Design of near-optimal waveforms for chest and abdominal compression and decompression in CPR using computer-simulated evolution

OBJECTIVE: To discover design principles underlying the optimal waveforms for external chest and abdominal compression and decompression during cardiac arrest and cardiopulmonary resuscitation (CPR). METHOD: A 14-compartment mathematical model of the human cardiopulmonary system is used to test successive generations of randomly mutated external compression waveforms during cardiac arrest and resuscitation. Mutated waveforms that produced superior mean perfusion pressure became parents for the next generation. Selection was based upon either systemic perfusion pressure (SPP = thoracic aortic minus right atrial pressure) or upon coronary perfusion pressure (CPP = thoracic aortic pressure minus myocardial wall pressure). After simulations of 64,414 individual CPR episodes, 40 highly evolved waveforms were characterized in terms of frequency, duty cycle, and phase. A simple, practical compression technique was then designed by combining evolved features with a constant rate of 80 min(-1) and duty cycle of 50%. RESULTS: All ultimate surviving waveforms included reciprocal compression and decompression of the chest and the abdomen to the maximum allowable extent. The evolved waveforms produced 1.5-3 times the mean perfusion pressure of standard CPR and greater perfusion pressure than other forms of modified CPR reported heretofore, including active compression-decompression (ACD)+ITV and interposed abdominal compression (IAC)-CPR. When SPP was maximized by evolution, the chest compression/abdominal decompression phase was near 70% of cycle time. When CPP was maximized, the abdominal compression/chest decompression phase was near 30% of cycle time. Near-maximal SPP/CPP of 60/21 mmHg (forward flow 3.8 L/min) occurred at a compromise compression frequency of 80 min(-1) and duty cycle for chest compression of 50%. CONCLUSIONS: Optimized waveforms for thoraco-abdominal compression and decompression include previously discovered features of active decompression and interposed abdominal compression. These waveforms can be used by manual (Lifestick-like) and mechanical (vest-like) devices to achieve short periods of near normal blood perfusion non-invasively during cardiac arrest.     

The Evolution of Abdominal Compression in Cardiopulmonary Resuscitation

Objective: To review the history of external abdominal compression as an adjunct to cardiopulmonary resuscitation (CPR), tracking the development of five major themes over the course of the 20th century: 1) augmentation of peripheral resistance by physical means, 2) risk of hepatic injury with abdominal compression, 3) counterpulsation vs sustained compression, 4) the abdominal pump mechanism, and 5) contact compression techniques.
Methods: Literature retrieved from successive MEDLINE English-language searches was reviewed with a special emphasis on work and concepts highlighted by participants at the First Purdue Conference on Interposed Abdominal Compression-CPR, September 1992.
Results: External abdominal compression of one form or another has been studied as a means of resuscitation by many investigators throughout the 20th century. Experimental and clinical studies have shown generally consistent evidence of hemodynamic augmentation by abdominal compression during various forms of CPR. Recent advances include a modified theoretical understanding of hemodynamic mechanisms and demonstration of clinical potential in humans. Inconsistencies in published results may be due to differences in mechanical techniques of abdominal compression. Based on these studies, a modified manual technique for "contact compression" of the abdominal aorta is recommended.
Conclusions: A technique for left-of-center, angled compression of the abdominal aorta against the crest of the spine is recommended. Further well-supervised and controlled clinical trials using this standardized technique are warranted as a prelude to more widespread clinical application of abdominal compression in CPR.     

Hemodynamics, Survival Benefits, and Complications of Interposed Abdominal Compression during Cardiopulmonary Resuscitation

Objective: To review and describe the hemodynamics and mechanism of benefit of interposed abdominal compression cardiopulmonary resuscitation (IAC-CPR) as well as the current complications and survival data withtheuseoflAC-CPR.
Methods: Critical review of selected, published English-language studies analyzing IAC-CPR. Overview of hemodynamic effects, complications, and survival data of IAC-CPR vs standard CPR.
Results: Several investigators have demonstrated improvements in coronary perfusion pressure, carotid and cerebral blood flows, and augmented venous return using IAC-CPR compared with standard CPR. Recently, IAC-CPR has been shown to improve survival from in-hospital cardiac arrest. To date, there has been no increase in complications seen with the use of abdominal compression during CPR.
Recommendations: IAC-CPR should be considered an adjunct to standard CPR for adult patients experiencing in-hospital cardiac arrest, after an adequate airway has been secured. More research is needed before IAC-CPR can be recommended for out-of-hospital cardiac arrest, for patients who have not been intubated, or for children.     

Experience with ketamine and sodium pentobarbital as anesthetics in a rat model of cardiac arrest and resuscitation

We review 7 years experience with the chest compression model of cardiac arrest and resuscitation, comparing two different anesthetics. Ketamine stimulates cardiac function and only mildly depresses respiration; of the two it provides easier resuscitation. However, ketamine severely depresses brain protein synthesis; in studies using this measure ketamine is unsuitable and another agent must be used. Sodium pentobarbital mildly depresses brain protein synthesis, but depresses both cardiac and respiratory function, making resuscitation more difficult. Use of alternate chest/abdominal pumping (Babbs resuscitation technique), with judicious use of intra-cardiac epinephrine (adrenaline), made resuscitation reliable under sodium pentobarbital as well.     

Open- versus closed-chest cardiac compressions in a canine model of pediatric cardiopulmonary resuscitation

Whether or not the principles of adult resuscitation apply to the pediatric population remains unknown. In order to study this issue, a pediatric animal model was developed using puppies 6-12 weeks of age and 2-8 kg in weight. Hemodynamic status was assessed using standard methods, and measured global cerebral blood flow was assessed using the nitrous oxide (Kety-Schmidt) technique after placement of a catheter in the sagittal sinus. In this initial study, five puppies resuscitated with closed-chest cardiac compression (CCCC) were compared with five receiving open-chest cardiac compression (OCCC). Although mean systolic arterial pressures were equal with both methods during resuscitation (40 versus 49 mm Hg, P = 0.19), OCCC produced a greater cardiac output and a higher cerebral blood flow (5 versus 18 ml/100 g/min, P = 0.008). Only one of five dogs treated with CCCC had a blood flow during resuscitation greater than 15 ml/100 g/min, as compared with four of five receiving OCCC. Finally, three of five dogs in the CCCC group experienced liver lacerations, while none who were resuscitated by OCCC sustained any gross visceral injuries.     

心肺复苏质量的影响指标分析

心肺复苏质量是影响心搏骤停生存率的关键,除开始心肺复苏时间外,反映心肺复苏质量的指标还包括按压频率、按压深度、按压位置、胸廓充分回弹、避免按压中断以及通气过度等,通过综合分析反映心肺复苏质量的指标参数,以期促进心肺复苏的质量的提高。     

Possible Reasons for the Variability of Human Responses to IAC-CPR

Objective: To propose reasons for the variability of the hemodynamic responses and survival data observed when interposed abdominal compression cardiopulmonary resuscitation (IAC-CPR) is performed on humans in cardiac arrest.
Methods: Critical content review of all studies performed in the United States examining IAC-CPR in humans and of selected animal studies addressing hemodynamic mechanisms of CPR. Articles in the English language dealing with human IAC-CPR studies from 1970–1993 were retrieved using the MEDLINE database of the National Library of Medicine.
Results: IAC-CPR does not consistently improve coronary perfusion pressure (CPP) over standard CPR in humans and is capable of decreasing as well as increasing CPP. This variability does not seem dependent on the manner in which abdominal compressions are performed. Because of the limited response to standard CPR, significant increases in return of spontaneous circulation would be expected with IAC-CPR if a large percentage of patients were to have favorable increases in CPP. However, other patients may be adversely affected by decreases in CPP during IAC-CPR, with unsuccessful resuscitation of those individuals. Return of spontaneous circulation also may be enhanced using IAC-CPR due to other factors reflected in the initial arrest rhythm and in arrest-population demographics.
Conclusion: IAC-CPR should not be recommended for routine use until the mechanism of its beneficial effects is known and until those patients who are likely to benefit from the technique can be better identified.     

Pre-hospital IAC-CPR versus standard CPR: paramedic resuscitation of cardiac arrests

Recent studies evaluating interposed abdominal compression cardiopulmonary resuscitation (IAC-CPR) have demonstrated a significant increase in cardiac output, mean arterial pressure, and cerebral perfusion, as compared with standard CPR. A clinical evaluation of IAC-CPR effectiveness on resuscitation outcome has not been reported. A prospective randomized study comparing IAC-CRP with standard CPR for resuscitation of prehospital cardiopulmonary arrest was undertaken using the Milwaukee County Paramedic System. The patients were randomized following endotracheal intubation into IAC-CPR and standard CPR groups. Since October 1983, 291 patients have qualified for the study group. Of these, 146 patients had standard CPR, and 45 (31%) were successfully resuscitated. Of the 145 patients treated with IAC-CPR, 40 (28%) were successfully resuscitated. Chi-square analysis reveals no significant difference between these groups. To determine whether abdominal compression increases regurgitation, the frequency of emesis before and after intubation was analyzed. No significant difference was found between the IAC-CPR and standard CPR groups. Thus, IAC-CPR applied by paramedics in the field to patients following intubation does not improve cardiac resuscitation rates.     

Chest Compression and Ventilation Rates during Cardiopulmonary Resuscitation: The Effects of Audible Tone Guidance

Objectives: To determine: 1) whether chest compressions during CPR are being performed according to American Heart Association (AHA) guidelines during cardiac arrest; and 2) the effect of an audio prompt to guide chest compressions on compliance with AHA guidelines and hemodynamic parameters associated with successful resuscitation. Methods: An observational clinical report and laboratory study was conducted. A research observer responded to a convenience sample of cardiac arrests within a 300-bed hospital and counted the rate of chest compressions and ventilations during CPR. To evaluate the effect of an audio prompt on CPR, health care providers performed chest compression without guidance using a porcine cardiac arrest model for 1 minute, followed by a second minute in which audio guidance was added. Chest compression rates, arterial and venous blood pressures, end-tidal CO₂ (ETCO₂) levels, and coronary perfusion pressures were measured and compared for the two periods. Results: Twelve in-hospital cardiac arrests were observed in the clinical part of the study. Only two of 12 patients had chest compressions performed within AHA guidelines. No patient had respirations performed within AHA guidelines. In the laboratory, 41 volunteers were tested, with 66% performing chest compressions outside the AHA standards for compression rate without audible tone guidance. With guided chest compressions, the mean (± SD) chest compression rate increased from 74 ± 22 to 100 ± 3/min (p < 0.01). End-tidal CO₂ levels increased from 15 ± 7 to 17 ± 7 torr (p < 0.01). Coronary perfusion pressure increased minimally with audible tone-guided chest compressions. Conclusions: The majority of Basic Cardiac Life Support-certified health care professionals did not perform CPR according to AHA-recommended guidelines. The use of audible tones to guide chest compression resulted in significantly higher chest compression rates and ETCO₂ levels.     

A 35-Year-Old Pregnant Woman Presenting with Sudden Cardiac Arrest Secondary to Peripartum Cardiomyopathy

Abstract

We present a case of successful resuscitation from cardiac arrest after 25 minutes of ventricular fibrillation (VF) secondary to peripartum cardiomyopathy. This case highlights a rare disease, but also, more importantly, the successful use of the five links of survival: early access to 9-1-1, early cardiopulmonary resuscitation (CPR), early defibrillation, early advanced life support, and postresuscitative care. We also demonstrate the importance of high-quality resuscitation practices in order to achieve a successful outcome. Manual compressions can be performed at a guidelines-compliant rate. With training, users are able to achieve high compression fractions. Pre/post shock delays can be minimized to further increase compression fraction. Nationally, CPR interruptions are often long. We recommend closer attention to uninterrupted 2-minute cycles of CPR, minimizing delays in CPR through training, and a focus on a closely choreographed approach. User review of transthoracic impedance feedback data should play a vital role in a cardiac arrest quality-improvement program.     

Theoretically Optimal Duty Cycles for Chest and Abdominal Compression during External Cardiopulmonary Resuscitation

Objective: To use an electronic model of human circulation to compare the hemodynamic effects of different durations of chest compression during external CPR, both with and without interposed abdominal compression (IAC).
Methods: An electrical analog model of human circulation was studied on digital computer workstations using SPICE, a general-purpose circuit simulation program. In the model the heart and blood vessels were represented as resistive-capacitive networks, pressures as voltages, blood flow as electric current, blood inertia as inductance, and cardiac and venous valves as diodes. External pressurization of the heart and great vessels, as would occur in IAC-CPR, was simulated by the alternate application of damped rectangular voltage pulses, first between intrathoracic vascular capacitances and ground, and then between intra-abdominal vascular capacitances and ground. With this model compression frequencies of 60, 80, and 100 cycles/min and duty cycles ranging from 10% to 90%, both with and without IAC, were compared.
Results: There was little difference in hemodynamics when the overall compression frequency was varied between 60 and 100 cycles/min, but the effects of duty cycle were substantial. During both standard CPR and IAC-CPR, total flow and coronary flow were greatest at chest compression durations equal to 30% of cycle time. Interposed abdominal compression substantially improved simulated systemic blood flow and perfusion pressure at all duty cycles, compared with standard CPR without abdominal compression. Mean arterial pressure > 75 mm Hg and artificial cardiac output > 2.0 L/min could be generated by 30% duty cycle compression with IAC. Coronary perfusion in the model is clearly optimized at 30% chest compression (i.e., high-impulse chest compression technique).
Conclusion: Combined high-impulse chest compressions and IACs maximize blood flow during CPR in the electrical analog model of human circulation.     

Eighth grade students become proficient at CPR and use of an AED following a condensed training programme

OBJECTIVE: To evaluate a new, 1-h, condensed training programme to teach continuous chest compression cardiopulmonary resuscitation (CCC-CPR) and automated external defibrillator (AED) skills to a cohort of eight grade public school students. METHODS: RESULTS: Thirty-three eligible subjects completed the programme; mean age 13.7 years; 48.5% female. Eight participants reported some prior training in CPR and AED use. Following initial training, 29/33 (87.8%) subjects demonstrated proficiency at CCC-CPR and AED application/operation in a mock adult cardiac arrest scenario. At four-weeks, 28/33 (84.8%) subjects demonstrated skill retention in similar scenario testing. Subjects also showed improvement in written knowledge regarding AED use as shown by scores on an AHA based written exam (60.9% versus 77.3%; p<0.001). CONCLUSION: With our focused, condensed training program, eighth grade public school students became proficient in CCC-CPR and AED use. This is the first study to document the ability of middle school students to learn and retain CCC-CPR and AED skills for adult sudden cardiac arrest victims with such a curriculum.     

Bolus thrombolytic infusion during prolonged refractory cardiac arrest of undiagnosed cause

Acute myocardial infarction (AMI) and pulmonary embolism (PE) account for about 70% of cardiac arrest. Although thrombolytic therapy is an effective therapy for both AMI and PE, it is not routinely recommended during cardiopulmonary resuscitation (CPR) for fear of life threatening bleeding complications. Numerous case reports and retrospective studies have suggested a beneficial effect of thrombolytics in cardiac arrest secondary to AMI and PE; however, we present a case of successful use of bolus thrombolytics during CPR in a patient with undifferentiated cardiac arrest (undiagnosed cause) after prolonged conventional resuscitation without success.     

Hemodynamic-directed cardiopulmonary resuscitation during in-hospital cardiac arrest

Cardiopulmonary resuscitation (CPR) guidelines assume that cardiac arrest victims can be treated with a uniform chest compression (CC) depth and a standardized interval administration of vasopressor drugs. This non-personalized approach does not incorporate a patient's individualized response into ongoing resuscitative efforts. In previously reported porcine models of hypoxic and normoxic ventricular fibrillation (VF), a hemodynamic-directed resuscitation improved short-term survival compared to current practice guidelines. Skilled in-hospital rescuers should be trained to tailor resuscitation efforts to the individual patient's physiology. Such a strategy would be a major paradigm shift in the treatment of in-hospital cardiac arrest victims.     

Mild therapeutic hypothermia after cardiac arrest - a nationwide survey on the implementation of the ILCOR guidelines in German intensive care units

AIM: To investigate the implementation of mild therapeutic hypothermia (MTH) after cardiac arrest into clinical practice. METHODS AND RESULTS: A structured evaluation questionnaire was sent to all German hospitals registered to have ICUs; 58% completed the survey. A total of 93 ICUs (24%) reported to use MTH. Of those, 93% started MTH in patients after out-of-hospital resuscitation with observed ventricular fibrillation and 72% when other initial rhythms were observed. Only a minority of ICUs initiate MTH in patients after cardiac arrest with cardiogenic shock (28%), whereas 48% regarded cardiogenic shock as a contra-indication for MTH. On average, target temperature was 33.1+/-0.6 degrees C and duration of cooling 22.9+/-4.9 h. Many centres used economically priced cold packs (82%) and cold infusions (80%) for cooling. The majority of the ICUs considered infection, hypotension and bleeding as relevant complications of hypothermia which was of therapeutic relevance in less than 25% of the cases. CONCLUSIONS: MTH is underused in German ICUs. Centres which use MTH widely follow the recommendations of ILCOR with respect to the indication and timing of cooling. In hospitals that use MTH the technique is considered to be safe and inexpensive. More efforts are needed to promote this therapeutic option and hypothermia since MTH has now been included into European advanced cardiovascular life support protocols.     

Hemodynamics of Interposed Abdominal Compression during Human Cardiopulmonary Resuscitation

Objective: Clinical studies of interposed abdominal compression CPR (IAC-CPR) have had diverse outcomes. This study compared the hemodynamics of standard CPR and IAC-CPR in humans.
Methods: A 24-month prospective nonrandomized analysis of hemo-dynamic parameters was performed in a convenience cohort of 20 adults who had had out-of-hospital, nontraumatic, normothermic cardiac arrests. The study took place in the resuscitation unit of a large urban hospital. Thoracic aortic and right atrial catheters were inserted and pressures were recorded during standard CPR and IAC-CPR. Coronary perfusion pressures (CPPs) were determined during standard CPR and IAC-CPR. The patients were separated into two groups based upon their responses to IAC-CPR. Responders had increases in CPP during IAC-CPR; nonresponders had decreases or no change in CPP during IAC-CPR. Aortic relaxation, right atrial relaxation, aortic compression, and right atrial compression phase pressures were compared between the two groups.
Results: CPPs increased in 13 patients and decreased in seven patients. The mean change in CPP with IAC-CPR was an increase of 5.8 ± 15.1 torr. An elevated right atrial compression phase pressure (RaComp) during standard CPR was predictive of an increase in CPP during IAC-CPR (p = 0.047). In those patients who showed improvements in CPP during IAC-CPR, mean aortic relaxation phase pressures (AoRelax) increased by 9.5 ± 14.2 torr (p = 0.026) and mean right atrial relaxation phase pressures (RaRelax) decreased by 2.6 ± 6.2 torr (p = 0.099) during IAC-CPR.
Conclusions: The variable effects of IAC-CPR on CPP appear to be multifactorial. The improvement in CPP that occurred in responders to IAC-CPR was secondary to an increase in AoRelax as well as a decrease in RaRelax.     

Quantification of ventilation volumes produced by compressions during emergency department cardiopulmonary resuscitation

Background

Clinical investigations have shown improved outcomes with primary compression cardiopulmonary resuscitation strategies. It is unclear whether this is a result of passive ventilation via chest compressions, a low requirement for any ventilation during the early aspect of resuscitation or avoidance of inadvertent over-ventilation.

Comparison of chest compression only and standard cardiopulmonary resuscitation for out-of-hospital cardiac arrest in Singapore

OBJECTIVE: Chest compression only cardiopulmonary resuscitation (CC-CPR) without ventilation has been proposed as an alternative to standard cardiopulmonary resuscitation (CPR) for bystanders. However, there has been controversy regarding the relative effectiveness of both of these techniques. We aim to compare the outcomes of cardiac arrest patients in the cardiac arrest and resuscitation epidemiology study who either received CC-CPR, standard CPR or no bystander CPR. METHODS: This prospective cohort study involved all out-of-hospital cardiac arrest (OHCA) patients attended to by emergency medical service (EMS) providers in a large urban centre. The data analyses were conducted secondarily on these collected data. The technique of bystander CPR was reported by paramedics who arrived at the scene. RESULTS: From 1 October 2001 to 14 October 2004, 2428 patients were enrolled into the study. Of these, 255 were EMS-witnessed arrests and were excluded. 1695 cases did not receive any bystander CPR, 287 had standard CPR and 154 CC-CPR. Patient characteristics were similar in both the standard and CC-CPR groups except for a higher incidence of residential arrests and previous heart disease sufferers in the CC-CPR group. Patients who received standard CPR (odds ratio (OR) 5.4, 95% confidence interval (CI) 2.1-14.0) or CC-CPR (OR 5.0, 95% CI 1.5-16.4) were more likely to survive to discharge than those who had no bystander CPR. There was no significant difference in survival to discharge between those who received CC-CPR and standard CPR (OR 0.9, 95% CI 0.3-3.1). CONCLUSION: We found that patients were more likely to survive with any form of bystander CPR than without. This emphasises the importance of chest compressions for OHCA patients, whether with or without ventilation.     

Clinical evaluation of active abdominal lifting and compression CPR in patients with cardiac arrest

Background

Chest compression is a standard recommendation during cardiopulmonary resuscitation (CPR). However, chest compression cannot be effectively applied under certain situations, such as chest wall deformity, rib fracture, or hemopneumothorax. An alternative method, abdominal compression, was reported to achieve better resuscitation outcomes in these patients.

Resuscitation Research: Future Directions and Ethical Issues

Cardiopulmonary resuscitation research is a vital area of research that has made significant contributions to medical care over the last several decades. Abundant information currently exists in the medical literature, as a result of research in the areas of cardiac arrest and outcomes, physiology of cardiac arrest, pharmacologic treatments, mechanical interventions, and societal and ethical issues. Despite numerous clinical trials demonstrating physiologic benefit of various interventions, few interventions have had as much impact on outcomes of cardiac arrest as have improvements in out-of-hospital response times and rapid availability of medical treatment. Although abundant information exists regarding physiologic aspects of resuscitation, relatively little information exists about ethical, psychological, and social aspects of resuscitation. In addition to attempts to improve outcomes of cardiac arrest, researchers should also strive to improve the experiences of patients and families involved. These realities provide future strategies and directions for the best use of resuscitation research resources; although physiologic and pharmacologic research will always have significant roles in the improvement of medical care, the rapid delivery of out-of-hospital care and ethical issues will be indispensable areas of research focus in the future.