t e l y a v a i l a b l e at the scene. Magnetic t a p e s a r e also v u l n e r a b l e to s t r a y magnetic fields.
Testing Since defibrillators are intended for i m m e d i a t e use, t h e y m u s t be tested r e g u l a r l y and have a built-in test capability. 1) Battery Test: A b u i l t - i n indicator, a light, should show when the capacity of the b a t t e r y has been d e p l e t e d to a k n o w n level. A pred e t e r m i n e d n u m b e r of defibrillation pulses should still be a v a i l a b l e when the indicator first w a r n s of a low battery. The b a t t e r y should be checked r e g u l a r l y while the u n i t is t u r n e d on, at the b e g i n n i n g of every shift, or a t least once a d a y w h e n it is not in use. 2) Functional Stored Energy Indicator: A n i n d i c a t o r l i g h t o r m e t e r should test the unit's a b i l i t y to store electrical e n e r g y in the output circuit. This and the battery test should be i n t e g r a l components of the defibrillator used in EMS since t h e y r a p i d l y indicate functional c a p a b i l i t y to t h e p e r s o n u s i n g t h e u n i t . The stored e n e r g y indicator is also useful in e v a l u a t i n g the performance capability of the b a t t e r y . Recommended defibrillator test procedures vary from m a n u f a c t u r e r to m a n u f a c t u r e r . Some believe t h a t excessive t e s t i n g is, in itself, counterproductive. 19
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3) D i a g n o s t i c D e l i v e r e d Energy Evaluation: The delivered energy may v a r y widely from the indicated s t o r e d e n e r g y in m a n y u n i t s . 2°-22 S i n c e d e l i v e r e d e n e r g y is t h e imp o r t a n t f a c t o r in d e f i b r i l l a t i o n , it should be e v a l u a t e d routinely. Commercially available t e s t i n s t r u m e n t s can e v a l u a t e this. The diagnostic delivered e n e r g y of each u n i t should be tested w e e k l y to indicate faults such as b r o k e n w i r e s in p a d d l e s or det e r i o r a t i o n of the e l e c t r i c a l components of the defibrillator.
General Recommendations E M S d e f i b r i l l a t o r / m o n i t o r systems should use nonfade type monitors. The m o n i t o r should be able to be s e p a r a t e d from the d e f i b r i l l a t o r and have its own power source. The system should also have a hard-copy readout of the h e a t e d stylus type. It should be clear w h e t h e r the source of the (electrocardiogram) signal is the p a d d l e s or t h e p a t i e n t cable. The monitor should have a provision for telemetry. 1) Weight: E M S d e f i b r i l l a t o r / m o n i t o r s y s t e m s s h o u l d w e i g h no more t h a n 18 kg (40 lbs) while maint a i n i n g a c c e p t a b l e r e l i a b i l i t y . 23 P a c k a g e s are a v a i l a b l e t h a t weigh less t h a n 11.25 kg (25 lbs) w i t h the defibrillator w e i g h i n g less t h a n 6.75 kg (15 lbs) and the m o n i t o r less t h a n 4.5 kg (10 lbs). 2) Reliability: The defibrillator a n d m o n i t o r s h o u l d be p r o t e c t e d a g a i n s t moisture, heat, v i b r a t i o n and shock e n c o u n t e r e d in EMS use. Applicable portions of certain milit a r y specifications can be considered. The Food and Drug A d m i n i s t r a t i o n will w r i t e s t a n d a r d s t h a t will provide additional guidance for the purchase of d e f i b r i l l a t o r / m o n i t o r systems. 23 Reliability m a y be comprised by the addition of seldom used features such as h e a r t r a t e m e t e r s and synchronizers. 3) P o w e r Source: The b a t t e r y of the d e f i b r i l l a t o r should provide at least 25 full energy discharges and two hours of m o n i t o r i n g t i m e before recharging. 4) M a i n t e n a n c e : O n l y t r a i n e d or f a c t o r y a u t h o r i z e d p e r s o n n e l should repair defibrillators and m o n i t o r s to i n s u r e r e l i a b l e r e p a i r and d i m i n i s h e d l i a b i l i t y problems. The d e f i b r i l l a t o r a n d m o n i t o r are a p a r t of EMS equipment. Compatibility with existing hardware, s p a r e parts, suppliers, etc, a n d expansion p l a n s should be considered when procuring defibrillators and monitors.*
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COMMUNICATIONS A C E P s u p p o r t s t h e concept of centralized, coordinated communications for EMS. 24
Public Access The public should have e a s y access to t h e system publicized t h r o u g h h i g h w a y signs, suitable notations on m a p s a n d in p u b l i c s e r v i c e directories, and a d v e r t i s i n g of emergency n u m b e r s and services. E a r l y notification systems linking remote areas with the EMS c o m m u n i c a t i o n center, ie, h i g h w a y e m e r g e n c y t e l e p h o n e or r a d i o - t e l e p h o n e s e r v i c e s , s h o u l d be u t i l i z e d to the fullest e x t e n t possible, where available. 1) Citizens B a n d Radio: Citiz e n s B a n d r a d i o is a b u r g e o n i n g m e t h o d of c o m m u n i c a t i o n a m o n g the g e n e r a l public and should a u g m e n t e a r l y n o t i f i c a t i o n systems. C e n t r a l EMS c o m m u n i c a t i o n facilities should m o n i t o r a d e s i g n a t e d CB channel. 2) T e l e p h o n e : The public should have access to a uniform emergency telephone n u m b e r t h a t is well publ i c i z e d a n d c a n be e a s i l y r e m e m bered. Efforts to d e s i g n a t e 911 as the u n i v e r s a l e m e r g e n c y t e l e p h o n e n u m b e r have been f r u s t r a t e d for a v a r i e t y of reasons, a4 If t h e s e roadblocks cannot be overcome, some alt e r n a t i v e telephone n u m b e r m i g h t be considered. In addition, a s t a n d a r d format should be developed for listi n g s in t e l e p h o n e d i r e c t o r i e s a n d other publications providing E M S information.
sponse is n e c e s s a r y a n d coordinate the response. 1) P e r s o n n e l : Personnel receivi n g c a l l s for a s s i s t a n c e s h o u l d be e m e r g e n c y m e d i c a l o p e r a t i o n s spec i a l i s t s , s p e c i a l l y t r a i n e d as rescue personnel as well as communication s y s t e m o p e r a t o r s to communicate with the public, rescue personnel a n d other public safety agencies. M u l t i l i n g u a l c a p a b i l i t y m a y be req u i r e d and, if so, should be available. 1 In addition, a s t a n d a r d glossary and communications protocol should be developed. 2) T e c h n i c a l C o o r d i n a t i o n : R e s c u e p e r s o n n e l s h o u l d be dispatched by direct voice communication. The emergency medical operations specialist should be capable of maintaining constant communication with rescue personnel, enroute to and on the scene, as well as with e m e r g e n c y d e p a r t m e n t s and hospit a l s , fire, s a f e t y , law e n f o r c e m e n t and other health personnel and, where necessary, local physicians. 3) M e d i c a l Direction: Rescue personnel e n r o u t e to the scene of an e m e r g e n c y should be able to i n s t i t u t e i m m e d i a t e and constant communicat i o n w i t h an e m e r g e n c y m e d i c a l f a c i l i t y , w h i c h in t u r n , s h o u l d be p r e p a r e d to provide medical supervision at the required level. Supervising physicians and nurses should be familiar with the capability and t r a i n i n g of rescue personnel a n d be t r a i n e d in u s e o f c o m m u n i c a t i o n and equipment. The communication e q u i p m e n t should be operated from a hospital emergency d e p a r t m e n t .
Operational Considerations
EMS System For each r e g i o n a l E M S s y s t e m an emergency medical operation center should be developed to handle citizen i n p u t from all access systems. The center should i n t e r p r e t the need for E M S s e r v i c e , d e c i d e w h a t re*Associate editors for this section were Stanley M. Zydlo, Jr, MD, chief of Emergency Services, Northwest Community Hospital, Arlington Heights, Illinois, and Leslie A. Geddes, PhD, director of Biomedical Engineering Center at Purdue University, West Lafayette, Indiana. Participants in this portion of the workshop, in addition to the above, were John J. Cahill, MD, director of Emergency Center, Lake County Memorial Hospital, Willoughby, Ohio; K a r l G. Mangold, MD, then vice president of ACEP, and Stanley V. Seiffert, vice president and director of marketing, PhysioControl Corporation, Redmond, Washington.
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A l t h o u g h a n y E M S s y s t e m is p r i m a r i l y concerned with the p a t i e n t in a n e m e r g e n c y situation, all EMS systems should be carefully p l a n n e d to ensure o p t i m u m use of the comm u n i t i e s ' economic and professional resources. The physician, to be medic a l l y r e s p o n s i b l e for t h e s y s t e m , m u s t play a major role in both planning and implementation. Perhaps the major consideration is to ensure t h a t t h e s y s t e m w i l l f u n c t i o n as p l a n n e d and t h a t ~ll components are compatible -- not only with each o t h e r but w i t h a n y n e i g h b o r i n g systems. A m o n g the individual questions to be considered in p l a n n i n g a syst e m are: 1) Definition of the service area, both geographically and demographically. 2) Definition of all p a r t i c i p a n t s - - i n s t i t u t i o n a l , p r i v a t e or p u b l i c
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agencies a n d their roles clarified. 3) Definition of technical needs and capabilities for the foreseeable future. The system should use both radio and telephone effectively. The p l a n n e d e q u i p m e n t m u s t be suitable for t h e local a r e a b e i n g s e r v e d . Where simple voice c o m m u n i c a t i o n is the only perceived need, this type e q u i p m e n t should be recommended. Where the p h y s i c i a n m e d i c a l l y responsible for the program determines t h a t more complex e q u i p m e n t is desirable, t h a t should be the recommendation. The considerations in developing a r e c o m m e n d a t i o n for the type of system required include: 1) Reliability and coverage. 2) The anticipated occurrence of s i m u l t a n e o u s events. 3) A n y budgetary limitations. 4) If needed, in the j u d g m e n t of the physician medically responsible for the p r o g r a m , the c a p a b i l i t y to communicate with rescue personnel in the field at the same time they are c o m m u n i c a t i n g with the emergency facility (duplex and/or multiplex capability). This applies both to voice and radio telemetry c o m m u n i c a t i o n of physiological m e a s u r e m e n t s . 3) T e l e m e t r y : T h e a b i l i t y to t r a n s m i t physiologic m e a s u r e m e n t s by telemetry expands the capability of rescue p e r s o n n e l by p e r m i t t i n g consultation with physicians and other supervising medical personnel at some distance from the site of a medical emergency. T e l e m e t r y is a valuable adjunct to a n EMS system. The u s e f u l n e s s of c o n t i n u o u s moni t o r i n g of such p h y s i o l o g i c a l d a t a should be determined by the physic i a n m e d i c a l l y r e s p o n s i b l e for the program. The c o n t i n u o u s recording of all such t r a n s m i s s i o n s is useful for review of activity, education of personnel, i m p r o v e m e n t of p a t i e n t care, education of the public, and research in system operations. Also, continuous r e c o r d i n g of b o t h voice a n d telemetry t r a n s m i s s i o n s m a y be essential for medicolegal purposes. All c o m m u n i c a t i o n s e q u i p m e n t is subject to certain i n h e r e n t technical l i m i t a t i o n s , m a n y of which are functions of the e n v i r o n m e n t . In the o p e r a t i o n of e m e r g e n c y m e d i c a l communications systems, reliable t r a n s m i s s i o n between the emergency medical facility and rescue personnel a t the p a t i e n t ' s side is e s p e c i a l l y necessary. Therefore, in addition to s e e k i n g competent technical advice in the design of a n emergency medical c o m m u n i c a t i o n system, intensive t e s t i n g of the components should be
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conducted in the system's e n v i r o n m e n t to determine both compatibility and function of all components.*
REFERENCES 1. Ewy GA: Defibrillator paddle electrodes. Cardiac Defibrillator Conference, Purdue University, West Lafayette, Indiana. Cosponsored by Biomedical Engineering Center, Purdue University and the American Association for Advancement of Medical Instrumentation. Engineering Station Document #0147, October 1975, pp 139-44. 2. Ewy GA, Taren D: Impedance to transthoracic DC dischargers: A model for testing interface materials. Med Instrum 12(1): 1978. 3. Geddes LA: Characteristics of defibrillating electrodes and living tissue. Cardiac Defibrillator Conference, Purdue University, West Lafayette, Indiana. Cosponsored by Biomedical Engineering Center, Purdue University and the American Association for Advancement of Medical Instrumentation. Engineering Station Document #00147, October 1975, pp 45-53. 4. Tam HW: Analysis and stimulation of postdefibrillation ECG recovery. Proceedings of the 29th Annual Conference on Engineering in Medicine and Biology. vol 18, Boston, pp 144. 5. Guidelines for selection and use of battery-operated defibrillation monitors. Emergency Care Research Institute Report. The EMT Journal 1: 62-67, 1977. 6. Geddes LA: Damped sinusoidal waveforms for ventricular defibrillation. Cardiac Defibrillator Conference, Purdue University, West Lafayette, Indiana. Cosponsored by Biomedical Engineering Center, Purdue University and the American Association for Advancement of Meical Instrumentation. Engineering Station Document #00147, October 1975, pp 55-60. 7. Tacker WA Jr, Geddes LA: Ventricular defibrillation. Journal of Clinical Equipment, January, 1977, p 14. 8. Dahl CF, Ewy GA, Warner ED, et al:
*Associate editors for this section were Terrence S. Carden, Jr, MD, director of Emergency Services, Highland Park Hospital Foundation, Highland Park, Illinois, and John S. Farquhar, MD, then chairman, Department of Emergency Medicine, University Hospital of Jacksonville, Jacksonville, Florida. Participants in this workshop, in addition to the above, were James J. Rybak, MD, member, Emergency Physicians Group, Highland Park, Illinois and J. Steve Adler, distribution manager, Advanced Systems, Motorola Communications and Electronics, Inc, Schaumburg, Illinois.
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Myocardial necrosis from direct current countershock; effect of paddle electrode size and time interval between discharges. Circulation 50:956, 1974. 9. Schuder JC, Stockle H, Gold JH: Effectiveness of transthoracic ventribular defibrillation with square and trapezoidal waveforms. Cardiac Defibrillator Conference, Purdue University, West Lafayette, Indiana. Cosponsored by Biomedical Engineering Center, Purdue University and the American Association for Advancement of Medical Instrumentation. Engineering Station Document #00147, October 1975, pp 109-114. 10. Tally RC: Field experience with a trapezoidal waveform defibrillator. Cardiac Defibrillator Conference, Purdue University, West Lafayette, Indiana. Cosponsored by Biomedical Engineering Center, Purdue University and the American Association for Advancement of Medical Instrumentation. Engineering Station Document #00147, October 1975, pp 137-138. 11. Tacker WA, Geddes LA, Rosborough JP, et al: Transchest ventricular defibrillation of heavy subjects using trapezoidal current wave forms. J Electrocardiol 8:237-240, 1975. 12. Koning G: Strength-duration curves for direct ventricular defibrillation with rectangular current pulses. Cardiac Defibrillator Conference, Purdue University, West Lafayette, Indiana. Cosponsored by Biomedical Engineering Center, Purdue University and the American Association for Advancement of Medical Instrumentation. E n g i n e e r i n g Station Document #00147, October 1975, pp 75-80. 13. Geddes LA: Electrical ventricular defibrillation. Cardiovascular Research Center Bulletin. Baylor College of Medicine. July-September 1871, No. 1. 14. Tacker WA Jr: Electrical dose for defibrillation. Cardiac Defibrillator Conference, Purdue University, West Lafayette, Indiana. Cosponsored by Biomedical Engineering Center, Purdue University and the American Association for Advancement of Medical Instrumentation. Engineering Station Document #00147, October 1975, pp 121-127. 15. Gutgesell HP: Pediatric defibrillations. Cardiac Defibrillator Conference, Purdue University, West Lafayette, Indiana. Cosponsored by Biomedical Engineering Center, Purdue University and the American Association for Advancement of Medical Instrumentation. Engineering Station Document #00147, October 1975, pp 65-66. 16. Pantridge JR, Adgey AAJ, Webb SW, et al: Electrical requirements for ventricular fibrillation, BR Med J 2:313-315, 1975. 17. Tacker WA Jr, Geddes LA, Cabler PS, et al: Electrical threshold for defibrillation of canine ventricles following myocardial infarction. A m Heart J 88:476-481, 1974.
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18. Tacker WA Jr, Geddes LA, Kline B, et al: Alteration of electrical defibrillation threshold by cardiac glycoside quabain. Cardiac Defibrillator Conference, Purdue University, West Lafayette, Indiana. Cosponsored by Biomedical Engineering Center, Purdue University and the American Association for Advancement of Medical Instrumentation. Engineering Station Document #00147, October 1975, pp 129-133. 19. Defibrillator testing, too much of a good thing is dangerous. Health Devices, 5:192-193, 1976. Published by the Emergency Care Research Institute, 5200
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Butler Pike, Plymouth Meeting, Pennsylvania 19462. 20. Ewy GA: Defibrillator output. Cardiac Defibrillator Conference, Purdue University, West Lafayette, Indiana. Cosponsored by Biomedical Engineering Center, Purdue University and the American Association for Advancement of Medical Instrumentation. Engineering Station Document #00147, October 1975, pp 33-38.
22. Stratbucker RA, Chambers W: Defibrillator performance characteristics, in '~Panel Discussion on Defibrillators" Journal of the Association for Advancement of Medical Instrumentation, 3:part 2, 1969. 23. Gausman MB: Electronic equipment requirements for emergency medical systems. IEEE Transactions on Vehicular Technology, November, 1976.
21. Finlay JB: Proposals for the Selection and Testing of DC Defibrillators. Biomedical Engineering Department, University Hospital, 339 Windermer Road, London, Ontario, Canada.
24. Emergency Medical Services: Problems, Programs and Policies, a statement prepared by the~::~ommittee on Public Policy of the American College of Emergency Physicians. JACEP 5:285-296, 1976.
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Workshop on EMS Technology--- Proceedings George Podgorny, MD* -editor Mark B. Gausman, PE, BEEt -coeditor J. Steve Adler, BSEE, M B A t - coeditor Las Croabas, Puerto Rico March •976 Podgorny G, Gausman MB, Adler JS: Proceedings of workshop on EMS technology, Las Croabas, Puerto Rico, March 1976. JACEP 7:66-70, February 1978. emergency medical services, technology; cardiac defibrillation; monitoring; equipment and supplies; communications. INTRODUCTION An EMS technology workshop was sponsored by the American College of Emergency Physicians (ACEP) in conjunction with its Winter Symposium in Puerto Rico. The framework, organization support and agenda were developed jointly by ACEP, Physio-Control Corporation and Motorola Communications and Electronics, Incorporated. The workshop brought together physicians knowledgeable in EMS and technical representatives from the bioengineering discipline and industry. Specifically, the workshop was organized into four committees to discuss defibrillation, monitoring, communications and transportation.* The workshop produced some suggested guidelines and specifications for the functional and technical requirements of EMS equipment.
DEFIBRILLATION A defibrillator is an electrical device t h a t delivers to the heart the amount of electrical energy required for conversion of abnormal rhythm. Although there are many types of defibrillators, these discussions and recommendations were limited to portable and battery operated defibrillators. Physician control of equipment selection, its utilization, and training of its users is vital.
Paddle Type and Size Most manufacturers use stainless steel paddle electrodes because of their corrosion resistance, ease of maintenance and durability. The resistivity of the metal in the defibrillator paddle is relatively unimportant since the impedance is determined mostly by the gel and the intervening tissue. Corroded paddles or accumulated dry paste or gel on the paddles will decrease conductivity. All paddles should, therefore, be thoroughly cleansed after each use. 1) P a d d l e S u r f a c e : The surface of the paddle electrodes should be brushed, not polished. A brushed or roughened metal surface offers better electrodeelectrolyte surface contact enhancing conductivity. A minimum electrode surface area of 50 sq cm is recommended to minimize tissue damage and assure adequate contact area. *From the Section on Education ACEP, t Physio-Control Corporation, and $Motorola Communications and Electronics, Incorporated. Workshop held March 1976 in Las Croabas, Puerto Rico. Participants were: Transportation - - David Nelson, MD, Lewellyn Stringer, MD, David R. Boyd, MD, Garry Briese, Fred Hill and Don VanSiclaa; Communications - Terrence Carden, Jr., MD, John Farquhar, MD, J. Rybak, MD, and Steve Adler; Monitoring - - Patrick Lilja, MD, Robert
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J. Rathburn, MD, Marty Briter, RN, Greg Heib, PhD, Ed Heilman and Mark Gausman; Defibrillation - - Stan Zydlo, MD, Les Geddes, PhD, Karl G. Mangold, MD, John J. Cahill, MD and Stanley M. Seiffert. Address for reprints: Steve Adler, Distribution Manager, Advanced Systems, Motorola Communications and Electronics, Incorporated, 1303 East Algonquin Road, Schaumburg, Illinois 60196.
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2) P a d d l e Design: P a d d l e s should be designed to p r e v e n t a n y of the electrode surfaces from coming in contact with the operator. The operator should be able to e x e r t full pressure w i t h o u t b e n d i n g or breaki n g the paddle. The o u t p u t c i r c u i t should be charged from a control on the paddles. The paddles should each have a button for d e l i v e r i n g the defibrillation pulse. This will provide a margin of safety should a single button be a c c i d e n t a l l y pressed. The cable from the paddles to the defibrillator should be a t least five feet long when fully extended. 3) Paddle Electrolyte S o l u - , tion: M a n y of t h e d i f f e r e n t g e l s , pastes, c r e a m s a n d u l t r a s o n i c oils used between the p a t i e n t and defibr i l l a t o r paddles r e s u l t in u n n e c e s s a r y tissue damage and highly variable delivered energy levels.~, 2 Elect r o c a r d i o g r a p h y c r e a m g e n e r a l l y has a r e s i s t i v i t y of 300 to 400 ohm cm a n d is not recommended for use with defibrillators, a l t h o u g h some m a n u als state t h a t such compounds can be used for this purpose. ~ Only low resistivity electrolytes, such as saline soaked pads or low r e s i s t i v i t y gels, are desirable. The p a d d l e e l e c t r o d e s a n d t h e gel t o g e t h e r should not have more t h a n 5 ohms resistance. 3 Some gels a c t as a t e m p o r a r y DC block at the electrode gel interface and d e l a y recovery of monitoring. 4 The gel should allow recovery of m o n i t o r i n g w i t h i n five seconds. 5 4) Paddles Placement: A n i m a l studies have shown t h a t one of the electrodes placed over the apical a r e a is o p t i m a l for d e f i b r i l l a t i o n . 6 However, there exists no definite quant i t a t i v e d a t a on h u m a n s for placem e n t o f t h e s e c o n d p a d d l e . I t is suggested t h a t h i g h r i g h t a n t e r i o r l a t e r a l t h o r a x below the clavicle, left infra-scapular and r i g h t m i d - l a t e r a l thoracic p l a c e m e n t s have proven effective 7 (Figure). S t u d i e s to d e t e r m i n e p r o p e r paddle p l a c e m e n t for best i n t r a c a r diac c u r r e n t density are needed. One method of study would be to a l w a y s record paddle placement, patient weight, e n e r g y setting, prior medication, n u m b e r of a t t e m p t s , a n d results. Possibly, t h e c u r r e n t l y used m i d s t e r n a l and apical position is not best. When possible, the paddles should be spaced at l e a s t o n e - h a l f of the paddle d i a m e t e r apart. The elect r o l y t e gel s h o u l d n o t b r i d g e t h e space between the paddles. ~,3,s
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F i g . Suggested paddle placement for defibrillation. From Tacker. 7
Defibrillator Waveform Two g e n e r a l types of waveforms are now in use: d a m p e d s i n u s o i d a l (Edmark, Lown, Gurvich) and trapezoidal.6, 9-11 T h e r e a r e also v a r i a tions in m a x i m u m delivered energy. Most currently available damped sinusoidal waveform defibrillators deliver a m a x i m u m of 320 joules of energy into a 50 ohm resistor, while some t r a p e z o i d a l d e f i b r i l l a t o r s deliver 250 joules. The effectiveness of one d e f i b r i l l a t o r c o m p a r e d w i t h a n o t h e r should n o t be j u d g e d on the b a s i s o f w a v e f o r m or d e l i v e r e d energy alone since m a n y o t h e r factors are involved.6, ~-~3 The e n e r g y dose concept based on the p a t i e n t ' s w e i g h t m a y be useful in d e t e r m i n i n g the proper e n e r g y for defibrillation. However, a t the prese n t time the information conflicts as to w h a t t h e d o s a g e s h o u l d be. 14-17 Drugs, metabolic state, t e m p e r a t u r e , hypoxia, m y o c a r d i a l ischemia and infarction all m o d i f y t h e s t r e n g t h of c o u n t e r - s h o c k r e q u i r e d to defibrill a t e . 17 A l t h o u g h s o m e d r u g s a r e known to raise a n d others to lower the e n e r g y t h r e s h o l d required to defibrillate, the effects of drugs used in cardiac m a n a g e m e n t on the r e q u i r e d e n e r g y level are l a r g e l y u n q u a n t i rated. TM
Monitoring and Recording For EMS use, the portable batt e r y d e f i b r i l l a t o r s h o u l d also have m o n i t o r i n g capability.
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1) Oscilloscopic Display: Oscilloscopic d i s p l a y s are c u r r e n t l y available in so-called ~bouncing ball" and nonfade types. ~Bouncing ball" types of displays require closer observation and more frequent a d j u s t m e n t for int e n s i t y . H o w e v e r , t h e y m a y be lighter in w e i g h t and less expensive. Nonfade displays are e a s i e r to read in the v a r y i n g a m b i e n t light conditions e n c o u n t e r e d in E M S b u t are n o r m a l l y more expensive. It seems t h a t the nonfade d i s p l a y is becoming more common i n EMS. 2) Hard Copy Display: Most currently available battery-operated defibrillators w i t h a h a r d copy w r i t e r use the h e a t e d stylus. The t r a c i n g s provide good c o n t r a s t and detail. In the future, voltage-sensitive p a p e r recorders m a y become available w h i c h c a n r e d u c e p o w e r consumption and e l i m i n a t e the problems of s t y l u s b u r n o u t a n d b r e a k a g e . However, t h e i r tracirrgs m a y have poorer r e s o l u t i o n . P e r m a n e n t tracings should be k e p t and be available for l a t e r retrieval. 3) Magnetic Tape: These devices are l i g h t w e i g h t and can record ECG and voice simultaneously. However, the data are not immed i a t e l y a v a i l a b l e at the scene. Magnetic t a p e s a r e also v u l n e r a b l e to s t r a y magnetic fields.
Testing Since defibrillators are intended for i m m e d i a t e use, t h e y m u s t be tested r e g u l a r l y and have a built-in test capability. 1) Battery Test: A b u i l t - i n indicator, a light, should show when the capacity of the b a t t e r y has been d e p l e t e d to a k n o w n level. A pred e t e r m i n e d n u m b e r of defibrillation pulses should still be a v a i l a b l e when the indicator first w a r n s of a low battery. The b a t t e r y should be checked r e g u l a r l y while the u n i t is t u r n e d on, at the b e g i n n i n g of every shift, or a t least once a d a y w h e n it is not in use. 2) Functional Stored Energy Indicator: A n i n d i c a t o r l i g h t o r m e t e r should test the unit's a b i l i t y to store electrical e n e r g y in the output circuit. This and the battery test should be i n t e g r a l components of the defibrillator used in EMS since t h e y r a p i d l y indicate functional c a p a b i l i t y to t h e p e r s o n u s i n g t h e u n i t . The stored e n e r g y indicator is also useful in e v a l u a t i n g the performance capability of the b a t t e r y . Recommended defibrillator test procedures vary from m a n u f a c t u r e r to m a n u f a c t u r e r . Some believe t h a t excessive t e s t i n g is, in itself, counterproductive. 19
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3) D i a g n o s t i c D e l i v e r e d Energy Evaluation: The delivered energy may v a r y widely from the indicated s t o r e d e n e r g y in m a n y u n i t s . 2°-22 S i n c e d e l i v e r e d e n e r g y is t h e imp o r t a n t f a c t o r in d e f i b r i l l a t i o n , it should be e v a l u a t e d routinely. Commercially available t e s t i n s t r u m e n t s can e v a l u a t e this. The diagnostic delivered e n e r g y of each u n i t should be tested w e e k l y to indicate faults such as b r o k e n w i r e s in p a d d l e s or det e r i o r a t i o n of the e l e c t r i c a l components of the defibrillator.
General Recommendations E M S d e f i b r i l l a t o r / m o n i t o r systems should use nonfade type monitors. The m o n i t o r should be able to be s e p a r a t e d from the d e f i b r i l l a t o r and have its own power source. The system should also have a hard-copy readout of the h e a t e d stylus type. It should be clear w h e t h e r the source of the (electrocardiogram) signal is the p a d d l e s or t h e p a t i e n t cable. The monitor should have a provision for telemetry. 1) Weight: E M S d e f i b r i l l a t o r / m o n i t o r s y s t e m s s h o u l d w e i g h no more t h a n 18 kg (40 lbs) while maint a i n i n g a c c e p t a b l e r e l i a b i l i t y . 23 P a c k a g e s are a v a i l a b l e t h a t weigh less t h a n 11.25 kg (25 lbs) w i t h the defibrillator w e i g h i n g less t h a n 6.75 kg (15 lbs) and the m o n i t o r less t h a n 4.5 kg (10 lbs). 2) Reliability: The defibrillator a n d m o n i t o r s h o u l d be p r o t e c t e d a g a i n s t moisture, heat, v i b r a t i o n and shock e n c o u n t e r e d in EMS use. Applicable portions of certain milit a r y specifications can be considered. The Food and Drug A d m i n i s t r a t i o n will w r i t e s t a n d a r d s t h a t will provide additional guidance for the purchase of d e f i b r i l l a t o r / m o n i t o r systems. 23 Reliability m a y be comprised by the addition of seldom used features such as h e a r t r a t e m e t e r s and synchronizers. 3) P o w e r Source: The b a t t e r y of the d e f i b r i l l a t o r should provide at least 25 full energy discharges and two hours of m o n i t o r i n g t i m e before recharging. 4) M a i n t e n a n c e : O n l y t r a i n e d or f a c t o r y a u t h o r i z e d p e r s o n n e l should repair defibrillators and m o n i t o r s to i n s u r e r e l i a b l e r e p a i r and d i m i n i s h e d l i a b i l i t y problems. The d e f i b r i l l a t o r a n d m o n i t o r are a p a r t of EMS equipment. Compatibility with existing hardware, s p a r e parts, suppliers, etc, a n d expansion p l a n s should be considered when procuring defibrillators and monitors.*
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COMMUNICATIONS A C E P s u p p o r t s t h e concept of centralized, coordinated communications for EMS. 24
Public Access The public should have e a s y access to t h e system publicized t h r o u g h h i g h w a y signs, suitable notations on m a p s a n d in p u b l i c s e r v i c e directories, and a d v e r t i s i n g of emergency n u m b e r s and services. E a r l y notification systems linking remote areas with the EMS c o m m u n i c a t i o n center, ie, h i g h w a y e m e r g e n c y t e l e p h o n e or r a d i o - t e l e p h o n e s e r v i c e s , s h o u l d be u t i l i z e d to the fullest e x t e n t possible, where available. 1) Citizens B a n d Radio: Citiz e n s B a n d r a d i o is a b u r g e o n i n g m e t h o d of c o m m u n i c a t i o n a m o n g the g e n e r a l public and should a u g m e n t e a r l y n o t i f i c a t i o n systems. C e n t r a l EMS c o m m u n i c a t i o n facilities should m o n i t o r a d e s i g n a t e d CB channel. 2) T e l e p h o n e : The public should have access to a uniform emergency telephone n u m b e r t h a t is well publ i c i z e d a n d c a n be e a s i l y r e m e m bered. Efforts to d e s i g n a t e 911 as the u n i v e r s a l e m e r g e n c y t e l e p h o n e n u m b e r have been f r u s t r a t e d for a v a r i e t y of reasons, a4 If t h e s e roadblocks cannot be overcome, some alt e r n a t i v e telephone n u m b e r m i g h t be considered. In addition, a s t a n d a r d format should be developed for listi n g s in t e l e p h o n e d i r e c t o r i e s a n d other publications providing E M S information.
sponse is n e c e s s a r y a n d coordinate the response. 1) P e r s o n n e l : Personnel receivi n g c a l l s for a s s i s t a n c e s h o u l d be e m e r g e n c y m e d i c a l o p e r a t i o n s spec i a l i s t s , s p e c i a l l y t r a i n e d as rescue personnel as well as communication s y s t e m o p e r a t o r s to communicate with the public, rescue personnel a n d other public safety agencies. M u l t i l i n g u a l c a p a b i l i t y m a y be req u i r e d and, if so, should be available. 1 In addition, a s t a n d a r d glossary and communications protocol should be developed. 2) T e c h n i c a l C o o r d i n a t i o n : R e s c u e p e r s o n n e l s h o u l d be dispatched by direct voice communication. The emergency medical operations specialist should be capable of maintaining constant communication with rescue personnel, enroute to and on the scene, as well as with e m e r g e n c y d e p a r t m e n t s and hospit a l s , fire, s a f e t y , law e n f o r c e m e n t and other health personnel and, where necessary, local physicians. 3) M e d i c a l Direction: Rescue personnel e n r o u t e to the scene of an e m e r g e n c y should be able to i n s t i t u t e i m m e d i a t e and constant communicat i o n w i t h an e m e r g e n c y m e d i c a l f a c i l i t y , w h i c h in t u r n , s h o u l d be p r e p a r e d to provide medical supervision at the required level. Supervising physicians and nurses should be familiar with the capability and t r a i n i n g of rescue personnel a n d be t r a i n e d in u s e o f c o m m u n i c a t i o n and equipment. The communication e q u i p m e n t should be operated from a hospital emergency d e p a r t m e n t .
Operational Considerations
EMS System For each r e g i o n a l E M S s y s t e m an emergency medical operation center should be developed to handle citizen i n p u t from all access systems. The center should i n t e r p r e t the need for E M S s e r v i c e , d e c i d e w h a t re*Associate editors for this section were Stanley M. Zydlo, Jr, MD, chief of Emergency Services, Northwest Community Hospital, Arlington Heights, Illinois, and Leslie A. Geddes, PhD, director of Biomedical Engineering Center at Purdue University, West Lafayette, Indiana. Participants in this portion of the workshop, in addition to the above, were John J. Cahill, MD, director of Emergency Center, Lake County Memorial Hospital, Willoughby, Ohio; K a r l G. Mangold, MD, then vice president of ACEP, and Stanley V. Seiffert, vice president and director of marketing, PhysioControl Corporation, Redmond, Washington.
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A l t h o u g h a n y E M S s y s t e m is p r i m a r i l y concerned with the p a t i e n t in a n e m e r g e n c y situation, all EMS systems should be carefully p l a n n e d to ensure o p t i m u m use of the comm u n i t i e s ' economic and professional resources. The physician, to be medic a l l y r e s p o n s i b l e for t h e s y s t e m , m u s t play a major role in both planning and implementation. Perhaps the major consideration is to ensure t h a t t h e s y s t e m w i l l f u n c t i o n as p l a n n e d and t h a t ~ll components are compatible -- not only with each o t h e r but w i t h a n y n e i g h b o r i n g systems. A m o n g the individual questions to be considered in p l a n n i n g a syst e m are: 1) Definition of the service area, both geographically and demographically. 2) Definition of all p a r t i c i p a n t s - - i n s t i t u t i o n a l , p r i v a t e or p u b l i c
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agencies a n d their roles clarified. 3) Definition of technical needs and capabilities for the foreseeable future. The system should use both radio and telephone effectively. The p l a n n e d e q u i p m e n t m u s t be suitable for t h e local a r e a b e i n g s e r v e d . Where simple voice c o m m u n i c a t i o n is the only perceived need, this type e q u i p m e n t should be recommended. Where the p h y s i c i a n m e d i c a l l y responsible for the program determines t h a t more complex e q u i p m e n t is desirable, t h a t should be the recommendation. The considerations in developing a r e c o m m e n d a t i o n for the type of system required include: 1) Reliability and coverage. 2) The anticipated occurrence of s i m u l t a n e o u s events. 3) A n y budgetary limitations. 4) If needed, in the j u d g m e n t of the physician medically responsible for the p r o g r a m , the c a p a b i l i t y to communicate with rescue personnel in the field at the same time they are c o m m u n i c a t i n g with the emergency facility (duplex and/or multiplex capability). This applies both to voice and radio telemetry c o m m u n i c a t i o n of physiological m e a s u r e m e n t s . 3) T e l e m e t r y : T h e a b i l i t y to t r a n s m i t physiologic m e a s u r e m e n t s by telemetry expands the capability of rescue p e r s o n n e l by p e r m i t t i n g consultation with physicians and other supervising medical personnel at some distance from the site of a medical emergency. T e l e m e t r y is a valuable adjunct to a n EMS system. The u s e f u l n e s s of c o n t i n u o u s moni t o r i n g of such p h y s i o l o g i c a l d a t a should be determined by the physic i a n m e d i c a l l y r e s p o n s i b l e for the program. The c o n t i n u o u s recording of all such t r a n s m i s s i o n s is useful for review of activity, education of personnel, i m p r o v e m e n t of p a t i e n t care, education of the public, and research in system operations. Also, continuous r e c o r d i n g of b o t h voice a n d telemetry t r a n s m i s s i o n s m a y be essential for medicolegal purposes. All c o m m u n i c a t i o n s e q u i p m e n t is subject to certain i n h e r e n t technical l i m i t a t i o n s , m a n y of which are functions of the e n v i r o n m e n t . In the o p e r a t i o n of e m e r g e n c y m e d i c a l communications systems, reliable t r a n s m i s s i o n between the emergency medical facility and rescue personnel a t the p a t i e n t ' s side is e s p e c i a l l y necessary. Therefore, in addition to s e e k i n g competent technical advice in the design of a n emergency medical c o m m u n i c a t i o n system, intensive t e s t i n g of the components should be
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conducted in the system's e n v i r o n m e n t to determine both compatibility and function of all components.*
REFERENCES 1. Ewy GA: Defibrillator paddle electrodes. Cardiac Defibrillator Conference, Purdue University, West Lafayette, Indiana. Cosponsored by Biomedical Engineering Center, Purdue University and the American Association for Advancement of Medical Instrumentation. Engineering Station Document #0147, October 1975, pp 139-44. 2. Ewy GA, Taren D: Impedance to transthoracic DC dischargers: A model for testing interface materials. Med Instrum 12(1): 1978. 3. Geddes LA: Characteristics of defibrillating electrodes and living tissue. Cardiac Defibrillator Conference, Purdue University, West Lafayette, Indiana. Cosponsored by Biomedical Engineering Center, Purdue University and the American Association for Advancement of Medical Instrumentation. Engineering Station Document #00147, October 1975, pp 45-53. 4. Tam HW: Analysis and stimulation of postdefibrillation ECG recovery. Proceedings of the 29th Annual Conference on Engineering in Medicine and Biology. vol 18, Boston, pp 144. 5. Guidelines for selection and use of battery-operated defibrillation monitors. Emergency Care Research Institute Report. The EMT Journal 1: 62-67, 1977. 6. Geddes LA: Damped sinusoidal waveforms for ventricular defibrillation. Cardiac Defibrillator Conference, Purdue University, West Lafayette, Indiana. Cosponsored by Biomedical Engineering Center, Purdue University and the American Association for Advancement of Meical Instrumentation. Engineering Station Document #00147, October 1975, pp 55-60. 7. Tacker WA Jr, Geddes LA: Ventricular defibrillation. Journal of Clinical Equipment, January, 1977, p 14. 8. Dahl CF, Ewy GA, Warner ED, et al:
*Associate editors for this section were Terrence S. Carden, Jr, MD, director of Emergency Services, Highland Park Hospital Foundation, Highland Park, Illinois, and John S. Farquhar, MD, then chairman, Department of Emergency Medicine, University Hospital of Jacksonville, Jacksonville, Florida. Participants in this workshop, in addition to the above, were James J. Rybak, MD, member, Emergency Physicians Group, Highland Park, Illinois and J. Steve Adler, distribution manager, Advanced Systems, Motorola Communications and Electronics, Inc, Schaumburg, Illinois.
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Myocardial necrosis from direct current countershock; effect of paddle electrode size and time interval between discharges. Circulation 50:956, 1974. 9. Schuder JC, Stockle H, Gold JH: Effectiveness of transthoracic ventribular defibrillation with square and trapezoidal waveforms. Cardiac Defibrillator Conference, Purdue University, West Lafayette, Indiana. Cosponsored by Biomedical Engineering Center, Purdue University and the American Association for Advancement of Medical Instrumentation. Engineering Station Document #00147, October 1975, pp 109-114. 10. Tally RC: Field experience with a trapezoidal waveform defibrillator. Cardiac Defibrillator Conference, Purdue University, West Lafayette, Indiana. Cosponsored by Biomedical Engineering Center, Purdue University and the American Association for Advancement of Medical Instrumentation. Engineering Station Document #00147, October 1975, pp 137-138. 11. Tacker WA, Geddes LA, Rosborough JP, et al: Transchest ventricular defibrillation of heavy subjects using trapezoidal current wave forms. J Electrocardiol 8:237-240, 1975. 12. Koning G: Strength-duration curves for direct ventricular defibrillation with rectangular current pulses. Cardiac Defibrillator Conference, Purdue University, West Lafayette, Indiana. Cosponsored by Biomedical Engineering Center, Purdue University and the American Association for Advancement of Medical Instrumentation. E n g i n e e r i n g Station Document #00147, October 1975, pp 75-80. 13. Geddes LA: Electrical ventricular defibrillation. Cardiovascular Research Center Bulletin. Baylor College of Medicine. July-September 1871, No. 1. 14. Tacker WA Jr: Electrical dose for defibrillation. Cardiac Defibrillator Conference, Purdue University, West Lafayette, Indiana. Cosponsored by Biomedical Engineering Center, Purdue University and the American Association for Advancement of Medical Instrumentation. Engineering Station Document #00147, October 1975, pp 121-127. 15. Gutgesell HP: Pediatric defibrillations. Cardiac Defibrillator Conference, Purdue University, West Lafayette, Indiana. Cosponsored by Biomedical Engineering Center, Purdue University and the American Association for Advancement of Medical Instrumentation. Engineering Station Document #00147, October 1975, pp 65-66. 16. Pantridge JR, Adgey AAJ, Webb SW, et al: Electrical requirements for ventricular fibrillation, BR Med J 2:313-315, 1975. 17. Tacker WA Jr, Geddes LA, Cabler PS, et al: Electrical threshold for defibrillation of canine ventricles following myocardial infarction. A m Heart J 88:476-481, 1974.
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18. Tacker WA Jr, Geddes LA, Kline B, et al: Alteration of electrical defibrillation threshold by cardiac glycoside quabain. Cardiac Defibrillator Conference, Purdue University, West Lafayette, Indiana. Cosponsored by Biomedical Engineering Center, Purdue University and the American Association for Advancement of Medical Instrumentation. Engineering Station Document #00147, October 1975, pp 129-133. 19. Defibrillator testing, too much of a good thing is dangerous. Health Devices, 5:192-193, 1976. Published by the Emergency Care Research Institute, 5200
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Butler Pike, Plymouth Meeting, Pennsylvania 19462. 20. Ewy GA: Defibrillator output. Cardiac Defibrillator Conference, Purdue University, West Lafayette, Indiana. Cosponsored by Biomedical Engineering Center, Purdue University and the American Association for Advancement of Medical Instrumentation. Engineering Station Document #00147, October 1975, pp 33-38.
22. Stratbucker RA, Chambers W: Defibrillator performance characteristics, in '~Panel Discussion on Defibrillators" Journal of the Association for Advancement of Medical Instrumentation, 3:part 2, 1969. 23. Gausman MB: Electronic equipment requirements for emergency medical systems. IEEE Transactions on Vehicular Technology, November, 1976.
21. Finlay JB: Proposals for the Selection and Testing of DC Defibrillators. Biomedical Engineering Department, University Hospital, 339 Windermer Road, London, Ontario, Canada.
24. Emergency Medical Services: Problems, Programs and Policies, a statement prepared by the~::~ommittee on Public Policy of the American College of Emergency Physicians. JACEP 5:285-296, 1976.
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