sign in sign up
<<
Home , Circulatory system

EMERGENCY CARDIOVASCULAR CARE 0733–8651/02 $15.00 .00

CIRCULATORY ADJUNCTS Newer Methods of Cardiopulmonary Resuscitation

Charles F. Babbs, MD, PhD

Conventional cardiopulmonary resuscita- mately the same way as it was in the 1960s. tion—what has come to be called standard In keeping with the engineering maxim that CPR—has changed little since first introduced ‘‘if you keep on doing what you’re doing, in the early 1960s by Kouwenhoven et al.1 you’ll keep on getting what you’ve got,’’ suc- Standard CPR requires chest compressions at cess rates for standard CPR have changed a rate of 80 to 100 compressions/min in con- little over the past 40 years.5–9 Between 15% junction with mouth-to-mouth rescue breath- and 40% of all victims of nontraumatic car- ing.2 Positive ventilations (PPVs) are diac arrest are resuscitated, and approxi- given at an overall rate in the range of about mately 5% to 10% live to leave the hospital. 8 to 12 ventilations/min, depending on Despite lack of significant change on the whether one is doing one- or two-rescuer surface, a neglected community of researchers CPR. Refinements of standard CPR since its has made substantial progress in the labora- introduction in the 1960s have included in- tory and in the clinic during this same 40- creasing the rate of chest compression from year period. Results have lead to much fun- 60 compressions/min to 80 compressions/ damental understanding of the circulatory min or more, which research shows matters and of cardiac ar- little,3 and recently decreasing the tidal vol- rest and resuscitation. A variety of alternative ume of the PPVs under certain circum- forms of CPR have been proposed and tested stances.2, 4 Elimination of the carotid in animals and in . All of these alter- check in the year 2000 guidelines has native methods apply more kinetic energy to abolished unnecessary delay in starting chest the victim, either by way of an additional compressions by lay rescuers. Otherwise, ex- rescuer or some type of mechanical device. ternal CPR today is performed in approxi- More energetic forms of CPR include high- impulse CPR, interposed abdominal compres- sion–CPR (IAC-CPR), active compression-de- The author has no financial interest, consulting ar- compression CPR (ACD-CPR), and vest CPR. rangement, or research contract with Ambu, CPRxLLC, or any other resuscitation device company that could be These derivatives of standard CPR have come construed as a conflict of interest. to be known as circulatory adjuncts.Bythe

From the Department of Basic Medical Sciences, Purdue University, West Lafayette, Indiana

CARDIOLOGY CLINICS

VOLUME 20 • NUMBER 1 • FEBRUARY 2002 37 38 BABBS year 2000, a convergence had occurred be- and the spine. As a result, forward tween laboratory knowledge about mecha- flow occurs through the aortic and pul- nisms of blood flow and clinical experience monic without mitral or tricuspid in- with the various adjuncts. This long-delayed competence. In particular, when the cardiac synthesis of research findings has led to im- pump mechanism is operative, the aortic proved forms of practical resuscitation (able is open, and the is closed to generate more blood flow and systemic during chest compression.13 The cardiac pressure during pump mechanism is also operative during through the efforts of the rescuers) based on open-chest cardiac massage. sound basic science principles. If there is one The thoracic pump mechanism was discov- certain truth in resuscitation science, stem- ered in the 1980s as a result of clinical obser- ming from the pioneering work of Redding10, vation by Criley et al14, 15 of cough CPR and Ralston et al,11 Weil and Tang,9 and Kern et extensive laboratory studies at Johns Hopkins al,12 it is this: Improved coronary and sys- University, led by Rudikoff et al16 and Weis- temic perfusion during cardiac ar- feldt.17 This pump is operative to the extent rest and CPR lead to improved immediate that chest compression causes a global rise in resuscitation success and improved likelihood intrathoracic pressure sufficient to blood of longer-term, neurologically intact survival. from the pulmonary vasculature, through the The improved hemodynamics, however, do , and into the periphery. When the tho- not come without a price, because more phys- racic pump mechanism is operative, the mi- ical work has to be done by or ma- tral and the aortic valves are open simultane- chine to generate more forward flow of blood. ously during chest compression.18–20 The heart Accordingly, adjuncts may not be appropriate acts as a conduit rather than a pumping for the lone rescuer faced with a collapsed chamber. coworker or loved one. Nevertheless, the time The abdominal pump mechanism was dis- has come for serious consideration of alterna- covered independently by workers in Great tive forms of resuscitation when adequate Britain, Japan, Israel, and the United States in equipment and trained personnel are avail- the latter half of the 20th century.21–26 This able, for example, in the emergency depart- mechanism has two components: (1) arterial ment of a hospital. This article focuses on the and (2) venous. The arterial component of the relevant physiology of cardiac arrest and CPR abdominal pump mechanism is operative to that makes possible the generation of sys- the extent that abdominal compression temic perfusion pressure substantially greater blood from the abdominal into the pe- than that provided by standard CPR. Thereaf- riphery against a closed . Thus, ter, selected practical aspects of applying cur- the aortic valve is closed during abdominal rently approved circulatory adjuncts in a hos- compression. The venous component of the pital setting are discussed. abdominal pump mechanism is operative to the extent that external abdominal pressure forces blood from the inferior vena cava MODERN PHYSIOLOGY OF BLOOD through the into the right ven- FLOW DURING CARDIOPULMONARY tricle (or through the tricuspid and pulmonic RESUSCITATION valves into the pulmonary vasculature). In this case, the right heart valves are open dur- At least three different mechanisms can move ing abdominal compression. blood during cardiac arrest and CPR: (1) the The operation of these three pumps— cardiac pump, (2) the thoracic pump, and (3) cardiac, thoracic, and abdominal—is related the abdominal pump. The cardiac pump to the fundamental architecture of the cardio- mechanism was the first to be recognized by vascular system. The physiology of the the original discoverers of closed-chest CPR.1 pumps has been demonstrated in relatively This pump mechanism is operative to the simple mathematical models that represent extent that external chest compression the essential features of the human cardiovas- squeezes the cardiac ventricles between the cular system.24, 27–31 Successful circulatory ad- CIRCULATORY ADJUNCTS 39 juncts generate greater blood flow than stan- and small people and large and small experi- dard CPR either by enhancing the operation mental animals. The author of this article uses of one of these pumps or by simultaneously the simplest realistic model of CPR physiol- invoking the action of multiple pumps. High- ogy to illustrate the actions of the basic pump impulse CPR,32–34 for example, aims to en- mechanisms and to demonstrate selected cir- hance the action of the cardiac pump mecha- culatory adjuncts. The exact values of vascu- nism. Vest CPR35, 36 aims to enhance the action lar compliances and resistances and other of the thoracic pump mechanism through the technical details of the model, which can be action of a pneumatic vest that is inflated and implemented in a spreadsheet, are fully de- deflated rapidly at a rate of 60 to 150 times/ scribed elsewhere.31 min. ACD-CPR37, 38 aims to improve filling of As a point of reference and calibration, Fig- the either the cardiac pump or the thoracic ure 1 illustrates pressures throughout a sim- pump by creating negative pressure in the plified cardiovascular system for a nonar- thorax between chest compressions. IAC- rested circulation of a hypothetical 70-kg CPR39–43 aims to invoke the abdominal pump man. In this instance, cardiac pump generates together with either chest pump. IAC-CPR left ventricular pressures (Ppump) of 122/2 and its derivative, Lifestick (Datascope, Fair- mm Hg at a of 80 beats/min (bpm). field, NJ) CPR,44 aim to combine thoracic and Systemic arterial is 119/82 (the abdominal pumps alternately, in such a way data point representing the exact minimum that the thoracic pump primes the abdominal diastolic pressure at 82 mm Hg is not plotted pump during one half of the cycle and the on the chart), is 95 mm abdominal pump primes the thoracic pump Hg, and is 5.0 L/min. These during the other half of the cycle. are classical textbook values for the normal Regarding the question of the effectiveness human .31 Note the essen- of these various adjuncts, it would be difficult tially normal arterial pulse waveforms and to compare and contrast all such methods in low systemic venous pressures. a single animal or clinical model; however, it Figure 2 illustrates the action of a pure is reasonable to use a mathematical model of cardiac pump CPR in the same circulatory the circulation that includes all three pumps.31 model during cardiac arrest. Steady-state con- Such a model can be used to simulate the ditions are shown after stable pressures have effects of various circulatory adjuncts in ex- been achieved by 20 prior compressions. In actly the same circulatory system, without this simulation, only the right and left ventri- model-to-model variation. It also serves to cles of the heart are compressed at a rate of demonstrate the relevant cardiovascular 80 compressions/min with a half sinusoidal physiology of CPR. waveform having a peak pressure of 60 mm An interesting feature of the circulatory Hg, a typical value reported in the literature model used in this article is the small number of standard CPR29. There is no intrinsic myo- of assumptions required to obtain realistic re- cardial contractility in this system, and there sults.31 These are limited to the existence of is no pump priming effect of atrial contrac- compliant vessels and resistive vascular beds, tion (which in some circumstances could exist the definition of compliance (⌬V/⌬P), normal for a few minutes in witnessed cardiac ar- (the arrangement of connected ves- rests). The cardiac pump produces reasonable sels and cardiac chambers), and a linear rela- aortic pressures and very small venous pulsa- tion between flow and pressure (Ohm’s Law: tions. Especially important to note are the low flow pressure/resistance).28–31 Although right-sided central venous pressures through- much more complex models of the circulation out the compression cycle. There is substan- can be created, only these basic assumptions tial coronary perfusion pressure (aortic to are needed to demonstrate the three mecha- right atrial gradient) throughout the cycle. nisms of blood flow during CPR and the rela- Forward flow is 2.5 L/min, and systemic per- tive utility of various circulatory adjuncts. fusion pressure is 47 mm Hg. This state of Circulatory systems that have these proper- affairs represents idealized classical external ties behave similarly, including those of large CPR in which ‘‘the heart is squeezed between 40 BABBS

Figure 1. Pressures in a mathematical model of the normal adult human circulation with the cardiac ventricles beating. The heart rate is 80 beats per minute (bpm). Pressures are plotted as a function of cycle time for the thoracic aorta (Pao), the right (Prh), the intrathoracic pump, here the left (Ppump), the (Paa), and the inferior vena cava (Pivc). SPP is mean systemic perfusion pressure (SPP) Pao Prh. Normal flow: flow 5.0 L/ min; SPP 95 mm Hg.

the sternum and the spine.’’45 It is also a rea- plished by the use of plungerlike devices (dis- sonable representation of open-chest CPR covered accidentally using a real toilet with manual cardiac compression, which plunger!37, 48) or by sticky adhesive pads that works by a pure cardiac pump mechanism. A make contact with the skin of the anterior similar state of affairs can occur in children chest or abdomen, such as those incorporated (and young pigs46, 47), who have small compli- into the Lifestick.44 This approach is known ant chest walls. as active compression- CPR (Fig- Figures 1 and 2 were generated using posi- ure 3). Currently, active decompression of the tive applied extravascular pressures during chest during CPR can be accomplished using the compression phase and zero extravascular a specially designed plunger applied to the pressure during the relaxation phase. A rela- human sternum,46, 49–51 which is sold commer- tively recent concept in the physiology of cially in Europe as the Ambu CardioPump CPR is the use of active decompression, (Ambu Inc., Glostrup, Denmark). rather than simple relaxation, between chest Figure 4 illustrates the steady-state effect compressions. Decompression can be accom- of active decompression of the chest to CIRCULATORY ADJUNCTS 41

Figure 2. Pressures in a mathematical model of the normal adult human circulation during cardiac arrest and Cardiopul- monary resuscitation (CPR) with a pure cardiac mechanism. The compression rate is 80 per minute. Cardiac compression CPR: flow 2.5 L/min; SPP 47 mm Hg.

20 mm Hg, the maximum reported in the Figure 4 the particular times near 0.55 sec- literature.50, 52, 53 This particular simulation is onds in the cycle when pump pressure is for cardiac pump CPR. Combining positive substantially less than right heart pressure. and negative chest pressures has a salubrious At this stage, enhanced pump filling occurs. effect upon hemodynamics. Cardiac filling is The result of enhanced pump filling is greater enhanced during the negative pressure phase, forward flow and greater perfusion pressures: so that greater output can be achieved 3.2 versus 2.5 L/min and 61 versus 47 mm on the next positive pressure phase. Note in Hg. When more energy is applied to the ar-

Figure 3. Active compression-decompression CPR (ACD-CPR) using a plungerlike de- vice. 42 BABBS

Figure 4. Pressures in a mathematical model of the normal adult human circulation during cardiac arrest and ACD-CPR with a pure cardiac pump mechanism. The compression rate is 80 per minute. Maximal chest compassion pressure is 60 mm Hg. Maximal decompression pressure is 20 mm Hg. Cardiac compression-decompression CPR: flow 3.2 L/min; SPP 61 mm Hg.

rested circulation in this manner, forward broad-chested adults. It also happens during flow improves. A potential advantage of the vest CPR, in which a pneumatic vest encircles use of negative and positive pressure phases, the chest to produce of compression rather than simply greater positive pressure, from all sides simultaneously. is that it is less traumatic to the victim. Also, In thoracic pump CPR, forward flow occurs needless compression of pumping chambers even though the heart is not being squeezed that are already empty is avoided. The use of between the sternum and the spine. Coronary a decompression phase compliments the use blood flow and systemic blood flow occur of a compression phase for all three pump when is greater than systemic mechanisms in CPR (see later discussion). venous or right heart pressure. As shown in When it works, the cardiac pump mecha- Figure 5, positive coronary and systemic per- nism is the most effective and natural of the fusion pressures occur mostly between com- three pumps in CPR. Its operation in external pressions, rather than during compressions. CPR, however, depends on good mechanical Because of the tendency toward equalization coupling between the sternum and the heart. of aortic and venous pressures during com- In most adults, the coupling of chest compres- pressions, forward flow with the thoracic sion to the heart is indirect, and a thoracic pump mechanism tends to be less, other fac- pump mechanism tends to predominate.20, 35, 54 tors being equal, than with the cardiac pump Thoracic pump CPR has a quite different set mechanism. In a thoracic pump model of Fig- of pressure profiles. Figure 5 illustrates the ure 5, forward flow is 0.94 L/min, and sys- action of a pure thoracic pump. In this simu- temic perfusion pressure is 18 mm Hg. lation, all intrathoracic blood–containing If a decompression phase is added (Fig. 6), chambers are pressurized equally at a rate of perfusion pressures are somewhat increased, 80 per minute with a peak pressure of 60 mm but to a lesser extent than with cardiac pump Hg, as before. This state of affairs happens in CPR. In this instance, forward flow is 1.14 L/ CIRCULATORY ADJUNCTS 43 min and systemic perfusion pressure is 22 is a combination of the cardiac and thoracic mm Hg. The difference in the responsiveness pumps. of the thoracic and cardiac pumps to negative Figure 7 illustrates the steady-state action pressure priming may be responsible for of a pure abdominal pump. In this simula- some of the discrepancies in the reported lit- tion, there is no chest compression. Abdomi- erature regarding the benefits of ACD-CPR in nal compression begins at time zero. Only the various models.31 The simulated improve- abdominal aorta and vena cava are com- ment in coronary perfusion pressures with pressed at a rate of 80 compressions/min ACD-CPR (61 mm Hg for a cardiac pump with a pressure of 110 mm Hg, values re- model and 22 mm Hg for a thoracic pump ported in the literature of IAC-CPR.39, 55, 56 model) are in keeping with the range of mea- Manual compression leading to periaortic sured coronary perfusion pressures in human pressures this high can be tolerated without patients during ACD-CPR. In one recent pain by a conscious person.57 Artificial circu- study,51 the generation of 20 mm Hg intra- lation can indeed be created by abdominal thoracic pressure during ACD was ensured compression only, as first observed experi- with the use of an inspiratory impedance mentally by Rosborough et al.58 During ab- valve. These investigators found coronary dominal compression, blood is squeezed from perfusion pressures of 40 to 45 mm Hg. These the aorta to the periphery by the positive results are consistent with those of Figures 4 intra-aortic pressure acting against a closed and 6, if one takes the modern consensus aortic valve. During abdominal relaxation, view20, 35, 54 that the operative pump mecha- the aortic valve opens, allowing filling of the nism in different animal and clinical models aortic pumping chamber from the left heart

Figure 5. Pressures in a mathematical model of the normal adult human circulation during cardiac arrest and CPR with a pure thoracic pump mechanism. The compression rate is 80 per minute. Maximal chest compression pressure is 60 mm Hg. Thoracic compression CPR: Flow 0.93 L/min; SPP 18 mm Hg. 44 BABBS

Figure 6. Pressures in a mathematical model of the normal adult human circulation during cardiac arrest and ACD-CPR with a pure thoracic pump mechanism. The compression rate is 80 per minute. Maximal chest compression pressure is 60 mm Hg. Maximal chest decompression pressure is 20 mm Hg. Thoracic compression-decompression CPR: flow 1.1 L/min; SPP 22 mm Hg. and . Only one valve is needed to filling when chest pump pressure is greater achieve forward flow, as can be demonstrated than thoracic aortic pressure near 0.4 seconds by deliberately rendering the other three in the cycle. At this time, the low resistance heart valves incompetent.29 It is important to aortic valve is open. With active abdominal note that the abdominal aortic pressure wave- decompression, the filling pressure differ- form at 0 to 0.2 seconds in the cycle leads the ences are more obvious than when abdominal thoracic aortic pressure waveform in time, decompression is absent. During subsequent indicating retrograde flow in the aorta. Pump abdominal compression positive pressure in pressures change very little, because the chest the aorta, which is greater than that in the pump is acting as a passive conduit. There is chest pump, closes the aortic valve. The a positive coronary perfusion pressure during slower rise of right heart pressures compared most of the compression cycle. Forward flow with inferior vena cava pressures is associ- is 1.3 L/min and coronary perfusion pressure ated with differences in the capacitances of is 25 mm Hg. these structures. Near 0.3 seconds of the cycle, Figure 8 shows the potential benefit of add- the chest pump, including the heart and ing active abdominal decompression (20 lungs, fills when right heart pressure exceeds mm Hg pulses) to abdominal compression. chest pump pressure. Thus forward flow oc- Such a manipulation is possible using a sticky curs around the entire circuit with abdominal adhesive abdominal pad, and has been imple- compression–decompression alone. As in the mented practically in the experimental Lifes- case of the cardiac and thoracic pumps, the tick device. In this simulation, there is still no addition of active decompression enhances chest compression. The abdominal pump is abdominal pump performance (see Fig. 8). CIRCULATORY ADJUNCTS 45

Figure 7. Pressures in a mathematical model of the normal adult human circulation during cardiac arrest and CPR with a pure abdominal pump mechanism. The compression rate is 80 per minute. Maximal abdominal compression pressure is 110 mm Hg. Abdominal compression CPR: flow 1.3 L/min; SPP 25 mm Hg.

COMBINING CHEST AND simplest and most studied form of IAC-CPR ABDOMINAL PUMPS involves a 50% duty cycle for both chest and abdominal phases. That is, the compression Given this theoretical background, it is a cycle is divided into two equal duration small conceptual leap to imagine combining phases, in which an extra rescuer manually chest and abdominal pump mechanisms. The compresses the abdomen during the relax- simplest and most practical such combination ation phase of chest compression.26, 42 With is called interposed abdominal compression–CPR alternating chest and abdominal compression, (Fig. 9). IAC-CPR invokes the abdominal the aortic valve is open during chest com- pump together with either the cardiac or tho- pression and closed during abdominal com- racic pump. The trick is to compress the abdo- pression. Chest pump outflow during chest men during chest , thereby operating compression fills the aorta, priming the ab- two pumps together in the same compression dominal pump. Abdominal-to-thoracic caval cycle. Alternation of chest and abdominal flow during abdominal compression fills the compression has the practical advantage of right heart and pulmonary vasculature, prim- avoiding trauma to the and has been ing the chest pump.31 Thus the two pumps proved extremely safe in animal and human work in concert. Improved venous return in- trials.43 Although other timing and phasing creases stroke output of the chest pump, in schemes have been investigated,23, 30, 44 the conjunction with either the thoracic pump 46 BABBS

Figure 8. Pressures in a mathematical model of the normal adult human circulation during cardiac arrest and ACD-CPR with a pure abdominal pump mechanism. The compression rate is 80 per minute. Maximal abdominal compression pres- sure is 110 mm Hg. Maximal abdominal decompression is 30 mm Hg. Abdominal compression-decompression CPR: flow 1.6 L/min; SPP 30 mm Hg.

mechanism or direct cardiac compression. ing CPR have been confirmed in 20 of 21 Abdominal compression also produces count- animal studies using canine and porcine erpressure on the abdominal aorta, inducing models.43, 60 After encouraging laboratory retrograde flow toward the heart and brain studies, clinical trials of IAC-CPR were per- between chest compressions.59 This abdomi- formed. Three randomized clinical trials of nal pump action on the arterial side increases IAC-CPR for in-hospital cardiac arrest have flow in a manner analogous to an intra-aortic shown statistically significant improvement balloon pump.29, 43 of outcome measures.42, 61–62 One randomized The effectiveness of such combined chest trial of prehospital IAC-CPR, combined, and abdominal compression was discovered when possible, with standard CPR in the empirically22, 26 long before the theoretical field, showed no difference in outcome.63 physiology had been worked out.27–31 Indeed These studies are summarized in Table 1. the positive hemodynamic effects of IAC dur- Pooled analysis of all available data for pre- CIRCULATORY ADJUNCTS 47

Figure 9. Interposed abdominal compression (IAC) CPR (IAC-CPR).

hospital and in-hospital resuscitations shows this instance, the cardiac and abdominal statistically significant improvement in the re- pump mechanisms are combined. (Even turn of spontaneous circulation with IAC- though more external force is applied to the CPR. When only in-hospital studies are exam- chest than to the abdomen in practice, typical ined, the effect of IAC becomes much greater intrathoracic pressure pulses are less than in- and is highly statistically significant. Pooled tra-abdominal pressure pulses because of the data from two studies that examined long- stiffness of the chest wall.) The double arterial term, neurologically intact survival following pressure peaks in Figure 10A attest to the in-hospital resuscitations show a positive ben- effects of the double pump approach. Sys- efit of IAC-CPR compared with standard temic perfusion pressure is sustained CPR. Thus strong preclinical and clinical evi- throughout both phases of the compression dence supports the use of IAC-CPR for in- cycle. Enhanced filling of the chest pump is hospital resuscitations. evident at cycle times near 0.7 seconds. Filling For the purpose of the present discussion, of the abdominal pump chamber (ie, the the hemodynamic benefits of IAC-CPR can aorta) can be seen at cycle times near 0.125 be demonstrated in the same mathematical seconds. The increased forward flow in this model with which basic physiology is investi- model 3.6 L/min with IAC versus 2.5 L/min gated. Figure 10A illustrates the addition of for cardiac pump CPR. Systemic perfusion 110 mm Hg IACs to 60 mm Hg peak thoracic pressure is 68 mm Hg versus 47 mm Hg for compressions in a cardiac pump model. In cardiac pump CPR. Thus the ratio of perfu-

Table 1. RESULTS OF CLINICAL STUDIES OF INTERPOSED ABDOMINAL COMPRESSION–CARDIOPULMONARY RESUSCITATION VERSUS STANDARD CARDIOPULMONARY RESUSCITATION IAC-CPR Standard P Outcome Measure Studies (%) CPR (%) Value Return of spontaneous circulation in- or out-of-hospital Mateer63 40/145 (28) 45/146 (31) .54 Ward 61 6/16 (38) 3/17 (18) .19 Sack42 29/48 (60) 14/55 (25) .00014 Sack62 33/67 (49) 21/76 (28) .0067 All 4 studies 108/276 (39) 83/294 (28) .0056 Return of spontaneous circulation after in-hospital Ward61 6/16 (38) 3/17 (18) .19 resuscitation Sack42 29/48 (60) 14/55 (25) .00014 Sack62 33/67 (49) 21/76 (28) .0067 All 3 studies 68/131 (52) 38/148 (26) .000003 Survival to discharge, neurologically intact after in- Ward61 1/16 (6) 0/17 (0) .3017 hospital resuscitation Sack42 8/48 (17) 3/55 (5) .0700 Both studies 9/64 (14) 3/72 (4) .0453 48 BABBS

Figure 10. See legend on opposite page sion during IAC-CPR to perfusion during ent animal and clinical models is a combina- standard CPR is 1.44 in a pure cardiac pump tion of the cardiac and thoracic pumps, these model. simulation results agree perfectly with the ag- Figure 10B illustrates the addition of 110 gregate results of laboratory and clinical re- mm Hg IACs to 60 mm Hg peak thoracic search on IAC-CPR, in which systemic perfu- compressions in a pure thoracic pump model, sion pressure or excretion illustrating similar effects of the double pump served as measures of overall forward approach when the thoracic and abdominal flow.26, 43, 59, 61 These research studies found a pump mechanisms are combined. The in- 1.5- to 2-fold improvement in perfusion with creased forward flow in this model is 2.1 L/ the addition of IAC. min with IAC versus 0.93 L/min for thoracic The safety of IACs, as reviewed pre- pump CPR. Systemic perfusion pressure is 39 viously,43 has been well documented in 426 mm Hg versus 18 mm Hg for thoracic pump humans, 151 dogs, and 14 pigs. Only one CPR. Thus, there is a roughly 2-fold ratio isolated case report of traumatic pancreatitis of perfusion during IAC-CPR to perfusion in a child describes local trauma from abdom- during standard CPR in a thoracic pump inal compression during CPR.64 These data model versus a roughly 1.5-fold ratio of per- compare favorably with the well-known and fusion during IAC-CPR to perfusion during frequent incidence of fracture and pulmo- standard CPR in a cardiac pump model. If nary contusion from chest compression dur- one takes the modern consensus view20, 35, 54 ing CPR.65–67 Increased emesis and aspiration that the operative pump mechanism in differ- from IAC have not been reported, and there CIRCULATORY ADJUNCTS 49

Figure 10. (Continued). Pressures in a mathematical model of the normal adult human circulation during cardiac arrest and IAC-CPR. The compression rate is 80 per minute. Maxi- mal chest compression pressure is 60 mmHg. Maximal abdominal compression pressure is 110mmHg.A, IAC- CPR with a pure cardiac pump mechanism: flow 3.6 L / min; SPP 68 mm Hg. B, IAC-CPR with a pure thoracic pump mechanism: flow 2.1 L/min; SPP 39 mm Hg.

is even evidence that if positive abdominal chest compression and abdominal decom- pressure is applied during ventilations from pression can be accomplished simultaneously the beginning of an arrest, the rate of gastric in the first half of the cycle, and abdominal inflation before endotracheal intubation is re- compression and chest decompression can be duced.68 accomplished simultaneously in the second Can we do even better? Theory suggests half of the cycle. that the answer is ‘‘yes.’’ Ordinary IAC-CPR, Recently a commercial venture has at- as studied experimentally over the past 20 tempted to implement this concept in a de- years, includes only positive pressure com- vice called the Lifestick (Datascope, Fairfield, pressions without active decompression. A NJ) (Fig. 11). The Lifestick is a mechanical logical extension of this line of thought is to device under development, with which one examine full four-phase CPR, which includes person can perform both chest and abdominal active compression and active decompression CPR. Compression is applied through a of the chest and the abdomen. All four phases rocker arm with adhesive pads attached to can be accomplished in a single cycle, because the chest and the abdomen. The broad chest 50 BABBS

Figure 11. Four-phase CPR with a Lifestick (Datascope, Fairfield, NJ).

compression pad of early models precludes dard CPR.69-70 Routine practical implementa- cardiac pump mechanism but also obviates tion of full four-phase CPR has yet to be . Because the chest and abdominal achieved, partly as a result of legal and com- pads are adhesive, it is possible to obtain a mercial wrangling unrelated to science and measure of upward retraction of the chest engineering; however, animal studies with a during the abdominal compression phase and prototype Lifestick device are encouraging.44 vice versa by a rocking motion of the device. The forgoing survey of resuscitation physi- Such a device in principle has the advantage ology suggests a significant potential for im- of permitting active compression and decom- provement of CPR through the appli- pression of both chest and abdomen.31 cation of combinations of positive and The hemodynamic potential of such four- negative pressure to the chest and the abdo- phase CPR is illustrated in Figure 12. Figure men. The most recent American Heart Associ- 12A shows cardiovascular pressures during ation guidelines2 for CPR and emergency car- cardiac pump and abdominal pump CPR diovascular care permit the judicious use of with active compression and decompression. two advanced forms of CPR at the discretion The four-phase method produces dramati- of a physician under conditions in which ade- cally large pressure fluctuations in the chest quate equipment and trained personnel are and abdominal vascular compartments, al- available. These approved adjuncts include though the external compression forces are IAC-CPR and ACD-CPR. As so-called ‘‘class no different than those used for standard CPR IIb’’ interventions, IAC- and ACD-CPR are or conventional IAC-CPR, and the applied considered within the standard of care, which external decompression forces are substan- reasonably prudent physicians can choose to tially less than the compression forces. Nearly use.71 IAC-CPR and ACD-CPR are considered normal systemic perfusion pressures are ob- optional or alternative interventions by most tained throughout the cycle. There is no re- experts. Technically these adjuncts could be striction of positive coronary and systemic performed together under the guidelines in perfusion pressure to the diastolic phase. For- selected clinical settings to achieve at least ward blood flow is 4.6 L/min, approaching a three-phase CPR, which has hemodynamic the textbook value of 5.0 L/min for the nor- benefits nearly as great as four-phase CPR.31 mal circulation in a 70-kg man. These levels This new state of affairs, in which emergency are a far cry from the 20% of normal forward department physicians have considerable flow that has come to be expected from stan- professional discretion, brings us to consider CIRCULATORY ADJUNCTS 51 practical aspects of implementing the new the victim or works astride the victim on his CPR adjuncts. or her knees. A blanket or pillow under the knees of the rescuer may allow the rescuer’s PRACTICAL ASPECTS OF ACTIVE arms and back to be straighter when using COMPRESSION-DECOMPRESSION the CardioPump device.72 Because the handle CARDIOPULMONARY is offset from the chest by about 15 cm, the RESUSCITATION rescuer’s shoulders need to be higher over the victim than in conventional CPR. If the Active compression-decompression CPR patient is on a table or raised surface, a stool requires use of a plungerlike device, sold as may be needed by the rescuer to provide the the CardioPump or ResQ-Pump (CPRx LLC, necessary elevation. Minneapolis, MN). With a two-handed grip While using a CardioPump, the arms on the handles of the device, a rescuer can should be straight and the back of the rescuer apply active compression and decompression. as close to vertical as possible. The elbows Teams in Europe, especially in Paris, have should be locked. Wrists should be firm, such been trained to use the CardioPump with as in gripping a tennis racquet. In this posi- good results, including improved survival at tion, the rescuer can work effectively by rai- 1 year after resuscitation compared with stan- sing and lowering the hips against gravity. As 72 dard CPR. Some studies have reported the rescuer’s hips are lowered in the kneeling mixed results with the CardioPump,73–77 per- position, the of the rescuer’s body haps as a result of less intensive training.78–79 can be used to apply compression. As the Those considering use of ACD-CPR are ad- rescuer’s hips are raised, the quadriceps mus- vised to train well in the use of the device cles of the anterior thigh can work to apply and repeat training often.78 Training manne- decompression while the rescuer’s arms re- quins and other educational materials are main straight.* available from Ambu Inc. (Glostrup, Den- As fatigue sets in, rescuers tend to revert to mark). former habitual methods of chest compres- At the time of this writing, the Ambu sion without decompression, and the benefits CardioPumps are not approved for use in of ACD-CPR are lost. Remembering to lift the United States by the US Food and Drug up during each cycle is the most challenging Administration. They are commercially avail- aspect of using a CardioPump device. A force able outside the United States and are manu- gauge on the handle indicates the target factured by Ambu, Inc. and marketed in the ranges of compression and decompression Western Hemisphere by CPRx LLC (Minne- force for chests of soft, normal, or stiff charac- apolis, MN). The CardioPump weighs 0.58 kg teristics. The gauge provides useful biofeed- and costs about $300. The vacuum cup is 135 back. The duty cycle for ACD-CPR is 50% mm in diameter and is made of soft silicone compression time, 50% decompression time. rubber. The cup can be removed for cleaning Further details of ACD-CPR methodology and for autoclave sterilization after use. The and training are described by Wik et al.78 vacuum cup is not electrically conducting and does not interfere with transchest electrical *The reader is encouraged to try this motion in the kneeling position while palpating the quadriceps, gluteus defibrillation; it has been designed to adhere maximus, and hamstring muscles. Note that when the to a variety of chest , including wet hips are raised when kneeling, the leg is extended and hairy skin, without losing contact with the the knee by the quadriceps and the thigh is ex- tended at the hip joint by the hamstrings. Posterior com- chest wall during decompression. Earlier partment (hamstring) muscles and the gluteus maximus models did not work well on women with muscles are also active in the kneeling position. Reliance larger , 80–81 and the cup may still seal on the large anterior and posterior thigh muscles and poorly in about 10% of women. gluteus muscles minimizes fatigue and keeps the aerobic for either male or female rescuers. These same Rescuer fatigue is a known problem with muscles also should be used as much as possible in ACD-CPR, because more energy is needed to the standing position to minimize fatigue. Upper-body perform ACD than to do active compression strength is not required, once rescuers learn to use leg 79, 82 muscles and not back muscles. Nevertheless, adequate alone. Back fatigue is definitely reduced if personnel need to be available so that frequent changes the rescuer either kneels beside the thorax of can occur every 3 to 5 minutes to avoid fatigue. 52 BABBS

Figure 12. See legend on opposite page

A major potential improvement in ACD- valve prevents inflow only when intratho- CPR is the use of an inspiratory impedance racic pressure is zero to 22 cm H2O with valve46 for victims with an established endo- respect to . The valve tracheal tube.51 This valve fits on the end of does not interfere with normal PPVs or with the endotracheal tube and prevents ‘‘decom- vigorous spontaneous negative pressure ven- pression of the decompression,’’ that is, an tilations, if the patient begins to gasp strongly inrush of air into the during the active enough to create at least 22 cm H2O negative decompression phase. The resulting increase pressure. If a pulse returns, however, the in- in the magnitude of the intrathoracic decom- spiratory impedance valve should be re- pression encourages even more chest pump moved immediately and the ventilation priming. The valve incorporates a pop-off fea- source reattached to the airway to allow nor- ture that is set to open when the intrathoracic mal spontaneous . The inspiratory pressure decreases below 22 cm H2O. The impedance valve is available commercially as CIRCULATORY ADJUNCTS 53

Figure 12. Pressures in a mathematical model of the normal adult human circulation during cardiac arrest and four-phase CPR. The compression rate is 80 per minute. Maximal chest compression pressure is 60 mm Hg. Maximal abdominal compression pressure is 110 mm Hg. Maximal chest de- compression pressure is 20 mm Hg. Maximal abdominal decompression pressure is 30 mm Hg. A, Four-phase CPR with cardiac pump: flow 4.6 L /min, SPP 86 mm Hg. B, Four-phase Lifestick CPR with thoracic pump: flow 2.7 L/ min; SPP 51 mm Hg. 54 BABBS a resuscitation device called the Resusci-Valve Hand Position and or ResQ-Valve (CPRx LLC, Minneapolis, Compression Technique MN). The valve is a disposable device that costs between $30 and $50. The umbilicus should be visible and not covered by the compressing hands. Just as chest compression is applied making contact with the heel of one hand, which is covered PRACTICAL ASPECTS OF by the heel of the other hand, abdominal INTERPOSED ABDOMINAL compression is applied in the same manner. COMPRESSION—CARDIOPULMONARY The heel of the rescuer’s bottom hand should RESUSCITATION lie along the midline of the abdomen. This midline position keeps the main force of com- pression over the abdominal vena cava and From a practical standpoint, the simplest, aorta. The fingers may be either extended or least expensive, and longest studied CPR ad- interlaced but should be kept off the abdo- junct is IAC-CPR. This method is essentially men. deviceless. There is no equipment cost, and A straight-armed abdominal compression there is no requirement for FDA approval. technique, similar to that used for chest com- IAC-CPR can be performed by two hands of pression, is ergonomically effective. Because a third rescuer, as shown in Figure 9. IAC- the abdomen is composed of soft tissues with- CPR is especially appropriate for in-hospital out the bony resistance of the rib cage, ade- resuscitations, where the dictum ‘‘When extra quate compressions do not require strong hands are free, do IAC’’ may well apply. IAC- muscular effort. In practical training, students CPR is performed most easily when the rescu- learn the force required to produce safe and ers compressing the chest and abdomen are effective 110 mm Hg pressure pulses within on opposite sides of the patient. Because the the abdomen using a folded blood pressure most favorable clinical results have been ob- cuff and gauge (see later discussion). The tained when IAC-CPR is applied from the depth of abdominal compression is not unlike beginning of resuscitation, early application that of chest compression, 1.5 to 2 inches, in of the technique is to be encouraged. Use of a normal sized, nonobese adult. For obese IAC-CPR as a last-ditch effort after pro- patients, greater compression depth may be longed, failed advanced cardiac life support necessary. Compressions can be delivered to (ACLS) is not recommended and has not been the abdominal compression point straight shown to be effective.61 Obviously, IAC is not down in the vertical plane, or to maximize recommended for pregnant women, persons aortic counterpulsation, from the left side of suspected of having an abdominal aortic an- the victim at 11 left of vertical.83 In principle, eurysm, or persons known to have had recent when IAC-CPR is performed properly, the abdominal surgery. carotid or femoral pulse demonstrates double The abdominal compression technique in peaks, denoting both chest and abdominal IAC-CPR involves rhythmic, manual com- compressions.31, 55 The clinical utility of as- pression of the mid-abdomen. The abdominal sessing a double pulse in this setting, how- compression point is located in the midline, ever, has not been investigated. halfway between the xiphoid process and the umbilicus. The recommended force of abdom- inal compression is that sufficient to generate Coordination of Chest and approximately 110 mm Hg external pressure Abdominal Compressions on the abdominal aorta and vena cava and is equivalent to that required to optimally pal- The rhythm of abdominal compression is pate the aortic pulse in a patient or volunteer natural and easy to learn. If the chest com- when the heart is beating normally.83 The pressor counts ‘‘one-and-two-and-three . . . ,’’ technique for compression of the abdomen is the abdominal rescuer applies pressure dur- similar in most respects to the technique for ing ‘‘and,’’ and releases pressure during each compression of the chest. counted number. The release of abdominal CIRCULATORY ADJUNCTS 55 pressure between chest compressions is 2. Wrap a standard blood pressure cuff needed for chest and abdominal pump mech- around a towel and place it in the ab- anisms to work together31 and also to avoid dominal compartment beneath the ab- entrapment of the right lobe of the liver under dominal compression point (5 cm head- the sternum when the chest is compressed. ward of the umbilicus) in the midline. Thus, abdominal pressure should be applied Bring the tubing, aneroid manometer whenever chest compressions are relaxed, gauge, and squeeze bulb out at beltline and abdominal pressure should be relaxed of the mannequin so that the gauge is whenever chest compressions are applied. visible to the trainees. Tape target pres- Abdominal pressure can maintained during sure markers on the manometer dial at ventilations to minimize gastric inflation if 120 mm Hg. Inflate cuff to a resting pres- no endotracheal tube is in place.68 The most sureof10mmHg. widely used and tested duty cycle is 50% 3. During practice sessions coach trainees chest/50% abdominal compression time. to hit the target pressure during IAC. There is some theoretical advantage to 30% The issue of how hard to press has been chest/70% abdominal compression time30, but addressed in detail elsewhere.83 this variation has not yet been tested in hu- If a mannequin is not available, a rolled mans. blood pressure cuff placed inside a rolled If two-rescuer CPR has been established towel is a useful training model. Successful and a third rescuer becomes available, this practice sessions can be conducted in as little person should take a position on the opposite as 5 minutes. The following sequence may side of the patient from the second rescuer be used: who is performing chest compressions, locate proper hand position, sense the rhythm of 1. The abdominal rescuer takes position on chest compressions, and begin then IACs. If opposite side of victim from chest com- rescuers doing chest and abdominal compres- pressor. sions wish to switch positions (abdominal 2. Chest compressor says, ‘‘You press here compressions are less tiring, because there is (pointing to the abdominal compression no ribcage resistance), it is natural for them point) whenever I release.’’ to slide headward and footward, respectively, 3. Chest compressor counts ‘‘one-and-two- during a ventilation, because they are on op- and-three. . . .’’ Abdominal rescuer ap- posite sides of the patient. plies pressure during ‘‘and.’’ 4. Start with slow-motion practice, and then gradually increase to a normal com- Training Individuals To Do pression rate. With this kind of practice Interposed Abdominal session, care professionals can be Compression–Cardiopulmonary taught to perform IAC with little time Resuscitation or trouble.

A detailed analysis of the ergonomic com- Combining Interposed plexity of IAC (available from the author on Abdominal Compression request) suggests that it is no more compli- with Active Compression- cated to learn and perform than is opening an Decompression–Cardiopulmonary airway. The following modifications of whole Resuscitation body mannequins for teaching three-rescuer IAC-CPR are performed easily and are inex- In selected research settings, there is good pensive: reason to investigate combining the methods 1. Add extra foam rubber to the lower tho- of ACD and IAC-CPR to create three-phase racic compartment of the mannequin CPR. Such a method is practically achievable and to the abdominal compartment to with current technology, omitting only the simulate subcostal soft tissues. fourth phase, active abdominal decompres- 56 BABBS sion, from full four-phase CPR. Advance ex- lives saved, there also could be greater num- perience with the two techniques separately, bers of people who are resuscitated and sub- is prudent before attempting to combine sequently die a day or so later. It is even them. Moreover, full consideration of the fol- possible, although not yet shown by pub- lowing warnings and caveats is in order. lished data, that more effective techniques of resuscitation might produce increased num- bers of individuals resuscitated to a lingering WARNINGS ABOUT THE GENERAL vegetative state. Clinical experience with the USE OF CIRCULATORY ADJUNCTS new modalities will be needed to determine which individuals are at greatest risk for this Because of the requirement for special most undesirable outcome. IAC- or ACD-CPR training and sometimes special equipment, cannot change underlying pathology or con- advanced forms of CPR are best performed trol the quality of care after resuscitation. in a hospital by trained health care providers. There is however, theoretical, experimental, Endotracheal intubation is prudent before and clinical evidence that these improved, instituting CPR adjuncts. Most studies of more energetic, and more aggressive resusci- IAC-CPR have required that an endotracheal tation methods can improve blood flow dur- tube be in place for fear of regurgitation in ing CPR, and in turn the probability of neuro- response to IAC (a fear not substantiated by logically intact short- and long-term survival. data43). Similarly, an endotracheal tube is de- sirable if ACD-CPR is performed with an in- spiratory impedance valve. The valve can be used with a tightly sealed facemask, but extra SUMMARY care must be taken to avoid leaks. It is extremely important in one’s enthusi- Principles of cardiovascular physiology tell asm for CPR adjuncts not to delay electrical us that during cardiac arrest and CPR, for- ventricular defibrillation when ventricular ward flow of blood can be generated by exter- fibrillation (VF) is present. New data confirm nal compression or decompression of either the old84, 85: that if VF has been present for less the chest or the abdomen. Standard CPR than 4 to 5 minutes, electrical defibrillation is utilizes only one of these modes—chest clearly the treatment of choice. For longer compression—and generates roughly 1 L/ down-times however, there is evidence that a min forward flow in an adult human,45 which vasopressor drug plus effective CPR, which is 20% of normal cardiac output. IAC-CPR produces good coronary perfusion pressure, uses two of these modes—chest compression can improve resuscitation success. As long as and abdominal compression—and generates defibrillation is not delayed, enhanced CPR roughly twice the forward flow, or 2 L/min methods, such as IAC-CPR, can potentially in an adult human.61 ACD-CPR uses two of benefit patients in the hands of trained health these modes—chest compression and chest care providers. decompression—and also generates roughly If initial shocks are not successful for VF, twice the forward flow as standard CPR,51 the rescuer should institute adjuncts early— although the results are somewhat model de- not as a last resort after failed ACLS. Adjuncts pendent. The studies by Sack et al86 with IAC- do not work on dead people. Their use after CPR and by Plaisance et al72 with ACD-CPR failed ACLS will only lead to unjustified cyni- suggest that when methods that double per- cism. fusion are employed methodically, resuscita- With more powerful and effective CPR mo- tion outcome in terms of short- and long-term dalities, one can expect an increased number survival are also roughly doubled.72, 86 This of discharge survivals72, 86; however, one also state of affairs is fortunate, because it is possi- must expect an increased number of individu- ble that factors, such as severe underlying als who survive only briefly. It is probably an disease or the quality of postresuscitation unavoidable result of multiplied probabili- care, could blunt or cancel positive effects of ties that, in addition to greater numbers of improved blood flow during the brief resusci- CIRCULATORY ADJUNCTS 57 tation period. Theoretically, full four-phase diopulmonary resuscitation. JAMA 236:1246–1250, 1976 CPR, including active compression and de- 15. Criley JM, Niemann JT, Rosborough JP, et al: The compression of both chest and abdomen, is heart is a conduit in CPR. Crit Care Med 9:373–374, capable of generating 4 L/min forward flow 1981 16. Rudikoff MT, Maughan WL, Effron M, et al: Mecha- or greater, which is 80% of normal, and there nisms of blood flow during cardiopulmonary resusci- is a reasonable prospect of achieving 100% of tation. Circulation 61:345–352, 1980 normal flow under conditions in which all 17. Weisfeldt ML: Physiology of cardiopulmonary resus- 87 citation. Ann Rev Med 32:435–442, 1981 four phases are optimized. Standard CPR is 18. Feneley MP, Maier GW, Gaynor JW, et al: Sequence clearly not the ultimate form of external CPR. of mitral valve motion and transmitral blood flow There is real, credible evidence that substan- during manual cardiopulmonary resuscitation in dogs. Circulation 76:363–375, 1987 tial improvements in resuscitation methods 19. Gall F: Incompetence of the atrioventricular valves and results will be possible in the next de- during cardiac massage. J Cardiovasc Surg 6:356– cade. 360, 1965 20. Paradis NA, Martin GB, Goetting MG, et al: Simulta- neous aortic, jugular bulb, and right atrial pressures during cardiopulmonary resuscitation in humans: In- sights into mechanisms. Circulation 80:361–368, 1989 References 21. Rainer EH, Bullough J: Respiratory and cardiac arrest during anaesthesia in children. BMJ 1024–1028, 1957 22. Ohomoto T, Miura I, Konno S: A new method of 1. Kouwenhoven WB, Jude JR, Knickerbocker GG: external cardiac massage to improve diastolic aug- Closed-chest cardiac massage. JAMA 173:1064–1067, mentation and prolong survival time. Ann Thorac 1960 Surg 21:284–290, 1976 2. Cummins RO: Guidelines 2000 for cardiopulmonary 23. Beyar R, Kishon Y, Kimmel E, et al: Intrathoracic and resuscitation and emergency cardiovascular care: In- abdominal pressure variations as an efficient method ternational consensus on science. Circulation for cardiopulmonary resuscitation: Studies in dogs 102(suppl I):I-1–I-384, 2000 compared with computer model results. Cardiovasc 3. Fitzgerald KR, Babbs CF, Frissora HA, et al: Cardiac Res 19:335–342, 1985 output during cardiopulmonary resuscitation at vari- 24. Babbs CF, Geddes LA: Effects of abdominal counter- ous compression rates and durations. American Jour- pulsation in CPR as demonstrated in a simple electri- nal of Physiology 241:H442–H448, 1981 cal model of the circulation. Ann Emerg Med 4. Idris AH: Reassessing the need for ventilation during 12:247, 1983 CPR. Ann Emerg Med 27:569–575, 1996 25. Coletti RH, Kaskel PS, Cohen SR, et al: Abdominal 5. Jude JR, Kouwenhoven WB, Knickerbocker GG: Car- counterpulsation (AC): A new concept in circulatory diac arrest: Report of application of external cardiac assistance. Trans Am Soc Artif Intern Organs 28:563– massage on 118 patients. JAMA 178:1063–1070, 1961 566, 1982 6. Kuisma M, Alaspaa A: Out-of-hospital cardiac arrests 26. Ralston SH, Babbs CF, Niebauer MJ: Cardiopulmo- of non-cardiac origin: Epidemiology and outcome. nary resuscitation with interposed abdominal com- Eur Heart J 18:1122–1128, 1997 pression in dogs. and Analgesia 61:645– 7. Cobb LA, Werner JA, Trobaugh GB: Sudden cardiac 651, 1982 death II: Outcome of resuscitation, management, and 27. Beyar R, Kishon Y, Sideman S, et al: Computer stud- future directions. Modern Concepts of Cardiovascu- ies of systemic and regional blood flow during car- lar Disease 49:37–42, 1980 diopulmonary resuscitation. Medical & Biological En- 8. Eisenberg MS, Hallstrom A: Long-term survival after gineering and Computing 22:499–506, 1984 out-of-hospital cardiac arrest. N Engl J Med 306:1340– 28. Babbs CF, Weaver JC, Ralston SH, et al: Cardiac, 1343, 1982 thoracic, and abdominal pump mechanisms in CPR: 9. Weil MH, Tang W: Cardiopulmonary resuscitation: Studies in an electrical model of the circulation. Am A promise as yet largely unfulfilled. Disease-a-month J Emerg Med 2:299–308, 1984 43:429–501, 1997 29. Babbs CF, Ralston SH, Geddes LA: Theoretical ad- 10. Redding JS: Abdominal compression in cardiopulmo- vantages of abdominal counterpulsation in CPR as nary resuscitation. Anesthesia and Analgesia 50:668– demonstrated in a simple electrical model of the cir- 675, 1971 culation. Ann Emerg Med 13:660–671, 1984 11. Ralston SH, Voorhees WD, Babbs CF: Intrapulmonary 30. Babbs CF, Thelander K: Theoretically optimal duty epinephrine during cardiopulmonary resuscitation: cycles for chest and abdominal compression during Improved regional blood flow and resuscitation in external cardiopulmonary resuscitation. Acad Emerg dogs. Ann Emerg Med 13:79–86, 1984 Med 2:698–707, 1995 12. Kern KB, Ewy GA, Voorhees WD, et al: Myocardial 31. Babbs CF: CPR techniques that combine chest and perfusion pressure: A predictor of 24-hour survival abdominal compression and decompression: Hemo- during prolonged cardiac arrest in dogs. Resuscita- dynamic insights From a spreadsheet model. Circula- tion 16:241–250, 1988 tion 100:2146–2152, 1999 13. Mair P, Furtwaengler W, Baubin M: Aortic-valve 32. Maier GW, Newton JR, Wolfe JA, et al: The influence function during cardiopulmonary resuscitation. N of manual chest compression rate on hemodynamic Engl J Med 329:1965–1966, 1993 support during cardiac arrest: High-impulse cardio- 14. Criley JM, Blaufuss AH, Kissel GL: Cough-induced pulmonary resuscitation. Circulation 74(suppl IV):IV- cardiac compression: A self-administered form of car- 51–IV-59, 1986 58 BABBS

33. Maier GW, Tyson GS, Olsen CO, et al: The physiology diopulmonary resuscitation: A randomized evalua- of external cardiac massage: High-impulse cardiopul- tion in patients in cardiac arrest. Circulation monary resuscitation. Circulation 70:86–101, 1984 101:989–994, 2000 34. Babbs CF: High-impulse compression CPR: Simple 52. Wik L, Naess PA, Ilebekk A, et al: Effects of various mathematics points to future research. Acad Emerg degrees of compression and active decompression Med 1:418–422, 1994 on haemodynamics, end-tidal CO2, and ventilation 35. Halperin HR, Tsitlik JE, Guerci AD, et al: Determi- during cardiopulmonary resuscitation of pigs. Resus- nants of blood flow to vital organs during cardiopul- citation 31:45–57, 1996 monary resuscitation in dogs. Circulation 73:539– 53. Sunde K, Wik L, Naess PA, et al: Effect of different 550, 1986 compression–decompression cycles on haemody- 36. Halperin HR, Tsitlik JE, Beyar R, et al: Intrathoracic namics during ACD-CPR in pigs. Resuscitation pressure fluctuations move blood during CPR: Com- 36:123–131, 1998 parison of hemodynamic data with predictions from 54. Chandra NC: Mechanisms of blood flow during CPR. a mathematical model. Ann Biomed Eng 15:385–403, Ann Emerg Med 22:281–288, 1993 1987 55. Berryman CR, Phillips GM: Interposed abdominal 37. Tucker KJ, Idris A: Clinical and laboratory investiga- compression-CPR in human subjects. Ann Emerg tions of active compression-decompression cardio- Med 13:226–229, 1984 pulmonary resuscitation [editorial]. Resuscitation 56. Lindner KH, Ahnefeld FW, Bowdler IM: Cardiopul- 28:1–7, 1994 monary resuscitation with interposed abdominal 38. Tucker KJ, Khan JH, Savitt MA: Active compression- compression after asphyxial or fibrillatory cardiac decompression resuscitation: Efects on pulmonary arrest in pigs. Anesthesiology 72:675–681, 1990 ventilation. Resuscitation 26:125–131, 1993 57. Babbs CF: Interposed abdominal compression-car- 39. Babbs CF, Tacker WA: Cardiopulmonary resuscita- diopulmonary resuscitation: Are we missing the tion with interposed abdominal compression. Circu- mark in clinical trials? [editorial]. Am Heart J lation 74(suppl IV):37–41, 1986 126:1035–1041, 1993 40. Babbs CF: Interposed abdominal compression-CPR: 58. Rosborough JP, Niemann JT, Criley JM, et al: Lower A case study in cardiac arrest research. Ann Emerg abdominal compression with synchronized ventila- Med 22:24–32, 1993 tion: A CPR modality. Circulation 64(IV):303, 1981 41. Einagle V, Bertrand F, Wise RA, et al: Interposed 59. Voorhees WD, Niebauer MJ, Babbs CF: Improved abdominal compressions and carotid blood flow dur- delivery during cardiopulmonary resuscita- ing cardiopulmonary resuscitation: Support for a tion with interposed abdominal compressions. Ann thoracoabdominal unit. Chest 93:1206–1212, 1988 Emerg Med 12:128–135, 1983 42. Sack JB, Kesselbrenner MB, Bregman D: Survival 60. Babbs CF, Sack JB, Kern KB: Interposed abdominal from in-hospital cardiac arrest with interposed ab- compression as an adjunct to cardiopulmonary resus- dominal counterpulsation during cardiopulmonary citation. Am Heart J 127:412–421, 1994 resuscitation. JAMA 267:379–385, 1992 61. Ward KR, Sullivan RJ, Zelenak RR, et al: A compari- 43. Sack JB, Kesselbrenner MB: Hemodynamics, survival son of interposed abdominal compression CPR and benefits, and complications of interposed abdominal standard CPR by monitoring end-tidal PCO2. Ann compression during cardiopulmonary resuscitation. Emerg Med 18:831–837, 1989 Acad Emerg Med 1:490–497, 1994 62. Sack JB, Kesselbrenner MB, Jarrad A: Interposed ab- 44. Tang W, Weil MH, Schock RB, et al: Phased chest dominal compression CPR and resuscitation outcome and abdominal compression-decompression: A new during and electromechanical dissociation. option for cardiopulmonary resuscitation. Circulation Circulation 86:1692–1700, 1992 95:1335–1340, 1997 63. Mateer JR, Steuven HA, Thompson BM, et al: Pre- hospital IAC-CPR versus standard CPR: Paramedic 45. DelGuercio L, Feins NR, Cohn JD, et al: Comparison resuscitation of cardiac arrests. Am J Emerg Med of blood flow during external and internal cardiac 3:143–146, 1985 massage in man. Circulation 31(suppl I):171–180, 64. Waldman PJ, Walters BL, Grunau C: Pancreatic injury 1965 associated with interposed abdominal compressions 46. Lurie KG, Coffeen P, Shultz J, et al: Improving active in pediatric cardiopulmonary resuscitation. Am J Em- compression-decompression cardiopulmonary resus- erg Med 2:510–512, 1984 citation with an inspiratory impedance valve. Circu- 65. Clark DT: Complications following closed-chest car- lation 91:1629–1632, 1995 diac massage. JAMA 181:337–338, 1962 47. Lindner KH, Pfenninger EG, Lurie KG, Schurmann 66. Nagel EL, Fine EG, Krischer JP, et al: Complications W, Lindner IM, Ahnefeld FW: Effects of active com- of CPR. Critical Care 9:424, 1981 pression-decompression resuscitation on myocardial 67. Silberberg B, Rachmaninoff N: Complications follow- and cerebral blood flow in pigs. Circulation 88:1254– ing external cardiac massage. Surg Gynecol Obstet 1263, 1993 119:6–10, 1964 48. Lurie KG, Lindo C, Chin J: CPR: The P stands for 68. Babbs CF, Schoenlein WE, Lowe MW: Gastric insuf- plumber’s helper. JAMA 264:1661, 1990 flation during IAC-CPR and standard CPR in a ca- 49. Cohen TJ, Tucker KJ, Lurie KG, et al: Active compres- nine model. Am J Emerg Med 3:99–103, 1985 sion-decompression: A new method of cardiopulmo- 69. Standards and guidelines for cardiopulmonary resus- nary resuscitation: Cardiopulmonary Resuscitation citation (CPR) and emergency cardiac care (ECC). Working Group. JAMA 267:2916–2923, 1992 JAMA 244:453–509, 1980 50. Chang MW, Coffeen P, Lurie KG, et al: Active com- 70. DI, Murphy RJ, Babbs CF, et al: Cardiac output pression-decompression CPR improves vital during CPR: A comparison of two methods. Crit perfusion in a dog model of ventricular fibrillation. Care Med 9:419–420, 1981 Chest 106:1250–1259, 1994 71. Cummins RO: Introduction to the international 51. Plaisance P, Lurie KG, Payen D: Inspiratory imped- guidelines 2000 for CPR and ECC. Circulation ance during active compression-decompression car- 102(suppl I):I-1–I-11, 2000 CIRCULATORY ADJUNCTS 59

72. Plaisance P, Adnet F, Vicaut E, et al: Benefit of active pre-hospital active compression-decompression compression-decompression cardiopulmonary resus- (ACD) cardiopulmonary resuscitation workshop: A citation as a prehospital advanced cardiac life sup- report and a review of ACD-CPR. Resuscitation : A randomized multicenter study. Circulation 30:191–202, 1995 95:955–961, 1997 80. Rabl W, Baubin M, Haid C, et al: Review of active 73. Panzer W, Bretthauer M, Klingler H, et al: ACD ver- compression-decompression cardiopulmonary resus- sus standard CPR in a prehospital setting. Resuscita- citation (ACD-CPR): Analysis of iatrogenic complica- tion 33:117–124, 1996 tions and their biomechanical explanation. Forensic 74. Schwab TM, Callaham ML, Madsen CD, et al: A Sci Int 89:175–183, 1997 randomized clinical trial of active compression-de- 81. Klintschar M, Darok M, Radner H: Massive injury to compression CPR versus standard CPR in out-of- the heart after attempted active compression-decom- hospital cardiac arrest in two cities. JAMA 273:1261– pression cardiopulmonary resuscitation. Int J Legal 1268, 1995 Med 111:93–96, 1998 75. Luiz T, Ellinger K, Denz C: Active compression-de- 82. Baubin M, Schirmer M, Nogler M, et al: Rescuer’s compression cardiopulmonary resuscitation does not work capacity and duration of cardiopulmonary re- improve survival in patients with prehospital cardiac suscitation. Resuscitation 33:135–139, 1996 arrest in a physician-manned emergency medical sys- 83. Babbs CF: IAC-CPR: Are we missing the mark in tem. J Cardiothorac Vasc Anesth 10:178–186, 1996 clinical trials? Am Heart J 126:1035–1041, 1993 76. Stiell IG, Hebert PC, Wells GA, et al: The Ontario 84. Yakaitis RW, Ewy GA, Otto CW, et al: Influence of time and therapy on ventricular defibrillation in trial of active compression-decompression cardiopul- dogs. Crit Care Med 8:157–163, 1980 monary resuscitation for in-hospital and prehospital 85. Marwick TH, Case C, Siskind V, et al: cardiac arrest. JAMA 275:1417–1423, 1996 of early high-dose adrenaline on outcome of ventric- 77. Mauer DK, Nolan J, Plaisance P, et al: Effect of active ular fibrillation. Lancet 2:66–68, 1988 compression-decompression resuscitation (ACD- 86. Sack JB, Kesselbrenner MB, Bregman D: Survival CPR) on survival: A combined analysis using indi- from in-hospital cardiac arrest with interposed ab- vidual patient data. Resuscitation 41:249–256, 1999 dominal counterpulsation during cardiopulmonary 78. Wik L, Schneider T, Baubin M, et al: Active compres- resuscitation. JAMA 267:379–385, 1992 sion-decompression cardiopulmonary resuscitation: 87. Babbs CF: Efficacy of interposed abdominal compres- Instructor and student manual for teaching and train- sion-cardiopulmonary resuscitation (CPR), active ing: Part II: A student and instructor manual. Resus- compression and decompression-CPR and Lifestick citation 32:206–212, 1996 CPR: Basic physiology in a spreadsheet model. Crit 79. Wik L, Mauer D, Robertson C: The first European Care Med 28:N199–202, 2000

Address reprint requests to Charles F. Babbs, MD, PhD Department of Basic Medical Sciences Purdue University West Lafayette, IN 47907–1246

e-mail: [email protected]