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Active compression-decompression cardiopulmonary resuscitation (CPR): The latest “new” CPR?
Active Compression-Decompression Cardiopulmonary Resuscitation (CPR): The Latest "New" CPR? HE O U T C O M E of resuscitation from cardiac arrest is dismal. Initial resuscitation rates of 40% and survival to hospital discharge of 10% to 15% are possible with an effective rapid-response emergency medical system for out-of-hospital cardiac arrests. ~,2 This level of survival is achieved only if basic life support is started within 4 minutes and defibrillation applied within 8 minutes. 1In most communities, results are much worse. Studies reporting large numbers of patients undergoing cardiopulmonary resuscitation (CPR) typically have initial resuscitation rates of 20% to 30% and survival to discharge of 3% to 50~. 3'4 In the United States, one-half million deaths per year are caused by coronary artery disease, and the majority are sudden deaths. 5 The severity of the myocardial injury is the primary determining factor for some of these victims. But for many, sudden death is presumed to be associated with arrhythmias rather than massive myocardial necrosis. Prompt provision of CPR by bystanders, an efficient emergency medical system (EMS), and early defibrillation should result in many saved lives. And it does. The main difference between usual survival statistics and the best results is widespread community CPR training and a rapid-response EMS system. If all communities met the standards of the best, approximately 50,000 additional lives could be saved. Faster definitive therapy improves survival better than any variations in CPR technique. Therefore, much effort has been devoted to designing a safe, effective automatic defibrillator that can be applied by untrained individuals. 2 Despite these considerations, the outcome of resuscitation from cardiac arrest is poor. Standard CPR achieves a cardiac output approximately 10% to 33% of normal. Since the development of closed chest compressions in 1960, 6 clinicians and researchers have been searching for a better way. The usual reasoning is that survival will be improved if only there were better blood flow and blood pressure during CPR. Early studies resulted in the addition of epinephrine to chest compressions and ventilation because of its long history and effectiveness in animals. 7,8 Recent suggestions that higher epinephrine doses would improve outcome have turned out to be unfounded. 3,4 Adjuncts to chest compressions were also investigated. Redding suggested that abdominal binding would help. 9 However, other early investigators stressed the potential for liver lacerations with binding, and it is not used clinically. TM More recently, investigations into circulatory physiology during CPR have led to several proposals for alternative techmques to standard closed chest compressions. Simultaneous ventilation and chest compression (so-called "new" CPR) was suggested by studies on the thoracic pump theory of blood flow in the 1970s. n Unfortunately, clinical trials found that it does not improve resuscitation success or survival. 12 Interposed abdominal compression-CPR (IACCPR) uses an additional rescuer to apply manual abdominal compression during the relaxation phase of chest compressions. 13Abdominal pressure is released when chest compression begins. A large randomized study of out-ofhospital cardiac arrest found no improvement in survival when IAC-CPR was compared with standard CPR, 14 al-
T
though a subsequent smaller study of in-hospital arrest demonstrated improved outcome using IAC-CPR. 15 The pneumatic CPR vest was developed to simulate the events of vigorous coughmg by inflating pneumatic bladders around the torso simultaneously with ventilation. 16Animal studies have found excellent hemodynamics and the ability to maintain viability for prolonged periods with this method. A recent preliminary human study using a modification of this technique found better aortic and coronary perfuslon pressures compared with standard CPR, but no improvement in survival. 17 For all these techniques, physiologic studies have been encouraging but none has been shown to consistently improve survival from cardiac arrest in clinical trials. The newest alternative technique is called active compression-decompression CPR (ACD-CPR). It developed from the anecdotal report of CPR performed with a plumber's helper applied to the anterior chest wallY Theoretically, active decompression of the chest wall might reduce intrathoracic pressure during the relaxation phase of chest compressions leading to improved venous return, increased stroke volume with compression, and better blood flow. A suction device that can be applied to the chest wall in order to enable active compression and decompression was developed. ~9 Comparison of standard CPR and ACD-CPR in shortterm cross-over studies in humans confirmed that active decompression reduced intrathoracic pressure and improved aortic and coronary perfuslon pressures. ~9,z° A carefully conducted study by Linder and colleagues compared hemodynamics and brain and heart blood flows between techniques m a porcine model of cardiac arrestY After 5 minutes of CPR, myocardial and cerebral blood flows were significantly higher with ACD-CPR compared with standard CPR. However, portending future clinical results, this difference was lost after administration of epinephrine and all animals in both groups were successfully resuscitated. When assessing clinical trials, it is important to note the end point being measured. Because CPR is a short-term intervention, restoration of spontaneous circulation or survival of 1 hour to hospital or intensive care unit (ICU) admission are frequently recorded. These short-term or intermediate (24-hour survival) end points might be important if unrelated in-hospital complications are influencing ultimate outcome. However, if progression of disease leads to death after hospital admission, improved immediate resuscitation has only prolonged dying. A worse scenario is somatic survival in a persistent vegetative state. Therefore, neurologically intact survival to hospital discharge must be the ultimate outcome of interest. During in-hospital cardiac arrest, two randomized trials of ACD-CPR comprising 62 and 53 patients have been reported. 22,23Immediate resusotation improved from 30% with standard CPR to 60% with ACD-CPR, and 24-hour survival was also improved. However, there was no difference in survival to discharge in either study. Two reports of out-of-hospital randomized trials of
Journal of Cardlothorac/c and VascularAnesthesla, Vo110, No 2 (February), 1996' pp 175-177
175
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CHARLES W OTTO
ACD-CPR have been published. 24,z5The trials were stopped early by the Food and Drug Administration (FDA) so that the intended sample sizes were not enrolled. Among 130 victims in St. Paul, MN, 24 there were statistically insignificant trends toward improved immediate resuscitation and ICU admission with ACD-CPR. There was statistically improved short-term survival in subsets of patients with short arrest times and rapid EMS response times, although no statistical adjustments were made for multiple comparisons. No differences were found in rates of hospital discharge or of return to baseline neurologic function. The second report pooled numbers from two studies, one in San Francisco and one in Fresno, CA, in order to attain the intended powerY Comparing ACD-CPR with standard CPR in a randomized cross-over design involving 860 total patients, there was no significant improvement or trend toward improvement in any early, intermediate, or longterm outcome variable or subset of patients. In this issue of the JOURNAL, Luiz and colleagues report the third major prehospital randomized clinical trial of ACD-CPR. 26 The study was performed on 56 arrest victims in Mannheim, Germany, and differs from the previous studies primarily m that randomization occurred on a case-by-case basis rather than a group cross-over design and that all resuscitation occurred at the scene directed by the physician present. The results are consistent with the California trials. There was no improvement or trend toward improvement in any outcome variable. The study may be somewhat underpowered because the number of patients was chosen on an extremely optimistic projection of early resuscitation. However, without even a trend toward better immediate resuscitation, it is unlikely that a major difference was missed. One of the more important observations from the study of Luiz et al is the improved outcome with standard CPR over historical controls. From 1992 to 1993, immediate resuscitation increased from 30% to 40% and survival to discharge from 7% to 13.3%. Similar findings were observed in the St. Paul trial. 24 Both groups suggested that a training effect during the study had contributed to improved performance of standard CPR. This is consistent with studies showing that performance is improved by simple reminders of proper technique, such as an audible rhythmic tone for proper compression r a t e F Perhaps the
most important message of these studies is that more lives could be saved if the current techniques were performed properly. Thus, ACD-CPR appears to be similar to IAC-CPR and the pneumatic vest. There is physiologic evidence of improved blood flow. Some studies showed improved early and intermediate outcomes, but none has found improved long-term survival. Two of the three pre-hospital studies found no evidence to support the use of the technique. Therefore, there seems little indication for its use at the current time. In addition to requiring extra equipment, most individuals find ACD-CPR very tiring to perform. The overwhelming majority of rescuers in Luiz' study found ACD-CPR to require more energy than standard CPR. Another bothersome, if minor, side effect of the technique is the high incidence of significant ecchymosis over the sternum associated with use of the suction device. About one third of victims show such skin lesions, and they can be quite disturbing to family members. 24-26 ACD-CPR remains an intriguing investigatlonal technique. Highest success has been found in studies on in-hospital arrest. In the United States, future investigations of the technique will be limited to in-hospital populations who give informed consent on hospital admission. The F D A has ruled that deferred consent or waiver of consent for resuscitation research is not consistent with protection of human subjects. This ruling resulted in the premature cessation of several of the studies cited here. 22,24,25 The current interpretation of regulations by a number of federal agencies regarding appropriate safeguards for human subjects is threatening the ability of investigators to conduct any resuscitation research on human subjects in the United States. There has been considerable discussion about this problem in several forums during the past 2 years. Unfortunately, little progress in resolving the issues has been made. Readers are referred to two excellent recent editorials for a complete discussion of this controversy. 28,29
Charles W. Otto, MD, FCCM Professor of Anesthesiology Associate Professor of Medicine University of Arizona College of Medicine Tucson, A Z
REFERENCES
1 Eisenberg MS, Bergner L, Hallstrom A: Cardiac resuscitation m the community. Importance of rapid provision and implications for program planning. JAMA 241 1905-1907, 1979 2 Weaver WD, Hill D, Fahrenbruch CE, et al Use of the automatic external defibrillator in the management of out-ofhospital cardmc arrest. N Engl J Med 319'661-666, 1988 3. Stlell IB, Hebert PC, Weitzman BN, et al High-dose epinephrine in adult cardiac arrest N Engl J Med 327 1045-1050, 1992 4. Brown CG. Martin DP, Pepe PE, et al' A comparison of standard-dose and high-dose epinephrine in cardmc arrest outside the hospital. N Engl J Med 327'1051-1055, 1992 5. Emergency Cardiac Care Committee and Subcommittees, American Heart Association. Guidelines for cardlopulmonary
resuscitation and emergency cardiac care. JAMA 268:2171-2295, 1992 6. Kouwenhoven WB, Jude JR, Knickerbocker GG: Closedchest cardiac massage. JAMA 173:1064-1067, 1960 7 Reddlng JS, Pearson JW: Evaluation of drugs for cardiac resuscitation Anesthesiology 24 203-207, 1963 8. Redding JS, Pearson JW: Resuscitation from ventricular fibrillation (drug therapy). JAMA 203:255-260, 1968 9 Reddlng JS: Abdominal compression in cardlopulmonary resuscitation Anesth Analg 50:668-675, 1971 10. Harris LC, I~rlmh B, Safar P. Augmentation of artificial circulation during cardiopulmonary resuscitation. Anesthesiology 28'730-734, 1967
INTRODUCTION
11. Rudikoff MJ, Maughan WL, Effrom M, et al: Mechanisms of blood flow during cardiopulmonary resuscitation. Circulation 61: 345-352, 1980 12. Kirscher JP, Fine EG, Weisfeld ML, et al: Comparison of pre-hospital conventional and simultaneous compression-ventxlatlon cardlopulmonary resuscitation. Crit Care Med 17:1263-1269, 1989 13. Babbs CF, Tacker WA: Cardlopulmonary resuscitataon with interposed abdommal compression Circulation 74:IV-37-IV-41, 1986 (suppl IV) 14. Mateer JF, Stueven HA, Thompson BM, et al: Pre-hospltal IAC-CPR versus standard CPR; paramedic resuscitation of cardiac arrests. Am J Emerg Med 3:143-146, 1985 15. Sack JB, Kesselbrenner MB, Bregman D: Survival from m-hospital cardiac arrest with interposed abdominal counterpulsatlon during cardiopulmonary resuscitation. JAMA 267:379-385, 1992 16. Criley JM, Nlernann JT, Rosborough JP, et al' Modifications of cardiopulmonary resuscitation based on the cough. Circulation 74'IV-42-IV-50, 1986 (suppl IV) 17. Halpern HR, Tsitlik JE, Belfand M, et al: A prehminary study of cardiopulmonary resuscitation by circumferential compression of the chest with use of a pneumatic vest. N Engl J Med 329:762-768, 1993 18. Lurie KG, Lmdo C, Chm J. CPR: The P stands for plumber's helper (letter) JAMA264:1661, 1990 19. Cohen TJ, Tucker KJ, Lurie KG, et al: Actwe compressiondecompression A new method of cardiopulmonary resuscitation. JAMA 267'2916-2923, 1992 20. Shultz JJ, Coffeen P, Sweeney M, et al: Evaluation of standard and active compressaon-decompression CPR m an acute human model of ventncular fibrillation. Circulation 89.684-693, 1994
177
21. Linder KH, Pfenulger EG, Lune KG, et al Effects of actwe compression-decompression resuscitation on myocardml and cerebral blood flow m pigs. Circulation 88"1254-1263, 1993 22. Cohen TJ, Goldner BG, Maccaro PC, et al: A comparison of active compression-decompression cardiopulmonary resuscitation for cardiac arrests occurring m the hospital. N Engl J Med 329:1918-1921, 1993 23. Tucker KJ, Galh F, Savltt MA, et al' Active compressiondecompression resuscitation' Effect of resusc~tatlon success after in-hospital cardiac arrest. J Am Coll Cardaol 24:201-209, 1994 24. Lurie KG, Shultz JJ, Callaham ML, et al. Evaluation of active compression-decompression CPR m wctlms of out-ofhospital cardiac arrest. JAMA 271.1405-1411, 1994 25. Schwab TM, Callaham ML, Madsen CD, et al: A randomized clinical trial of active compression-decompression CPR vs standard CPR in out-of-hospital cardiac arrest m two cities. JAMA 273:1261-1268, 1995 26. Lmz T, Elhnger K, Denz C' Actwe compression-decompression CPR does not improve survival in patients with pre-hospital cardiac arrest in a physician manned EMS systems J Cardlothorac Vasc Anesth 10'178-186, 1996 27. Kern KB, Sanders AB, Ralfe J, et al: A study of chest compression rates during cardiopulmonary resuscitation m humans. The Importance of rate-directed compressions. Arch Intern Med 152:145-149, 1992 28 Olson CM. The letter or the spirit. Consent for research in CPR. JAMA 271.1445-1447, i994 (editorial) 29. Olson CM, Rennle D' Plungers or polemics. Active compression-decompression CPR and federal policy (Editorial) JAMA 273"1229-1230, 1995
T
though a subsequent smaller study of in-hospital arrest demonstrated improved outcome using IAC-CPR. 15 The pneumatic CPR vest was developed to simulate the events of vigorous coughmg by inflating pneumatic bladders around the torso simultaneously with ventilation. 16Animal studies have found excellent hemodynamics and the ability to maintain viability for prolonged periods with this method. A recent preliminary human study using a modification of this technique found better aortic and coronary perfuslon pressures compared with standard CPR, but no improvement in survival. 17 For all these techniques, physiologic studies have been encouraging but none has been shown to consistently improve survival from cardiac arrest in clinical trials. The newest alternative technique is called active compression-decompression CPR (ACD-CPR). It developed from the anecdotal report of CPR performed with a plumber's helper applied to the anterior chest wallY Theoretically, active decompression of the chest wall might reduce intrathoracic pressure during the relaxation phase of chest compressions leading to improved venous return, increased stroke volume with compression, and better blood flow. A suction device that can be applied to the chest wall in order to enable active compression and decompression was developed. ~9 Comparison of standard CPR and ACD-CPR in shortterm cross-over studies in humans confirmed that active decompression reduced intrathoracic pressure and improved aortic and coronary perfuslon pressures. ~9,z° A carefully conducted study by Linder and colleagues compared hemodynamics and brain and heart blood flows between techniques m a porcine model of cardiac arrestY After 5 minutes of CPR, myocardial and cerebral blood flows were significantly higher with ACD-CPR compared with standard CPR. However, portending future clinical results, this difference was lost after administration of epinephrine and all animals in both groups were successfully resuscitated. When assessing clinical trials, it is important to note the end point being measured. Because CPR is a short-term intervention, restoration of spontaneous circulation or survival of 1 hour to hospital or intensive care unit (ICU) admission are frequently recorded. These short-term or intermediate (24-hour survival) end points might be important if unrelated in-hospital complications are influencing ultimate outcome. However, if progression of disease leads to death after hospital admission, improved immediate resuscitation has only prolonged dying. A worse scenario is somatic survival in a persistent vegetative state. Therefore, neurologically intact survival to hospital discharge must be the ultimate outcome of interest. During in-hospital cardiac arrest, two randomized trials of ACD-CPR comprising 62 and 53 patients have been reported. 22,23Immediate resusotation improved from 30% with standard CPR to 60% with ACD-CPR, and 24-hour survival was also improved. However, there was no difference in survival to discharge in either study. Two reports of out-of-hospital randomized trials of
Journal of Cardlothorac/c and VascularAnesthesla, Vo110, No 2 (February), 1996' pp 175-177
175
176
CHARLES W OTTO
ACD-CPR have been published. 24,z5The trials were stopped early by the Food and Drug Administration (FDA) so that the intended sample sizes were not enrolled. Among 130 victims in St. Paul, MN, 24 there were statistically insignificant trends toward improved immediate resuscitation and ICU admission with ACD-CPR. There was statistically improved short-term survival in subsets of patients with short arrest times and rapid EMS response times, although no statistical adjustments were made for multiple comparisons. No differences were found in rates of hospital discharge or of return to baseline neurologic function. The second report pooled numbers from two studies, one in San Francisco and one in Fresno, CA, in order to attain the intended powerY Comparing ACD-CPR with standard CPR in a randomized cross-over design involving 860 total patients, there was no significant improvement or trend toward improvement in any early, intermediate, or longterm outcome variable or subset of patients. In this issue of the JOURNAL, Luiz and colleagues report the third major prehospital randomized clinical trial of ACD-CPR. 26 The study was performed on 56 arrest victims in Mannheim, Germany, and differs from the previous studies primarily m that randomization occurred on a case-by-case basis rather than a group cross-over design and that all resuscitation occurred at the scene directed by the physician present. The results are consistent with the California trials. There was no improvement or trend toward improvement in any outcome variable. The study may be somewhat underpowered because the number of patients was chosen on an extremely optimistic projection of early resuscitation. However, without even a trend toward better immediate resuscitation, it is unlikely that a major difference was missed. One of the more important observations from the study of Luiz et al is the improved outcome with standard CPR over historical controls. From 1992 to 1993, immediate resuscitation increased from 30% to 40% and survival to discharge from 7% to 13.3%. Similar findings were observed in the St. Paul trial. 24 Both groups suggested that a training effect during the study had contributed to improved performance of standard CPR. This is consistent with studies showing that performance is improved by simple reminders of proper technique, such as an audible rhythmic tone for proper compression r a t e F Perhaps the
most important message of these studies is that more lives could be saved if the current techniques were performed properly. Thus, ACD-CPR appears to be similar to IAC-CPR and the pneumatic vest. There is physiologic evidence of improved blood flow. Some studies showed improved early and intermediate outcomes, but none has found improved long-term survival. Two of the three pre-hospital studies found no evidence to support the use of the technique. Therefore, there seems little indication for its use at the current time. In addition to requiring extra equipment, most individuals find ACD-CPR very tiring to perform. The overwhelming majority of rescuers in Luiz' study found ACD-CPR to require more energy than standard CPR. Another bothersome, if minor, side effect of the technique is the high incidence of significant ecchymosis over the sternum associated with use of the suction device. About one third of victims show such skin lesions, and they can be quite disturbing to family members. 24-26 ACD-CPR remains an intriguing investigatlonal technique. Highest success has been found in studies on in-hospital arrest. In the United States, future investigations of the technique will be limited to in-hospital populations who give informed consent on hospital admission. The F D A has ruled that deferred consent or waiver of consent for resuscitation research is not consistent with protection of human subjects. This ruling resulted in the premature cessation of several of the studies cited here. 22,24,25 The current interpretation of regulations by a number of federal agencies regarding appropriate safeguards for human subjects is threatening the ability of investigators to conduct any resuscitation research on human subjects in the United States. There has been considerable discussion about this problem in several forums during the past 2 years. Unfortunately, little progress in resolving the issues has been made. Readers are referred to two excellent recent editorials for a complete discussion of this controversy. 28,29
Charles W. Otto, MD, FCCM Professor of Anesthesiology Associate Professor of Medicine University of Arizona College of Medicine Tucson, A Z
REFERENCES
1 Eisenberg MS, Bergner L, Hallstrom A: Cardiac resuscitation m the community. Importance of rapid provision and implications for program planning. JAMA 241 1905-1907, 1979 2 Weaver WD, Hill D, Fahrenbruch CE, et al Use of the automatic external defibrillator in the management of out-ofhospital cardmc arrest. N Engl J Med 319'661-666, 1988 3. Stlell IB, Hebert PC, Weitzman BN, et al High-dose epinephrine in adult cardiac arrest N Engl J Med 327 1045-1050, 1992 4. Brown CG. Martin DP, Pepe PE, et al' A comparison of standard-dose and high-dose epinephrine in cardmc arrest outside the hospital. N Engl J Med 327'1051-1055, 1992 5. Emergency Cardiac Care Committee and Subcommittees, American Heart Association. Guidelines for cardlopulmonary
resuscitation and emergency cardiac care. JAMA 268:2171-2295, 1992 6. Kouwenhoven WB, Jude JR, Knickerbocker GG: Closedchest cardiac massage. JAMA 173:1064-1067, 1960 7 Reddlng JS, Pearson JW: Evaluation of drugs for cardiac resuscitation Anesthesiology 24 203-207, 1963 8. Redding JS, Pearson JW: Resuscitation from ventricular fibrillation (drug therapy). JAMA 203:255-260, 1968 9 Reddlng JS: Abdominal compression in cardlopulmonary resuscitation Anesth Analg 50:668-675, 1971 10. Harris LC, I~rlmh B, Safar P. Augmentation of artificial circulation during cardiopulmonary resuscitation. Anesthesiology 28'730-734, 1967
INTRODUCTION
11. Rudikoff MJ, Maughan WL, Effrom M, et al: Mechanisms of blood flow during cardiopulmonary resuscitation. Circulation 61: 345-352, 1980 12. Kirscher JP, Fine EG, Weisfeld ML, et al: Comparison of pre-hospital conventional and simultaneous compression-ventxlatlon cardlopulmonary resuscitation. Crit Care Med 17:1263-1269, 1989 13. Babbs CF, Tacker WA: Cardlopulmonary resuscitataon with interposed abdommal compression Circulation 74:IV-37-IV-41, 1986 (suppl IV) 14. Mateer JF, Stueven HA, Thompson BM, et al: Pre-hospltal IAC-CPR versus standard CPR; paramedic resuscitation of cardiac arrests. Am J Emerg Med 3:143-146, 1985 15. Sack JB, Kesselbrenner MB, Bregman D: Survival from m-hospital cardiac arrest with interposed abdominal counterpulsatlon during cardiopulmonary resuscitation. JAMA 267:379-385, 1992 16. Criley JM, Nlernann JT, Rosborough JP, et al' Modifications of cardiopulmonary resuscitation based on the cough. Circulation 74'IV-42-IV-50, 1986 (suppl IV) 17. Halpern HR, Tsitlik JE, Belfand M, et al: A prehminary study of cardiopulmonary resuscitation by circumferential compression of the chest with use of a pneumatic vest. N Engl J Med 329:762-768, 1993 18. Lurie KG, Lmdo C, Chm J. CPR: The P stands for plumber's helper (letter) JAMA264:1661, 1990 19. Cohen TJ, Tucker KJ, Lurie KG, et al: Actwe compressiondecompression A new method of cardiopulmonary resuscitation. JAMA 267'2916-2923, 1992 20. Shultz JJ, Coffeen P, Sweeney M, et al: Evaluation of standard and active compressaon-decompression CPR m an acute human model of ventncular fibrillation. Circulation 89.684-693, 1994
177
21. Linder KH, Pfenulger EG, Lune KG, et al Effects of actwe compression-decompression resuscitation on myocardml and cerebral blood flow m pigs. Circulation 88"1254-1263, 1993 22. Cohen TJ, Goldner BG, Maccaro PC, et al: A comparison of active compression-decompression cardiopulmonary resuscitation for cardiac arrests occurring m the hospital. N Engl J Med 329:1918-1921, 1993 23. Tucker KJ, Galh F, Savltt MA, et al' Active compressiondecompression resuscitation' Effect of resusc~tatlon success after in-hospital cardiac arrest. J Am Coll Cardaol 24:201-209, 1994 24. Lurie KG, Shultz JJ, Callaham ML, et al. Evaluation of active compression-decompression CPR m wctlms of out-ofhospital cardiac arrest. JAMA 271.1405-1411, 1994 25. Schwab TM, Callaham ML, Madsen CD, et al: A randomized clinical trial of active compression-decompression CPR vs standard CPR in out-of-hospital cardiac arrest m two cities. JAMA 273:1261-1268, 1995 26. Lmz T, Elhnger K, Denz C' Actwe compression-decompression CPR does not improve survival in patients with pre-hospital cardiac arrest in a physician manned EMS systems J Cardlothorac Vasc Anesth 10'178-186, 1996 27. Kern KB, Sanders AB, Ralfe J, et al: A study of chest compression rates during cardiopulmonary resuscitation m humans. The Importance of rate-directed compressions. Arch Intern Med 152:145-149, 1992 28 Olson CM. The letter or the spirit. Consent for research in CPR. JAMA 271.1445-1447, i994 (editorial) 29. Olson CM, Rennle D' Plungers or polemics. Active compression-decompression CPR and federal policy (Editorial) JAMA 273"1229-1230, 1995