Augmented efficacy of external CPR by intermittent occlusion of the ascending aorta

Intra-aortic balloon pump synchronized with chest compressions improves outcome during cardiopulmonary resuscitation in experimental cardiac arrest

BACKGROUND

Intra-aortic balloon pump (IABP) and resuscitative endovascular balloon occlusion of the aorta (REBOA) are two endovascular intervention methods for circulatory support. The aim of this study was to compare the hemodynamic effects of simultaneous mechanical chest compressions (MCC) with IABP, REBOA and those with only MCC (overall and detailed in the MCC cycle) and return of spontaneous circulation (ROSC) during cardiopulmonary resuscitation (CPR) in experimental non-traumatic cardiac arrests (CA).

METHOD

CA was electrically induced (ventricular fibrillation) in 24 anesthetized pigs, which then were randomized to MCC synchronized IABP (n = 8), total occluded REBOA (n = 8), or control (n = 8). After 10 min of CA, CPR with MCC was started followed by one of the interventions after one minute of CPR. Every other minute after MCC start, the pigs were defibrillated with 200 J if VF/ventricular tachycardia, and after six minutes, adrenaline was administered and repeated every four minutes. The proportions of ROSC were calculated. Hemodynamic variables, including systemic blood and coronary perfusion pressures (CPP), and carotid and iliac blood flows, were collected and analyzed with 0.02 s resolution.

RESULTS

In both the IABP and REBOA groups, 7 of 8 animals (87.5 %) achieved ROSC, in contrast with 2 of 8 (25 %) in the control group (P = 0.04). IABP and REBOA significantly increased systemic arterial pressure (P = 0.002 and P = 0.015, respectively), and REBOA also increased CPP and carotid blood flow when compared to controls (P = 0.007 and P = 0.03, respectively). Animals with IABP had a preserved blood flow in the iliac artery during CPR. No differences were detected after ROSC in hemodynamic, metabolic, and organ injury variables between the REBOA and IABP groups.

CONCLUSION

Both IABP and REBOA increased the proportion of ROSC compared to controls. However, REBOA occluded distal blood flow, while IABP maintained it. This study suggests that MCC synchronized IABP could be an adjunct in the treatment of non-traumatic CA.

A protocol for the ERICA-ARREST feasibility study of Emergency Resuscitative Endovascular Balloon occlusion of the Aorta in Out-of-Hospital Cardiac Arrest

Background

Fewer than one in ten out-of-hospital cardiac arrest (OHCA) patients survive to hospital discharge in the UK. For prehospital teams to improve outcomes in patients who remain in refractory OHCA despite advanced life support (ALS); novel strategies that increase the likelihood of return of spontaneous circulation, whilst preserving cerebral circulation, should be investigated. Resuscitative Endovascular Balloon Occlusion of the Aorta (REBOA) has been shown to improve coronary and cerebral perfusion during cardiopulmonary resuscitation. Early, prehospital initiation of REBOA may improve outcomes in patients who do not respond to standard ALS. However, there are significant clinical, technical, and logistical challenges with rapidly delivering prehospital REBOA in OHCA; and the feasibility of delivering this intervention in the UK urban-rural setting has not been evaluated.

Methods

The Emergency Resuscitative Endovascular Balloon Occlusion of the Aorta in Out-of-Hospital Cardiac Arrest (ERICA-ARREST) study is a prospective, single-arm, interventional feasibility study. The trial will enrol 20 adult patients with non-traumatic OHCA. The primary objective is to assess the feasibility of performing Zone I (supra-coeliac) aortic occlusion in patients who remain in OHCA despite standard ALS in the UK prehospital setting. The trial's secondary objectives are to describe the hemodynamic and physiological responses to aortic occlusion; to report key time intervals; and to document adverse events when performing REBOA in this context.

Discussion

Using compressed geography, and targeted dispatch, alongside a well-established femoral arterial access programme, the ERICA-ARREST study will assess the feasibility of deploying REBOA in OHCA in a mixed UK urban and rural setting.Trial registration.ClinicalTrials.gov (NCT06071910), registration date October 10, 2023, https://classic.clinicaltrials.gov/ct2/show/NCT06071910.

Endovascular aortic occlusion improves return of spontaneous circulation after longer periods of cardiopulmonary resuscitation: A translational study in pigs

Introduction

Resuscitative endovascular balloon occlusion of the aorta (REBOA) has emerged as an adjunct to CPR for nontraumatic cardiac arrest (NTCA). This translational study investigated the impact of varying low-flow duration (15- vs 30-mins) on REBOA's hemodynamic performance and ability to achieve return of spontaneous circulation (ROSC) in a porcine model.

Methods

Thirty-two pigs were anesthetized and placed into ventricular fibrillation. All animals received a 4-min no-flow period before CPR was initiated. Animals were randomized into four groups: 15- vs 30-minutes of CPR; REBOA vs. no-REBOA. After completion of 15- or 30-minute low-flow, ACLS was initiated and REBOA was inflated in experimental animals.

Results

In the 15-mins groups, there were no differences in the rates of ROSC between REBOA (4/8, 50%) and control (4/8, 50%; p = 0.99). However, in the 30-min groups, the REBOA animals had a significantly higher rate of ROSC (6/8, 75%) compared to control (1/8, 12.5%; p = 0.04). In the 7-mins after REBOA deployment in the 30-min animals there was a statistically significant difference in coronary perfusion pressure (REBOA 42.1 mmHg, control 3.6 mmHg, p = 0.038). Importantly, 5/6 animals that obtained ROSC in the 30-min group with REBOA re-arrested at least once, with 3/6 maintaining ROSC until study completion.

Conclusion

In our porcine model of NTCA, REBOA preferentially improved hemodynamics and ROSC after a 30-mins period of low-flow CPR. REBOA may be a viable strategy to improve ROSC after prolonged downtime, however, more hemodynamic support will be required to maintain ROSC.

Optimizing hemodynamic function during cardiopulmonary resuscitation

PURPOSE OF REVIEW

The purpose of this narrative review is to provide an update on hemodynamics during cardiopulmonary resuscitation (CPR) and to describe emerging therapies to optimize perfusion.

RECENT FINDINGS

Cadaver studies have shown large inter-individual variations in blood distribution and anatomical placement of the heart during chest compressions. Using advanced CT techniques the studies have demonstrated atrial and slight right ventricular compression, but no direct compression of the left ventricle. A hemodynamic-directed CPR strategy may overcome this by allowing individualized hand-placement, drug dosing, and compression rate and depth. Through animal studies and one clinical before-and-after study head-up CPR has shown promising results as a potential strategy to improve cerebral perfusion. Two studies have demonstrated that placement of an endovascular balloon occlusion in the aorta (REBOA) can be performed during ongoing CPR.

SUMMARY

Modern imaging techniques may help increase our understanding on the mechanism of forward flow during CPR. This could provide new information on how to optimize perfusion. Head-up CPR and the use of REBOA during CPR are novel methods that might improve cerebral perfusion during CPR; both techniques do, however, still await clinical testing.

Randomized blinded trial of automated REBOA during CPR in a porcine model of cardiac arrest

BACKGROUND

Resuscitative endovascular balloon occlusion of the aorta (REBOA) reportedly elevates arterial blood pressure (ABP) during non-traumatic cardiac arrest.

OBJECTIVES

This randomized, blinded trial of cardiac arrest in pigs evaluated the effect of automated REBOA two minutes after balloon inflation on ABP (primary endpoint) as well as arterial blood gas values and markers of cerebral haemodynamics and metabolism.

METHODS

Twenty anesthetized pigs were randomized to REBOA inflation or sham-inflation (n = 10 in each group) followed by insertion of invasive monitoring and a novel, automated REBOA catheter (NEURESCUE® Catheter & NEURESCUE® Assistant). Cardiac arrest was induced by ventricular pacing. Cardiopulmonary resuscitation was initiated three min after cardiac arrest, and the automated REBOA was inflated or sham-inflated (blinded to the investigators) five min after cardiac arrest.

RESULTS

In the inflation compared to the sham group, mean ABP above the REBOA balloon after inflation was higher (inflation: 54 (95%CI: 43-65) mmHg; sham: 44 (33-55) mmHg; P = 0.06), and diastolic ABP was higher (inflation: 38 (29-47) mmHg; sham: 26 (20-33) mmHg; P = 0.02), and the arterial to jugular oxygen content difference was lower (P = 0.04). After return of spontaneous circulation, mean ABP (inflation: 111 (95%CI: 94-128) mmHg; sham: 94 (95%CI: 65-123) mmHg; P = 0.04), diastolic ABP (inflation: 95 (95%CI: 78-113) mmHg; sham: 78 (95%CI: 50-105) mmHg; P = 0.02), CPP (P = 0.01), and brain tissue oxygen tension (inflation: 315 (95%CI: 139-491)% of baseline; sham: 204 (95%CI: 75-333)%; P = 0.04) were higher in the inflation compared to the sham group.

CONCLUSION

Inflation of REBOA in a porcine model of non-traumatic cardiac arrest improves central diastolic arterial pressure as a surrogate marker of coronary artery pressure, and cerebral perfusion.

INSTITUTIONAL PROTOCOL NUMBER

2017-15-0201-01371.

The use of resuscitative endovascular balloon occlusion of the aorta (REBOA) for non-traumatic cardiac arrest: A review

Resuscitative endovascular balloon occlusion of the aorta (REBOA) has been proposed as a novel approach to managing non-traumatic cardiac arrest (NTCA). During cardiac arrest, cardiac output ceases and perfusion of vital organs is compromised. Traditional advanced cardiac life support (ACLS) measures and cardiopulmonary resuscitation are often unable to achieve return of spontaneous circulation (ROSC). During insertion of REBOA a balloon-tipped catheter is placed into the femoral artery and advanced in a retrograde manner into the aorta while the patient is undergoing cardiopulmonary resuscitation (CPR). The balloon is then inflated to fully occlude the aorta. The literature surrounding the use of aortic occlusion in non-traumatic cardiac arrest is limited to animal studies, case reports and one recent non-controlled feasibility trial. In both human and animal studies, preliminary data show that REBOA may improve coronary and cerebral perfusion pressures and key physiologic parameters during cardiac arrest resuscitation, and animal data have demonstrated improved rates of ROSC. Multiple questions remain before REBOA can be considered as an adjunct to ACLS. If demonstrated to be effective clinically, REBOA represents a potentially cost-effective and generalizable intervention that may improve quality of life for patients with non-traumatic cardiac arrest.

Resuscitative Endovascular Balloon Occlusion of the Aorta in Experimental Cardiopulmonary Resuscitation: Aortic Occlusion Level Matters

Introduction:

Aortic occlusion during cardiopulmonary resuscitation (CPR) increases systemic arterial pressures. Correct thoracic placement during the resuscitative endovascular balloon occlusion of the aorta (REBOA) may be important for achieving effective CPR.

Hypothesis:

The positioning of the REBOA in the thoracic aorta during CPR will affect systemic arterial pressures.

Methods:

Cardiac arrest was induced in 27 anesthetized pigs. After 7 min of CPR with a mechanical compression device, REBOA in the thoracic descending aorta at heart level (zone Ib, REBOA-Ib, n = 9), at diaphragmatic level (zone Ic, REBOA-Ic, n = 9) or no occlusion (control, n = 9) was initiated. The primary outcome was systemic arterial pressures during CPR.

Results:

During CPR, REBOA-Ic increased systolic blood pressure from 86 mmHg (confidence interval [CI] 71–101) to 128 mmHg (CI 107–150, P < 0.001). Simultaneously, mean and diastolic blood pressures increased significantly in REBOA-Ic (P < 0.001 and P = 0.006, respectively), and were higher than in REBOA-Ib (P = 0.04 and P = 0.02, respectively) and control (P = 0.005 and P = 0.003, respectively). REBOA-Ib did not significantly affect systemic blood pressures. Arterial pH decreased more in control than in REBOA-Ib and REBOA-Ic after occlusion (P = 0.004 and P = 0.005, respectively). Arterial lactate concentrations were lower in REBOA-Ic compared with control and REBOA-Ib (P = 0.04 and P < 0.001, respectively).

Conclusions:

Thoracic aortic occlusion in zone Ic during CPR may be more effective in increasing systemic arterial pressures than occlusion in zone Ib. REBOA during CPR was found to be associated with a more favorable acid–base status of circulating blood. If REBOA is used as an adjunct in CPR, it may be of importance to carefully determine the aortic occlusion level.

The study was performed following approval of the Regional Animal Ethics Committee in Linköping, Sweden (application ID 418).

[Resuscitative endovascular balloon occlusion of the aorta : Option for incompressible trunk bleeding?]

Hemorrhage is the single largest cause of avoidable death in trauma patients, whereby in civil emergency medicine in Europe most life-threatening hemorrhages occur in the abdomen and the pelvis. This is one reason why endovascular balloon occlusion of the aorta (EBOA), a procedure especially established in vascular surgery, is increasingly propagated for rapid bleeding control in these patients. This review article provides a comprehensive overview of the technique, indications, contraindications and complications of resuscitative endovascular balloon occlusion of the aorta (REBOA). Additionally, outcomes reported in in the currently available literature are summarized and discussed. From this practical and user-oriented consequences for future successful introduction of REBOA in the field of emergency medicine are deduced.

Resuscitative Endovascular Balloon Occlusion of the Aorta: Review of the Literature and Applications to Veterinary Emergency and Critical Care

While hemorrhagic shock might be the result of various conditions, hemorrhage control and resuscitation are the corner stone of patient management. Hemorrhage control can prove challenging in both the acute care and surgical settings, especially in the abdomen, where no direct pressure can be applied onto the source of bleeding. Resuscitative endovascular balloon occlusion of the aorta (REBOA) has emerged as a promising replacement to resuscitative thoracotomy (RT) for the management of non-compressible torso hemorrhage in human trauma patients. By inflating a balloon at specific levels (or zones) of the aorta to interrupt blood flow, hemorrhage below the level of the balloon can be controlled. While REBOA allows for hemorrhage control and augmentation of blood pressure cranial to the balloon, it also exposes caudal tissue beds to ischemia and the whole body to reperfusion injury. We aim to introduce the advantages of REBOA while reviewing known limitations. This review outlines a step-by-step approach to REBOA implementation, and discusses common challenges observed both in human patients and during translational large animal studies. Currently accepted and debated indications for REBOA in humans are discussed. Finally, we review possible applications for veterinary patients and how REBOA has the potential to be translated into clinical veterinary practice.

The role of resuscitative endovascular balloon occlusion of the aorta (REBOA) as an adjunct to ACLS in non-traumatic cardiac arrest

Non-traumatic cardiac arrest is a major public health problem that carries an extremely high mortality rate. If we hope to increase the survivability of this condition, it is imperative that alternative methods of treatment are given due consideration. Balloon occlusion of the aorta can be used as a method of circulatory support in the critically ill patient. Intra-aortic balloon pumps have been used to temporize patients in cardiogenic shock for decades. More recently, resuscitative endovascular balloon occlusion of the aorta (REBOA) has been utilized in the patient in hemorrhagic shock or cardiac arrest secondary to trauma. Aortic occlusion in non-traumatic cardiac arrest has the effect of reducing the vascular volume that the generated cardiac output is distributed across. This augments myocardial and cerebral perfusion, increasing the probability of a return to a good quality of life for the patient. This phenomenon has been the subject of numerous animal studies dating back to the early 1980s; however, the human evidence is limited to several small case series. Animal research has demonstrated improvements in cerebral and coronary perfusion pressure during ACLS that lead to statistically significant differences in mortality. Several case series in humans have replicated these findings, suggesting the efficacy of this procedure. The objectives of this review are to: 1) introduce the reader to REBOA 2) review the physiology of NTCA and examine the current limitations of traditional ACLS 3) summarize the literature regarding the efficacy and feasibility of aortic balloon occlusion to support traditional ACLS.

A comparison between head cooling begun during cardiopulmonary resuscitation and surface cooling after resuscitation in a pig model of cardiac arrest

OBJECTIVE

Employing transnasal head-cooling in a pig model of prolonged ventricular fibrillation, we compared the effects of 4 hrs of head-cooling started during cardiopulmonary resuscitation with those of 8 hrs of surface-cooling started at 2 hrs after resuscitation on 96-hr survival and neurologic outcomes.

DESIGN

Prospective controlled animal study.

SETTING

University-affiliated research laboratory.

SUBJECTS

Domestic pigs.

INTERVENTIONS

Twenty-four male pigs were subjected to 10 min of untreated ventricular fibrillation followed by 5 min of cardiopulmonary resuscitation. In the head-cooling group, hypothermia was started with cardiopulmonary resuscitation and continued for 4 hrs after resuscitation. In the surface-cooling group, systemic hypothermia with a cooling blanket was started, in accord with current clinical practices, at 2 hrs after resuscitation and continued for 8 hrs. Methods in the control animal studies were identical except for temperature interventions.

MEASUREMENTS AND MAIN RESULTS

All animals were resuscitated except for one animal in each of the surface-cooling and control groups. After 5 min of cardiopulmonary resuscitation, jugular vein temperature was significantly decreased in the head-cooled animals. However, there were no differences in pulmonary artery temperatures among the three groups at that time. Nevertheless, both head-cooled and surface-cooled animals had an improved 96-hr survival after resuscitation. Significantly better neurologic outcomes were observed in early head-cooled animals in the first 3 days after resuscitation.

CONCLUSION

Early head-cooling during cardiopulmonary resuscitation continuing for 4 hrs after resuscitation produced favorable survival and neurologic outcomes in comparison with delayed surface-cooling of 8 hrs duration.

Defibrillation delivered during the upstroke phase of manual chest compression improves shock success

OBJECTIVE

The current standard of manual chest compression during cardiopulmonary resuscitation requires pauses for rhythm analysis and shock delivery. However, interruptions of chest compression greatly decrease the likelihood of successful defibrillations, and significantly better outcomes are reported if this interruption is avoided. We therefore undertook a prospective randomized controlled animal study in an electrically induced ventricular fibrillation pig model to assess the effects of timing of defibrillation on the manual chest compression cycle on the defibrillation threshold.

DESIGN

Prospective, randomized, controlled animal study.

SETTING

University-affiliated research laboratory.

SUBJECTS

Yorkshire-X domestic pigs (Sus scrofa).

INTERVENTIONS

In eight domestic male pigs weighing between 24 and 31 kg, ventricular fibrillation was electrically induced and untreated for 10 secs. Manual chest compression was then performed and continued for 25 secs with the protection of an isolation blanket. The depth and frequency of chest compressions were guided by a cardiopulmonary resuscitation prompter. Animals were randomized to receive a biphasic electrical shock in five different compression phases with a predetermined energy setting. A control phase was chosen at a constant 2 secs after discontinued chest compression. A grouped up-down defibrillation threshold testing protocol was used to compare the success rate at different coupling phases. After a recovery interval of 4 mins, the sequence was repeated for a total of 60 test shocks for each animal.

MEASUREMENTS AND MAIN RESULTS

No difference in coronary perfusion pressure before delivering of the shock was observed among the six study phases. The defibrillation success rate, however, was significantly higher when shocks were delivered in the upstroke phase of manual chest compression.

CONCLUSION

Defibrillation efficacy is maximal when electrical shock is delivered during the upstroke phase of manual chest compression.

Microcirculation during cardiac arrest and resuscitation

OBJECTIVE

Direct observations of the microcirculation using orthogonal polarization spectral imaging have attracted attention and revealed that, especially in cardiogenic and distributive shock, there is discordance between the macrocirculation and the microcirculation. We evaluated serial changes and the effects of epinephrine on microcirculatory blood flow in the most severe form of circulatory failure, namely, cardiac arrest.

DESIGN AND SETTING

: Controlled laboratory animal study.

SUBJECTS AND INTERVENTIONS

A total of 15 pigs were subjected to 5 mins of ventricular fibrillation and 5 mins of precordial compression before electrical defibrillation was attempted. In a subset, six animals received 1 mg of epinephrine after 1 min of precordial compression.

MEASUREMENTS AND MAIN RESULTS

Microcirculatory blood flow was visualized in the sublingual mucosa at baseline and 0.5, 1, and 5 mins of ventricular fibrillation, at 1 and 5 mins of precordial compression, and at 1 and 5 mins after return of spontaneous circulation. In addition, coronary perfusion pressure was recorded. Microcirculatory blood flow decreased dramatically in the 0.5 min after the onset of ventricular fibrillation. Precordial compression partially restored microcirculatory blood flow in each animal but to a significantly greater extent in animals that achieved return of spontaneous circulation. These changes were paralleled by similar changes in coronary perfusion pressure. Both variables were highly correlated. Administration of epinephrine resulted in a massive reduction of microcirculatory blood flow that lasted for >/=5 mins.

CONCLUSIONS

In this model, microcirculatory blood flow was highly correlated with macrocirculatory hemodynamics, including coronary perfusion pressure in distinction with septic shock. Administration of epinephrine dramatically decreased microcirculatory blood flow.

Microvascular blood flow during cardiopulmonary resuscitation is predictive of outcome

There is growing evidence that microcirculatory blood flow is the ultimate determinant of the outcome in circulatory shock states. We therefore examined changes in the microcirculation accompanying the most severe form of circulatory failure, namely cardiac arrest and the effects of subsequent cardiopulmonary resuscitation. Ventricular fibrillation was electrically induced in nine pigs and untreated for 5min prior to beginning closed chest cardiac compression and attempting electrical defibrillation. Orthogonal polarization spectral imaging was utilized for visualization of the sublingual microcirculation at baseline, 0.5, 1, 3 and 5min after onset of ventricular fibrillation and at 1 and 5min after start of chest compression. Images were also obtained 1 and 5min after restoration of spontaneous circulation. Microvascular flow was graded from 0 (no flow) to 3 (normal flow). Aortic and right atrial pressures were measured and coronary perfusion pressure was computed continuously. Microcirculatory blood flow decreased to less than one-fourth within 0.5min after inducing ventricular fibrillation. Precordial compression partially restored microvascular flow in each animal. In animals that were successfully resuscitated, microvascular flow was significantly greater after 1 and 5min of chest compression than in animals with failed resuscitation attempts. Microvascular blood flow was highly correlated with coronary perfusion pressure (r=0.82, p<0.01). Microvascular blood flow in the sublingual mucosa is therefore closely related to coronary perfusion pressure during cardiopulmonary resuscitation and both are predictive of outcome.

Cardiopulmonary resuscitation in patients with a Nuss bar--a case report and review of the literature

Pectus excavatum (PE) is a common chest wall deformity that may produce a variety of physiological and psychological effects in children and adolescents. In addition, some of these patients have associated cardiac diseases (ie, mitral valve prolapse and Marfan syndrome). Recently, a minimally invasive surgical repair of PE that requires sternal bar placement has become increasingly frequent to enhance patients' cardiopulmonary functioning as well as their self-esteem. However, despite this innovative technique, it is possible for such patients to have a cardiac arrest while their sternal bar is in place. Whether the presence of a metal bar on the underside of their sternum may hinder resuscitative chest compressions (cardiopulmonary resuscitation) is an issue that concerns us, our patients, and their families; the answer requires further investigation. We present a 21-year-old man with PE who underwent a minimally invasive pectus repair but had a fatal cardiac event before bar removal. Paramedics conducting cardiopulmonary resuscitation on the patient later reported that they were unable to deliver effective cardiac compressions and that the sternal bar may have contributed to this.

Fixed-energy biphasic waveform defibrillation in a pediatric model of cardiac arrest and resuscitation

OBJECTIVE

For adults, 150-J fixed-energy, impedance-compensating biphasic truncated exponential (ICBTE) shocks are now effectively used in automated defibrillators. However, the high energy levels delivered by adult automated defibrillators preclude their use for pediatric patients. Accordingly, we investigated a method by which adult automated defibrillators may be adapted to deliver a 50-J ICBTE shock for pediatric defibrillation.

DESIGN

Prospective, randomized study.

SETTING

A university-affiliated research institution.

SUBJECT

Domestic piglets.

INTERVENTIONS

We initially investigated four groups of anesthetized mechanically ventilated piglets weighing 3.8, 7.5, 15, and 25 kg. Ventricular fibrillation was induced with an AC current delivered to the right ventricular endocardium. After 7 mins of untreated ventricular fibrillation, a conventional manual defibrillator was used to deliver up to three 50-J ICBTE shocks. If ventricular fibrillation was not reversed, a 1-min interval of precordial compression preceded a second sequence of up to three shocks. The protocol was repeated until spontaneous circulation was restored, or for a total of 15 mins. In a second set of experiments, we evaluated a 150-J biphasic adult automated defibrillator that was operated in conjunction with energy-reducing electrodes such as to deliver 50-J shocks. The same resuscitation protocol was then exercised on piglets weighing 3.7, 13.5, and 24.2 kg.

MEASUREMENTS AND MAIN RESULTS

All animals were successfully resuscitated. Postresuscitation hemodynamic and myocardial function quickly returned to baseline values in both experimental groups, and all animals survived.

CONCLUSION

An adaptation of a 150-J biphasic adult automated defibrillator in which energy-reducing electrodes delivered 50-J shocks successfully resuscitated animals ranging from 3.7 to 25 kg without compromise of postresuscitation myocardial function or survival.

Evolution of the stone heart after prolonged cardiac arrest

OBJECTIVES

We hypothesized that progressive impairment in diastolic function during cardiopulmonary resuscitation (CPR) precedes evolution of the "stone heart" after failure of CPR. We therefore measured sequential changes in left ventricular (LV) volumes and free-wall thickness of the heart during CPR in an experimental model.

DESIGN

Prospective, observational animal study.

SETTING

Medical research laboratory in an university-affiliated research and educational institute.

SUBJECTS

Domestic pigs.

METHODS

Ventricular fibrillation (VF) was induced in 40 anesthetized male domestic pigs weighing between 38 kg and 43 kg. After 4 min, 7 min, or 10 min of untreated VF, electrical defibrillation was attempted. Failing to reverse VF in each instance, precordial compression at a rate of 80/min was begun coincident with mechanical ventilation. Coronary perfusion pressures (CPPs) were computed from the differences in time-coincident diastolic aortic and right atrial pressures. Left ventricular (LV) systolic and diastolic ventricular volumes and thickness of the LV free wall were estimated with transesophageal echocardiography. The stroke volumes (SVs) were computed from the differences in decompression diastolic and compression systolic volumes. Free-wall thickness was measured on the hearts at autopsy.

RESULTS

Significantly greater CPPs were generated with the 4 min of untreated cardiac arrest. Progressive reductions in LV diastolic and SV and increases in LV free-wall thickness were documented with increasing duration of untreated VF. A stone heart was confirmed at autopsy in each animal that failed resuscitative efforts. Correlations with indicator dilution method and physical measurements at autopsy corresponded closely with the echocardiographic measurements.

CONCLUSION

Progressive impairment in diastolic function terminates in a stone heart after prolonged intervals of cardiac arrest.

Effect of intra-aortic occlusion balloon in external thoracic compressions during CPR in pigs

This study was performed to compare the effectiveness of external thoracic compressions with and without intra-aortic occlusion balloon with capnography and coronary and cerebral perfusion pressure (CPP) in the normothermic and traumatic-less cardiopulmonary arrest provoked by a ventricular fibrillation in pigs. This was an experimental study (cross-over study) in 14 pigs with similar characteristics (23 +/- 2 kg, 10-12 weeks of age). After an 8-minute nonintervention period, the cardiopulmonary resuscitation (CPR) consists of 4 periods of 5 minutes alternating CPR with and without intra-aortic occlusion balloon. Main outcomes measured are end-tidal CO(2) (ETCO(2)); intra-aortic, coronary, and cerebral perfusion pressures; blood gas analysis; and blood lactate concentration. At the end of each period, levels are obtained. Postmortem study was made. Inflation of the occlusion balloon provokes an expansion in the ETCO(2) of about 38%. The coronary perfusion pressure initially goes from 10.21 to 29.0 mm Hg after the occlusion of the aorta, which means an increase of 150%. The CPP goes from 12.54 to 39.71 mm Hg after the balloon was inflated, which means an increase of 200%. In all cases the differences are statistically significant (P <.0001). These increases are less important in the final periods. Intra-aortic balloon occlusion increased ETCO(2), coronary, and cerebral perfusion pressures. An early application of this technique was important.

Adverse outcomes of interrupted precordial compression during automated defibrillation

BACKGROUND

Current versions of automated external defibrillators (AEDs) require frequent stopping of chest compression for rhythm analyses and capacity charging. The present study was undertaken to evaluate the effects of these interruptions during the operation of AEDs.

METHODS AND RESULTS

Ventricular fibrillation was electrically induced in 20 male domestic swine weighing between 37.5 and 43 kg that were untreated for 7 minutes before CPR was started. Defibrillation was attempted with up to 3 sequential 150-J biphasic shocks, but each was preceded by 3-, 10-, 15-, or 20-second interruptions of chest compression. The interruptions corresponded to those that were mandated by commercially marketed AEDs for rhythm analyses and capacitor charge. The sequence of up to 3 electrical shocks and delays were repeated at 1-minute intervals until the animals were successfully resuscitated or for a total of 15 minutes. Spontaneous circulation was restored in each of 5 animals in which precordial compression was delayed for 3 seconds before the delivery of the first and subsequent shocks but in none of the animals in which the delay was >15 seconds before the delivery of the first and subsequent shocks. Longer intervals of CPR interventions were required, and there was correspondingly greater failure of resuscitation in close relationship to increasing delays. The durations of interruptions were inversely related to the durations of subthreshold levels of coronary perfusion pressure. Postresuscitation arterial pressure and left ventricular ejection fraction were more severely impaired with increasing delays.

CONCLUSIONS

Interruptions of precordial compression for rhythm analyses that exceed 15 seconds before each shock compromise the outcome of CPR and increase the severity of postresuscitation myocardial dysfunction.

[New aspects and perspectives on cardiac arrest]

OBJECTIVES

To analyse the current knowledge based on the experimental and the clinical research studies focused on the main fields of cardiopulmonary resuscitation.

DATA SOURCES

International guidelines and recent review articles. Data collected from the Medline database with the key word: cardiac arrest.

STUDY SELECTION

Research studies published during the last ten years were reviewed. Relevant clinical information was extracted and discussed when it induced changes in guidelines.

DATA SYNTHESIS

Promising improvements on basic and advanced life supports are proposed. Chest compressions prevail over ventilation. Alternatives to classical chest compressions are tested. Ventilatory volume must be reduced from 1000 to approximatively 500 mL for each breath with oxygen. Biphasic waveform defibrillators and automated external defibrillators will be considered as the best devices in the near future. Some non-catecholaminergic vasopressors could reduce the use of epinephrine for advanced cardiac life support. Lidocaine could be replaced by amiodarone as anti-arrhythmic drug of choice. New post-resuscitation therapeutic strategies are evaluated, especially coronary reperfusion when the cause of cardiac arrest is cardiac.

CONCLUSION

Many fields of cardiopulmonary resuscitation are investigated. Some relevant informations are included in the last international guidelines published in 2000, but most of them need complementary studies before other changes could be recommended for routine practice.

A comparison of biphasic and monophasic waveform defibrillation after prolonged ventricular fibrillation

STUDY OBJECTIVE

To compare the effects of biphasic defibrillation waveforms and conventional monophasic defibrillation waveforms on the success of initial defibrillation, postresuscitation myocardial function, and duration of survival after prolonged duration of untreated ventricular fibrillation (VF), including the effects of epinephrine.

DESIGN

Prospective, randomized, animal study.

SETTING

Animal laboratory and university-affiliated research and educational institute.

PARTICIPANTS

Domestic pigs.

INTERVENTIONS

VF was induced in 20 anesthetized domestic pigs receiving mechanical ventilation. After 10 min of untreated VF, the animals were randomized. Defibrillation was attempted with up to three 150-J biphasic waveform shocks or a conventional sequence of 200-J, 300-J, and 360-J monophasic waveform shocks. When reversal of VF was unsuccessful, precordial compression was performed for 1 min, with or without administration of epinephrine. The protocol was repeated until spontaneous circulation was restored or for a maximum of 15 min.

MEASUREMENTS AND RESULTS

No significant differences in the success of initial resuscitation or in the duration of survival were observed. However, significantly less impairment of myocardial function followed biphasic shocks. Administration of epinephrine reduced the total electrical energy required for successful resuscitation with both biphasic and monophasic waveform shocks.

CONCLUSIONS

Lower-energy biphasic waveform shocks were as effective as conventional higher-energy monophasic waveform shocks for restoration of spontaneous circulation after 10 min of untreated VF. Significantly better postresuscitation myocardial function was observed after biphasic waveform defibrillation. Administration of epinephrine after prolonged cardiac arrest decreased the total energy required for successful resuscitation.

Physician interpretation and quantitative measures of electrocardiographic ventricular fibrillation waveform

OBJECTIVES

The characteristics of the ventricular fibrillation (VF) waveform may influence treatment decisions and the likelihood of therapeutic success. However, assessment of VF as being fine or coarse and the distinction between fine VF and asystole are largely subjective. The authors sought to determine the level of agreement among physicians for interpretation of varying VF waveforms, and to compare these subjective interpretations with quantitative measures.

METHODS

Six-second segments of waveform from LIFEPAK 300 units were collected. Fifty segments, including 45 VF and five ventricular tachycardia (VT) distracters, were graphed to simulate rhythm strips. These waveforms were quantitatively described using scaling exponent, root-mean-squared amplitude, and centroid frequency. Thirty-two emergency medicine residents were asked to interpret the arrhythmias as VT, "coarse" VF, "fine" VF, or asystole. Their responses were compared with the qantitative measures. Interphysician agreement was assessed with the kappa statistic.

RESULTS

One thousand four hundred forty interpretations were analyzed. There was fair agreement between physicians about the classification of arrhythmias (kappa = 0.39). Mean values associated with coarse VF, fine VF, and asystole differed in all three quantitative measure categories. The decision whether to defibrillate was highly correlated with the distinction between VF and asystole (Pearson chi-square = 1,170.40, df = 1, p[two-sided] < 0.001).

CONCLUSIONS

With only fair agreement on the threshold of fine VF and asystole, defibrillation decisions are largely subjective and caregiver-specific. These data suggest that quantitative measures of the VF waveform could augment the current standard of subjective classification of VF by emergency care providers.

Improved cerebral blood supply and oxygenation by aortic balloon occlusion combined with intra-aortic vasopressin administration during experimental cardiopulmonary resuscitation

BACKGROUND

Intravenous administration of vasopressin during cardiopulmonary resuscitation (CPR) has been shown to improve myocardial and cerebral blood flow. Aortic balloon occlusion during CPR may also augment myocardial and cerebral blood flow and can be used as a central route for the administration of resuscitative drugs. We hypothesized that, as compared with intravenously administered vasopressin, the administration of this drug above the site of an aortic balloon occlusion would result in a greater increase in cerebral perfusion and oxygenation during CPR and after restoration of spontaneous circulation (ROSC).

METHODS

Twenty piglets were subjected to 5 min of ventricular fibrillation followed by 8 min of closed-chest CPR and were treated with 0.4 U kg(-1) boluses of vasopressin intravenously (the IV-vasopressin group with sham aortic balloon) or above the site for an aortic balloon occlusion (the balloon-vasopressin group). The aortic balloon catheter was inflated in the latter group 1 min after commencement of CPR and was deflated within 1 min after ROSC. Systemic blood pressures, cerebral cortical blood flow, cerebral tissue pH and PCO2 were monitored continuously and the cerebral oxygen extraction ratio was calculated.

RESULTS

During CPR, arterial blood pressure and cerebral perfusion pressure were greater in the balloon-vasopressin group, as compared with the IV-vasopressin group. These pressures did not differ between the groups after ROSC. Cerebral cortical blood flow was not significantly greater in the balloon-vasopressin group during CPR, whereas significantly higher cortical blood flow levels were recorded after ROSC. Cerebral tissue pH decreased in the IV-vasopressin group during the post-resuscitation hypoperfusion period. In contrast, decreasing pressures during the hypoperfusion period did not result in increasing tissue acidosis in the balloon-vasopressin group.

CONCLUSIONS

During CPR, intra-aortic vasopressin combined with aortic balloon occlusion resulted in significantly greater perfusion pressures but not in greater cerebral cortical blood flow. After ROSC, however, a greater increase in cortical blood flow was recorded in the balloon-vasopressin group, even though the aortic balloon was deflated and perfusion pressures did not differ between the groups. This suggests that vasopressin predominantly gives vasoconstrictive effects on cerebral cortical vessels during CPR, but results in cerebral cortical vasodilatation after ROSC.

Suspended animation for delayed resuscitation from prolonged cardiac arrest that is unresuscitable by standard cardiopulmonary-cerebral resuscitation

Standard cardiopulmonary-cerebral resuscitation fails to achieve restoration of spontaneous circulation in approximately 50% of normovolemic sudden cardiac arrests outside hospitals and in essentially all victims of penetrating truncal trauma who exsanguinate rapidly to cardiac arrest. Among cardiopulmonary-cerebral resuscitation innovations since the 1960s, automatic external defibrillation, mild hypothermia, emergency (portable) cardiopulmonary bypass, and suspended animation have potentials for clinical breakthrough effects. Suspended animation has been suggested for presently unresuscitable conditions and consists of the rapid induction of preservation (using hypothermia with or without drugs) of viability of the brain, heart, and organism (within 5 mins of normothermic cardiac arrest no-flow), which increases the time available for transport and resuscitative surgery, followed by delayed resuscitation. Since 1988, we have developed and used novel dog models of exsanguination cardiac arrest to explore suspended animation potentials with hypothermic and pharmacologic strategies using aortic cold flush and emergency portable cardiopulmonary bypass. Outcome evaluation was at 72 or 96 hrs after cardiac arrest. Cardiopulmonary bypass cannot be initiated rapidly. A single aortic flush of cold saline (4 degrees C) at the start of cardiac arrest rapidly induced (depending on flush volume) mild-to-deep cerebral hypothermia (35 degrees to 10 degrees C), without cardiopulmonary bypass, and preserved viability during a cardiac arrest no-flow period of up to 120 mins. In contrast, except for one antioxidant (Tempol), explorations of 14 different drugs added to the aortic flush at room temperature (24 degrees C) have thus far had disappointing outcome results. Profound hypothermia (10 degrees C) during 60-min cardiac arrest induced and reversed with cardiopulmonary bypass achieved survival without functional or histologic brain damage. Further plans for the systematic development of suspended animation include the following: a) aortic flush, combining hypothermia with mechanism-specific drugs and novel fluids; b) extension of suspended animation by ultraprofound hypothermic preservation (0 degrees to 5 degrees C) with cardiopulmonary bypass; c) development of the most effective suspended animation protocol for clinical trials in trauma patients with cardiac arrest; and d) modification of suspended animation protocols for possible use in normovolemic ventricular fibrillation cardiac arrest, in which attempts to achieve restoration of spontaneous circulation by standard external cardiopulmonary resuscitation-advanced life support have failed.

Ascending versus descending aortic balloon pumping: organ and myocardial perfusion during ischemia

BACKGROUND

The ICS-Supracor (Abiomed, Danvers, MA) is a preshaped ascending aorta balloon pump. We compared the effects of this catheter with the classical descending intraaortic balloon pump (IABP). The study focused on hemodynamic effects, myocardial blood flow in normal and ischemic regions, cerebral perfusion, and peripheral organ perfusion.

METHODS

We placed a stenosis on the lateral branch of the coronary artery to reduce flow 50% (sheep). Measurements included hemodynamic changes, myocardial blood flow, and organ flow (colored microspheres) at baseline, after stenosis, during IABP support, and during ICS support.

RESULTS

Counterpulsation with the ICS led to a significantly higher peak diastolic aortic augmentation than with the IABP (IABP, 99 +/- 14 mm Hg; ICS, 140 +/- 29 mm Hg; p = 0.003). There was no significant change in cerebral perfusion or peripheral organ perfusion. Myocardial blood perfusion was significantly increased by the IABP as well as the ICS. This effect was seen in ischemic and nonischemic regions (subendocardial and subepicardial). The ICS improved myocardial blood flow significantly more than the IABP (IABP, 0.65 +/- 0.1 mL/min/g; ICS, 0.94 +/- 0.06 mL/min/g; p = 0.0005).

CONCLUSIONS

The ICS increases myocardial blood flow in ischemic regions significantly more than the IABP, without impairment of cerebral flow. Assessment of vascular complications, peripherally and in the ascending aorta, has to await results of clinical trials.

Cardiopulmonary and cerebral resuscitation

The future of cardiopulmonary resuscitation lies in new technologies for monitoring and generating vital organ perfusion during cardiac arrest and the post-resuscitation phase and in pharmacologic agents that will enhance ROSC and reverse ischemia-reperfusion injury. ROSC is the first step toward survival, so interventions that improve ROSC deserve further investigation. Long-term survival with good neurologic recovery is the critical endpoint. Interventions recommended for clinical practice must therefore demonstrate improved long-term survival. The resources required to provide many of the interventions discussed in this article, principally invasive perfusion technologies, cannot be justified unless there is clear benefit. The allocation of such resources to provide intensive resuscitation and post-resuscitation support will need to be addressed from medical and societal viewpoints.

Effect of phased chest and abdominal compression-decompression cardiopulmonary resuscitation on myocardial and cerebral blood flow in pigs

OBJECTIVE

This study was designed to assess the effects of a phased chest and abdominal compression-decompression cardiopulmonary resuscitation (CPR) device, Lifestick, vs. standard CPR on vital organ blood flow in a porcine CPR model.

DESIGN

Prospective, randomized laboratory investigation using an established porcine model with instrumentation for measurement of hemodynamic variables, vital organ blood flow, blood gases, and return of spontaneous circulation.

SETTING

University hospital research laboratory.

SUBJECTS

Twelve domestic pigs.

INTERVENTIONS

After 4 mins of untreated ventricular fibrillation, either the Lifestick CPR device (n = 6) or standard CPR (n = 6) was started and maintained for an additional interval of 6 mins before attempting defibrillation.

MEASUREMENTS AND MAIN RESULTS

During CPR, but before epinephrine, use of the Lifestick CPR device resulted in significantly higher (p < .05) mean (+/- SD) coronary perfusion pressure (23+/-9 vs. 10+/-7 mm Hg), cerebral perfusion pressure (29+/-11 vs. 18+/-10 mm Hg), mean arterial pressure (49+/-10 vs. 36+/-13 mm Hg), end-tidal carbon dioxide (32+/-11 vs. 20+/-7 mm Hg), left ventricular myocardial blood flow (44+/-19 vs. 19+/-12 mL x min(-1) x 100 g(-1)), and total cerebral blood flow (29+/-10 vs. 14+/-12 mL x min(-1) x 100 g(-1)). After 45 microg/kg epinephrine, hemodynamic and vital organ blood flow variables increased to comparable levels in both groups.

CONCLUSIONS

Compared with standard CPR, the Lifestick CPR device increased significantly hemodynamic variables and vital organ blood flow during CPR before epinephrine administration.

Intra-aortic administration of epinephrine above an aortic balloon occlusion during experimental CPR does not further improve cerebral blood flow and oxygenation

Balloon occlusion of the descending aorta during cardiopulmonary resuscitation (CPR) improves coronary and cerebral blood flow. In comparison with an equivalent dose administered through a central venous catheter it has been suggested that epinephrine administration above the aortic occlusion might produce a more rapid increase in coronary perfusion pressure and a shorter time to restoration of spontaneous circulation (ROSC). In a recent study, however, outcome was not improved after intra-aortic epinephrine administration. We hypothesised that epinephrine administered above the aortic occlusion could impose adverse effects on cerebral blood flow and oxygenation, possibly because of an alpha-adrenergic mediated vasoconstriction in the cerebral vascular beds. Twenty-six piglets underwent 5 min of non intervention cardiac arrest followed by 8 min of closed-chest CPR. They were randomised to receive bolus doses of 45 microg/kg epinephrine either above the aortic occlusion or through a central venous catheter. Cerebral cortical blood flow was continuously measured using laser-Doppler technique. Cerebral tissue pH and PCO(2) were also measured using a multi-parameter fiberoptic device and cerebral oxygen extraction was calculated. Balloon inflation resulted in an immediate enhancement of cerebral cortical blood flow. Each of the epinephrine boluses through the central venous catheter resulted in a transient increase in cerebral cortical blood flow. When administered above the aortic balloon occlusion, epinephrine did not result in a further increase in cerebral cortical blood flow, though a significant increase in cerebral perfusion pressure was recorded throughout the CPR period. Cerebral tissue pH monitoring revealed severe acidosis during CPR and long after ROSC, which was refractory to buffering. No differences in the cerebral oxygen extraction ratio were observed between the groups. In conclusion, epinephrine administration above an aortic balloon occlusion was unable to improve cerebral blood flow and oxygenation. In fact, it may even attenuate the beneficial effects of aortic balloon occlusion on cerebral blood flow due to an alpha-adrenergic mediated cerebral vasoconstriction. Further studies, including dose-response and volumes of distribution, are needed to identify the effective beneficial dosage of epinephrine during aortic occlusion with the least possible adverse effects.

Hypothermic aortic arch flush for preservation during exsanguination cardiac arrest of 15 minutes in dogs

BACKGROUND

Trauma victims rarely survive cardiac arrest from exsanguination. Survivors may suffer neurologic damage. Our hypothesis was that a hypothermic aortic arch flush of 500 mL of isotonic saline solution at 4 degrees C, compared with 24 degrees C (room temperature), administered at the start of prolonged exsanguination cardiac arrest (CA) would improve functional neurologic outcome in dogs.

METHODS

Seventeen male hunting dogs were prepared under light N2O-halothane anesthesia. The animals were randomized into two groups: group I (n = 9) received 4 degrees C isotonic saline flush and group II (n = 6) received 24 degrees C flush. Two additional dogs received no flush. While spontaneously breathing, the dogs underwent normothermic (tympanic membrane temperature [Ttm] = 37.5 degrees C) exsanguination over 5 minutes to cardiac arrest, assured by electric induction of ventricular fibrillation. After 2 minutes of arrest, the flush was administered over 1 minute into the aortic arch by means of a 13 French balloon-tipped catheter inserted by means of the femoral artery. After 15 minutes of CA, resuscitation was with closed-chest cardiopulmonary bypass, return of shed blood, and defibrillation. For the first 12 hours after CA, core temperature was maintained at 34 degrees C. Mechanical ventilation was continued to 20 hours and intensive care to 72 hours, when final evaluation and perfusion-fixation killing for brain histologic damage scoring were performed.

RESULTS

Three dogs in group I were excluded because of extracerebral complications. All 14 dogs that followed protocol survived. During CA, the Ttm decreased to 33.6 +/- 1.2 degrees C in group I and 35.9 +/- 0.4 degrees C in group II (p = 0.002). At 72 hours, in group I, all dogs achieved an overall performance category (OPC) of 1 (normal). In group II, 1 dog was OPC 2 (moderate disability), 3 dogs were OPC 3 (severe disability), and 2 dogs were OPC 4 (coma). Both dogs without flush were OPC 4. Neurologic deficit scores (NDS 0% = normal, 100% = brain death) were 1 +/- 1% in group I and 41 +/- 12% in group II (p < 0.05). The two dogs without flush achieved an NDS of 47% and 59%. Total brain histologic damage scores were 35 +/- 28 in group I and 82 +/- 17 in group II (p < 0.01); and 124 and 200 in the nonflushed dogs.

CONCLUSION

At the start of 15 minutes of exsanguination cardiac arrest in dogs, hypothermic aortic arch flush allows resuscitation to survival with normal neurologic function and histologically almost clean brains.

The effects of biphasic and conventional monophasic defibrillation on postresuscitation myocardial function

OBJECTIVES

The purpose of this study was to compare the effects of biphasic defibrillation waveforms and conventional monophasic defibrillation waveforms on the success of initial defibrillation, postresuscitation myocardial function and duration of survival after prolonged ventricular fibrillation (VF).

BACKGROUND

We have recently demonstrated that the severity of postresuscitation myocardial dysfunction was closely related to the magnitude of the electrical energy of the delivered defibrillation shock. In the present study, the effects of fixed 150-J low-energy biphasic waveform shocks were compared with conventional monophasic waveform shocks after prolonged VF.

METHODS

Twenty anesthetized, mechanically ventilated domestic pigs were investigated. VF was induced with an AC current delivered to the right ventricular endocardium. After either 4 or 7 min of untreated ventricular fibrillation (VF), the animals were randomized for attempted defibrillation with up to three 150-J biphasic waveform shocks or conventional sequence of 200-, 300- or 360-J monophasic waveform shocks. If VF was not reversed, a 1-min interval of precordial compression preceded a second sequence of up to three shocks. The protocol was repeated until spontaneous circulation was restored or for a total of 15 min.

RESULTS

Monophasic waveform defibrillation after 4 or 7 min of untreated VF resuscitated eight of 10 pigs. All 10 pigs treated with biphasic waveform defibrillation were successfully resuscitated. Transesophageal echo-Doppler, arterial pressure and heart rate measurements demonstrated significantly less impairment of cardiovascular function after biphasic defibrillation.

CONCLUSIONS

Lower-energy biphasic waveform shocks were as effective as conventional higher energy monophasic waveform shocks for restoration of spontaneous circulation after 4 and 7 min of untreated VF. Significantly better postresuscitation myocardial function was observed after biphasic waveform defibrillation.

Intra-aortic administration of epinephrine above aortic occlusion does not alter outcome of experimental cardiopulmonary resuscitation

Intra-aortic balloon occlusion during experimental cardiopulmonary resuscitation (CPR) improves coronary perfusion pressure and resuscitability and provides unique access to the central circulation. It has been hypothesized that administration of epinephrine into the aortic arch in combination with aortic occlusion would further improve haemodynamics during CPR, resuscitability and 24 h survival. In 16 anaesthetised dogs intravascular catheters were placed for hemodynamic and blood gas monitoring. An aortic balloon catheter was placed by femoral artery insertion with its tip just distal to the left subclavian artery. Ventricular fibrillation for 7.5 min without CPR, 2.5 min of Basic Life Support with chest compressions and ventilation with 100% oxygen were followed by 30 min of Advanced Cardiac Life Support (ACLS) with systemic canine drug dosages. The intra-aortic balloon was inflated when ACLS started and gradually deflated shortly after restoration of spontaneous circulation (ROSC). Epinephrine, in 100 microg/kg boluses every 5 min until the heart was restarted or 30 min had elapsed was administered through the intra-aortic catheter in the experimental group (n = 8) and via a central venous catheter in the control group (n = 8). Coronary perfusion pressure increased during the ACLS period in both groups (P < 0.05) with no difference between the groups and there was no difference in the frequency of ROSC (experimental group 5/8, control group 4/8). Furthermore with respect to 24 h survival, there was no difference between the experimental group (2/8) and the control group (3/8). Severe macroscopic haemorrhagic necrosis of the myocardium in the dogs with ROSC was found in 4/5 in the experimental group compared to 1/4 in the control group. In conclusion, intra-aortic administration of 100 microg/kg epinephrine doses combined with aortic occlusion during experimental CPR did not alter outcome.

Improved haemodynamics and restoration of spontaneous circulation with constant aortic occlusion during experimental cardiopulmonary resuscitation

Continuous balloon occlusion of the descending aorta is an experimental method that may improve blood flow to the myocardium and the brain during cardiopulmonary resuscitation (CPR). The aim of the present investigation was to evaluate the effects of this intervention on haemodynamics and the frequency of restoration of spontaneous circulation. Ventricular fibrillation was induced in 39 anaesthetised piglets, followed by an 8-min non-intervention interval. In a haemodynamic study (n = 10), closed chest CPR was performed for 7 min before the intra-aortic balloon was inflated. This intervention increased mean arterial blood pressure by 20%, reduced cardiac output by 33%, increased coronary artery blood flow by 86%, and increased common carotid artery blood flow by 62%. All these changes were statistically significant. Administration of epinephrine further increased mean arterial blood pressure and coronary artery blood flow, while cardiac output and common carotid artery blood flow decreased. In a study of short-term survival, nine out of 13 animals (69%) in the balloon group and in three out of 13 animals (23%) in the control group had spontaneous circulation restored. The difference between these two proportions was 0.46, which was statistically significant with a 95% confidence interval from 0.12 to 0.80. In conclusion, balloon occlusion of the descending aorta increased coronary and common carotid artery blood flow and the frequency of restoration of spontaneous circulation. It was also noted that epinephrine appears to augment the redistribution of blood flow caused by the aortic occlusion.

Cardiopulmonary resuscitation: a review for clinicians

Attempts at cardiopulmonary resuscitation (CPR) date from antiquity, but it is only in the last 50 years that a scientifically-based methodology has been developed. External chest compressions is the standard method for managing circulatory arrest, however, numerous alterations of this technique have been proposed in attempts to improve outcome from CPR. Defibrillation is the single most important therapy for the management of ventricular fibrillation or pulseless ventricular tachycardia. Adrenergic agents used to improve myocardial and cerebral perfusion are also the subject of considerable investigation with new agents entering clinical study. This paper reviews the history, current techniques and pharmacotherapy as well as controversial issues in the management of patients with cardiac arrest.

Cardiopulmonary resuscitation: a promise as yet largely unfulfilled

After failure of initial external defibrillation, restoration of spontaneous circulation is largely contingent on rapid and effective reversal of myocardial ischemia by both mechanical and pharmacologic means. Despite the introduction of modern cardiopulmonary resuscitation (CPR) more than 35 years ago, its universal acceptance, and its wide implementation, no improvements in outcome excepting early defibrillation have been documented over these many years. The science of CPR therefore is still in its infancy. It was incorrectly assumed that all that needs to be known is known and that the need for scientific research was therefore not apparent. Accordingly, serious resuscitation research was neither encouraged nor equitably supported. The ABCs of CPR currently provide for the establishment of a patent airway (A) and intermittent positive pressure ventilation, preferably with oxygen-enriched air (B). These are to be immediately followed with precordial compression (C). This ordering of priorities, however, is based on consensus rather than objective outcome measurements. The ABCs recently have been seriously challenged on the basis of results of both experimental and clinical studies. Conventional external precordial compression restores systemic blood flow. It may be used by both professional and nonprofessional CPR providers, especially bystanders, because of its apparent simplicity and noninvasiveness. However, manual or mechanical external precordial compression typically generates cardiac outputs that represent less than 30% of normal values. Coronary blood flow, which is critical for restoration of spontaneous circulation, is correspondingly reduced. Accordingly, several alternatives to conventional precordial compression have been proposed with the intent of increasing cardiac output and both coronary and cerebral blood flows. Among the large number of pharmaceutical agents initially recommended for cardiac resuscitation, only agents that produce peripheral vasoconstriction are of proved benefit. Epinephrine has been the preferred vasopressor agent for the management of cardiac arrest for more than 35 years because of its alpha-adrenergic effects. However, the potentially adverse effects of epinephrine are related to its beta-adrenergic inotropic actions. The beta-adrenergic actions account for disproportionate increases in myocardial oxygen consumption with increased severity of myocardial ischemic injury and provocation of ectopic ventricular tachycardia and ventricular fibrillation. Nevertheless, epinephrine remains the drug of choice, although adrenergic drugs with selective alpha-adrenergic actions or nonadrenergic vasoconstrictor drugs are likely to emerge as useful alternatives. Experimental and clinical observations have led to identification of continuous monitoring of both end-tidal carbon dioxide and ventricular fibrillation waveforms as practical noninvasive guides because they are highly correlated with both cardiac output and coronary blood flow. Both end-tidal carbon dioxide and ventricular fibrillation waveforms now serve as predictors of the likelihood of successful resuscitation. These two measurements may now be used to guide interventions and especially to assure optimal precordial compression. It is well established that sudden death among adults is predominantly due to malignant ventricular arrhythmias and ventricular fibrillation. Early defibrillation serves as an unequivocally effective immediate intervention. Minimally trained first responders and members of the general public are being enfranchised to use automated external defibrillators for very early defibrillation. Use of these devices by bystanders is the most promising new intervention since CPR was first proposed in the early 1960s. Postresuscitation ventricular dysrhythmias and heart failure are now called postresuscitation myocardial dysfunction. This complication has been recognized as a leading cause of the high postresuscitation mor

Effects of intra-aortic balloon occlusion on hemodynamics during, and survival after cardiopulmonary resuscitation in dogs

OBJECTIVE

To evaluate the effect of balloon occlusion of the proximal descending aorta during cardiopulmonary resuscitation (CPR) on hemodynamics, restoration of spontaneous circulation, and 24-hr survival.

DESIGN

Prospective, randomized, controlled trial.

SETTING

Experimental laboratory in a university hospital.

SUBJECTS

Eighteen anesthetized dogs. INTERVENTIONS; Catheters were placed for hemodynamic and blood gas monitoring. An aortic balloon catheter was placed with its tip just distal to the left subclavian artery. After 10 mins of ventricular fibrillation without CPR, 3 mins of Basic Life Support (chest compressions and ventilation with 100% oxygen) was followed by up to 30 mins of Advanced Cardiac Life Support with canine drug dosages. In the treatment group (n = 8), the intra-aortic balloon was inflated when Advanced Cardiac Life Support started and not deflated until shortly after restoration of spontaneous circulation. The control animals (n = 10) were treated with an identical resuscitation but without intra-aortic balloon occlusion.

MEASUREMENTS AND MAIN RESULTS

In the treatment group, coronary perfusion pressure was greater during Advanced Cardiac Life Support (p = .026). Restoration of spontaneous circulation was more frequent (7/8 dogs) as compared with the control group (3/10 dogs) (p = .025). There was a trend toward greater 24-hr survival in the treatment group (5/8 dogs) than in the control group (3/10 dogs).

CONCLUSIONS

Balloon occlusion of the proximal descending aorta during experimental CPR improves restoration of spontaneous circulation. Further laboratory and human studies are needed to determine the clinical efficacy of this technique.

Future directions for resuscitation research. V. Ultra-advanced life support

Standard external cardiopulmonary resuscitation (SECPR) frequently produces very low perfusion pressures, which are inadequate to achieve restoration of spontaneous circulation (ROSC) and intact survival, particularly when the heart is diseased. Ultra-advanced life support (UALS) techniques may allow support of vital organ systems until either the heart recovers or cardiac repair or replacement is performed. Closed-chest emergency cardiopulmonary bypass (CPB) provides control of blood flow, pressure, composition and temperature, but has so far been applied relatively late. This additional low-flow time may preclude conscious survival. An easy, quick method for vessel access and a small preprimed system that could be taken into the field are needed. Open-chest CPR (OCCPR) is physiologically superior to SECPR, but has also been initiated too late in prior studies. Its application in the field has recently proven feasible. Variations of OCCPR, which deserve clinical trials inside and outside hospitals, include 'minimally invasive direct cardiac massage' (MIDCM), using a pocket-size plunger-like device inserted via a small incision and 'direct mechanical ventricular actuation' (DMVA), using a machine that pneumatically drives a cup placed around the heart. Other novel UALS approaches for further research include the use of an aortic balloon catheter to improve coronary and cerebral blood flow during SECPR, aortic flush techniques and a double-balloon aortic catheter that could allow separate perfusion (and cooling) of the heart, brain and viscera for optimal resuscitation of each. Decision-making, initiation of UALS methods and diagnostic evaluations must be rapid to maximize the potential for ROSC and facilitate decision-making regarding long-term circulatory support versus withdrawal of life support for hopeless cases. Research and development of UALS techniques needs to be coordinated with cerebral resuscitation research.

Recent advances in cardiopulmonary resuscitation

Mechanical and pharmacologic measures intended to increase blood flow to vital organs are the mainstay of therapy for patients in cardiac arrest. Several new cardiopulmonary resuscitation (CPR) techniques as well as novel devices and pharmacologic agents have been developed and tested since the first report of manual closed chested CPR over three decades ago. These recent mechanical and pharmacologic advances in the treatment of cardiac arrest are described. Some of these new techniques, devices, and drug therapies are presently undergoing clinical evaluation in patients in cardiac arrest. While many of these new methods and techniques have shown promise in small clinical trials in humans, none have yet to be found to be conclusively superior to manual closed chested CPR and treatment with standard pharmacologic agents.

Selective aortic arch perfusion during cardiac arrest: enhanced resuscitation using oxygenated perflubron emulsion, with and without aortic arch epinephrine

STUDY OBJECTIVE

To evaluate selective aortic arch perfusion (SAAP) with an oxygenated fluorocarbon emulsion, with and without aortic arch epinephrine during cardiac arrest.

METHODS

This randomized, controlled study, undertaken at a university research laboratory, involved 15 mixed-breed dogs. After 10 minutes of ventricular fibrillation and 30 seconds of CPR, the dogs were randomized to three groups, each comprising five dogs. Group 1 (controls) dogs were given CPR and intravenous epinephrine, .01 mg/kg, at 10.5 minutes and then every 3 minutes. Group 2 dogs (IVE-SAAP) were treated with CPR and intravenous epinephrine (IVE) in the same fashion as the control group but were also subjected to SAAP with 275 mL of oxygenated 60% wt/vol perflubron emulsion over 30 seconds. Group 3 dogs (AoE-SAAP) received the same treatment as the IVE-SAAP group, except that the first epinephrine dose was given intraaortically.

RESULTS

Coronary perfusion pressure (CPP) increased during SAAP in both the IVE-SAAP and AoE-SAAP groups but was greater in the AoE-SAAP group. CPR diastolic CPP after SAAP was significantly greater in the AoE-SAAP group than in the control group. Return of spontaneous circulation (ROSC) occurred in two control dogs, all five IVE-SAAP dogs, and all five AoE-SAAP dogs. The time elapsed from the initiation of CPR to ROSC was 6.1 +/- 1.9 minutes in the AoE-SAAP group, compared with 11.0 +/- 5.8 minutes in the IVE-SAAP group.

CONCLUSION

SAAP with oxygenated perflubron emulsion improved ROSC, both with and without aortic arch epinephrine. The combination of SAAP with perflubron emulsion and aortic arch epinephrine resulted in higher CPP and more rapid ROSC.

Haemodynamic effects of descending aortic occlusion during cardiopulmonary resuscitation

We describe two patients who both suffered a cardiac arrest whilst maintained on an intra-aortic balloon pump. In an attempt to improve coronary and cerebral blood flow during cardiopulmonary resuscitation, the intra-aortic balloon was inflated to occlude the descending aorta and preferentially direct blood to the cerebral and coronary circulation. In case 1, mean radial artery pressure rose from 71/14 mmHg (mean = 33 mmHg) to 92/24 mmHg (mean = 47 mmHg). Diastolic right atrial pressure was 16 mmHg both with the balloon deflated and inflated. In patient 2, mean radial artery pressure rose from 48/21 mmHg (mean = 25 mmHg) to 62/26 mmHg (mean = 36 mmHg). Right atrial pressure was 90/6 mmHg (mean 34 mmHg) with the balloon deflated and 104/8 mmHg (mean = 40 mmHg) with the balloon inflated. Coronary artery perfusion pressure in case 1 increased from -2 to 8 mmHg and in case 2 increased from 15 to 18 mmHg. These results suggest that occlusion of the descending aorta during cardiac massage may improve coronary and cerebral perfusion pressures. Animal studies are consistent with these findings and show that aortic occlusion may significantly improve outcome from cardiac arrest.

Active compression-decompression cardiopulmonary resuscitation does not improve survival in patients with prehospital cardiac arrest in a physician-manned emergency medical system

OBJECT

To examine the efficacy of a new method of cardiac resuscitation, active compression-decompression cardiopulmonary resuscitation (ACD CPR), in prehospital cardiac arrest.

DESIGN

Prospective, randomized, controlled trial.

SETTING

Physician-manned Mobile Intensive Care Unit (MICU) of a university hospital, serving a population of 200,000.

PARTICIPANTS

Adult patients with prehospital nontraumatic cardiac arrest treated by the MICU.

INTERVENTIONS

Patients were randomized to standard chest compression according to American Heart Association (AHA) recommendations (group 1, 30 patients) or to the new technique (group 2, 26 patients). ACD was performed by use of a hand-held suction device. In both groups, advanced life support was performed as recommended by the AHA.

MEASUREMENTS AND MAIN RESULTS

Rate of patients regaining a spontaneous circulation (ROSC), hospital discharge rate, and mean carbon dioxide content during resuscitation were recorded. ROSC rates in groups 1 and 2 were 40% and 38.5%, respectively. Four patients (13.3%) in group 1 and three patients (11.5%) in group 2 were discharged (group 1 v group 2: n.s.). Anatomic conditions precluded the application of ACD CPR in 5 patients. The new technique was found to impose greater physical efforts than STD CPR. Capnography was performed in 23 patients (mean value: STD CPR: 11.9 +/- 4.7 mmHg, ACD CPR: 13.7 +/- 4.9 mmHg [n.s.]).

CONCLUSIONS

ACD CPR did not improve, outcome and practical performance was complicated. Therefore, this technique should not be performed routinely, or without strict supervision in prehospital cardiac arrest.