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Mechanized cardiopulmonary resuscitation: Past, present, and future
Research
Seminars
Mechanized Cardiopulmonary Resuscitation: Past, Present, and Future C. E. BARKALOW,
MA
The development of a successful external cardiac defibrillator by Kouwenhouven et al,’ and their revival of the concept of cardiac compression through the intact chest, published in 1960, gave promise of a new era in resuscitation in which body perfusion, as well as ventilation, could be maintained as a first aid procedure, and cardioversion could be achieved without the need for a thoractomy. Despite the fact that today, 24 years later, CPR based on current standards of performance must be regarded as a marginally successful technique, one must be truly impressed with its widespread acceptance by the medical profession, the heart associations, the American National Red Cross, the providers of emergency medicine both in and out of the hospital, and lay persons of whom hundreds of thousands have been trained in the technique and to whom the letters “CPR” have a readily understood meaning. Perhaps it is not surprising, then, that despite the marginality of the procedure, many successful resuscitations continue to be reported. The “epidemic of sudden unexpected death“ is pervasive in our society. This fact, coupled with the widely disseminated knowledge and practice of CPR, provides, statistically, many opportunities to practice this form of first aid. Although some investigators might contest the claim, the current standards for performing CPR as published in 1980, authored by a panel of professionals representing the American Heart Association, the National Research Council, and the American National Red Cross, estimate that CPR performed to these standards provides adequate support for over 40% of patients, to the extent that electrical cardioversion is possible. Today this may well be regarded as highly Received igan.
from Michigan
Instruments,
Inc., Grand Rapids, Mich-
Manuscript received November 12, 1983; revision received uary 30, 1984; revision accepted February 2, 1984.
Jan-
Address reprint requests to Mr. Barkalow: Michigan Instruments, Inc., 6300 28th Street SE, Grand Rapids, MI 49506. Key Words: Cardiopulmonary resuscitation, defibrillation. 262
optimistic; however, reduction by a factor of 2, or even 3, still results in a highly significant total of successful outcomes. Moreover, because of the number of cases treated by providers of prehospital or in-hospital medical care, even small improvements in the success rate, as might be attained by more extensive training, optimization of present techniques, or improved protocols for performing CPR, can lead to significant advances in the statistics of survival. Thus, from a public health point of view, progress in cardiopulmonary resuscitation technology holds much promise and much current interest. THE VALUE OF MECHANIZED CARDIOPULMONARY RESUSCITATION There are three basic reasons establishing the need for mechanical equipment used to perform CPR: 1. Equipment used in the scientific study of CPR per se, providing constant levels of support and protocol, and providing on-call capabilities for selection of varied, predetermined CPR protocols for “cause and effect” investigations. 2. Mechanical equipment that can be designed to optimize CPR performance based on the present standards for strictly manual CPR. Commerically available gas-powered machines can be engineered to overcome all of the shortcomings of the mechanical technique, and can efficiently, safely, and for extended periods provide optimal support levels otherwise requiring two ore more persons to perform. 3. Mechanical devices can be engineered to perform CPR to new protocols, optimized for machine resuscitation per se, without consideration for manual limitations (both physical and mental), and can provide “second aid” support levels transcending “first aid” CPR in much the same way that modern ventilatory resuscitators transcend the first aid manual methods of artificial respiration. At the same time it should be stated that mechanized equipment will never replace the manual first aid techniques, for obvious reasons. The goal is, and always will be, to provide mechanized
BARKALOW
n MECHANIZED
CPR
equipment that can be brought to bear as early as possible to increase the probability of a successful outcome. MECHANIZED EQUIPMENT OF THE PAST Following the early 1959-1960, there was opment of mechanized It was recognized would be an arduous
work of Kouwenhoven et al in a flurry of effort in the develCRP equipment. quite early that manual CPR though possible task and that
FIGURE 3 (above). The Harkins-Bramson synchronous cardiomassage machine (Hallikainen Instruments). FIGURE 4 (below).
The Westinghouse
electro-
“iron heart.”
t
FIGURE I (above). The Beck-Rand unit for closed-chest pulmonary resuscitation. FIGURE 2 (below).
The heart reactivator.
cardio-
there would be problems of training, fatigue, assurance of control, and physical limitations (e.g., a petite female nurse applying CPR to a robust man). Thus, most of the effort to develop mechanized equipment was aimed at optimizing standard CPR performance. By the middle 1960s many devices were marketed for the purpose of providing support based on current manual standards and intended for routine use in hospital and ambulance. Figures 1 through 6 show some of these devices, only a few of which remain in production at present. However, at least one of the early mechanized units was designed for “programmable CPR,” intended to investigate the optimization of CPR protocol. This device (Fig. 7), engineered by Barkalow and co-workers was used in experiments starting in 1960. The experiments were conducted and reported by Birch et al.* Animal studies used two baboons, one pig, and several 263
AMERICAN
JOURNAL
OF EMERGENCY
MEDICINE
n Volume 2, Number 3 W May 1984
significant in determining mean AV pressure differential. 2. The ratio of systolic/diastolic timing did appear significant, optimal perfusion potential being obtained at a 70:30 ratio. 3. Positive pressure ventilation, whether randomized or synchronized relative to chest compression, had a postivie influence on perfusion potential. Indeed, to evaluate the effect of varying parameters of chest compression on perfusion pev se, one needed to interrupt ventilation in order to obtain stable nonaugmented readings. Figure 8 shows the effect of duration of systole on perfusion potential, later corroborated by investigations elsewhere.3 At that time, one of the authors of the report just described2 was a member of the CPR committee of the American Heart Association, and it seems likely that the results reported from this study were of some influence on the early standards for CPR set by that committee. Shortly thereafter, Wilder et al4 reported similar findings linking intermittent positive pressure ventilation with increases in perfusion potential. Indeed, those authors proposed the possibility of frequent ventilations, not to improve blood gas exchange but to enhance cardiac output during ECC. In retrospect, the mechanics of squeezing the heart between sternum and spine without embarrassing valve competence may seem questionable. Yet, at that time, few persons expressed doubts about this perhaps simplistic explanation. Observations of the effect of positive pressure ventilation in improving perfusion potential were explained by the theory of “improved venous return” to the right side of the heart. In those years, direct cardiac mechanical compression of the
FIGURE 5 (nbove). FIGURE 6 (below). Tech Laboratories).
The Cardi-activator (Cardiac Products Corp.). The Tamband heart-lung resuscitator (Medi-
dogs. The overall effectiveness of closed chest external cardiac compression (ECC) was impressive. Several experiments were performed under aseptic conditions and resulted in long-term survival. In this study, mean AV pressure differentials across the femoral bed were used as an indicator of perfusion potential, and the effects of varied protocol were validated by frequent returns to control protocol. On the basis of usable data from only a few dogs, the following observations were reported: 1. The rate of cardiac compression (cycles per minute, or cpm), within limits, did not appear to be 264
FIGURE -7. Early programmable chest compr&&, used for studies at Buttenvorth Hospital, Grand Rapids, Michigan, 19601963 (Michigan Instruments, Inc.).
BARKALOW n MECHANIZED CPR
-Rem
_.
.
i
IO
20
a0
40 DURATION
FIGURE 8.
External cardiac compression:
ED OF -L
oil
70 %
effect of duration of systole. Force: 60 lb. Rate: 60 cpm. Data gathered April 6, 1962.
heart was the generally accepted theoretic mechanism for ejection of blood from the thorax during external chest compression (Fig. 9), a view supported at the National Research Council/American Heart Association meeting of 1966. Another national conference on CPR, sponsored jointly by the American Heart Association and the National Academy of Sciences, was held in 1973. The first published national standard for the performance of manual CPR emerged from the meeting.’ Indeed, all of the equipment for standard CPR was, and still is, based on the physiologic explanations of CPR contained in that document and in the 1966 proceedings of the National Research Council/American Heart Association.6 Between 1962 and 1968 there was little activity in CPR research. In 1968, a special punched-card programmable experimental cardiopulmonary resuscitator (Fig. lo), which provided the capability of variable, repeatable CPR programming, was developed for Dr. Joel Nobel at the Emergency Care Research Institute. This equipment was later used by Chandra et a16at Johns Hopkins University and became the basis for their studies aimed at the optimization of CPR protocol. In the 1970s the work of this group7 and that of Criley, Niemann, and associatess9 clarified the significance of the pulmonary bed as a blood pump, influenced by cycled intrathoracic pressures. Neverthe-
less, these investigators could not define the pulmonary bed as the only available CPR pump, and older CPR techniques were not displaced. Indeed, to some investigators it seemed quite logical that both mechanisms for the pumping of blood, particularly in the human being, might be utilized, and that such a combination might well result in levels of support greater than either modality alone. In 1979, a more sophisticated programmable unit was developed, which used pencil-marked IBM computer cards to set specific CPR protocols over a wide range of flexibility (Fig. 1l).‘O PRESENT STATUS OF MECHANIZED EQUIPMENT FOR CARDIOPULMONARY RESUSCITATION Insofar as “standard” CPR units are concerned, only three such devices are in current production: (1) the Thumper@ cpr device (Michigan Instruments, Inc., Grand Rapids, Michigan) (2) the HLR (Brunswick Manufacturing Co., Boston, Massachusetts) and (3) the Reanimator 3000 (W. Sohngen Gmbh, Austria (Figs. 12, 13, and 14). Basically, all these units attempt to optimize CPR on the basis of current American Heart Association standards. There are differences in the mechanism of ventilation; the Thumper@ unit utilizes a full flow, pressure limited, time cycled principle; the HLR uses the discharge of a fixed volume of gas, stored under 265
AMERICAN
JOURNAL
OF EMERGENCY
MEDICINE
n Volume 2, Number 3 n May 1984
scribed individual protocols “read only memory” chips.
stored on one or more
THE FUTURE OF MECHANIZED CARDIOPULMONARY RESUSCITATION Current research is intended to bring about significant improvement in support levels over present CPR methods. Referring back to earlier observations that lung ventilation per se,in conjunction with chest compression, had a positive effect on blood pumping, it was to be expected that equipment aimed at inducing high intrathoracic pressures in combination with chest compression woud be investigated. One form of this technique, now called synchronized compression ventilation CPR (SCV-CPR) is currently being used in clinical field test trials (Fig. 16). Specifications for the equipment originated from the Johns Hopkins University investigators. The equipment was engineered and pro-
FIGURE 9. The physiology of external cardiac compression, as it was understood in 1966. (From Proceedings of the National Research Council/American Heart Association, 1967.)
relatively high pressure (up to 20 psi) in a small container; and the Austrian unit stores exhaust gas from chest compression in a flexible bag (test lung) for subsequent discharge into the lungs. The basic alternative to the present resuscitators is manual CPR, since both are based on the same standards. The advantages of mechanical over manual are significant, since the mechanical devices can be designed to provide optimal performance to the standards, are nontiring, do not need retraining, and replace two-person teams. Nearly 20 years of field experience with these units has established them as valuable devices for basic life support and advanced cardiac life support. To this writer’s knowledge, only two definitive studies’1q12of mechanical versus manual CPR have been reported supporting this statement. However, several case reports 13-15and one statistical field study16 support the conclusion that mechanical CPR equipment performing to manual standards can be a successful life support technique. In a small but significant proportion of attempts, viability is maintained, frequently for a long time. In these cases, cardiac output levels, cerebral perfusion levels, and blood gases are at least adequate. Also, defibrillation after CPR is successful in a small but significant number of cases, with return of endogenous heart function indicating that myocardial tone in these cases has been adequately maintained. In current experiments, the latest in programmable CPR devices (Fig. 15) uses a microprocessor for control and sets CPR protocol by instant recall of pre266
Punched-card programmable carFIGURE 10 (above and center). diopulmonary resuscitator (Michigan Instruments, Inc., 1968). FIGURE 11 (below). Marked-card programmable cardiopulmonary resuscitator (Michigan Instruments, Inc., 1979).
BARKALOW w MECHANIZED CPR
duced by Michigan Instruments, Inc. Sixteen units are currently being employed in the study, under NIH grant and administered by the University of Florida and Johns Hopkins University. Other investigators are concentrating efforts in somewhat different directions. Some are studying various forms of abdominal compression. Babbs er u/17,18 and Walker et al have independently reported that abdominal counterpulsation pressure combined with standard chest compression produces significant increases in total cardiac output and in cerebral and possibly coronary perfusion levels. Still other investigators20 are working with equipment that attempts to simulate “cough CPR.” Most of this equipment uses inflatable garments (vests) with cyclic tilling and emptying, although in at least one case21 the Thumper@ cpr device has been used to compress a sealed air bag garment. Some investigators, however, disagree with the theory that the pulmonary bed can be regarded as the primary blood pump. Maier et a122have reported results from a most elegant dog experiment in which pairs of sonic transmitter/sensors were implanted along major heart axes. Sonic impulse traverse times then provided a direct measurement of axial cardiac dimensions. Other sensors also implanted were aortic and coronary EM flowmeters, and pressure transducers. After five to six weeks of healing, subcutaneous sensor terminals were excised, and closed chest compression experiments were performed. It was reported that cardiac dimensions changed during chest compression in a way that indicated direct mechanical compression. (Heart thickness was reduced, while width and length increased.) Also, heart dimensions increased along all three axes during diastolic ventilation, thus lending credence to earlier speculation that heart filling improved during ventilation. This field of research is still somewhat controversial. One problem is the difficulty of finding an animal model for such studies that can be meaningfully applied to the human situation. Dog chest anatomy is extremely variable in the mongrel animals usually used for such studies, with a more pointed chest and a larger proportion of tissue space between sternum and heart than in the human body. Babbs et up3 observed in dogs a significant threshold for sternal deflection before measurable cardiac output was observed. Rosborough (unpublished studies, 1982- 1983) has reported frequent liver lacerations in dogs subjected only to sternal compression, although such lacerations had not been observed in this writer’s earlier research.2 In dogs and in other animals with pointed chests, it is difficult to maintain the animal’s supine position during cyclic sternal compression, requiring some form of stabilization device such as a V cradle in contact with the animal’s rib cage, which might well
FIGURE 12 (nbove). The Thumper@ Model 1004 cardiopulmonary resuscitator (Michigan Instruments, Inc.). FIGURE 13 (center). facturing Co.). FIGURE 14 (below). Austria).
The Model SO-90 HLR (Brunswick ManuThe Reanimator
3000 (W. Sohngen Gmbh,
267
AMERICAN
JOURNAL
OF EMERGENCY
MEDICINE
FIGURE 15 (above). Microprocessor-programmed nary resuscitator (Michigan Instruments, Inc.). FIGURE 16 (below). Inc.).
n Volume 2, Number 3 m May 1984
cardiopulmo-
The SCV-CPR unit (Michigan Instruments,
inhibit rib flexure and is a condition not found in compressing the human chest. Similar problems exist with baboon* and swine models. With swine, Lambrew and Hodgkin (unpublished studies, 1979) have reported a significant inciRosborough (unpublished dence of “stone-heart.” studies, 1982-1983) reports the successful use of the rhesus monkey, but the great difference in size between the adult human and monkey chests is a flaw in this model; also, the risk of herpes B simian virus infection exists for experimenters who have not acquired immunity. The chimpanzee might be an attractive model, but the cost is prohibitive. Thus, no completely satisfactory animal model for CPR has been found. Moreover, ethical considerations limit clinical experiments. Another problem in such experiments is the effect of various anesthetic agents used in animal research. 268
The barbiturates appear to be brain protective’4,‘5 as opposed to other types of anesthetic agents (e.g., ketamine), thus, perhaps, improving long term survival results. Much research is needed in pharmacology as applied during CPR. Currently, calcium blocking agents26 and epinephrine loading19y27are receiving much attention, as well as bretylium tosylate28*29 for use in ventricular fibrillation, and methoxamine as a possible preferred substitute for epinephrine.30.3’ It seems probable that the following aspects of mechanized CPR will be subjected to intensive study: 1. Synchronized compression ventilation CPR, in which high intrathoracic pressures are obtained during chest compression by “clamping” of the airway during several cycles of chest compression, during which lung ventilation is continued during chest relaxation (diastole) at benign pressure levels. 2. Cyclic abdominal compression during chest relaxation (abdominal counterpulsation) either by a plunger or by an inflatable garment. 3. Combined CPR and defibrillator with a precordial electrode built into the compressor’s chest pad. and with a posterior electrode under the patient’s back, with application of defibrillator shock synchronized to chest compression so that the shock is given near the peak of compression, yielding minimum electrode resistance and minimum path length. 4. A variation of the above technique in which the posterior electrode is replaced by an electrode on an esophageal tube directly beneath the heart. Early animal experiments indicate that this pathway may be an ideal path for minimum energy defibrillation32 (Redding JS et al. Unpublished information). All of these efforts are intended to bring about significant improvements over the present methods, which must still be considered only marginally successful. All suggest the need for more complex and demanding CPR protocols, mandating the use of mechanical devices. Unlike currently available equipment, which aims to optimize manual CPR technique, present and future investigations will doubtlessly concentrate on defining and developing optimal mechanical CPR. REFERENCES 1. Kouwenhoven WB, Jude JR, Knickerbocker GG. Closed chest cardiac massage. JAMA 1960;1?3:1064. 2. Birch LH, Kenney LJ, Doornbos F, et al. A study of external cardiac compression. J Mich Med Sot 1962;61:1346. 3. Taylor GJ, Tucker WM, Greene HL, et al. Importance of prolonged compression during cardiopulmonary resuscitation in man. N Engl J Med 1977;296:1515. 4. Wilder RJ, Weir D, Rush D, et al. Methods of coordinating ventilation in closed chest cardiac massage in the dog. Surgery 1963;53:166. 5. Standards of cardiopulmonary resuscitation (CPR) and emergency cardiac care (ECC). JAMA 1974;227:837.
BARKALOW
6. Proceedings of the National Research Council/American Heart Association. Washington, DC: National Academy of Sciences, 1967:97-101. 7. Chandra N, Rudikoff M, Weisfeldt ML. Simultaneous chest compression and ventilation at high ariway pressure during cardiopulmonary resuscitation. Lancet 1980; 1:175. 8. Criley JM, Blaufuss AN, Kissel GL. Cough-induced cardiac compression. JAMA 1976;236:1246. 9. Niemann JT, Rosborough JP, Hausknecht M, et al. Pressure synchronized cineangiography during experimental cardiopulmonary resuscitation. Circulation 1981;64:985. 10. Krischer JP, Melker RJ, Barkalow CE. A programmable resuscitator for evaluation of CPR standards. Med lnstrum 1980;14:1. 11. Taylor GJ, Rubin R, Tucker M, et al. External cardiac compression: A randomized comparison of mechanical and manual techniques. JAMA 1978;240:644. 12. McDonald JL. Systolic and mean arterial pressures during manual and mechanical CPR in humans. Ann Emerg Med 1982;11:292. 13. Gomez-Arnau J, Criado A, Martinez MV, et al. Hyperkalemic cardiac arrest: Prolonged heart massage and simultaneous hemodialysis. Crit Care Med 1981;9:556. 14. Lilja GP, Hill M, Ruiz E, et al. Clinical assessment of patients undergoing CPR in the emergency department. JACEP 1979;8:81-83. 15. Sims JK, Penick M. How much CPR is enough CPR? (Letter) JACEP 1978;7:218-220. 16. Vasu, CM. The need for protocol. Emergency 1978;10:6. 17. Ralston S, Babbs C, Niebauer M. Cardiopulmonary resuscitation with interposed abdominal compression in dogs. Anesth Analg 1982;61:645. 18. Voorhees W, Niebauer M, Babbs C. Improved oxygen delivery during cardiopulmonary resuscitation and interposed abdominal compressions. Ann Emerg Med 1983;12:128. 19. Walker J, Bruestle J, White B, et al. Perfusion of the cerebral cortex using abdominal counterpulsation during CPR. Am J Emerg Med (in press). 20. Lute JM, Ross BK, O’Quin RJ, et al. Regional blood flow during cardiopulmonary resuscitation in dogs using si-
21.
22.
23.
24.
25.
n MECHANIZED
CPR
multaneous and nonsimultaneous compression and ventilation. Circulation 1983;67:2. Rosborough JP, Niemann JT, Criley JM, et al. Lower abdominal compression with synchronized ventilation: A CPR modality (abstract). Circulation 1981;64(Suppl IV):IV-303. Maier GW, Olsen CO, Tyson GS, et al. The physiology of external cardiac massage in the intact dog (abstract). Circulation 1981;64(Suppl IV):IV-303. Babbs C, Voorhees Wm, Fitzgerald K, et al. Relationship of blood pressure and flow during CPR to chest compression amplitude: Evidence for an effective compression threshold. Ann Emerg Med 1983;12:527. Bleyaert AL, Nemoto EM, Safar P, et al. Thiopental amelioration of brain damage after global ischemia in monkeys. Anesthesiology 1978;49:390. Safar P: Amelioration of post-ischemic brain damage with barbiturates. Stroke 1980;15:1.
26. Winegar CP, Orzie H, White BC, et al: Early amelioration of neurologic deficit by lidoflazime after fifteen minutes of cardiopulmonary arrest in dogs. Ann Emerg Med 1983;12:471. 27. Yakaitis RW, Otto CW, Blitt CD: Relative importance of alpha and beta adrenergic receptors during resuscitation. Crit Care Med 1979;7:293-296. 28. Nowak RM, Bodnar TJ, Dronen S, et al. Bretylium tosylate as initial treatment for cardiopulmonary arrest: Randomized comparison with placebo. Ann Emerg Med 1981;10:404. 29. Harrison EE, Amey BD: The use of bretylium in prehospital ventricular fibrillation. Am J Emerg Med 1983; 1 :l-6. 30. Livesay JJ, Follette DM, Fey KK, et al: Optimizing myocardial supply/demand balance with alpha adrenegeric drugs during cardiac resuscitation. J Thorac Cardiovasc Surg 1978; 98:794. 31. Redding JS, Haynes RR, Thomas JD: Drug therapy suscitation from electromechanical dissociation. Care Med 1983; 11:681.
in reCrit
32. Elam JO. Esophageal electrocardiography and low-energy ventricular defibrillation. In Safar P, Elam JO (eds). Advances in Cardiopulmonary Resuscitation. New York: Springer-Verlag, 1977:167-174.
269
Seminars
Mechanized Cardiopulmonary Resuscitation: Past, Present, and Future C. E. BARKALOW,
MA
The development of a successful external cardiac defibrillator by Kouwenhouven et al,’ and their revival of the concept of cardiac compression through the intact chest, published in 1960, gave promise of a new era in resuscitation in which body perfusion, as well as ventilation, could be maintained as a first aid procedure, and cardioversion could be achieved without the need for a thoractomy. Despite the fact that today, 24 years later, CPR based on current standards of performance must be regarded as a marginally successful technique, one must be truly impressed with its widespread acceptance by the medical profession, the heart associations, the American National Red Cross, the providers of emergency medicine both in and out of the hospital, and lay persons of whom hundreds of thousands have been trained in the technique and to whom the letters “CPR” have a readily understood meaning. Perhaps it is not surprising, then, that despite the marginality of the procedure, many successful resuscitations continue to be reported. The “epidemic of sudden unexpected death“ is pervasive in our society. This fact, coupled with the widely disseminated knowledge and practice of CPR, provides, statistically, many opportunities to practice this form of first aid. Although some investigators might contest the claim, the current standards for performing CPR as published in 1980, authored by a panel of professionals representing the American Heart Association, the National Research Council, and the American National Red Cross, estimate that CPR performed to these standards provides adequate support for over 40% of patients, to the extent that electrical cardioversion is possible. Today this may well be regarded as highly Received igan.
from Michigan
Instruments,
Inc., Grand Rapids, Mich-
Manuscript received November 12, 1983; revision received uary 30, 1984; revision accepted February 2, 1984.
Jan-
Address reprint requests to Mr. Barkalow: Michigan Instruments, Inc., 6300 28th Street SE, Grand Rapids, MI 49506. Key Words: Cardiopulmonary resuscitation, defibrillation. 262
optimistic; however, reduction by a factor of 2, or even 3, still results in a highly significant total of successful outcomes. Moreover, because of the number of cases treated by providers of prehospital or in-hospital medical care, even small improvements in the success rate, as might be attained by more extensive training, optimization of present techniques, or improved protocols for performing CPR, can lead to significant advances in the statistics of survival. Thus, from a public health point of view, progress in cardiopulmonary resuscitation technology holds much promise and much current interest. THE VALUE OF MECHANIZED CARDIOPULMONARY RESUSCITATION There are three basic reasons establishing the need for mechanical equipment used to perform CPR: 1. Equipment used in the scientific study of CPR per se, providing constant levels of support and protocol, and providing on-call capabilities for selection of varied, predetermined CPR protocols for “cause and effect” investigations. 2. Mechanical equipment that can be designed to optimize CPR performance based on the present standards for strictly manual CPR. Commerically available gas-powered machines can be engineered to overcome all of the shortcomings of the mechanical technique, and can efficiently, safely, and for extended periods provide optimal support levels otherwise requiring two ore more persons to perform. 3. Mechanical devices can be engineered to perform CPR to new protocols, optimized for machine resuscitation per se, without consideration for manual limitations (both physical and mental), and can provide “second aid” support levels transcending “first aid” CPR in much the same way that modern ventilatory resuscitators transcend the first aid manual methods of artificial respiration. At the same time it should be stated that mechanized equipment will never replace the manual first aid techniques, for obvious reasons. The goal is, and always will be, to provide mechanized
BARKALOW
n MECHANIZED
CPR
equipment that can be brought to bear as early as possible to increase the probability of a successful outcome. MECHANIZED EQUIPMENT OF THE PAST Following the early 1959-1960, there was opment of mechanized It was recognized would be an arduous
work of Kouwenhoven et al in a flurry of effort in the develCRP equipment. quite early that manual CPR though possible task and that
FIGURE 3 (above). The Harkins-Bramson synchronous cardiomassage machine (Hallikainen Instruments). FIGURE 4 (below).
The Westinghouse
electro-
“iron heart.”
t
FIGURE I (above). The Beck-Rand unit for closed-chest pulmonary resuscitation. FIGURE 2 (below).
The heart reactivator.
cardio-
there would be problems of training, fatigue, assurance of control, and physical limitations (e.g., a petite female nurse applying CPR to a robust man). Thus, most of the effort to develop mechanized equipment was aimed at optimizing standard CPR performance. By the middle 1960s many devices were marketed for the purpose of providing support based on current manual standards and intended for routine use in hospital and ambulance. Figures 1 through 6 show some of these devices, only a few of which remain in production at present. However, at least one of the early mechanized units was designed for “programmable CPR,” intended to investigate the optimization of CPR protocol. This device (Fig. 7), engineered by Barkalow and co-workers was used in experiments starting in 1960. The experiments were conducted and reported by Birch et al.* Animal studies used two baboons, one pig, and several 263
AMERICAN
JOURNAL
OF EMERGENCY
MEDICINE
n Volume 2, Number 3 W May 1984
significant in determining mean AV pressure differential. 2. The ratio of systolic/diastolic timing did appear significant, optimal perfusion potential being obtained at a 70:30 ratio. 3. Positive pressure ventilation, whether randomized or synchronized relative to chest compression, had a postivie influence on perfusion potential. Indeed, to evaluate the effect of varying parameters of chest compression on perfusion pev se, one needed to interrupt ventilation in order to obtain stable nonaugmented readings. Figure 8 shows the effect of duration of systole on perfusion potential, later corroborated by investigations elsewhere.3 At that time, one of the authors of the report just described2 was a member of the CPR committee of the American Heart Association, and it seems likely that the results reported from this study were of some influence on the early standards for CPR set by that committee. Shortly thereafter, Wilder et al4 reported similar findings linking intermittent positive pressure ventilation with increases in perfusion potential. Indeed, those authors proposed the possibility of frequent ventilations, not to improve blood gas exchange but to enhance cardiac output during ECC. In retrospect, the mechanics of squeezing the heart between sternum and spine without embarrassing valve competence may seem questionable. Yet, at that time, few persons expressed doubts about this perhaps simplistic explanation. Observations of the effect of positive pressure ventilation in improving perfusion potential were explained by the theory of “improved venous return” to the right side of the heart. In those years, direct cardiac mechanical compression of the
FIGURE 5 (nbove). FIGURE 6 (below). Tech Laboratories).
The Cardi-activator (Cardiac Products Corp.). The Tamband heart-lung resuscitator (Medi-
dogs. The overall effectiveness of closed chest external cardiac compression (ECC) was impressive. Several experiments were performed under aseptic conditions and resulted in long-term survival. In this study, mean AV pressure differentials across the femoral bed were used as an indicator of perfusion potential, and the effects of varied protocol were validated by frequent returns to control protocol. On the basis of usable data from only a few dogs, the following observations were reported: 1. The rate of cardiac compression (cycles per minute, or cpm), within limits, did not appear to be 264
FIGURE -7. Early programmable chest compr&&, used for studies at Buttenvorth Hospital, Grand Rapids, Michigan, 19601963 (Michigan Instruments, Inc.).
BARKALOW n MECHANIZED CPR
-Rem
_.
.
i
IO
20
a0
40 DURATION
FIGURE 8.
External cardiac compression:
ED OF -L
oil
70 %
effect of duration of systole. Force: 60 lb. Rate: 60 cpm. Data gathered April 6, 1962.
heart was the generally accepted theoretic mechanism for ejection of blood from the thorax during external chest compression (Fig. 9), a view supported at the National Research Council/American Heart Association meeting of 1966. Another national conference on CPR, sponsored jointly by the American Heart Association and the National Academy of Sciences, was held in 1973. The first published national standard for the performance of manual CPR emerged from the meeting.’ Indeed, all of the equipment for standard CPR was, and still is, based on the physiologic explanations of CPR contained in that document and in the 1966 proceedings of the National Research Council/American Heart Association.6 Between 1962 and 1968 there was little activity in CPR research. In 1968, a special punched-card programmable experimental cardiopulmonary resuscitator (Fig. lo), which provided the capability of variable, repeatable CPR programming, was developed for Dr. Joel Nobel at the Emergency Care Research Institute. This equipment was later used by Chandra et a16at Johns Hopkins University and became the basis for their studies aimed at the optimization of CPR protocol. In the 1970s the work of this group7 and that of Criley, Niemann, and associatess9 clarified the significance of the pulmonary bed as a blood pump, influenced by cycled intrathoracic pressures. Neverthe-
less, these investigators could not define the pulmonary bed as the only available CPR pump, and older CPR techniques were not displaced. Indeed, to some investigators it seemed quite logical that both mechanisms for the pumping of blood, particularly in the human being, might be utilized, and that such a combination might well result in levels of support greater than either modality alone. In 1979, a more sophisticated programmable unit was developed, which used pencil-marked IBM computer cards to set specific CPR protocols over a wide range of flexibility (Fig. 1l).‘O PRESENT STATUS OF MECHANIZED EQUIPMENT FOR CARDIOPULMONARY RESUSCITATION Insofar as “standard” CPR units are concerned, only three such devices are in current production: (1) the Thumper@ cpr device (Michigan Instruments, Inc., Grand Rapids, Michigan) (2) the HLR (Brunswick Manufacturing Co., Boston, Massachusetts) and (3) the Reanimator 3000 (W. Sohngen Gmbh, Austria (Figs. 12, 13, and 14). Basically, all these units attempt to optimize CPR on the basis of current American Heart Association standards. There are differences in the mechanism of ventilation; the Thumper@ unit utilizes a full flow, pressure limited, time cycled principle; the HLR uses the discharge of a fixed volume of gas, stored under 265
AMERICAN
JOURNAL
OF EMERGENCY
MEDICINE
n Volume 2, Number 3 n May 1984
scribed individual protocols “read only memory” chips.
stored on one or more
THE FUTURE OF MECHANIZED CARDIOPULMONARY RESUSCITATION Current research is intended to bring about significant improvement in support levels over present CPR methods. Referring back to earlier observations that lung ventilation per se,in conjunction with chest compression, had a positive effect on blood pumping, it was to be expected that equipment aimed at inducing high intrathoracic pressures in combination with chest compression woud be investigated. One form of this technique, now called synchronized compression ventilation CPR (SCV-CPR) is currently being used in clinical field test trials (Fig. 16). Specifications for the equipment originated from the Johns Hopkins University investigators. The equipment was engineered and pro-
FIGURE 9. The physiology of external cardiac compression, as it was understood in 1966. (From Proceedings of the National Research Council/American Heart Association, 1967.)
relatively high pressure (up to 20 psi) in a small container; and the Austrian unit stores exhaust gas from chest compression in a flexible bag (test lung) for subsequent discharge into the lungs. The basic alternative to the present resuscitators is manual CPR, since both are based on the same standards. The advantages of mechanical over manual are significant, since the mechanical devices can be designed to provide optimal performance to the standards, are nontiring, do not need retraining, and replace two-person teams. Nearly 20 years of field experience with these units has established them as valuable devices for basic life support and advanced cardiac life support. To this writer’s knowledge, only two definitive studies’1q12of mechanical versus manual CPR have been reported supporting this statement. However, several case reports 13-15and one statistical field study16 support the conclusion that mechanical CPR equipment performing to manual standards can be a successful life support technique. In a small but significant proportion of attempts, viability is maintained, frequently for a long time. In these cases, cardiac output levels, cerebral perfusion levels, and blood gases are at least adequate. Also, defibrillation after CPR is successful in a small but significant number of cases, with return of endogenous heart function indicating that myocardial tone in these cases has been adequately maintained. In current experiments, the latest in programmable CPR devices (Fig. 15) uses a microprocessor for control and sets CPR protocol by instant recall of pre266
Punched-card programmable carFIGURE 10 (above and center). diopulmonary resuscitator (Michigan Instruments, Inc., 1968). FIGURE 11 (below). Marked-card programmable cardiopulmonary resuscitator (Michigan Instruments, Inc., 1979).
BARKALOW w MECHANIZED CPR
duced by Michigan Instruments, Inc. Sixteen units are currently being employed in the study, under NIH grant and administered by the University of Florida and Johns Hopkins University. Other investigators are concentrating efforts in somewhat different directions. Some are studying various forms of abdominal compression. Babbs er u/17,18 and Walker et al have independently reported that abdominal counterpulsation pressure combined with standard chest compression produces significant increases in total cardiac output and in cerebral and possibly coronary perfusion levels. Still other investigators20 are working with equipment that attempts to simulate “cough CPR.” Most of this equipment uses inflatable garments (vests) with cyclic tilling and emptying, although in at least one case21 the Thumper@ cpr device has been used to compress a sealed air bag garment. Some investigators, however, disagree with the theory that the pulmonary bed can be regarded as the primary blood pump. Maier et a122have reported results from a most elegant dog experiment in which pairs of sonic transmitter/sensors were implanted along major heart axes. Sonic impulse traverse times then provided a direct measurement of axial cardiac dimensions. Other sensors also implanted were aortic and coronary EM flowmeters, and pressure transducers. After five to six weeks of healing, subcutaneous sensor terminals were excised, and closed chest compression experiments were performed. It was reported that cardiac dimensions changed during chest compression in a way that indicated direct mechanical compression. (Heart thickness was reduced, while width and length increased.) Also, heart dimensions increased along all three axes during diastolic ventilation, thus lending credence to earlier speculation that heart filling improved during ventilation. This field of research is still somewhat controversial. One problem is the difficulty of finding an animal model for such studies that can be meaningfully applied to the human situation. Dog chest anatomy is extremely variable in the mongrel animals usually used for such studies, with a more pointed chest and a larger proportion of tissue space between sternum and heart than in the human body. Babbs et up3 observed in dogs a significant threshold for sternal deflection before measurable cardiac output was observed. Rosborough (unpublished studies, 1982- 1983) has reported frequent liver lacerations in dogs subjected only to sternal compression, although such lacerations had not been observed in this writer’s earlier research.2 In dogs and in other animals with pointed chests, it is difficult to maintain the animal’s supine position during cyclic sternal compression, requiring some form of stabilization device such as a V cradle in contact with the animal’s rib cage, which might well
FIGURE 12 (nbove). The Thumper@ Model 1004 cardiopulmonary resuscitator (Michigan Instruments, Inc.). FIGURE 13 (center). facturing Co.). FIGURE 14 (below). Austria).
The Model SO-90 HLR (Brunswick ManuThe Reanimator
3000 (W. Sohngen Gmbh,
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AMERICAN
JOURNAL
OF EMERGENCY
MEDICINE
FIGURE 15 (above). Microprocessor-programmed nary resuscitator (Michigan Instruments, Inc.). FIGURE 16 (below). Inc.).
n Volume 2, Number 3 m May 1984
cardiopulmo-
The SCV-CPR unit (Michigan Instruments,
inhibit rib flexure and is a condition not found in compressing the human chest. Similar problems exist with baboon* and swine models. With swine, Lambrew and Hodgkin (unpublished studies, 1979) have reported a significant inciRosborough (unpublished dence of “stone-heart.” studies, 1982-1983) reports the successful use of the rhesus monkey, but the great difference in size between the adult human and monkey chests is a flaw in this model; also, the risk of herpes B simian virus infection exists for experimenters who have not acquired immunity. The chimpanzee might be an attractive model, but the cost is prohibitive. Thus, no completely satisfactory animal model for CPR has been found. Moreover, ethical considerations limit clinical experiments. Another problem in such experiments is the effect of various anesthetic agents used in animal research. 268
The barbiturates appear to be brain protective’4,‘5 as opposed to other types of anesthetic agents (e.g., ketamine), thus, perhaps, improving long term survival results. Much research is needed in pharmacology as applied during CPR. Currently, calcium blocking agents26 and epinephrine loading19y27are receiving much attention, as well as bretylium tosylate28*29 for use in ventricular fibrillation, and methoxamine as a possible preferred substitute for epinephrine.30.3’ It seems probable that the following aspects of mechanized CPR will be subjected to intensive study: 1. Synchronized compression ventilation CPR, in which high intrathoracic pressures are obtained during chest compression by “clamping” of the airway during several cycles of chest compression, during which lung ventilation is continued during chest relaxation (diastole) at benign pressure levels. 2. Cyclic abdominal compression during chest relaxation (abdominal counterpulsation) either by a plunger or by an inflatable garment. 3. Combined CPR and defibrillator with a precordial electrode built into the compressor’s chest pad. and with a posterior electrode under the patient’s back, with application of defibrillator shock synchronized to chest compression so that the shock is given near the peak of compression, yielding minimum electrode resistance and minimum path length. 4. A variation of the above technique in which the posterior electrode is replaced by an electrode on an esophageal tube directly beneath the heart. Early animal experiments indicate that this pathway may be an ideal path for minimum energy defibrillation32 (Redding JS et al. Unpublished information). All of these efforts are intended to bring about significant improvements over the present methods, which must still be considered only marginally successful. All suggest the need for more complex and demanding CPR protocols, mandating the use of mechanical devices. Unlike currently available equipment, which aims to optimize manual CPR technique, present and future investigations will doubtlessly concentrate on defining and developing optimal mechanical CPR. REFERENCES 1. Kouwenhoven WB, Jude JR, Knickerbocker GG. Closed chest cardiac massage. JAMA 1960;1?3:1064. 2. Birch LH, Kenney LJ, Doornbos F, et al. A study of external cardiac compression. J Mich Med Sot 1962;61:1346. 3. Taylor GJ, Tucker WM, Greene HL, et al. Importance of prolonged compression during cardiopulmonary resuscitation in man. N Engl J Med 1977;296:1515. 4. Wilder RJ, Weir D, Rush D, et al. Methods of coordinating ventilation in closed chest cardiac massage in the dog. Surgery 1963;53:166. 5. Standards of cardiopulmonary resuscitation (CPR) and emergency cardiac care (ECC). JAMA 1974;227:837.
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6. Proceedings of the National Research Council/American Heart Association. Washington, DC: National Academy of Sciences, 1967:97-101. 7. Chandra N, Rudikoff M, Weisfeldt ML. Simultaneous chest compression and ventilation at high ariway pressure during cardiopulmonary resuscitation. Lancet 1980; 1:175. 8. Criley JM, Blaufuss AN, Kissel GL. Cough-induced cardiac compression. JAMA 1976;236:1246. 9. Niemann JT, Rosborough JP, Hausknecht M, et al. Pressure synchronized cineangiography during experimental cardiopulmonary resuscitation. Circulation 1981;64:985. 10. Krischer JP, Melker RJ, Barkalow CE. A programmable resuscitator for evaluation of CPR standards. Med lnstrum 1980;14:1. 11. Taylor GJ, Rubin R, Tucker M, et al. External cardiac compression: A randomized comparison of mechanical and manual techniques. JAMA 1978;240:644. 12. McDonald JL. Systolic and mean arterial pressures during manual and mechanical CPR in humans. Ann Emerg Med 1982;11:292. 13. Gomez-Arnau J, Criado A, Martinez MV, et al. Hyperkalemic cardiac arrest: Prolonged heart massage and simultaneous hemodialysis. Crit Care Med 1981;9:556. 14. Lilja GP, Hill M, Ruiz E, et al. Clinical assessment of patients undergoing CPR in the emergency department. JACEP 1979;8:81-83. 15. Sims JK, Penick M. How much CPR is enough CPR? (Letter) JACEP 1978;7:218-220. 16. Vasu, CM. The need for protocol. Emergency 1978;10:6. 17. Ralston S, Babbs C, Niebauer M. Cardiopulmonary resuscitation with interposed abdominal compression in dogs. Anesth Analg 1982;61:645. 18. Voorhees W, Niebauer M, Babbs C. Improved oxygen delivery during cardiopulmonary resuscitation and interposed abdominal compressions. Ann Emerg Med 1983;12:128. 19. Walker J, Bruestle J, White B, et al. Perfusion of the cerebral cortex using abdominal counterpulsation during CPR. Am J Emerg Med (in press). 20. Lute JM, Ross BK, O’Quin RJ, et al. Regional blood flow during cardiopulmonary resuscitation in dogs using si-
21.
22.
23.
24.
25.
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multaneous and nonsimultaneous compression and ventilation. Circulation 1983;67:2. Rosborough JP, Niemann JT, Criley JM, et al. Lower abdominal compression with synchronized ventilation: A CPR modality (abstract). Circulation 1981;64(Suppl IV):IV-303. Maier GW, Olsen CO, Tyson GS, et al. The physiology of external cardiac massage in the intact dog (abstract). Circulation 1981;64(Suppl IV):IV-303. Babbs C, Voorhees Wm, Fitzgerald K, et al. Relationship of blood pressure and flow during CPR to chest compression amplitude: Evidence for an effective compression threshold. Ann Emerg Med 1983;12:527. Bleyaert AL, Nemoto EM, Safar P, et al. Thiopental amelioration of brain damage after global ischemia in monkeys. Anesthesiology 1978;49:390. Safar P: Amelioration of post-ischemic brain damage with barbiturates. Stroke 1980;15:1.
26. Winegar CP, Orzie H, White BC, et al: Early amelioration of neurologic deficit by lidoflazime after fifteen minutes of cardiopulmonary arrest in dogs. Ann Emerg Med 1983;12:471. 27. Yakaitis RW, Otto CW, Blitt CD: Relative importance of alpha and beta adrenergic receptors during resuscitation. Crit Care Med 1979;7:293-296. 28. Nowak RM, Bodnar TJ, Dronen S, et al. Bretylium tosylate as initial treatment for cardiopulmonary arrest: Randomized comparison with placebo. Ann Emerg Med 1981;10:404. 29. Harrison EE, Amey BD: The use of bretylium in prehospital ventricular fibrillation. Am J Emerg Med 1983; 1 :l-6. 30. Livesay JJ, Follette DM, Fey KK, et al: Optimizing myocardial supply/demand balance with alpha adrenegeric drugs during cardiac resuscitation. J Thorac Cardiovasc Surg 1978; 98:794. 31. Redding JS, Haynes RR, Thomas JD: Drug therapy suscitation from electromechanical dissociation. Care Med 1983; 11:681.
in reCrit
32. Elam JO. Esophageal electrocardiography and low-energy ventricular defibrillation. In Safar P, Elam JO (eds). Advances in Cardiopulmonary Resuscitation. New York: Springer-Verlag, 1977:167-174.
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