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.     

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.     

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.     

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.     

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。     

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.     

Surface Cooling for Rapid Induction of Mild Hypothermia After Cardiac Arrest: Design Determines Efficacy

Objectives: Recently, a novel cooling pad was developed for rapid induction of mild hypothermia after cardiac arrest. The aim of this study was to evaluate the cooling efficacy of three different pad designs for in‐hospital cooling. Methods: Included in this prospective interventional study were patients with esophageal temperature (Tes) > 34°C on admission. The cooling pad consists of multiple cooling units, filled with a combination of graphite and water, which is precooled to –18°C (design A) or to –9°C (designs B and C) before use. The designs of the cooling pad differed in number, shape, and thickness of the cooling units, with weights of 9.7 kg (design A), 5.3 kg (design B), and 6.2 kg (design C). All three designs were tested in sequential order and were changed according to the results found in the previous trial. Cooling was started after admission until Tes = 34°C, when the cooling pad was removed. The target temperature of Tes = 32–34°C was maintained for 24 hours. Data are presented as medians and interquartile ranges (IQRs = 25%–75%) or proportions. Results: Cooling rates were 3.4°C/hour (IQR = 2.5–3.7) with design A (n = 12), 2.8°C/hour (IQR = 1.6–3.3) with design B (n = 7), and 2.9°C/hour (IQR = 1.9–3.6) with design C (n = 10; p = 0.5). To reach 34°C, the cooling pad had to be exchanged with a new one due to melting and therefore depleting cooling capacity in three patients with design A, in five patients with design B, and in no patient with design C (p = 0.004). Conclusions: With adequate design and storage temperature, the cooling pad proved to be efficient for rapid in‐hospital cooling of patients resuscitated from cardiac arrest. ACADEMIC EMERGENCY MEDICINE 2010; 17:360–367 © 2010 by the Society for Academic Emergency Medicine     

Who Gets Bystander Cardiopulmonary Resuscitation in a Witnessed Arrest?

Objective: To identify characteristics associated with provision of bystander CPR in witnessed out-of-hospital cardiac arrest cases.
Methods: An observational, prospective, cohort study was performed using cardiac arrest cases as identified by emergency medical services (EMS) agencies in Oakland County, MI, from July 1, 1989, to December 31, 1993. All patients who sustained a witnessed arrest prior to arrival of EMS personnel were reviewed.
Results: Of the 927 patients meeting entry criteria, the 229 patients receiving bystander CPR were younger: 60.9 ± 14.7 vs 67.9 ± 14.7 years (p < 0.01). Most (76.6%) cardiac arrests occurred in the home. In a multivariate logistic model, only the location of arrest outside the home was a significant predictor of receiving bystander CPR [odds ratio (OR) 3.8; 99% CI 2.5, 5.9]. Arrests outside the home were associated with significantly improved outcome, with 18.2% of out-of-home and 8.2% of in-home victims discharged from the hospital alive (OR 2.5; 99% CI 1.4, 4.4).
Conclusion: Patients who have had witnessed cardiac arrests outside the home are nearly 4 times more likely to receive bystander CPR, and are twice as likely to survive. This observation emphasizes the need for CPR training of family members in the authors' locale. This phenomenon may also represent a significant con-founder in studies of out-of-hospital cardiac arrest and resuscitation.     

Association of Drug Therapy with Survival in Cardiac Arrest: Limited Role of Advanced Cardiac Life Support Drugs

OBJECTIVE: To generate hypotheses regarding the association of standard Advanced Cardiac Life Support (ACLS) drugs with human cardiac arrest survival. METHODS: This observational cohort study was conducted over a two-year period in the wards, intensive care units, and EDs of two tertiary care hospitals. Included werc adult patients who suffered cardiac arrest either inside or outside the hospital and who required epinephrine according to standard ACLS guidelines. Six standard ACLS drugs (given while CPR was in progress) were assessed for association with survival from resuscitation to one hour and to hospital discharge by univariate and multivariate logistic regression analyses. RESULTS: In the 529 patients studied, initial cardiac rhythm had no impact on the association between drug administration and survival. The time of drug administration (quartile of ACLS period) was associated with resuscitation for atropine (p < 0.05) and lidocaine (p < 0.01). The odds ratios (95% CIs) for successful resuscitation, after multivariate adjustment for potential confounders, were: a respiratory initiating cause, 3.7 (2.1 -6.4); each 5-minute increase in CPR-ACLS interval, 0.5 (0.4-0.7); each 5-minute duration of ACLS. 0.9 (()1.8- 1.0; atropine, 1.2 (1.0-1.3); bretylium. (0.4 (0.1-1.1); calcium 0.8 (0.2-2.4); lidocaine, 0.9 (0.7-1.1); procainamide. 21.0 (5.2-84.0) d sodium bicarbonate 1.2 (1.0-1.6). All other potential confounding variables entered into the model were not significantly associated with resuscitation. CONCLUSION: Initiating cause of arrest, time to ACLS, and duration of ACLS were important correlates of survival. Other than procainaimide, standard ACLS drugs had relatively little association with survival, but timing of administration may be an important factor. Further research using definitive large randomized controlled trials is warranted to assess the role of drug therapy in improving cardiac arrest survival.     

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.     

Rescuer Fatigue in the Elderly: Standard vs. Hands-only CPR

Background

Hands-only cardiopulmonary resuscitation (HO-CPR) is recommended as an alternative to standard CPR (STD-CPR). Studies have shown a degradation of adequate compressions with HO-CPR after 2 min when performed by young, healthy medical students. Elderly rescuers' ability to maintain an adequate compression rate and depth until emergency medical services (EMS) arrives is unknown.

Objectives

The specific aim of this study was to compare elderly rescuers' ability to maintain adequate compression rate and depth during HO-CPR and STD-CPR in a manikin model.

Methods

In this prospective, randomized crossover study, 17 elderly volunteers performed both HO-CPR and STD-CPR, separated by at least 2 days, on a manikin model for 9 min each. The primary endpoint was the number of adequate chest compressions (> 38 mm) delivered per minute. Secondary endpoints were total compressions, compression rate, and the number of breaks taken for rest.

Results

There was no difference in the number of adequate compressions between groups in the first minute; however, the STD-CPR group delivered significantly more adequate chest compressions in minutes 2–9 (p < 0.05). The total number of compressions delivered was significantly greater in the HO-CPR than STD-CPR group when considering the entire resuscitation period. A significantly greater number of rescuers took breaks for rest during HO-CPR than STD-CPR.

Conclusions

Although HO-CPR resulted in a greater number of overall compressions than STD-CPR, STD-CPR resulted in a greater number of adequate compressions in all but the first minute of resuscitation.     

A standardized Code Blue Team eliminates variable survival from in-hospital cardiac arrest

Background

Recent studies suggest that time of day affects survival from in-hospital cardiac arrest. Lower survival rates are observed during nights and on weekends, except in areas with consistent physician care, such as the Emergency Department. Since 1997, our hospital has utilized a standard, hospital-wide “Code Blue Team” (CBT) to respond to cardiac arrests at any time. This team is always led by an emergency physician, and includes specially trained nurses.

Objective

To assess if time of day or week affects survival from in-hospital cardiac arrest when a trained, consistent, emergency physician-led CBT is implemented.

Methods

This is an analysis of prospectively collected data on initial survival rates (return of spontaneous circulation >20 min) of all cardiac arrests that were managed by the CBT from 2000 to 2008. Cardiac arrests were also subcategorized based on initial cardiac rhythm. Survival rates were compared according to time of day or week.

Results

A total of 1692 cardiac arrests were included. There was no significant difference in the overall rate of initial survival between day/evening vs. night hours (odds ratio [OR] 1.04, 95% confidence interval [CI] 0.83–1.29), or between weekday vs. weekend hours (OR 1.10, 95% CI 0.85–1.38). This held true for all cardiac rhythms.

Conclusion

At our institution, there is no significant difference in survival from cardiac arrest when a standardized “Code Blue Team” is utilized, regardless of the time of day or week.     

CPR Induced Consciousness During Out-of-Hospital Cardiac Arrest: A Case Report on an Emerging Phenomenon

Background: High quality cardiopulmonary resuscitation (CPR) has produced a relatively new phenomenon of consciousness in patients with vital signs absent. Further research is necessary to produce a viable treatment strategy during and post resuscitation. Objective: To provide a case study done by paramedics in the field illustrating the need for sedation in a patient whose presentation was consistent with CPR induced consciousness. Resuscitative challenges are provided as well as potential future treatment options to minimize harm to both patients and prehospital providers. Case Report: A 52-year-old male presented as a witnessed out-of-hospital cardiac arrest (OHCA). During CPR the patient began to exhibit signs of life including severe agitation and thrashing of his limbs while CPR was ongoing for ventricular fibrillation prior to defibrillation. Resuscitation became considerably more complicated due to the violent and counterintuitive motions done by the patient during their own resuscitation. Despite the atypical presentation of cardiac arrest the patient was successfully resuscitated employing high quality CPR, standard advanced life support (ALS) care as well as two double sequential external defibrillation shocks. The patient underwent emergency percutaneous coronary intervention (PCI) for a 100% occlusion of his left anterior descending artery (LAD). The patient returned home 3 days later fully recovered with a Cerebral Performance Score of 1. Conclusion: CPR induced consciousness is emerging as a new phenomenon challenging providers of high quality CPR during cardiac arrest resuscitation. Our case report describes the manifestations of CPR induced consciousness as well as the resuscitative challenges which occur during resuscitation. Further research is required to determine the true frequency of this condition as well as treatment algorithms that would allow for appropriate and safe management for both the patient and EMS providers.     

Pancreatic injury associated with interposed abdominal compressions in pediatric cardiopulmonary resuscitation

A case in which conventional CPR was augmented with interposed abdominal compressions on a child is reported. Animal studies and electrical models of this new form of CPR have demonstrated improved hemodynamics without instance of intra-abdominal injury. In this case, intraperitoneal visceral injury was noticed in the form of blood within the stomach and small intestine and parenchymal hemorrhage within the pancreas. Similar pancreatic injury has not been reported with conventional pediatric CPR, and caution may have to be exercised if this form of CPR with interposed abdominal compressions is to be used on children.