Immediate countershock versus cardiopulmonary resuscitation before countershock in a 5-minute swine model of ventricular fibrillation arrest

STUDY OBJECTIVE: Prior laboratory and clinical studies demonstrate that cardiopulmonary resuscitation (CPR) preceding countershock of prolonged ventricular fibrillation (VF) increases the likelihood of successful cardiac resuscitation. The lower limit of VF duration at which time preshock CPR provides no benefit has not been specifically studied. The purpose of this study was to compare countershock and cardiac resuscitation outcome between immediate countershock of VF of 5-minute duration and CPR without drug therapy before countershock in a swine model. METHODS: VF was induced in anesthetized and instrumented swine. After 5 minutes of VF, animals received 1 of 2 treatments. Animals in group 1, a "historical" control group (n=20), received immediate countershock followed by CPR and repeated shocks if needed. Group 2 animals (n=11) received CPR for 90 seconds preceding countershock, then continued CPR and repeated countershock if necessary. Drugs were not administered to either group, and resuscitation efforts were discontinued if a perfusing rhythm was not restored within 10 minutes of the first countershock. First shock success rate (defined as termination of VF), the number of shocks required to terminate VF, and the cardiac resuscitation rate were compared between groups. RESULTS: The first shock terminated VF in 13 of 20 group 1 animals and 2 of 11 group 2 animals (P =.023). All but 1 animal in group 1 developed pulseless electrical activity after countershock. All but 1 animal in group 1 were eventually successfully resuscitated with CPR and repeated shocks if necessary. Four group 2 animals could not be resuscitated (P =.042). CONCLUSION: Although effective in improving outcome of prolonged VF, CPR preceding countershock of VF of 5-minute duration does not improve the response to the first shock, decrease the incidence of postshock pulseless electrical activity, or the rate of return of circulation. In this study, CPR preceding countershock resulted in a significantly lower cardiac resuscitation rate.     

Hyperkalemia and ionized hypocalcemia during cardiac arrest and resuscitation: possible culprits for postcountershock arrhythmias?

STUDY OBJECTIVE: Early countershock of ventricular fibrillation (VF) has been shown to improve immediate and long-term outcome of out-of-hospital cardiac arrest. However, studies indicate that countershock of prolonged VF most commonly results in asystole or a nonperfusing bradyarrhythmia (pulseless electrical activity [PEA]), which rarely respond to current therapy. The cause of these postcountershock rhythm disturbances is not well understood but may be related to electrical injury of the globally ischemic myocardium or to local metabolic abnormalities that impair impulse formation and cardiac contraction. The purpose of this study was to evaluate changes in serum potassium and free calcium homeostasis during cardiac arrest and advanced cardiac life support (ACLS) interventions. METHODS: After sedation, intubation, anesthesia, and instrumentation, VF was induced in 13 dogs. After 7.5 minutes of VF, animals were immediately countershocked, standard closed-chest CPR was initiated, and epinephrine was administered (1 mg in repeated doses if necessary). RESULTS: Ten animals could not be resuscitated despite 20 minutes of ACLS interventions. In these animals, a progressive increase in serum potassium was observed from the onset of ACLS to the termination of resuscitation efforts (4.3+/-.6 to 6.0+/-.8 mEq/L, P<.01). A significant increase was observed within 10 minutes of beginning ACLS measures. This was accompanied by a decrease in ionized calcium concentration over the same period (4.95+/-.40 to 3.44 mg/dL, P<.01). The decrease in ionized calcium was significant within 5 minutes of ACLS interventions. Nine of these 10 animals had either postcountershock asystole or PEA at the termination of resuscitative efforts. The increase in potassium was not related to acidemia. Successfully resuscitated animals did not demonstrate these electrolyte changes. CONCLUSION: Ionized hypocalcemia and hyperkalemia occur during prolonged resuscitative efforts and may be related to dysfunctional transcellular ionic transport mechanisms. These cations play important roles in cardiac electrical and contractile activity and may play a role in refractory postcountershock rhythm disturbances.     

Predictive indices of successful cardiac resuscitation after prolonged arrest and experimental cardiopulmonary resuscitation

To determine if clinically accessible hemodynamic and blood gas measurements are of value in predicting outcome of countershock after prolonged ventricular fibrillation (VF) and artificial cardiopulmonary support, 14 dogs were studied during 30 minutes of VF using two randomly assigned closed-chest techniques. Seven dogs underwent conventional CPR; the other seven were supported with a pneumatic thoracic vest and abdominal binder, which were inflated synchronously with the airway. Ascending aortic (Ao), right atrial (RA), and instantaneous coronary perfusion pressures (Ao - RA) were measured at five-minute intervals. Ao and RA blood samples were analyzed at 10, 20, 25 and 30 minutes for PO2, PCO2, and pH. After 25 minutes, 1 mg epinephrine was given intravenously, and five minutes later defibrillation was attempted. If unsuccessful, repeated countershocks, conventional pharmacologic therapy, and artificial support were continued. If a perfusing spontaneous cardiac rhythm did not result within an additional 30 minutes, the experiment was terminated. Six animals developed a perfusing cardiac rhythm after one or more countershocks (Group 1); eight failed to develop a perfusing rhythm after repeated countershocks and an additional 30 minutes of resuscitative effort (Group 2). Five Group 1 dogs received vest/binder artificial support. When measured values were averaged over the study period, Group 1 was found to have a significantly greater Ao end-diastolic pressure (AoEDP) and peak diastolic coronary perfusion pressure (CPP) when compared to Group 2 (23 +/- 6 vs 14 +/- 8 mm Hg, P less than .05; and 22 +/- 6 vs 5 +/- 10 mm Hg, P less than .01, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)     

Extracorporeal circulation as an alternative to open-chest cardiac compression for cardiac resuscitation.

Open-chest direct cardiac compression represents a more potent but highly invasive option for cardiac resuscitation when conventional techniques of closed-chest cardiac resuscitation fail after prolonged cardiac arrest. We postulated that venoarterial extracorporeal circulation might be a more effective intervention with less trauma. In the setting of human cardiac resuscitation, however, controlled studies would be limited by strategic constraints. Accordingly, the effectiveness of open-chest cardiac compression was compared with that of extracorporeal circulation after a 15-min interval of untreated ventricular fibrillation in a porcine model of cardiac arrest. Sixteen domestic pigs were randomized to resuscitation by either peripheral venoarterial extracorporeal circulation or open-chest direct cardiac compression. During resuscitation, epinephrine was continuously infused into the right atrium, and defibrillation was attempted by transthoracic countershock at 2-min intervals. Systemic blood flows averaged 198 ml.kg-1.min-1 with extracorporeal circulation. This contrasted with direct cardiac compression, in which flows averaged only 40 ml.kg-1.min-1. Coronary perfusion pressure, the major determinant of resuscitability on the basis of earlier studies, was correspondingly lower (94 vs 29 mm Hg). Extracorporeal circulation, in conjunction with transthoracic DC countershock and epinephrine, successfully reestablished spontaneous circulation in each of eight animals after 15 min of untreated ventricular fibrillation. This contrasted with the outcome after open-chest cardiac compression, in which spontaneous circulation was reestablished in only four of eight animals (p = .038). We conclude that extracorporeal circulation is a more effective alternative to direct cardiac compression for cardiac resuscitation after protracted cardiac arrest.     

Is a pressor necessary during aortic perfusion and oxygenation therapy of cardiac arrest?

STUDY OBJECTIVE: Occlusion of the descending aorta and infusion of oxygenated ultrapurified polymerized bovine hemoglobin may improve the efficacy of advanced cardiac life support (ACLS). Because selective aortic perfusion and oxygenation (SAPO) directly increases coronary perfusion pressure, exogenous epinephrine may not be required. The purpose of this study was to determine whether exogenous epinephrine is necessary during SAPO by comparing the rate of return of spontaneous circulation and aortic and coronary perfusion pressures during ACLS-SAPO in animals treated with either intra-aortic epinephrine or saline solution. METHODS: A prospective, randomized, interventional before-after trial with a canine model of ventricular fibrillation cardiac arrest and ACLS based on external chest compression was performed. The ECG, right atrial, aortic arch, and esophageal pulse pressures were measured continuously. A descending aortic occlusion balloon catheter was placed through the femoral artery. Ventricular fibrillation was induced, and no therapy was given during the 10-minute arrest time. Basic life support was then initiated and normalized by standardization of esophageal pulse pressure and central aortic blood gases. After 3 minutes of basic life support, the aortic occlusion balloon was inflated, and 0.01 mg/kg epinephrine or saline solution was administered through the aortic catheter followed by 450 mL of ultrapurified polymerized bovine hemoglobin over 2 minutes. Defibrillation was then attempted. The outcomes and changes in intravascular pressures were compared. RESULTS: Aortic pressures were higher during infusions in animals treated with epinephrine. During infusion, the mean aortic relaxation pressure increased by 58+/-5 mm Hg in animals that had received epinephrine versus 20+/-11 mm Hg in those that had received saline placebo. The coronary perfusion pressure during infusion increased by 52+/-8 mm Hg in animals that had received epinephrine versus 26+/-10 mm Hg in those that had received saline. Only 2 of 7 animals in the placebo group had return of spontaneous circulation versus 7 of 8 in the epinephrine group. CONCLUSION: The addition of epinephrine to ACLS-SAPO increases vital organ perfusion pressures and improves outcome from cardiac arrest. There appears to be a profound loss of arterial vasomotor tone after prolonged arrest. This loss of vasomotor tone may make exogenous pressors necessary for resuscitation after prolonged cardiac arrest.     

Monophasic versus biphasic transthoracic countershock after prolonged ventricular fibrillation in a swine model

OBJECTIVE: We sought to compare the defibrillation efficacy of a low-energy biphasic truncated exponential (BTE) waveform and a conventional higher-energy monophasic truncated exponential (MTE) waveform after prolonged ventricular fibrillation (VF). BACKGROUND: Low energy biphasic countershocks have been shown to be effective after brief episodes of VF (15 to 30 s) and to produce few postshock electrocardiogram abnormalities. METHODS: Swine were randomized to MTE (n = 18) or BTE (n = 20) after 5 min of VF. The first MTE shock dose was 200 J, and first BTE dose 150 J. If required, up to two additional shocks were administered (300, 360 J MTE; 150, 150 J BTE). If VF persisted manual cardiopulmonary resuscitation (CPR) was begun, and shocks were administered until VF was terminated. Successful defibrillation was defined as termination of VF regardless of postshock rhythm. If countershock terminated VF but was followed by a nonperfusing rhythm, CPR was performed until a perfusing rhythm developed. Arterial pressure, left ventricular (LV) pressure, first derivative of LV pressure and cardiac output were measured at intervals for 60 min postresuscitation. RESULTS: The odds ratio of first-shock success with BTE versus MTE was 0.67 (p = 0.55). The rate of termination of VF with the second or third shocks was similar between groups, as was the incidence of postshock pulseless electrical activity (15/18 MTE, 18/20 BTE) and CPR time for those animals that were resuscitated. Hemodynamic variables were not significantly different between groups at 15, 30 and 60 min after resuscitation. CONCLUSIONS: Monophasic and biphasic waveforms were equally effective in terminating prolonged VF with the first shock, and there was no apparent clinical disadvantage of subsequent low-energy biphasic shocks compared with progressive energy monophasic shocks. Lower-energy shocks were not associated with less postresuscitation myocardial dysfunction.     

Postcountershock pulseless rhythms: response to CPR, artificial cardiac pacing, and adrenergic agonists

Clinically, countershock of ventricular fibrillation (VF) may result in asystole or a pulseless rhythm in more than 50% of attempts. We conducted a study to assess the effects of immediate artificial pacing, CPR, and adrenergic drug therapy in the management of postcountershock pulseless rhythms. Thirty-four episodes of VF followed by countershock were studied in eight anesthetized dogs. Transducer-tipped catheters were positioned in the ascending aorta (Ao) and right atrium (RA). A bipolar pacing catheter was advanced to the apex of the right ventricle and a catheter for measurement of coronary sinus blood flow (CSQ) (continuous thermodilution technique) was positioned in the coronary sinus. VF was induced electrically and a countershock at 400 J was given two minutes later; CPR was not performed during VF episodes. Countershock was followed by asystole or a pulseless rhythm in all animals. Immediate endocardial pacing (0.1 to 5 mA) of bradyarrhythmias produced electrical capture but did not result in arterial pressure pulses in any animal. After pacing, CPR was performed for two minutes or until restoration of spontaneous circulation (ROSC). During CPR, the diastolic coronary perfusion gradient (Ao-RA) was 20 +/- 7 mm Hg (mean +/- SD) and CSQ was 14 +/- 7 mL/min/100 g (53% +/- 43% of control). ROSC followed CPR of less than two minutes duration in 24% of VF study episodes. If ROSC did not follow two minutes of CPR, 1 mg epinephrine, or 50 micrograms or 100 micrograms isoproterenol was given IV.(ABSTRACT TRUNCATED AT 250 WORDS)     

Comparison of epinephrine and phenylephrine for resuscitation and neurologic outcome of cardiac arrest in dogs

A study was done comparing resuscitability and 24-hour neurologic outcome in fibrillating dogs that were treated with either phenylephrine (a primary alpha agonist) or epinephrine. Ventricular fibrillation was induced electrically in 18 dogs. After three minutes, standard CPR was instituted using a mechanical resuscitator. Dogs were given phenylephrine or epinephrine at nine minutes and defibrillation was attempted at 12 minutes. Dogs underwent hemodynamic monitoring and pharmacologic support, if necessary, for an additional 90 minutes. At four, eight, 12, and 24 hours, a standard neurologic examination was performed and deficit scores were assigned by an observer blinded to the drug given. Fourteen of the 18 dogs were resuscitated. There were no statistically significant differences in the epinephrine- or phenylephrine-treated groups with regard to number of animals resuscitated, time and interventions required for resuscitation, initial cardiac rhythm post resuscitation, or occurrence of ventricular fibrillation during resuscitation. No differences were found in arterial, central venous, or myocardial perfusion pressures during CPR. Phenylephrine-treated dogs tended to have higher mean pressures in the critical care period (15 to 30 minutes), although this was not significant. Total neurologic deficit scores were 127.8 +/- 83.8 for the phenylephrine-treated group and 129.4 +/- 87.4 for the epinephrine group. No significant differences were found in the level of consciousness, cranial nerve function, motor skills, or general behavior scores. We conclude that there is no difference in neurologic or cardiovascular outcome when phenylephrine is compared to epinephrine in a canine model of cardiac arrest and cardiopulmonary resuscitation.     

Precountershock cardiopulmonary resuscitation improves ventricular fibrillation median frequency and myocardial readiness for successful defibrillation from prolonged ventricular fibrillation: a randomized,controlled swine study

STUDY OBJECTIVE: After prolonged ventricular fibrillation (VF), precountershock cardiopulmonary resuscitation (CPR) will improve myocardial "readiness" for defibrillation compared with immediate defibrillation. METHODS: After 10 minutes of untreated VF, 32 swine (27+/-1 kg) were randomly assigned to receive immediate countershocks (DEFIB), CPR for 3 minutes followed by countershocks (CPR), or CPR for 3 minutes plus intravenous epinephrine followed by countershocks (CPR+EPI). VF waveform was evaluated by fast Fourier transformation. RESULTS: VF amplitude and median frequency by fast Fourier transformation decreased during the untreated VF interval in all groups, and the median frequency subsequently increased during each minute of precountershock CPR. Although the VF median frequency in the 3 groups did not differ after 10 minutes of untreated VF (8.9+/-0.8 Hz versus 8.4+/-0.5 Hz versus 7.3+/-0.5 Hz, respectively), immediately before the first shock the VF median frequency was much lower in the DEFIB group than in either the CPR or CPR+EPI groups (8.9+/-0.8 Hz versus 13.1+/-0.8 Hz versus 13.8+/-0.9 Hz, respectively; P <.01). None of the 10 animals in the DEFIB group attained return of spontaneous circulation after the first set of shocks versus 5 of 10 animals in the CPR group and 6 of 12 animals in the CPR+EPI group (DEFIB versus each CPR group; P <.05). Cardiac output 1 hour after resuscitation was substantially worse in the DEFIB group than in the CPR or CPR+EPI groups (74+/-7 mL/kg per minute versus 119+/-7 mL/kg per minute versus 104+/-15 mL/kg per minute; P <.05). CONCLUSION: Precountershock CPR can result in substantial physiologic benefits compared with immediate defibrillation in the setting of prolonged VF. Moreover, these benefits can be attained with or without the addition of intravenous epinephrine.     

Predictive value of the ECG in determining cardiac resuscitation outcome in a canine model of postcountershock electromechanical dissociation after prolonged ventricular fibrillation

The purpose of our study was to determine if the surface ECG in postcountershock electromechanical dissociation (EMD) is of value in predicting return of effective myocardial contractile function during CPR. Nine dogs were subjected to five minutes of ventricular fibrillation (VF) without CPR followed by countershock and closed-chest CPR. Intravascular pressures, coronary perfusion pressure, and coronary sinus flow were measured during conventional CPR. After countershock, and before CPR, the frequencies of the following ECG variables were assessed: the presence or absence of P waves, an abnormal QRS duration (greater than 100 ms), a prolonged QTc (greater than 430 ms), and a bradyarrhythmia (QRS rate less than 60/min). Twenty-three episodes of postcountershock EMD were studied. Countershock after prolonged VF without CPR was always followed by EMD. The mean values of ECG variables were not significantly different (P greater than .05) between animals successfully resuscitated and those that were not. The sensitivity, specificity, and predictive values of individual ECG variables in estimating successful cardiac resuscitation exhibited a wide range of values. The QTc had the highest sensitivity (1.00), but the lowest specificity (0.08). The presence or absence of P waves had the highest specificity (0.62), but a sensitivity of only 0.40. QRS rate had the greatest positive predictive value (0.48) but a negative predictive value of 0.46 for successful cardiac resuscitation. The QTc had the greatest negative predictive value (1.00) but a positive predictive value of only 0.45. Multiple regression analysis using the study ECG variables as independent variables demonstrated that ECG variables were not related to outcome.(ABSTRACT TRUNCATED AT 250 WORDS)     

Neurologic benefits from the use of early cardiopulmonary resuscitation

The efficacy of bystander CPR in resuscitation from cardiac arrest when defibrillation is available within five to six minutes has been questioned. Epidemiologic studies from different cities have shown conflicting results. We conducted a study to determine the effect of early CPR versus no CPR on resuscitability, 24-hour survival, and neurologic deficit in an animal model of cardiac arrest. Twenty-two mongrel dogs were subjected to five minutes of electrically induced ventricular fibrillation. In 11 dogs, closed-chest massage and ventilation with room air was begun immediately and was continued for five minutes. The other 11 dogs received no CPR. At five minutes defibrillation was attempted and advanced cardiac life support (ACLS) protocols were followed until the animal was resuscitated or died. No statistical difference in resuscitability or 24-hour survival between the two groups was demonstrated. Eight of 11 "early CPR" animals were resuscitated and survived 24 hours; six of 11 "no CPR" dogs were resuscitated, and five lived for 24 hours. A significant difference was demonstrated by the Student t test in neurologic deficit and ease of resuscitation. "Early CPR" dogs had no neurologic deficit, while "no CPR" dogs had a 41% deficit (P less than .01). "Early CPR" dogs were resuscitated in significantly less time once ACLS was started (29 versus 317 seconds), and required less electrical energy (100 versus 560 J), fewer countershocks (1.3 versus 4.0), and less epinephrine (0.1 versus 1.7 mg) than did "no CPR" animals. In this animal model of cardiac arrest, early CPR was shown to be beneficial to neurologic function and ease of resuscitation, even when ACLS was provided within five minutes.     

The effect of bicarbonate on resuscitation from cardiac arrest.

STUDY OBJECTIVES: This study attempted to determine the effect of bicarbonate administration on resuscitation in a porcine model of prolonged cardiac arrest. DESIGN: After instrumentation, 26 swine were subjected to ventricular fibrillation for 15 minutes (16 animals) or 20 minutes (ten animals) with no resuscitative efforts. INTERVENTIONS: Resuscitation attempts with open-chest cardiac massage and epinephrine were used in all animals after the arrest period. The experimental group was given sodium bicarbonate (3 mEq/kg), and the control group received 3% saline (5 mL/kg) at the initiation of cardiac massage. MEASUREMENTS: Resuscitation success, hemodynamics, and arterial and mixed venous gases were compared in the bicarbonate and hypertonic saline-treated groups. RESULTS: There was no difference in resuscitation rates between bicarbonate and nonbicarbonate-treated swine. After 15 minutes of ventricular fibrillation, six of eight bicarbonate-treated swine were resuscitated successfully compared with five of eight hypertonic saline-treated animals. None of the five bicarbonate-treated or five hypertonic saline-treated swine that underwent 20 minutes of ventricular fibrillation were resuscitated. The arterial and mixed venous pH values were significantly different in the bicarbonate-treated animals from values in the control group. There was no difference in systolic or diastolic blood pressures or myocardial perfusion pressure between the bicarbonate and hypertonic saline-treated animals. CONCLUSION: Despite correlation of arterial and venous acidemia, the use of sodium bicarbonate did not improve resuscitation from prolonged cardiac arrest.     

Use of naloxone during cardiac arrest and CPR: potential adjunct for postcountershock electrical-mechanical dissociation

Naloxone has been shown to increase arterial pressure in hemorrhagic and septic shock. To determine if naloxone has salutary effects during cardiac arrest with conventional closed-chest cardiopulmonary resuscitation (CPR), ten dogs were studied during 20 minutes of ventricular fibrillation (VF) and CPR and during a 30-minute postcountershock period. Central aortic (Ao) and right atrial (RA) systolic and end-diastolic (EDP) pressures, instantaneous Ao-RA pressure difference (coronary perfusion pressure), and electromagnetic Ao flow were measured. Ao and RA samples were analyzed during a control period and at five-minute intervals during CPR for PO2, PCO2, and pH. During VF, a piston-cylinder device was used to perform anteroposterior sternal depressions and positive pressure ventilations (100% O2) at standard rates and ratios. After 15 minutes of CPR, animals were randomized and given either naloxone (5 mg/kg) or epinephrine (1 mg). Defibrillation was attempted five minutes later using 1 J/kg and then, if necessary, 2, 4, 8, 12, and 16 J/kg until VF was terminated or the maximum energy dose was reached. If VF persisted or if countershock resulted in asystole or a nonperfusing rhythm (electrical-mechanical dissociation [EMD]), the alternate drug (naloxone or epinephrine) was then given. Measured systolic pressures, coronary perfusion pressures, aortic flow, and blood gases were not significantly different during the control period or at five, ten, and 15 minutes of VF and CPR between animal groups prior to drug administration. When compared to hemodynamic values measured at 15 minutes, naloxone had no significant effect on pressures or aortic flow measured five minutes after administration.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of application of force to self-adhesive defibrillator pads on transthoracic electrical impedance and countershock success.

STUDY OBJECTIVE: To examine the effect of the application of force to self-adhesive defibrillator pads on transthoracic electrical impedance and countershock success. METHODS: A prospective, randomized, controlled pilot study was carried out in an experimental animal laboratory, involving 32 mixed-breed swine weighing 36.5 to 55.7 kg each. Ventricular fibrillation (VF) was induced, and the animals were randomly allocated to 1 of 4 groups, with 8 animals per group. Animals in groups I and II remained in VF for 30 seconds; those in groups III and IV remained in VF for 5 minutes. At the end of the VF period, up to 3 countershocks were given. In groups I and III, countershocks were delivered through the self-adhesive defibrillator pads alone; in groups II and IV, they were delivered through the defibrillator pads with 25 lb of applied force. Any animal without return of spontaneous circulation after 3 countershocks was given epinephrine after 1 minute of CPR, followed by 1 additional minute of CPR and 1 additional countershock if required. RESULTS: The main measurements included baseline and countershock transthoracic impedance, cumulative countershock success rate, and 30-minute survival rate. Application of 25 lb of force to the defibrillator pads significantly decreased transthoracic impedance, compared with baseline values (group II, 15. 1% decrease; group IV, 16.1% decrease). The first-shock success rate was higher when force was applied during the countershock (87.5% versus 50% for groups II and I, respectively; 62.5% and 37.5% for groups IV and III, respectively). In the animals who experienced 5 minutes of VF, there were greater rates of success after the second, third, and fourth countershocks when force was applied (group IV) than when no force was applied (group III). Groups I and II (VF for 30 seconds) demonstrated 100% survival at 30 minutes. Group IV had a higher 30-minute survival rate (3/8 animals) than did group III (1/8). However, the rates of countershock success and 30-minute survival were not statistically different among the groups. CONCLUSION: Application of force to self-adhesive defibrillator pads decreases transthoracic impedance during countershock. This effect may contribute to improving the countershock success rate.     

Artificial perfusion techniques during cardiac arrest: questions of experimental focus versus clinical need

Contemporary cerebral-cardiopulmonary resuscitation investigations in the experimental laboratory have defined mechanisms for blood flow during closed-chest CPR and have demonstrated that the current CPR technique produces limited systemic perfusion. Modified closed-chest CPR techniques usually improve perfusion. Unfortunately few laboratory CPR studies have actually investigated resuscitation and survival. In addition, the animal model employed (prolonged ventricular fibrillation) may have limited clinical relevance, based on clinical experience and resuscitation practice, and data reporting techniques and their interpretation may be affected by control values that are not normal because of the effects of anesthetics. Closed-chest CPR was intended to buy time until a countershock could be delivered. Clinical and laboratory experience indicate that this goal can be met. Cerebral perfusion during closed-chest CPR is low, but adequacy from a functional perspective following restoration of circulation has not been carefully studied. Preservation of neuronal integrity after restoration of spontaneous circulation may be more important than cerebral perfusion during cardiac arrest and CPR. The role and benefit of open-chest CPR have yet to be determined, because this technique will most likely be used after conventional CPR failure. New and different experimental models are required to meet clinical needs and challenges. The alliance between practitioner and investigator should be strengthened if common goals are to be attained.     

Use of cardiopulmonary bypass, high-dose epinephrine, and standard-dose epinephrine in resuscitation from post-countershock electromechanical dissociation.

STUDY OBJECTIVE: To determine the effects of cardiopulmonary bypass with standard-dose epinephrine, high-dose epinephrine, and standard-dose epinephrine on perfusion pressures, myocardial blood flow, and resuscitation from post-countershock electromechanical dissociation. DESIGN: Prospective, controlled laboratory investigation using a canine cardiac arrest model randomized to receive one of three resuscitation therapies. INTERVENTIONS: After the production of post-countershock electromechanical dissociation, 25 animals received ten minutes of basic CPR and were randomized to receive cardiopulmonary bypass with standard-dose epinephrine, high-dose epinephrine, or standard-dose epinephrine. MEASUREMENTS AND MAIN RESULTS: Myocardial blood flow was measured using a colored microsphere technique at baseline, during basic CPR, and after intervention. Immediate and two-hour resuscitation rates were determined for each group. Return of spontaneous circulation was achieved in eight of eight cardiopulmonary bypass with standard-dose epinephrine compared with four of eight high-dose epinephrine and three of eight standard-dose epinephrine animals (P less than .04). One animal was resuscitated with CPR alone and was excluded. Survival to two hours was achieved in five of eight cardiopulmonary bypass with standard-dose epinephrine, four of eight high-dose epinephrine, and three of eight standard-dose epinephrine animals (NS). Coronary perfusion pressure increased significantly in the cardiopulmonary bypass with standard-dose epinephrine group when compared with the other groups (cardiopulmonary bypass with standard-dose epinephrine, 76 +/- 45 mm Hg; high-dose epinephrine, 24 +/- 12 mm Hg; standard-dose epinephrine, 3 +/- 14 mm Hg; P less than .005). Myocardial blood flow was higher in cardiopulmonary bypass with standard-dose epinephrine and high-dose epinephrine animals compared with standard-dose epinephrine animals but did not reach statistical significance. Cardiac output increased during cardiopulmonary bypass with standard-dose epinephrine (P = .001) and standard-dose epinephrine (NS) compared with basic CPR but decreased after epinephrine administration in the high-dose epinephrine group (NS). CONCLUSION: Resuscitation from electromechanical dissociation was improved with cardiopulmonary bypass and epinephrine compared with high-dose epinephrine or standard-dose epinephrine alone. However, there was no difference in survival between groups. Cardiopulmonary bypass with standard-dose epinephrine resulted in higher cardiac output, coronary perfusion pressure, and a trend toward higher myocardial blood flow. A short period of cardiopulmonary bypass with epinephrine after prolonged post-countershock electromechanical dissociation cardiac arrest can re-establish sufficient circulation to effect successful early resuscitation.     

Comparison of standard external CPR, open-chest CPR, and cardiopulmonary bypass in a canine myocardial infarct model

STUDY OBJECTIVES: After cardiac arrest, open-chest CPR (OCCPR) and cardiopulmonary bypass (CPB) have demonstrated higher resuscitation rates when compared individually with standard external CPR (SECPR). We compared all three techniques in a canine myocardial infarct ventricular fibrillation model. TYPE OF PARTICIPANTS: Twenty-six mongrel dogs were block-randomized to receive SECPR and advanced life support (nine), CPB (nine), or OCCPR (eight). DESIGN AND INTERVENTIONS: All dogs received left anterior descending coronary artery occlusion followed by four minutes of ventricular fibrillation without CPR and eight minutes of Thumper CPR. At 12 minutes, dogs received one of three resuscitation techniques. After resuscitation, all animals received four hours of intensive care. Animals that were resuscitated had histochemical determination of ischemic and necrotic myocardial areas. MEASUREMENTS: Intravascular pressures were measured and coronary perfusion pressure was calculated during baseline, cardiac arrest, resuscitation, and postresuscitation periods. Percent necrotic myocardium, percent ischemic myocardium, and necrotic-to-ischemic ratios were determined for resuscitated animals. Epinephrine dosage and number of countershocks were determined for each group. MAIN RESULTS: Nine of nine CPB and six of nine OCCPR, compared with two of eight SECPR animals, were resuscitated (P less than .01). Three of nine CPB and OCCPR and two of eight SECPR dogs survived to four hours (P = NS). Coronary perfusion pressure two minutes after institution of technique was significantly higher with CPB (75 +/- 37 mm Hg) and OCCPR (56 +/- 31 mm Hg) than in SECPR animals (16 +/- 16 mm Hg, P less than .04). Epinephrine required for resuscitation was significantly less with CPB (0.10 +/- 0.02 mg/kg) than for SECPR (0.28 +/- 0.11 mg/kg, P less than .002). The ratio of necrotic to ischemic myocardium at four hours was significantly lower with CPB (0.15 +/- 0.31) and OCCPR (0.39 +/- 0.25) than for SECPR (1.16 +/- 0.31, P less than .02). CONCLUSION: OCCPR and CPB produce higher coronary perfusion pressures and improved resuscitation rates from ventricular fibrillation when compared with SECPR in this canine myocardial infarct cardiac arrest model. CPB and OCCPR yielded similar resuscitation results, although less epinephrine was required with CPB.     

Prehospital experience with defibrillation of coarse ventricular fibrillation: a ten-year review

Early defibrillation of patients with coarse ventricular fibrillation has been implicated as a predictor of survival in prehospital cardiac arrest. A retrospective study of our experience with prehospital defibrillation was conducted to define the relationship between rapid delivery of first countershock and survival, determine whether a relationship exists between the number of countershocks delivered and the save rate, and assist clinicians with general guidelines for termination of advanced life support efforts in the presence of ventricular fibrillation refractory to multiple defibrillation attempts. During the ten-year study period, adult, nontraumatic, nonpoisoned, witnessed arrests with an initial rhythm of coarse ventricular fibrillation were reviewed. Of 1,497 patients, 25% survived, 13% were paramedic-witnessed (PW) arrests, and 87% were non-paramedic-witnessed (NPW) arrests. The mean PW shock time, defined as time from arrest to first shock, was 1.6 +/- 3.7 minutes with a save rate of 37%. The mean NPW shock time was 10.2 +/- 5.1 minutes with a save rate of 23% (P less than or equal to .001). Thirty-two percent of PW arrests were converted to a spontaneous rhythm with pulses after the first countershock compared with 9% of NPW arrests (P less than or equal to .001). There was a dramatic decrease in PW arrests obtaining a perfusing rhythm after the first countershock attempt with each minute delay in electrical countershock up to three minutes; a plateau effect was evident after three minutes.(ABSTRACT TRUNCATED AT 250 WORDS)     

Cardiac resuscitability with cardiopulmonary bypass after increasing ventricular fibrillation times in dogs

Previous studies in dogs have shown resuscitation from prolonged cardiac arrest to conscious survival to be more effective with the use of cardiopulmonary bypass (CPB) than with standard advanced cardiac life support. This study compared cardiovascular resuscitability with CPB only after varying periods of cardiac arrest without artificial circulatory support in a canine model. Group 1 (ten) was subjected to ventricular fibrillation for 15 minutes; group 2 (ten) for 20 minutes; and group 3 (ten) for 30 minutes. All received total CPB after ventricular fibrillation without advanced cardiac life support to defibrillation at two to five minutes and partial CPB to four hours. In all three groups CPB with epinephrine generated normal coronary perfusion pressure and increased ventricular fibrillation amplitude significantly. In groups 1 and 2, CPB reperfusion allowed for successful defibrillation in less than five minutes, weaning from CPB in all dogs at four hours, and stable spontaneous circulation thereafter. In group 3, only five of ten dogs could be weaned from bypass at four hours, and all died early with myocardial necroses. It was concluded that CPB may be of value in the setting of prolonged cardiac arrest when advanced cardiac life support has not been provided or is unable to restore spontaneous heart-beat.     

Cardiopulmonary bypass in a model of acute myocardial infarction and cardiac arrest

Cardiopulmonary bypass (CPB) reperfusion has demonstrated improved resuscitation rates in ventricular fibrillation cardiac arrest models. To investigate the effectiveness of CPB reperfusion in an ischemic cardiac arrest setting, simulating the clinical scenario of myocardial ischemia preceding sudden cardiac death, we developed a canine model of acute myocardial infarction followed by ventricular fibrillation. Sixteen dogs were randomly assigned to two groups. Group 1 (eight) had ventricular fibrillation induced without left anterior descending coronary artery occlusion. Group 2 (eight) had a thrombogenic copper coil placed in the left anterior descending artery and showed ECG evidence of acute myocardial infarction before induction of ventricular fibrillation. CPR commenced after eight minutes of ventricular fibrillation. Epinephrine 0.05 mg/kg and NaHCO3 1.0 mEq/kg were administered at ten minutes. CPB was begun at 12 minutes and continued for one hour. Myocardial ischemic and necrotic areas were determined in four-hour survivors by dual histochemical staining. All animals were resuscitated; all eight group 1 and six of eight group 2 animals survived to four hours. With the onset of CPB, coronary perfusion pressures increased significantly by 68.6 +/- 31.8 (SD) mm Hg in group 1 and 56.2 +/- 34.6 mm Hg in group 2 over those obtained with CPR (P less than .001).(ABSTRACT TRUNCATED AT 250 WORDS)