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Transfemoral balloon aortic occlusion during open cardiopulmonary resuscitation improves myocardial and cerebral blood flow
JOURNAL
OF SURGICAL
RESEARCH
49,
217-221
(1990)
Transfemoral Balloon Aortic Occlusion during Open Cardiopulmonary Resuscitation Improves Myocardial and Cerebral Blood Flow’ PAUL A. SPENCE, M.D., FRCS(C), HIROSHI Departments
IIDA, M.D.,
ROBERT M. LUST, PH.D., W. RANDOLPH CHITWOOD, JR., M.D., You Su SUN, M.D., AND ERLE H. AUSTIN III, M.D., FACS
of Cardiac Surgery and Physiology, East Carolina University
School of Medicine,
FACS,
Greenville, North Carolina 27858-4354
Submitted for publication November 20, 1989
These experiments were designed to determine whether the limited cardiac output during open cardiac massage could be preferentially directed to the coronary and cerebral vessels by balloon occlusion of the descending thoracic aorta. Sixteen dogs were instrumented to monitor cardiac output and left atrial, right atrial, right ventricular, left ventricular, and arterial blood pressures. Measurements of myocardial and cerebral blood flow distribution during massage were made using the radioactive microsphere technique. Each animal underwent two episodes of fibrillation and resuscitation. In one episode the arrest was managed by open massage alone, and in the other, open massage was accompanied by balloon occlusion, with the order randomized. When compared to control, open cardiac massage was associated with a significant decrease in mean arterial pressure; however, the addition of balloon occlusion produced a 130% increase in the mean arterial pressure that was obtained during open CPR (control, 93 + 5 mm Hg; massage alone, 35 + 2 mm Hg; massage + balloon, 76 + 2 mm Hg, P < 0.01). In a similar fashion, although the absolute blood flow was reduced by 50% when compared to control, the blood flow (ml/min/g) to the brain and heart during massage was 100% better when balloon occlusion was employed (brain: control, 0.41+ 0.03; massage only, 0.05 f 0.01; massage + balloon, 0.25 k 0.02, P < 0.01; heart: control, 1.46 k 0.11; massage alone, 0.35 + 0.05; massage + balloon, 0.71 + 0.05, P < 0.01). These results suggest that aortic occlusion significantly increased myocardial and cerebral perfusion patterns during ventricular fibrillation and open cardiac massage. Percutaneous transfemoral balloon aortic occlusion during CPR may be a useful adjunct to standard therapy. o 1990 Academic
Press.
Inc.
INTRODUCTION
The outcome of patients who undergo cardiopulmonary resuscitation (CPR) depends largely on the successful ’ Presented at the Annual Meeting of the Association for Academic Surgery, Louisville, KY, November 15-l&1989.
restoration of cardiac and cerebral function [ 11. Flow to both of these organs is markedly reduced during resuscitation efforts [2-61. For many years surgeons have been trained to cross-clamp the aorta during open cardiac massage when an emergency thoracotomy is performed during cardiac arrest. Increasing experience with femoral cannulation and the widespread availability of cardiac catheterization, percutaneous balloon angioplasty, and intraaortic balloon counterpulsation suggests that transfemoral occlusion of the aorta, producing a hemodynamic equivalent to the open cross-clamp technique, might be feasible during CPR. These experiments were designed to determine whether the limited cardiac output during cardiopulmonary resuscitation could be preferentially directed to the coronary and cerebral vessels by balloon occlusion of the descending thoracic aorta just past the origin of the subclavian artery. METHODS
Sixteen anesthetized (pentobarbital, 30 mg/kg iv bolus, supplemented pm) adult mongrel dogs, weighing between 19 and 24 kg, were intubated and ventilated with room air. Adjustments to the ventilator were made to maintain arterial POz above 90 mm Hg, arterial oxygen saturation above 93%) and arterial PC02 between 38 and 42 mm Hg. Blood gases were sampled routinely and bicarbonate was administered as needed to maintain arterial pH between 7.37 and 7.43. A left thoracotomy was performed and both internal mammary arteries were cannulated: one with a fluid-filled catheter for arterial blood sample withdrawal, and the other with a Millar catheter-tipped pressure transducer (Millar Instruments, Houston, Texas) to monitor arterial blood pressure. The pericardium was widely excised. The pulmonary artery was carefully dissected free from any connective tissue attachments and encircled with an electromagnetic flow probe (Zepeda Instruments, Seattle, WA) which was used to monitor cardiac output. Purse-string sutures were placed in the right atria1 appendage, and a fluid-filled catheter was inserted to measure right atria1 pressure. A second Millar catheter was inserted, advanced into the right ventricle and used
217 All
oozz-4804/90 $1.50 Copyright 0 1990 by Academic Press, Inc. rights of reproduction in any form reserved.
218
JOURNAL
OF SURGICAL
RESEARCH:
to monitor right ventricular pressure. In a similar fashion purse-string sutures were also placed in the left atria1 appendage. Through one set a fluid-filled catheter was placed and used to monitor left atria1 pressure and for injection of radioactive microspheres. Through the other pursestring a third Millar catheter was inserted, advanced into the left ventricle, and used to monitor left ventricular pressure. All catheters, probes, and transducers were connected to a polygraph (Hewlett-Packard Instruments, Los Angeles, CA) and monitored continuously for the duration of the experiment. A femoral cut down was performed, and an intraaortic balloon catheter (Datascope, Paramus, New Jersey) was advanced to the level of the origin of the subclavian artery. The position of the balloon was confirmed manually through the thoracotomy. The balloon was left deflated at this time, and the presence of the balloon did not significantly influence resting hemodynamics. Baseline measurements of cardiac output and right atrial, left atrial, arterial, right ventricular, and left ventricular pressures were obtained. The first microsphere injection, used to establish control perfusion patterns, was made at this time. The hearts were then fibrillated with a short burst of altering current. Open chest manual cardiac resuscitation was then performed at a rate of 100 compressions per minute. Ninety seconds after the onset of fibrillation and the initiation of cardiac massage, samples of all hemodynamic measurements were obtained, and the second microsphere injection was made. After 3 min of fibrillation and open cardiac massage the hearts were defibrillated and the animals were allowed to recover for 30 min. Due to the short period of CPR in these experiments, no systemic heparinization was used. In all cases, return to baseline hemodynamic parameters for a period of not less than 15 min was confirmed. This included the stabilization of all arterial blood gas parameters. The hearts were then fibrillated with an alternating current for a second time and the episode was repeated. A third injection of microspheres was made and data sampling again occurred 90 set after the initiation of open cardiopulmonary resuscitation. At the end of 3 min, the animals were again successfully defibrillated and allowed to return to stable baseline values. In one of the two episodes, the intraaortic balloon was inflated, but the episode in which the balloon was inflated was selected at random. At the end of the experiment, the animals were euthanized by lethal overdose. The heart and brain were removed and placed in fixative for later sectioning. Blood flow distribution was determined using lo-pm radioactive microspheres (New England Nuclear, Boston, MA) according to the reference withdrawal method of Rudolph and Heymann [7]. The injection techniques as well as the withdrawal and tissue sectioning procedures have been detailed previously [8]. Briefly, reference arterial withdrawal at a known, fixed rate was begun 15 set before microsphere injection and continued for at least 2 min after the injection. One milliliter (approximately 3 X lo6
VOL. 49, NO. 3, SEPTEMBER
1990
spheres) of agitated ultrasonic solution labeled with scandium-46, niobium-95, or ruthenium-103 were selected at random and injected into the left atrium. Streaming or nonuniform distribution of the microspheres in these experiments was checked by comparing flows to the right and the left cortex. Lateral differences in cortical flows of more than 15% were criteria for disregarding ail data obtained from that injection. In the present study no data were excluded on this criteria. Samples of the left ventricle, right ventricle, interventricular septum, left and right cerebral cortex, cerebellum, and medullary brain stem were weighed and analyzed for gamma activity (Packard Instrument Co., Sterling, VA). By computer analysis, counts were then translated to flow values and normalized for tissue weight to yield blood flow determinations in milliliters/minute/gram. Analysis of variance for repeated measures with appropriate post-hoc tests were used to determine statistical significance between all blood flow and hemodynamic determinations. Significance in all cases were determined at the P < 0.01 level. In conducting these experiments we adhered strictly to the Guiding Principles for the Care and Use of Laboratory Animals developed by the American Physiological Society. RESULTS
Cardiac output fell during open cardiac massage from a prefibrillation value of 2.28 f .08 liters/min to 1.10 + .09 and 1.19 * .08 in the massage alone and massage + balloon groups, respectively. While the decrease in both CPR groups was significantly different from control, neither of the CPR groups was different from each other. Similarly, increases in right and left atria1 pressures from control values of 4 and 5 mm Hg, respectively, to 10 and 11 mm Hg were observed during CPR, but again no significant differences were detected between the CPR groups. Mean arterial pressure fell immediately during fibrillation and could be maintained at only 38% of control values by open cardiac massage alone. Addition of the balloon occlusion to the massage procedures produced an increase in mean arterial pressure of 114% above open massage alone and restored mean arterial pressure to 81% of control values (Fig. 1). Figure 2 demonstrates that a significant gradient in peak systolic pressure developed between the left ventricle and the aorta during open cardiac massage alone, suggesting a significant loss in the transfer of developed pressure. In contrast, peak arterial pressures were not significantly different from peak left ventricular pressures when open massage was accompanied by balloon occlusion. There was better maintenance of peripheral resistance with balloon occlusion, as evidenced by the increased diastolic arterial pressure that was maintained in this group (Fig. 3). A summary of the differences in pressure patterns observed in the two CPR groups can be seen from the sample tracings shown in Fig. 4. The coronary perfusion gradient, calculated as the difference between arterial diastolic pressure and left ventricular end-dia-
SPENCE
n q Control q CPR + balloon l
H 70E 60.E. $3 502 $ 40a 30-
* pc.01 “.s control * pg.01 vs no balloon
ET AL.: BALLOON
OCCLUSION
DURING
219
CPR
q
Control @ CPR + balloon
CPR - no balloon ** * T g
60
L
50
If
40
a'u
30
n
CPR no balloon
** I
* pc.01 vs control ** pc.01 vs no balloon
20
20 10
10
0
0
Ao
FIG. 1. Changes in mean arterial pressure with fibrillation and open cardiac massage, with or without accompanying balloon occlusion.
stolic pressure, decreased to 15% of control during fibrillation and massage. Addition of balloon occlusion to the open cardiac massage increased the coronary perfusion gradient more than 300% from massage alone and restored the coronary perfusion gradient to approximately 70% of control (Fig. 5). Calculated blood flow to the heart and brain averaged between 12 and 20% of control values during open CPR alone, but were in excess of 50% of control values when open CPR was accompanied by balloon occlusion (Figs. 6 and 7). DISCUSSION
The concept of aortic occlusion during open cardiac resuscitation is not new. For many years, surgeons have been trained to clamp the aorta when open cardiac massage was performed in the setting of an emergency thoracotomy, although we could find no experimental literature to explain this practice. Preliminary experiments using manual clamping of the descending aorta had suggested that such an occlusion would produce beneficial results. Employing the intravascular balloon was decided upon, in part, as a prelude to an eventual closed-chest
fii! Control n CPR - no balloon q CPR + balloon
140 120 H E a, 2 %
* p<.o1 “S control ** pc.01 vs no balloon
FIG. arterial clusion. balloon
LV
Ao
LV
Ao
LV
3. Changes in diastolic left ventricular (LV) and ascending (AO) pressures during open CPR, with or without balloon ocNote better maintenance of arterial diastolic pressures in the occlusion group.
application. Also, in previous experiments from our laboratory, we had demonstrated that balloon occlusion could successfully manipulate the distribution of the limited cardiac output to theoretically protect the spinal cord during proximal cross-clamp procedures [9]. This lead us to speculate that balloon occlusion of the thoracic aorta might also be useful in improving cerebral perfusion and coronary perfusion during CPR. The results of these experiments suggest that balloon occlusion of the aorta during open cardiac resuscitation improves the mean pressure in the aorta and the coronary perfusion gradient. Myocardial and cortical blood flow measurements indicate that balloon occlusion significantly improves perfusion to the heart and brain in these animals. It appears that aortic balloon occlusion prevents run-off of the reduced cardiac output through the peripheral circulation. Thus, the restricted cardiac output which can be generated during CPR can be preferentially directed to the brain and heart. Since myocardial perfusion and cerebral perfusion are the major determinants of recovery following cardiopulmonary resuscitation, rapid transfemoral balloon aortic occlusion during standard cardiopulmonary resuscitation may be a reasonable measure in emergency centers where there is considerable experience with femoral cannulation. Previous investigators have demonstrated the beneficial effects of epinephrine during cardiopulmonary resusci-
100 80 60
t
40
”
LV
Ao
LV
Ao
LV
Ao
FIG. 2. Changes in peak systolic left ventricular (LV) and ascending arterial (AO) blood pressures with fibrillation and open cardiac massage, with or without accompanying balloon occlusion. Note the large difference between LV and A0 systolic pressures in the massage only group.
FIG. 4. CPR perfusion patterns. Sample arterial (AO) and left ventricular (LV) pressure tracings obtained during manual CPR without and with balloon occlusion of the descending thoracic aorta.
220
JOURNAL
OF SURGICAL
RESEARCH:
VOL. 49, NO. 3, SEPTEMBER 1.60
80 w
70 60 a $ E a, ? &2
1990
* **
n
CPR - no balloon
p<.o1 YS control p<.Ol vs no balloon
50
a
1.20
z :E
1.00
c. 6 ii B
40 30
**
CPR - no balloon
* p<.o1 "S Control pc.01 YS no balloon
.80 .60
i2 20
.40
10
.20 0
0
FIG. 5. Calculated coronary perfusion pressure gradient during CPR with and without balloon occlusion.
tation [3]. One of the proposed mechanisms for the beneficial effect of this drug is the prevention of run-off in the peripheral circulation. Balloon occlusion may act as a very selective measure to direct the flow to critical target organs. The potential deleterious effects of CPR with balloon occlusion include aortic trauma and possible aortic rupture. Also, there could be ischemic damage in organs distal to the site of occlusion, including the GI tract, kidneys, and spinal cord. However, if cardiac function can be restored more expeditiously with CPR and aortic occlusion, it may be possible to reverse the effects of ischemia in peripheral organs after successful CPR. It may be necessary to limit the period of balloon occlusion of the aorta if CPR becomes prolonged. Also, with prolonged CPR, the question of systemic heparinization would have to be addressed, as this can significantly influence recovery under those circumstances. In addition, prolonged usage or closed chest application of this technique will require the question of synchronization to be addressed. Whether the balloon should be inflated or deflated in synchronization with chest compression or ventilation remains to be determined. Since there was direct manual compression of the heart in these experiments, many of the arguments
i ;o$ylballoonn s 2 2
0.35
l
**
p<.o1 "S control p<.Ol vs no baloon
CPR - no balloon
__
0.30
.E 2
0.25
IL.
0.20
B g
0.15 0.10
FIG. 6. Microsphere derived blood flow patterns in the cerebral cortex during CPR with and without balloon occlusion. Note the large increase in perfusion that accompanies balloon occlusion and CPR.
FIG. 7. Microsphere derived blood flow patterns to a representative (posterior papillary, midventricular) region of the left ventricle. As might be expected from the increase in perfusion pressure previously demonstrated in the balloon occlusion group, there was also a large, significant increase in myocardial blood flow during this intervention when compared to massage alone.
regarding compression and thoracic pump mechanisms in the closed chest are not relevant. Presumably, a fixed increase in peripheral vascular resistance is better in this model than some period of synchronized decrease in resistance. As it relates to distal organ perfusion, we considered this less vital since myocardial and cerebral tissues are irreversibly injured much sooner than most visceral organs. However, in prolonged or closed chest applications, these factors would have to be reexamined. This model studied only the effects of cardiopulmonary resuscitation in an open chest model. The effects of balloon occlusion during closed chest CPR may be considerably different. Furthermore, the effects of varying heart rates in the face of aortic occlusion may be different than in the situation when the aorta is not occluded. Further studies are necessary to determine whether CPR with balloon occlusion would be effective in a standard closed chest situation. Additional studies would also be necessary to determine the influence of cardiac compression rate during balloon occlusion on differential perfusion patterns. In summary, this investigation suggests that balloon occlusion during open chest cardiopulmonary resuscitation may preferentially increase cerebral and myocardial flows. Additional studies are necessary to identify whether this technique is useful during closed chest CPR and to understand the effects of balloon occlusion on distal organ ischemia. ACKNOWLEDGMENTS The authors acknowledge the technical assistance mad-Moghadam and Kathy Dennis in the conduct of The assistance of Kay Stallings and Laurie Rouse of the manuscript and Mike Dulude in the preparation is also recognized.
of Roshanak Etethese experiments. in the preparation of the illustrations
REFERENCES 1.
Taylor, G. J., Rubin, R., Tucker, M., Greene, H. L., Rudikoff, M. T., and Weisfeldt, M. L. External cardiac compression: A ran-
SPENCE domized comparison of mechanical Amer. Med. Assoc. 240: 644, 1978.
ET AL.: BALLOON
and manual
techniques.
J.
Halperin, H. R., Tsitlik, J. E., Guerci, A. D., Mellits, E. D., Levin, H. R., Shi, A. Y., Chandra, N., and Weisfeldt, M. L. Determinants of blood flow to vital organs during cardiopulmonary resuscitation in dogs. Circulation 73: 539, 1986. Michael, J. R., Guerci, A. D., Coehler, R. C., J. E., Chandra, N., Niedermeyer, E., Rogers, R. J., and Weisfeldt, M. L. Mechanisms by augments cerebrial and myocardial perfusion monary resuscitation in dogs. Circulation 69:
Shi, A. Y., Tsitlik, M. C., Traystman, which epinephrine during cardiopul822, 1984.
Bellamy, R. F., DeGuzman, L. R., and Pedersen, D. C. Coronary blood flow during cardiopulmonary resuscitation in swine. Circulation 69: 174, 1984. Wolfe, J. A., Maier, G. W., Newton, J. R., Glower, D. D., Tyson, G. S., Spratt, J. A., Rankin, J. S., and Olsen, C. 0. Physiologic
OCCLUSION
DURING
CPR
221
determinants of coronary blood flow during external cardiac massage. J. Thorac. Cardiouasc. Surg. 95: 523, 1988. 6. Halperin, H. R., Guerci, A. D., Char&a, N., Herskowitz, A., Tsitlik, J. E., Niskanen, R. A., Wurmb, E., and Weisfeldt, M. L. Vest inflation without simultaneous ventilation during cardiac arrest in dogs: Improved survival from prolonged cardiopulmonary resuscitation. Circulation 74: 1407, 1986. 7. Rudolph, A. M., and Heymann, M. A. The circulation of the fetus in utero: Methods for studying distribution of blood flow, cardiac output and organ blood flow. Circ. Res. 21: 136, 1967. 8. Lust, R. M., Beggerly, C. E., Morrison, R. F., Austin, E. H., and Chitwood, W. R. Improved protection of chronically inflowed-limited myocardium with retrograde coronary sinus cardioplegia. Circulation ‘78: 111-217, 1988. g Sun, Y. S., Lust, R. M., Spence, P. A., Iida, H., Pollock, S. B., Williams, J. M., and Austin, E. H. Spinal cord protection by balloon occlusion of the distal aorta during proximal aortic cross-clamping. Surg. Forum 15: 196, 1989.
OF SURGICAL
RESEARCH
49,
217-221
(1990)
Transfemoral Balloon Aortic Occlusion during Open Cardiopulmonary Resuscitation Improves Myocardial and Cerebral Blood Flow’ PAUL A. SPENCE, M.D., FRCS(C), HIROSHI Departments
IIDA, M.D.,
ROBERT M. LUST, PH.D., W. RANDOLPH CHITWOOD, JR., M.D., You Su SUN, M.D., AND ERLE H. AUSTIN III, M.D., FACS
of Cardiac Surgery and Physiology, East Carolina University
School of Medicine,
FACS,
Greenville, North Carolina 27858-4354
Submitted for publication November 20, 1989
These experiments were designed to determine whether the limited cardiac output during open cardiac massage could be preferentially directed to the coronary and cerebral vessels by balloon occlusion of the descending thoracic aorta. Sixteen dogs were instrumented to monitor cardiac output and left atrial, right atrial, right ventricular, left ventricular, and arterial blood pressures. Measurements of myocardial and cerebral blood flow distribution during massage were made using the radioactive microsphere technique. Each animal underwent two episodes of fibrillation and resuscitation. In one episode the arrest was managed by open massage alone, and in the other, open massage was accompanied by balloon occlusion, with the order randomized. When compared to control, open cardiac massage was associated with a significant decrease in mean arterial pressure; however, the addition of balloon occlusion produced a 130% increase in the mean arterial pressure that was obtained during open CPR (control, 93 + 5 mm Hg; massage alone, 35 + 2 mm Hg; massage + balloon, 76 + 2 mm Hg, P < 0.01). In a similar fashion, although the absolute blood flow was reduced by 50% when compared to control, the blood flow (ml/min/g) to the brain and heart during massage was 100% better when balloon occlusion was employed (brain: control, 0.41+ 0.03; massage only, 0.05 f 0.01; massage + balloon, 0.25 k 0.02, P < 0.01; heart: control, 1.46 k 0.11; massage alone, 0.35 + 0.05; massage + balloon, 0.71 + 0.05, P < 0.01). These results suggest that aortic occlusion significantly increased myocardial and cerebral perfusion patterns during ventricular fibrillation and open cardiac massage. Percutaneous transfemoral balloon aortic occlusion during CPR may be a useful adjunct to standard therapy. o 1990 Academic
Press.
Inc.
INTRODUCTION
The outcome of patients who undergo cardiopulmonary resuscitation (CPR) depends largely on the successful ’ Presented at the Annual Meeting of the Association for Academic Surgery, Louisville, KY, November 15-l&1989.
restoration of cardiac and cerebral function [ 11. Flow to both of these organs is markedly reduced during resuscitation efforts [2-61. For many years surgeons have been trained to cross-clamp the aorta during open cardiac massage when an emergency thoracotomy is performed during cardiac arrest. Increasing experience with femoral cannulation and the widespread availability of cardiac catheterization, percutaneous balloon angioplasty, and intraaortic balloon counterpulsation suggests that transfemoral occlusion of the aorta, producing a hemodynamic equivalent to the open cross-clamp technique, might be feasible during CPR. These experiments were designed to determine whether the limited cardiac output during cardiopulmonary resuscitation could be preferentially directed to the coronary and cerebral vessels by balloon occlusion of the descending thoracic aorta just past the origin of the subclavian artery. METHODS
Sixteen anesthetized (pentobarbital, 30 mg/kg iv bolus, supplemented pm) adult mongrel dogs, weighing between 19 and 24 kg, were intubated and ventilated with room air. Adjustments to the ventilator were made to maintain arterial POz above 90 mm Hg, arterial oxygen saturation above 93%) and arterial PC02 between 38 and 42 mm Hg. Blood gases were sampled routinely and bicarbonate was administered as needed to maintain arterial pH between 7.37 and 7.43. A left thoracotomy was performed and both internal mammary arteries were cannulated: one with a fluid-filled catheter for arterial blood sample withdrawal, and the other with a Millar catheter-tipped pressure transducer (Millar Instruments, Houston, Texas) to monitor arterial blood pressure. The pericardium was widely excised. The pulmonary artery was carefully dissected free from any connective tissue attachments and encircled with an electromagnetic flow probe (Zepeda Instruments, Seattle, WA) which was used to monitor cardiac output. Purse-string sutures were placed in the right atria1 appendage, and a fluid-filled catheter was inserted to measure right atria1 pressure. A second Millar catheter was inserted, advanced into the right ventricle and used
217 All
oozz-4804/90 $1.50 Copyright 0 1990 by Academic Press, Inc. rights of reproduction in any form reserved.
218
JOURNAL
OF SURGICAL
RESEARCH:
to monitor right ventricular pressure. In a similar fashion purse-string sutures were also placed in the left atria1 appendage. Through one set a fluid-filled catheter was placed and used to monitor left atria1 pressure and for injection of radioactive microspheres. Through the other pursestring a third Millar catheter was inserted, advanced into the left ventricle, and used to monitor left ventricular pressure. All catheters, probes, and transducers were connected to a polygraph (Hewlett-Packard Instruments, Los Angeles, CA) and monitored continuously for the duration of the experiment. A femoral cut down was performed, and an intraaortic balloon catheter (Datascope, Paramus, New Jersey) was advanced to the level of the origin of the subclavian artery. The position of the balloon was confirmed manually through the thoracotomy. The balloon was left deflated at this time, and the presence of the balloon did not significantly influence resting hemodynamics. Baseline measurements of cardiac output and right atrial, left atrial, arterial, right ventricular, and left ventricular pressures were obtained. The first microsphere injection, used to establish control perfusion patterns, was made at this time. The hearts were then fibrillated with a short burst of altering current. Open chest manual cardiac resuscitation was then performed at a rate of 100 compressions per minute. Ninety seconds after the onset of fibrillation and the initiation of cardiac massage, samples of all hemodynamic measurements were obtained, and the second microsphere injection was made. After 3 min of fibrillation and open cardiac massage the hearts were defibrillated and the animals were allowed to recover for 30 min. Due to the short period of CPR in these experiments, no systemic heparinization was used. In all cases, return to baseline hemodynamic parameters for a period of not less than 15 min was confirmed. This included the stabilization of all arterial blood gas parameters. The hearts were then fibrillated with an alternating current for a second time and the episode was repeated. A third injection of microspheres was made and data sampling again occurred 90 set after the initiation of open cardiopulmonary resuscitation. At the end of 3 min, the animals were again successfully defibrillated and allowed to return to stable baseline values. In one of the two episodes, the intraaortic balloon was inflated, but the episode in which the balloon was inflated was selected at random. At the end of the experiment, the animals were euthanized by lethal overdose. The heart and brain were removed and placed in fixative for later sectioning. Blood flow distribution was determined using lo-pm radioactive microspheres (New England Nuclear, Boston, MA) according to the reference withdrawal method of Rudolph and Heymann [7]. The injection techniques as well as the withdrawal and tissue sectioning procedures have been detailed previously [8]. Briefly, reference arterial withdrawal at a known, fixed rate was begun 15 set before microsphere injection and continued for at least 2 min after the injection. One milliliter (approximately 3 X lo6
VOL. 49, NO. 3, SEPTEMBER
1990
spheres) of agitated ultrasonic solution labeled with scandium-46, niobium-95, or ruthenium-103 were selected at random and injected into the left atrium. Streaming or nonuniform distribution of the microspheres in these experiments was checked by comparing flows to the right and the left cortex. Lateral differences in cortical flows of more than 15% were criteria for disregarding ail data obtained from that injection. In the present study no data were excluded on this criteria. Samples of the left ventricle, right ventricle, interventricular septum, left and right cerebral cortex, cerebellum, and medullary brain stem were weighed and analyzed for gamma activity (Packard Instrument Co., Sterling, VA). By computer analysis, counts were then translated to flow values and normalized for tissue weight to yield blood flow determinations in milliliters/minute/gram. Analysis of variance for repeated measures with appropriate post-hoc tests were used to determine statistical significance between all blood flow and hemodynamic determinations. Significance in all cases were determined at the P < 0.01 level. In conducting these experiments we adhered strictly to the Guiding Principles for the Care and Use of Laboratory Animals developed by the American Physiological Society. RESULTS
Cardiac output fell during open cardiac massage from a prefibrillation value of 2.28 f .08 liters/min to 1.10 + .09 and 1.19 * .08 in the massage alone and massage + balloon groups, respectively. While the decrease in both CPR groups was significantly different from control, neither of the CPR groups was different from each other. Similarly, increases in right and left atria1 pressures from control values of 4 and 5 mm Hg, respectively, to 10 and 11 mm Hg were observed during CPR, but again no significant differences were detected between the CPR groups. Mean arterial pressure fell immediately during fibrillation and could be maintained at only 38% of control values by open cardiac massage alone. Addition of the balloon occlusion to the massage procedures produced an increase in mean arterial pressure of 114% above open massage alone and restored mean arterial pressure to 81% of control values (Fig. 1). Figure 2 demonstrates that a significant gradient in peak systolic pressure developed between the left ventricle and the aorta during open cardiac massage alone, suggesting a significant loss in the transfer of developed pressure. In contrast, peak arterial pressures were not significantly different from peak left ventricular pressures when open massage was accompanied by balloon occlusion. There was better maintenance of peripheral resistance with balloon occlusion, as evidenced by the increased diastolic arterial pressure that was maintained in this group (Fig. 3). A summary of the differences in pressure patterns observed in the two CPR groups can be seen from the sample tracings shown in Fig. 4. The coronary perfusion gradient, calculated as the difference between arterial diastolic pressure and left ventricular end-dia-
SPENCE
n q Control q CPR + balloon l
H 70E 60.E. $3 502 $ 40a 30-
* pc.01 “.s control * pg.01 vs no balloon
ET AL.: BALLOON
OCCLUSION
DURING
219
CPR
q
Control @ CPR + balloon
CPR - no balloon ** * T g
60
L
50
If
40
a'u
30
n
CPR no balloon
** I
* pc.01 vs control ** pc.01 vs no balloon
20
20 10
10
0
0
Ao
FIG. 1. Changes in mean arterial pressure with fibrillation and open cardiac massage, with or without accompanying balloon occlusion.
stolic pressure, decreased to 15% of control during fibrillation and massage. Addition of balloon occlusion to the open cardiac massage increased the coronary perfusion gradient more than 300% from massage alone and restored the coronary perfusion gradient to approximately 70% of control (Fig. 5). Calculated blood flow to the heart and brain averaged between 12 and 20% of control values during open CPR alone, but were in excess of 50% of control values when open CPR was accompanied by balloon occlusion (Figs. 6 and 7). DISCUSSION
The concept of aortic occlusion during open cardiac resuscitation is not new. For many years, surgeons have been trained to clamp the aorta when open cardiac massage was performed in the setting of an emergency thoracotomy, although we could find no experimental literature to explain this practice. Preliminary experiments using manual clamping of the descending aorta had suggested that such an occlusion would produce beneficial results. Employing the intravascular balloon was decided upon, in part, as a prelude to an eventual closed-chest
fii! Control n CPR - no balloon q CPR + balloon
140 120 H E a, 2 %
* p<.o1 “S control ** pc.01 vs no balloon
FIG. arterial clusion. balloon
LV
Ao
LV
Ao
LV
3. Changes in diastolic left ventricular (LV) and ascending (AO) pressures during open CPR, with or without balloon ocNote better maintenance of arterial diastolic pressures in the occlusion group.
application. Also, in previous experiments from our laboratory, we had demonstrated that balloon occlusion could successfully manipulate the distribution of the limited cardiac output to theoretically protect the spinal cord during proximal cross-clamp procedures [9]. This lead us to speculate that balloon occlusion of the thoracic aorta might also be useful in improving cerebral perfusion and coronary perfusion during CPR. The results of these experiments suggest that balloon occlusion of the aorta during open cardiac resuscitation improves the mean pressure in the aorta and the coronary perfusion gradient. Myocardial and cortical blood flow measurements indicate that balloon occlusion significantly improves perfusion to the heart and brain in these animals. It appears that aortic balloon occlusion prevents run-off of the reduced cardiac output through the peripheral circulation. Thus, the restricted cardiac output which can be generated during CPR can be preferentially directed to the brain and heart. Since myocardial perfusion and cerebral perfusion are the major determinants of recovery following cardiopulmonary resuscitation, rapid transfemoral balloon aortic occlusion during standard cardiopulmonary resuscitation may be a reasonable measure in emergency centers where there is considerable experience with femoral cannulation. Previous investigators have demonstrated the beneficial effects of epinephrine during cardiopulmonary resusci-
100 80 60
t
40
”
LV
Ao
LV
Ao
LV
Ao
FIG. 2. Changes in peak systolic left ventricular (LV) and ascending arterial (AO) blood pressures with fibrillation and open cardiac massage, with or without accompanying balloon occlusion. Note the large difference between LV and A0 systolic pressures in the massage only group.
FIG. 4. CPR perfusion patterns. Sample arterial (AO) and left ventricular (LV) pressure tracings obtained during manual CPR without and with balloon occlusion of the descending thoracic aorta.
220
JOURNAL
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RESEARCH:
VOL. 49, NO. 3, SEPTEMBER 1.60
80 w
70 60 a $ E a, ? &2
1990
* **
n
CPR - no balloon
p<.o1 YS control p<.Ol vs no balloon
50
a
1.20
z :E
1.00
c. 6 ii B
40 30
**
CPR - no balloon
* p<.o1 "S Control pc.01 YS no balloon
.80 .60
i2 20
.40
10
.20 0
0
FIG. 5. Calculated coronary perfusion pressure gradient during CPR with and without balloon occlusion.
tation [3]. One of the proposed mechanisms for the beneficial effect of this drug is the prevention of run-off in the peripheral circulation. Balloon occlusion may act as a very selective measure to direct the flow to critical target organs. The potential deleterious effects of CPR with balloon occlusion include aortic trauma and possible aortic rupture. Also, there could be ischemic damage in organs distal to the site of occlusion, including the GI tract, kidneys, and spinal cord. However, if cardiac function can be restored more expeditiously with CPR and aortic occlusion, it may be possible to reverse the effects of ischemia in peripheral organs after successful CPR. It may be necessary to limit the period of balloon occlusion of the aorta if CPR becomes prolonged. Also, with prolonged CPR, the question of systemic heparinization would have to be addressed, as this can significantly influence recovery under those circumstances. In addition, prolonged usage or closed chest application of this technique will require the question of synchronization to be addressed. Whether the balloon should be inflated or deflated in synchronization with chest compression or ventilation remains to be determined. Since there was direct manual compression of the heart in these experiments, many of the arguments
i ;o$ylballoonn s 2 2
0.35
l
**
p<.o1 "S control p<.Ol vs no baloon
CPR - no balloon
__
0.30
.E 2
0.25
IL.
0.20
B g
0.15 0.10
FIG. 6. Microsphere derived blood flow patterns in the cerebral cortex during CPR with and without balloon occlusion. Note the large increase in perfusion that accompanies balloon occlusion and CPR.
FIG. 7. Microsphere derived blood flow patterns to a representative (posterior papillary, midventricular) region of the left ventricle. As might be expected from the increase in perfusion pressure previously demonstrated in the balloon occlusion group, there was also a large, significant increase in myocardial blood flow during this intervention when compared to massage alone.
regarding compression and thoracic pump mechanisms in the closed chest are not relevant. Presumably, a fixed increase in peripheral vascular resistance is better in this model than some period of synchronized decrease in resistance. As it relates to distal organ perfusion, we considered this less vital since myocardial and cerebral tissues are irreversibly injured much sooner than most visceral organs. However, in prolonged or closed chest applications, these factors would have to be reexamined. This model studied only the effects of cardiopulmonary resuscitation in an open chest model. The effects of balloon occlusion during closed chest CPR may be considerably different. Furthermore, the effects of varying heart rates in the face of aortic occlusion may be different than in the situation when the aorta is not occluded. Further studies are necessary to determine whether CPR with balloon occlusion would be effective in a standard closed chest situation. Additional studies would also be necessary to determine the influence of cardiac compression rate during balloon occlusion on differential perfusion patterns. In summary, this investigation suggests that balloon occlusion during open chest cardiopulmonary resuscitation may preferentially increase cerebral and myocardial flows. Additional studies are necessary to identify whether this technique is useful during closed chest CPR and to understand the effects of balloon occlusion on distal organ ischemia. ACKNOWLEDGMENTS The authors acknowledge the technical assistance mad-Moghadam and Kathy Dennis in the conduct of The assistance of Kay Stallings and Laurie Rouse of the manuscript and Mike Dulude in the preparation is also recognized.
of Roshanak Etethese experiments. in the preparation of the illustrations
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