Agent-based modeling: Population limits and large timescales.

Modeling, simulation, and analysis of interacting agent systems is a broad field of research, with existing approaches reaching from informal descriptions of interaction dynamics to more formal, mathematical models. In this paper, we study agent-based models (ABMs) given as continuous-time stochastic processes and their pathwise approximation by ordinary and stochastic differential equations (SDEs) for medium to large populations. By means of an appropriately adapted transfer operator approach, we study the behavior of the ABM process on long time scales. We show that, under certain conditions, the transfer operator approach allows us to bridge the gap between the pathwise results for large populations on finite timescales, i.e., the SDE limit model, and approaches built to study dynamical behavior on long time scales like large deviation theory. The latter provides a rigorous analysis of rare events including the associated asymptotic rates on timescales that scale exponentially with the population size. We demonstrate that it is possible to reveal metastable structures and timescales of rare events of the ABM process by finite-length trajectories of the SDE process for large enough populations. This approach has the potential to drastically reduce computational effort for the analysis of ABMs.

Gambian cultural beliefs, attitudes and discourse on reproductive health and mortality: Implications for data collection in surveys from the interviewer's perspective.

BACKGROUND: A community's cultural beliefs, attitudes and discourse can affect their responses in surveys. Knowledge of these cultural factors and how to comply with them or adjust for them during data collection can improve data quality. OBJECTIVE: This study describes implications of features of Gambian culture related to women's reproductive health, and mortality, when collecting data in surveys. METHODS: 13 in-depth interviews of female interviewers and a focus group discussion among male interviewers were conducted in two rural health and demographic surveillance systems as well as three key informant interviews in three regions in The Gambia. RESULTS: From the fieldworker's viewpoint, questions relating to reproduction were best asked by women as culturally pregnancies should be concealed, and menstruation is considered a sensitive topic. Gambians were reluctant to speak about decedents and the Fula did not like to be counted, potentially affecting estimation of mortality. Asking about siblings proved problematic among the Fula and Serahule communities. Proposals made to overcome these challenges were that culturally-appropriate metaphors and symbols should be used to discuss sensitive matters and to enumerating births/deaths singly instead of collecting summary totals, which had threatening connotations. This was as opposed to training interviewers to ask standardised and precise verbatim questions. CONTRIBUTION: This paper presents indigenous Gambian solutions by fieldworkers to culturally sensitive topics when collecting pregnancy outcomes and mortality data in demographic and health surveys. For researchers collecting maternal mortality data, it highlights the potential shortcomings of the sibling history methodology.

Type 2M von Willebrand disease - more often misidentified than correctly identified.

INTRODUCTION: Appropriate diagnosis of von Willebrand disease (VWD), including differential identification of qualitative vs. quantitative von Willebrand factor (VWF) defects has important management implications, but remains problematic. AIM: The aim of the study was to assess whether 2M VWD, defining qualitative defects not associated with loss of high molecular weight (HMW) VWF, is often misidentified, given highly variable reported frequency ranging from 0 to ~60% of all type 2 VWD. METHODS: A comparative evaluation of laboratory ability to appropriately identify 2M VWD (n = 4) vs. HMW VWF reduction (n = 4), as sent to participants of an international external quality assessment programme. RESULTS: Laboratories had considerably greater difficulty identifying type 2M VWD, correctly identifying these on average only 29.4% of occasions, with the 70.6% error rate representing use of insufficient test panels (41.7%), misinterpretation of test results (10.0%) and analytical errors (13.3%). One type 2M case, giving a median of 49 U dL(-1) VWF:Ag, was more often misidentified as type 2A/2B VWD (46.7%) than 2M (34.8%). Another 2M case, giving a median of 189 U dL(-1) VWF:Ag, was instead often misidentified as being normal (non-VWD) (36.4%), with identifications of type 2A/2B VWD (13.6%) also represented. In comparison, errors in identification of HMW VWF reduced samples only averaged 11.5%, primarily driven by use of insufficient test panels (6.3%) or misinterpretation of results (4.2%) and infrequently analytical errors (1.0%). CONCLUSION: Type 2M VWD is more often misidentified (70.6%) than correctly identified as 2M VWD (29.4%), and potentially explaining the relative under-reported incidence of 2M VWD in the literature.

Epidemiological analysis of the dynamic and diversity of Salmonella spp. in five German pig production clusters using pheno- and genotyping methods: an exploratory study.

An exploratory study in five conventional pig production clusters was carried out to investigate the dynamic and diversity of Salmonella spp. within different production stages and sample site categories (pooled feces, direct and non-direct environment). Observing two production cycles per production cluster, a total of 1276 samples were collected along the pig production chain. Following a microbiological examination via culture, 2246 subcultures were generated out of 285 Salmonella positive samples and analysed by pheno- and genotyping methods. Based on a combination of serotyping, MLVA (multiple-locus variable-number tandem repeat (VNTR) analysis), PFGE (pulse-field gel electrophoresis) and MLST (multilocus sequence typing), an amount of 22.3% Salmonella positive samples were characterized in clonal lineages and its variants. Within each production cluster, one main clonal lineage could be identified and persisted over both production cycles with a large diversity of variants and a wide distribution in sample site categories and production stages. Results underline the importance of biosecurity with emphasis on the environment to prevent persistence and circulation of Salmonella within herds. Furthermore, the combined implementation of MLVA, PFGE and MLST with conventional culture techniques for isolate classification could be successfully applied as an effective and valuable tool for identifying similar pattern of Salmonella occurrence within pig production clusters.

Alcohol consumption and expectations of its effects in the border region of Pomerania: comparison of German and Polish adolescents.

The study focused on expectations of alcohol effects and patterns of consumption in German and Polish adolescents in the border region of Pomerania. In 2005/2006 a cross-sectional study was conducted in various schools. Adolescents with an average age of 14 from one German town (Greifswald) and two Polish towns (Szczecin and Kolobrzeg) were assessed using the ESPAD (European School Project on Alcohol and Other Drugs) questionnaire. Altogether 757 (444 Polish and 313 German) students in their 7th and 8th grades were assessed. Differences between alcohol consumption patterns and expectations between Germany and Poland, and relationships between alcohol consumption and anticipated alcohol effects were tested. There is a difference in patterns of consumption between the two countries. Among all adolescents, expectations of positive alcohol effects dominated, and the negative effects were estimated to be less likely. In a country-specific comparison, German students estimated the occurrence of positive as well as negative effects to be likely. Adolescents who consumed a lot of alcohol in both countries estimated the positive effects to be stronger. Adolescents are more focused on short-term experiences than the long-term consequences of alcohol consumption. The results show potential targets for prevention and intervention of future risky consumption and alcohol use disorders.

The Utstein template and the effect of in-hospital decisions: the impact of do-not-attempt resuscitation status on survival to discharge statistics.

BACKGROUND: Variables for reporting outcome of pre-hospital cardiac arrest have been delineated in the Utstein style template. The primary outcome statistic is survival to hospital discharge (SHD). The template allows comparisons of pre-hospital care systems and has been used to determine the benefit of pre-hospital interventions. Post-resuscitation care has not been standardized and in-hospital events that affect SHD are not considered in the template. STUDY PURPOSE: To determine the frequency and timing with which do-not-attempt resuscitation (DNAR) status is conferred following resuscitation from pre-hospital cardiac arrest and to assess the impact of this action on SHD. METHODS: A 4-year retrospective, observational cohort study of all adult patients successfully resuscitated from nontraumatic pre-hospital cardiac arrest and admitted to a single municipal teaching hospital. Study variables included age, witnessed arrest, bystander cardiopulmonary resuscitation (CPR), initial rhythm documented by paramedics, hospital admission rate, frequency and time at which DNAR status was conferred, and SHD. RESULTS: Four hundred and eighteen adult patients experienced pre-hospital arrest and received standard advanced cardiac life support interventions during the study period. Seventy-nine patients (19%; 95% confidence interval (CI), 15-23%) survived to be admitted to the hospital. Fifty-four of these patients (68%; 96% CI, 57-78%) were subsequently placed in DNAR status. Only one of these patients had a living will or advanced directive prior to cardiopulmonary arrest. In 37 DNAR patients (68%; 95% CI, 54-81%), DNAR status was conferred within 24 h of hospital admission. For patients made DNAR within 24 h of admission, 38% had a witnessed arrest, 22% had ventricular fibrillation as the first documented arrest rhythm, and 29% received bystander CPR. When patients made DNAR are included in the calculation of SHD rate, the SHD rate for the study period was 5.3% (95% CI, 3.3-7.8%). If DNAR patients are excluded, the SHD was 6.1% (95% CI, 3.8-9.0%), representing a 15% increase in SHD rate. CONCLUSION: In-hospital care and medical decision making are not considered in the Utstein template and can have a significant effect on reported survival statistics. When assessing the benefit of pre-hospital interventions, it may be preferable to consider survival to hospital admission as the primary outcome statistic until such time as post-resuscitation care after hospital admission is rigidly standardized.

Outcome of out-of-hospital postcountershock asystole and pulseless electrical activity versus primary asystole and pulseless electrical activity.

OBJECTIVE: In the prehospital setting, countershock terminates ventricular fibrillation (VF) in about 80% of cases. However, countershock is most commonly followed by asystole or pulseless electrical activity (PEA). The consequences of such a countershock outcome have not been well studied. The purpose of this investigation was to compare the outcome of prehospital VF victims shocked into asystole or PEA with that of patients whose first documented rhythm was asystole or PEA (primary asystole or PEA). DESIGN: Observational, retrospective study conducted over 5 yrs (1995-1999). SETTING: A municipal hospital with a catchment area of >200,000. PATIENTS: Consecutive adult patients with out-of-hospital nontraumatic cardiopulmonary arrest of cardiac origin. Patients found in VF who developed asystole or PEA after countershocks (group 1) and patients found in asystole or PEA (primary asystole or PEA) (group 2) were included if the reported downtime was <10 min. INTERVENTIONS: None. MEASUREMENTS AND RESULTS: Study end points included restoration of circulation (defined as a pulse for any duration), survival to hospital admission, and survival to hospital discharge. Ratios were determined, 95% confidence intervals were calculated, and observed differences were compared. For group 1 patients (n = 101), 61% of patients had a bystander-witnessed collapse and 34% received bystander cardiopulmonary resuscitation. For group 2 patients (n = 140), collapse was bystander witnessed in 71% and 45% received bystander cardiopulmonary resuscitation. These differences were not statistically significant. Restoration of circulation was significantly more frequent in group 2 than group 1 (42% vs. 16%, p <.001) as was survival to hospital admission (36% vs. 11%, p =.001). Survival to hospital discharge was greater in group 2 patients, but the difference failed to achieve statistical significance (10% vs. 3%, p =.062). CONCLUSIONS: Countershock of prolonged VF followed by a nonperfusing rhythm has a worse prognosis than primary asystole or PEA and may be related to myocardial electrical injury.

Experimental studies on precordial compression or defibrillation as initial interventions for ventricular fibrillation.

Countershock of prolonged ventricular fibrillation is usually followed by asystole or a nonperfusing rhythm. Data from three laboratory investigations indicate that administration of epinephrine and cardiopulmonary resuscitation (CPR) preceding countershock of prolonged ventricular fibrillation significantly improves cardiac resuscitation outcome compared with immediate countershock (relative risk reduction of failed resuscitation, 0.61). Preliminary investigations indicate that a similar improvement is not observed when the ventricular fibrillation period is of shorter duration, e.g., 5 mins. This time interval is probably at the lower limit at which CPR preceding shock of ventricular fibrillation provides benefit in terms of cardiac resuscitation. A single clinical trial of "CPR first" supports the use of a brief period of CPR before countershock of prolonged ventricular fibrillation. Additional trials with and without epinephrine are anticipated.

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

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

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

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

Transthoracic monophasic and biphasic defibrillation in a swine model: a comparison of efficacy, ST segment changes, and postshock hemodynamics.

OBJECTIVE: Biphasic waveforms for transthoracic defibrillation (DF) have been tested extensively after brief (15 s) episodes of VF in animal models and in patients undergoing electrophysiologic testing. The purpose of this study was to compare the effects mono- and biphasic waveforms for DF on postdefibrillation ST segments and left ventricular pressure, markers of myocardial injury, after more extended periods of VF (30 and 90 s). METHODS: 21 anesthetized and instrumented swine were randomized to truncated exponential monophasic or biphasic waveform DF. VF was induced electrically and 30 s later, DF with the designated waveform was attempted with a shock dose of 200 J. If unsuccessful, 300 J and then 360 J were administered if necessary. Following return to control hemodynamic values and normalization of the surface ECG, VF was again induced and, after 90 s, DF was attempted as in the 30 s VF period. CPR was not performed during VF and each animal was countershocked with only one waveform for both VF episodes. Waveforms were compared for frequency of first shock defibrillation success, surface ECG indicators of myocardial injury (ST segment changes at 10, 20, and 30 s after countershock) and time to return to pre-VF hemodynamics after successful DF, an indicator of postshock ventricular function. RESULTS: Successful first shock conversion rates at 30 and 90 s were 60 and 63% for monophasic and 64 and 82% for biphasic (NS). Biphasic DF after 30 s produced ST segment changes (measured 10 s after DF) in 1/10 animals while six of eight animals in the monophasic group showed ST segment changes (P=0.013). After 90 s of VF, ST segment changes were observed in 6/8 in the monophasic group and 2/10 in the biphasic group (P=0.054). Differences in the time to hemodynamic recovery (return to control peak left ventricular pressure) were not observed between biphasic and monophasic waveforms after 30 or 90 s of VF. CONCLUSIONS: Monophasic and biphasic transthoracic defibrillation are equally effective in terminating VF of 30 and 90 s duration and restoring a perfusing rhythm. The biphasic waveform produced less ECG evidence of transient myocardial injury. However, there was no difference in the rate of return to control hemodynamics. ST segment changes following countershock of VF of brief duration are transient and of questionable significance.

Endotracheal versus intravenous epinephrine and atropine in out-of-hospital "primary" and postcountershock asystole.

STUDY OBJECTIVE: Pulmonary blood flow during cardiac arrest and cardiopulmonary resuscitation (CPR) is <20% of normal, and transalveolar drug absorption is likely to be minimal. Animal and clinical CPR studies have not addressed the use of endotracheal (ET) epinephrine in doses currently recommended for adults (twice the intravenous dose). The purpose of this study was to compare the effects of ET and intravenous drugs on cardiac rhythm in the prehospital setting. DESIGN: A 3-yr (1995-1997) retrospective review of all cardiac arrests transported to a single, municipal teaching institution was performed. PATIENTS: Patients >18 yrs in atraumatic cardiac arrest whose first documented field rhythm was asystole with time-to-definitive care of < or =10 mins (primary asystole) and patients found in ventricular fibrillation who developed postcountershock asystole (secondary asystole) were included. Patients were grouped according to route of drug administration (i.v., ET, or no drug therapy) as well as rhythm (primary or secondary asystole). A positive response to drug therapy was defined as any subsequent rhythm other than asystole during continued prehospital resuscitation. MEASUREMENTS AND MAIN RESULTS: A total of 136 patients met inclusion criteria. The following groups were defined: group 1, primary asystole/i.v. drugs (n = 39); group 2, postcountershock asystole/i.v. drugs (n = 39); group 3, primary asystole/ET drugs (n = 25); group 4, postcountershock asystole/ET drugs (n = 18); and group 5, primary or secondary asystole/no drug therapy (n = 15). Significant differences were not observed between groups with respect to age, gender, witnessed arrest, frequency of bystander CPR, or time-to-definitive care. The positive rhythm response rate was significantly greater in group 1 (64%) and group 2 (69%) (both p < .01) than in Group 3 (12%) or group 4 (11%). The response rate in the control group was 20% and not significantly different from either ET group. The intravenous groups also had a significantly greater rate of return of spontaneous circulation (17%) when compared with the ET groups (0%) (p = .005). CONCLUSION: We conclude that the currently recommended doses of epinephrine and atropine administered endotracheally are rarely effective in the setting of cardiac arrest and CPR.

Multidisciplinary team renal rehabilitation: interventions and outcomes.

Multidisciplinary team renal rehabilitation produces positive patient outcomes by broadening the knowledge base and evening out the work load. Rehabilitation is no longer viewed as an extra program to patient care done by a few people but seen as an integral part of the patients' care and dialysis treatment. Focusing on the 5E's of renal rehabilitation developed by the Life Options Rehabilitation Advisory Council, Renal Care Group of the Midwest, Inc has achieved positive clinical patient outcomes, such as meeting dialysis adequacy benchmark goals. Interventions and outcomes of two of the 5E's, education and exercise, are discussed.

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

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

Outcome from out-of-hospital cardiac arrest caused by nonventricular arrhythmias: contribution of successful resuscitation to overall survivorship supports the current practice of initiating out-of-hospital ACLS.

STUDY OBJECTIVE: Studies indicate that ventricular tachycardia (VT) and ventricular fibrillation (VF) are no longer the most common rhythms initially documented in out-of-hospital sudden cardiac death. Although the outcome from asystole and rhythms designated as pulseless electrical activity (PEA) is reported as poor (approximately 1% survival), resuscitative efforts for these patients are still encouraged. The purpose of this study was to determine the potential contribution that this patient group makes to overall survivorship. METHODS: During this 2-year prospective study, all patients in cardiopulmonary arrest who were transported to the study institution after out-of-hospital Advanced Cardiac Life Support (ACLS) interventions were considered eligible for inclusion. Patients younger than 18 years of age and those in posttraumatic arrest were excluded. Age, sex, first-documented arrest rhythm, presence of a witness to the arrest, performance of bystander CPR, survival to hospital discharge, and functional status at discharge were recorded. RESULTS: A total of 197 patients met the inclusion criteria. The initial rhythm was VF/VT in 59 (30%; 95% confidence interval [CI], 24% to 37%) and asystole/PEA in 138 (70%; 95% CI, 64% to 76%). There was 1 hospital survivor in the VT/VF group; 9 patients (7%; 95% CI, 4% to 13%) in the asystole/PEA group survived to hospital discharge. Of the asystole/PEA survivors, 100% (95% CI, 66% to 100%) had a witnessed arrest and 56% (95% CI, 21% to 86%) received bystander CPR. Fifty-six percent (95% CI, 21% to 86%) of the asystole/PEA survivors were discharged at a functional level equivalent to that preceding arrest. CONCLUSION: In this study, patients in asystole/PEA comprised 90% of the survivors. The outcome for patients with asystole/PEA whose arrest was witnessed and who received bystander CPR may be greater than previously estimated and supports the current practice of initiating aggressive out-of-hospital ACLS in this patient group.

Hemodynamic effects of repeated doses of epinephrine after prolonged cardiac arrest and CPR: preliminary observations in an animal model.

STUDY PURPOSE: To assess the hemodynamic response to repeated doses of epinephrine (EPI) in an animal model of prolonged cardiac arrest and CPR. DESIGN: Basic laboratory investigation. Fourteen canines were subjected to electrically induced ventricular fibrillation (VF) followed by 7.5 min of VF without CPR. INTERVENTIONS: After 7.5 min of VF, manual closed-chest CPR (80-100 compressions per minute, compression to ventilation ratio 8:1) was initiated. Countershocks were performed, recommended advanced cardiac life support drugs were given, and CPR was continued until restoration of spontaneous circulation (ROSC) or for 20 min. Epinephrine, 1 mg (approximately 0.04 mg kg(-1)), was administered when indicated and at recommended time intervals. METHODS: Aortic and right atrial pressures were measured with micromanometer catheters before and after EPI, and CPR coronary perfusion pressure (CPP) was calculated (CPR diastolic aortic to right atrial pressure difference). Survival was defined as maintenance of ROSC for 30 min. RESULTS: Countershocks after 7.5 min resulted in asystole in ten animals and persistant VF in four. In those animals successfully resuscitated (n = 3), the change in CPP was 21 +/- 11 mm Hg after the first dose of EPI. Only one animal required a second dose of EPI. The majority of the study group (n = 11) could not be resuscitated. The increase in CPP after EPI averaged only 3 +/- 2 mm Hg and subsequent doses produced no significant effect on CPP (2 +/- 4 mm Hg). CONCLUSIONS: The hemodynamic response to the first dose of EPI determines if the critical CPP needed for ROSC and survival will occur. Repeat doses of EPI do not appear to improve CPP to a degree to affect clinically meaningful measures of outcome, i.e., successful countershock and survival.

Effects of adding links to "the chain of survival" for prehospital cardiac arrest: a contrast in outcomes in 1975 and 1995 at a single institution.

STUDY OBJECTIVE: The concept of a "chain of survival" to improve outcome from prehospital cardiac arrest has been defined and promulgated over the last two decades. The purpose of this study was to compare outcomes of prehospital cardiac arrest in 1975 and 1995 at a single institution. METHODS: This longitudinal, before-after study compares published data collected at our municipal, tertiary care in 1974-1975 with data collected prospectively in 1995. The 1975 study group served as control subjects (n = 120). We enrolled an equal number of consecutive patients who met inclusion criteria in the 1995 cohort (consecutive patients who experienced prehospital arrest and who received prehospital Advanced Cardiac Life Support (ACLS) measures during the two study periods). Patients younger than 18 years or with posttraumatic arrest were excluded. Between 1975 and 1995 the following "links" in the "chain of survival" were added to the prehospital care system: (1) 911 access and dispatch, (2) paramedic endotracheal intubation, (3) EMT automated defibrillation, (4) standing out-of-hospital orders before hospital radiotelemetry contact, and (5) introduction of American Heart Association ACLS algorithms. RESULTS: The following significant differences (chi 2) were observed between the study periods: prevalence of ventricular fibrillation or tachycardia (42% in 1975 versus 28% in 1995, P = .021), prevalence of asystole or pulseless electrical activity as the first documented rhythm (58% versus 72%, P = .021), survival to hospital discharge (22% versus 9%, P = .007), and percent of survivors of ventricular fibrillation or tachycardia (30% versus 0%, P = .004). Eighty-six percent of the 1995 cohort had advanced chronic disease and 29% experienced cardiopulmonary arrest in a nursing home. CONCLUSION: Survival decreased dramatically during the 20-year study period. This may be because of the high incidence of chronic disease, the greater frequency of asystole and pulseless electrical activity, and the inclusion of patients with "end-of-life" arrests in which ACLS protocol was initiated in the 1995 cohort. The patient population in which ACLS is initiated is the weakest link in the "chain of survival."