The ACLS score. Predicting survival from out-of-hospital cardiac arrest

Clinical Predictive Models of Sudden Cardiac Arrest: A Survey of the Current Science and Analysis of Model Performances

Background

More than 500 000 sudden cardiac arrests (SCAs) occur annually in the United States. Clinical predictive models (CPMs) may be helpful tools to differentiate between patients who are likely to survive or have good neurologic recovery and those who are not. However, which CPMs are most reliable for discriminating between outcomes in SCA is not known.

Methods and Results

We performed a systematic review of the literature using the Tufts PACE (Predictive Analytics and Comparative Effectiveness) CPM Registry through February 1, 2020, and identified 81 unique CPMs of SCA and 62 subsequent external validation studies. Initial cardiac rhythm, age, and duration of cardiopulmonary resuscitation were the 3 most commonly used predictive variables. Only 33 of the 81 novel SCA CPMs (41%) were validated at least once. Of 81 novel SCA CPMs, 56 (69%) and 61 of 62 validation studies (98%) reported discrimination, with median c‐statistics of 0.84 and 0.81, respectively. Calibration was reported in only 29 of 62 validation studies (41.9%). For those novel models that both reported discrimination and were validated (26 models), the median percentage change in discrimination was −1.6%. We identified 3 CPMs that had undergone at least 3 external validation studies: the out‐of‐hospital cardiac arrest score (9 validations; median c‐statistic, 0.79), the cardiac arrest hospital prognosis score (6 validations; median c‐statistic, 0.83), and the good outcome following attempted resuscitation score (6 validations; median c‐statistic, 0.76).

Conclusions

Although only a small number of SCA CPMs have been rigorously validated, the ones that have been demonstrate good discrimination.

External validation of the ROSC after cardiac arrest (RACA) score in a physician staffed emergency medical service system

Background

The return of spontaneous circulation (ROSC) after cardiac arrest (RACA) score may have implications as a quality indicator for the emergency medical services (EMS) system. We aimed to validate this score externally in a physician staffed urban EMS system.

Methods

We conducted a retrospective cohort study. Data on resuscitation attempts from the Helsinki EMS cardiac arrest registry from 1.1.2008 to 31.12.2010 were collected and analyzed. For each attempted resuscitation the RACA score variables were collected and the score calculated. The endpoint was ROSC defined as palpable pulse over 30 s. Calibration was assessed by comparing predicted and observed ROSC rates in the whole sample, separately for shockable and non-shockable rhythm, and separately for resuscitations lead by a specialist, registrar or medical supervisor (i.e., senior paramedic). Data are presented as medians and interquartile ranges. Statistical testing included chi-square test, the Mann-Whitney U test, Hosmer-Lemeshow goodness of fit test and calculation of 95% confidence intervals (CI) for proportions.

Results

A total of 680 patients were included of whom 340 attained ROSC. The RACA score was higher in patients with ROSC (0.62 [0.46–0.69] than in those without (0.46 [0.36–0.57]) (p < 0.001). Observed against predicted ROSC indicated reasonable calibration overall (p = 0.30), with better calibration in patients with a shockable initial rhythm (p = 0.75) than in patients with a non-shockable rhythm (p = 0.04). There was no statistical difference between observed and predicted ROSC rates in resuscitations attended by a specialist (50% vs 53%, 95% CI 45–55) or registrar (55% vs 53%, 95% CI 48–62), but rates were lower than predicted in resuscitations lead by a medical supervisor (36% vs 49%, 95% CI 25–47).

Discussion

Developing a practical severity-of-illness scoring system for out-of-hospital cardiac arrest patients would allow patient heterogeneity adjustment and measurement of quality of care in analogy to commoly used severity-of-illness- scores developed for the similar purposes for the general intensive care unit population. However, transferring RACA score to another country with different population and EMS system might affect the performance and generalizability of the score.

Conclusions

This study found a good overall calibration and moderate discrimination of the RACA score in a physician staffed urban EMS system which suggests external validity of the score. Calibration was suboptimal in patients with a non-shockable rhythm which may due to a local do-not-attempt-resuscitation policy. The lower than expected overall ROSC rate in resuscitations attended by medical supervisors requires further study.

Subsequent shock deliveries are associated with increased favorable neurological outcomes in cardiac arrest patients who had initially non-shockable rhythms

Introduction

Previous studies evaluating whether subsequent conversion to shockable rhythms in patients who had initially non-shockable rhythms was associated with altered clinical outcome reported inconsistent results. Therefore, we hypothesized that subsequent shock delivery by emergency medical service (EMS) providers altered clinical outcomes in patients with initially non-shockable rhythms.

Methods

We tested for an association between subsequent shock delivery in EMS resuscitation and clinical outcomes in patients with initially non-shockable rhythms (n = 11,481) through a survey of patients after out-of-hospital cardiac arrest in the Kanto region (SOS-KANTO) 2012 study cohort, Japan. The primary investigated outcome was 1-month survival with favorable neurological functions. The secondary outcome variable was the presence of subsequent shock delivery. We further evaluated the association of interval from initiation of cardiopulmonary resuscitation to shock with clinical outcomes.

Results

In the univariate analysis of initially non-shockable rhythms, patients who received subsequent shock delivery had significantly increased frequency of return of spontaneous circulation, 24-hour survival, 1-month survival, and favorable neurological outcomes compared to the subsequent not shocked group (P <0.0001). In the multivariate logistic regression analysis, subsequent shock was significantly associated with favorable neurological outcomes (vs. not shocked; adjusted P = 0.0020, odds ratio, 2.78; 95 % confidence interval, 1.45–5.30). Younger age, witnessed arrest, initial pulseless electrical activity rhythms, and cardiac etiology were significantly associated with the presence of subsequent shock in patients with initially non-shockable rhythms.

Conclusions

In this study of cardiac arrest patients with initially non-shockable rhythms, patients who received early defibrillation by EMS providers had increased 1-month favorable neurological outcomes.

Electronic supplementary material

The online version of this article (doi:10.1186/s13054-015-1028-0) contains supplementary material, which is available to authorized users.

[Prognostic assessment as the basis for limiting therapy in unconscious patients after cardiopulmonary resuscitation]

BACKGROUND

The prognosis of patients who have been resuscitated after cardiac arrest is still unfavourable and long-term results have only slightly improved. As a consequence, intensivists are frequently confronted with the question of limiting active therapeutic efforts for patients in prolonged coma. The history of the patient and circumstances of the resuscitation are of limited value with regard to reliable decisions.

THERAPEUTIC DECISION-MAKING

Clinical and electrophysiological neurologic techniques as well as biomarkers and diagnostic imaging are, therefore, the basis for prognostication and potential consecutive therapeutic decisions. Sedation, relaxation and particularly therapeutic hypothermia have great influence on the test results. These influences have to be excluded before results can be validated. With regard to therapeutic hypothermia a reliable neurologic evaluation as a basis for limiting treatment is only possible after rewarming. Moreover results of multiple tests should be in agreement before a decision to limit treatment can be made. Finally it must be kept in mind that the absence of unfavourable test results is not proof of a good prognosis.

CONCLUSION

The decision to limit treatment can not be made on the basis of a single adverse prognostic sign, but requires a comprehensive clinical diagnostic assessment.

Shorter time until return of spontaneous circulation is the only independent factor for a good neurological outcome in patients with postcardiac arrest syndrome

OBJECTIVE

Few studies have reported factors that result in a better neurological outcome in patients with postcardiac arrest syndrome (PCAS) following return of spontaneous circulation (ROSC). We investigated the factors affecting neurological outcome in terms of both prehospital care and treatments after arrival at hospital in patients with PCAS.

METHODS

The study enrolled patients with cardiogenic cardiac arrest who were admitted to an intensive care unit after ROSC with PCAS. We investigated the association of the following factors with outcome: age, gender, witness to event present, bystander cardiopulmonary resuscitation (CPR) performed, ECG waveform at the scene, time interval from receipt of call to arrival of emergency personnel, time interval from receipt of call to arrival at hospital, prehospital defibrillation performed, special procedures performed by emergency medical technician, and time interval from receipt of call to ROSC, coronary angiography/percutaneous coronary intervention (PCI) and therapeutic hypothermia performed.

RESULTS

The study enrolled 227 patients with PCAS. Compared with the poor neurological outcome group, the good neurological outcome group had a statistically significant higher proportion of the following factors: younger age, male, witness present, bystander CPR performed, first ECG showed ventricular fibrillation/pulseless ventricular tachycardia, defibrillation performed during transportation, short time interval from receipt of call to ROSC, coronary angiography/PCI and therapeutic hypothermia performed. Of these factors, the only independent factor associated with good neurological outcome was the short time interval from receipt of the call to ROSC.

CONCLUSIONS

In the present study, shortening time interval from receipt of call to ROSC was the only important independent factor to achieve good neurological outcome in patients with PCAS.

Blood ammonia and lactate levels on hospital arrival as a predictive biomarker in patients with out-of-hospital cardiac arrest

INTRODUCTION

No reliable predictor for the prognosis of out-of-hospital cardiac arrest (OHCA) on arrival at hospital has been identified so far. We speculate that ammonia and lactate may predict patient outcome.

METHODS

This is a prospective observational study. Non-traumatic OHCA patients who gained sustained return of spontaneous circulation and were admitted to acute care unit were included. Blood ammonia and lactate levels were measured on arrival at hospital. The patients were classified into two groups: 'favourable outcome' group (Cerebral Performance Category CPC1-2 at 6-months' follow-up) and 'poor outcome' group (CPC3-5). Basal characteristics obtained from the Utstein template and biomarker levels were compared between these two outcome groups. Independent predictors were selected from all candidates using logistic regression analysis.

RESULTS

A total of 98 patients were included. Ammonia and lactate levels in the favourable outcome group (n=10) were significantly lower than those in poor outcome group (n=88) (p<0.05, respectively). On receiver operating characteristic analysis, the optimal cut-off value for predicting favourable outcome was determined as 170 μg dl(-1) of ammonia and 12.0 mmol l(-1) of lactate (area under the curve; 0.714 and 0.735, respectively). Logistic regression analysis identified ammonia (≤170 μg dl(-1)), therapeutic hypothermia and witnessed by emergency medical service personnel as independent predictors of favourable outcome. When both these biomarker levels were over threshold, positive predictive value (PPV) for poor outcome was calculated as 100%.

CONCLUSIONS

Blood ammonia and lactate levels on arrival are independent prognostic factors for OHCA. PPV with the combination of these biomarkers predicting poor outcome is high enough to be useful in clinical settings.

A prediction survival model for out-of-hospital cardiopulmonary resuscitations

AIMS

The aims of this study were to double check old (Resuscitation Predictor Scoring [RPS], Advanced Cardiac Life Support, and Early Prediction Score [EPS]) and form new (Serbian Quality of Life immediately [SR-QOLi], Serbian Quality of Life short-term [SR-QOLs], and Serbian Quality of Life long-term [SR-QOLl]) scores for survival prediction in out-of-hospital cardiopulmonary resuscitation (OHCPR) in Serbia.

METHODS

A prospective, 2-year, multicentric study was designed. By the means of the Utstein style, OHCPR performed and its outcome were followed. In every patient, immediate (i) (Return of Spontaneus Circulation [ROSC] >20 min), short-term (s) (to hospital discharge), and long-term [1] (1 year upon) survival after the OHCPR, under the application of RPS, ASCLS, and EPS models, was evaluated. We assessed the association between survival rate and individual predictors of OHCPR using RPS, ASCLS, and EPS: cardiopulmonary resuscitation (CPR) started (>4 or <4 minutes after out-of-hospital cardiac arrest), swallowing activity (present or not), the primary arrest mode (cardiac or respiratory), and initial pupillar photoreaction (present or absent). By the successive-logistic and linear-regression analysis method, the additional model of the type SR-QOL (SR-QOLi, SR-QOLs, and SR-QOLl) was created.

RESULTS

We found that bystander CPR, witnessed arrest, shockable rhythms, CPR within 4 minutes, pupillar photoreaction, and primary cardiac arrest mode were associated with improved survival. Cumulative survival upon OHCPR was 12.7% for immediate, 11.3% before patient's discharge, and 10% after 12 months. Applied on our sample, standard scores displayed satisfactory (RPS) and good (Advanced Cardiac Life Support and EPS) degree of survival prediction in OHCPR. In receiver operator characteristic (ROC) analysis, SR-QOLi (ROC = 0.833) and SR-QOLs (ROC = 0.882) were defined as a good models and SR-QOLl (ROC = 0.913) was defined as an excellent model for prediction of outpatient CPR outcomes.

CONCLUSION

In the course of the research, SR-QOL models were created for prediction of the immediate (SR-QOLi), short-term (SR-QOLs), and long-term (SR-QOLl) survival after the OHCPR, better predictions in our environment.

Validation of 3 termination of resuscitation criteria for good neurologic survival after out-of-hospital cardiac arrest

STUDY OBJECTIVE

Several termination of resuscitation criteria have been proposed to identify patients who will not survive to hospital discharge after out-of-hospital cardiac arrest. However, only 1 set has been derived to specifically predict survival to hospital discharge with good neurologic function. The objectives of this study were to externally validate the basic life support (BLS) termination of resuscitation, advanced life support (ALS) termination of resuscitation, and neurologic termination of resuscitation criteria and compare their abilities to predict survival to hospital discharge with good neurologic function after out-of-hospital cardiac arrest.

METHODS

This was a secondary analysis of the Denver Cardiac Arrest Registry. Consecutive adult nontraumatic cardiac arrest patients in Denver County from January 1, 2003, through December 31, 2004, were included in the study. The BLS termination of resuscitation, ALS termination of resuscitation, and neurologic termination of resuscitation criteria were applied to the cohort, and their predictive proportions and 95% confidence intervals (CIs) were calculated for each set of criteria.

RESULTS

Of the 715 patients included in this study, the median age was 65 years (interquartile range 52 to 78 years), and 69% were male patients. In addition, 223 (31%) had return of spontaneous circulation, 175 (24%) survived to hospital admission, 58 (8%) survived to hospital discharge, and 42 (6%) survived to hospital discharge with good neurologic function. The proportion of patients with good neurologic survival to hospital discharge correctly identified for continued resuscitation was 100% (95% CI 92% to 100%) for all 3 termination of resuscitation criteria. The proportion of patients with poor neurologic survival to hospital discharge or no survival to hospital discharge correctly identified as eligible for termination of resuscitation was 36% (95% CI 32% to 40%) with the BLS termination of resuscitation criteria, 25% (95% CI 22% to 29%) with the ALS termination of resuscitation criteria, and 6% (95% CI 4% to 8%) with the neurologic termination of resuscitation criteria. Use of the BLS termination of resuscitation criteria would have reduced transport of the largest number of patients.

CONCLUSION

All 3 termination of resuscitation criteria had equally high abilities to identify patients requiring continued resuscitation. The BLS termination of resuscitation criteria, however, had the best combined ability to predict good neurologic survival and poor neurologic survival or death. These findings and the relative simplicity of the BLS termination of resuscitation criteria support their use.

Ventricular fibrillation induced by transoesophageal cardiac pacing: A new model of cardiac arrest in rats

OBJECTIVE

To investigate whether transoesophageal cardiac pacing can induce ventricular fibrillation (VF) and how long the cardiac pacing has to be sustained to prevent the reversion of the VF induced.

METHODS

A pacing electrode was inserted orally into the oesophagus and high-frequency ventricular pacing was performed so as to elicit VF in 25 Sprague-Dawley rats. Incidences of VF and time of cardiac pacing were observed and recorded. Four minutes after onset of VF cardiopulmonary resuscitation (CPR) was initiated.

RESULTS

A short interval of high-frequency ventricular pacing caused an immediate drop of blood pressure, loss of pulse and increase of right atrial pressure in the same time frame. When the cardiac pacing was terminated, VF was elicited at least once or more than once in all of the 25 rats. However, the VF elicited by the burst stimulation could be defibrillated spontaneously. With the prolongation (120-180 s) of cardiac pacing, the incidence of defibrillation of VF decreased from 100 to 0%. VF persisted in 19 of 25 animals, developed into asystole in 5 of 25 animals and converted into pulseless electrical activity in 1 of 25 animals prior to CPR. Following CPR 22 of 25 animals were resuscitated.

CONCLUSIONS

Transoesophageal cardiac pacing can induce VF in rats. However, the cardiac pacing is required for at least 120-180 s to ensure that VF does not spontaneously convert. We can use the technique to establish a new and simpler rat cardiac arrest (CA) model, which may facilitate experimental investigation on CPR.

Monitoring intervention programmes for out-of-hospital cardiac arrest in a mixed urban and rural setting

BACKGROUND

Only a few data are available on the survival rate following out-of-hospital cardiac arrest in different Italian settings. We report an analysis of a 10-year experience in a mixed rural/urban setting, the main variables associated with survival, and the preliminary results of the implementation of an automated external defibrillator (AED) programme operated by lay volunteers on the effectiveness of the existing Emergency Medical Service (EMS).

METHODS

We report data from an observational cohort study on all adults, resuscitated from witnessed cardiac arrest between 1994 and 2004 in the district area of Forlì (Italy). The AED programme was introduced in 2002. Entry variables, time intervals and nodal events were tested according to Utstein recommendations. The predictors of favourable outcomes (Overall Performance Category 1-2) were identified by logistic regression analysis.

RESULTS

The witnessed cardiac arrest rate was 27/100,000 population per year (95% confidence interval, 18-38). The initial rhythm was shockable in 241/479 cases (50.3%). After resuscitation, 55 (11.5%) subjects had a favourable outcome at discharge and 38 (7.9%) at 1 year. Time-to-treatment was longer for EMS than for AED-equipped units (median, 8 min interquartile range, 6-10 (467 cases) versus 6 min interquartile range, 4-8 (13 cases); P<0.013), but the final results of the AED programme were poor, with only 1 subject saved/171,000 inhabitants in 2 years. Positive outcome predictors were male sex, younger age, shockable rhythms, low number of defibrillations, and no history of hypertension, diabetes, myocardial infarction or congestive heart failure.

CONCLUSIONS

Even in a mixed urban/rural setting, survival from out-of-hospital cardiac arrest is dependent on well-known predictors. In our setting, the number of cases saved by an AED programme is limited when accompanied by an efficient traditional EMS. The allocation of resources to an AED programme should be reconsidered in a mixed rural/urban setting.

Prediction rules for estimating neurologic outcome following out-of-hospital cardiac arrest

BACKGROUND

No valid model has been developed to predict survival following out-of-hospital cardiac arrest. The purpose of this study was to develop a prediction model for meaningful survival following out-of-hospital cardiac arrest using variables available during resuscitation.

METHODS

This was a retrospective cohort study. Consecutive adult cardiac arrest patients were studied between 1994 and 2001. Variables included age, sex, race/ethnicity, arrest location, whether the arrest was witnessed, initial rhythm, whether CPR was performed, patient downtime, paramedic response time, survival to hospital discharge, and Glasgow Coma Score (GCS) at hospital discharge. Classification and Regression Tree analysis was used to develop decision rules to predict meaningful survival, as defined by the patient's discharge GCS.

RESULTS

Of the 754 patients, 16 (2%) survived with a GCS > or =13, 15 (2%) survived with a GCS = 14, and 5 (0.7%) survived with a GCS = 15. The decision rule for survival with a GCS > or = 13 incorporated whether the arrest was witnessed and the patient's age, resulting in a negative predictive value (NPV) of 99.8%. The rule for survival with a GCS > or = 14 incorporated the initial arrest rhythm, whether the arrest was witnessed, and the patient's age, resulting in a NPV of 99.6%. The rule for survival with a GCS = 15 incorporated only the interval between collapse and the initiation of life support, resulting in a NPV of 99.8%.

CONCLUSIONS

This study reports decision rules for potential meaningful survival following out-of-hospital cardiac arrest with high NPVs for each. Future studies need to be performed to prospectively validate these models.

Is the ACLS score a valid prediction rule for survival after cardiac arrest?

The ACLS (advanced cardiac life support) Score was previously developed to predict survival from out-of-hospital cardiac arrest. Whether the arrest was witnessed, initial cardiac rhythm, performance of bystander cardiopulmonary resuscitation (CPR), and the response time of the paramedic unit were determined to be predictive of survival. However, the ACLS Score has not been validated in other emergency medical services systems.

OBJECTIVES

The purpose of this study was to externally validate the ACLS Score in one patient population.

METHODS

This was a retrospective cohort study performed at an urban county teaching hospital. The study population consisted of consecutive adult patients treated for out-of-hospital, nontraumatic cardiac arrest, and transported to the authors' institution between November 1, 1994, and September 30, 2001. Patient records for all cardiac arrests during the study period were reviewed. Study variables included witnessed arrest, initial arrest rhythm, bystander CPR, paramedic response time, and survival to hospital discharge. Predicted probability of survival to hospital discharge was calculated for each patient using the ACLS Score. The overall predicted and observed survival rates were compared using Flora's Z score. The Hosmer-Lemeshow test was used to evaluate the model's goodness-of-fit over a range of survival probabilities.

RESULTS

Of 754 cardiac arrest patients enrolled in the study period, 575 (76%) patients had documentation that allowed scoring using the ACLS Score. Twenty-five (4%) patients survived to hospital discharge. The predicted number of survivors based on the ACLS Score was 104 (18%), yielding a Flora's Z statistic of -4.46 (p < 0.0001). After categorizing predicted survival probabilities into four categories, the resulting Hosmer-Lemeshow statistic was 210 (p << 10(-6)). Both goodness-of-fit statistics demonstrated extremely poor fit of the model. A receiver operating characteristic (ROC) curve was created, yielding an area under the ROC curve of 0.33 (95% CI = 0.19 to 0.47), signifying extremely poor discrimination.

CONCLUSIONS

The previously published ACLS Score was not valid when applied to an external cohort of out-of-hospital cardiac arrest patients. An externally valid model is needed to predict survival to hospital discharge following out-of-hospital cardiac arrest.

Effect of extreme temperatures on drugs for prehospital ACLS

Advanced cardiac life support drugs undergo a wide range of temperature exposures in the prehospital setting. Although manufacturers place temperature restrictions for drug stability on their products, it has been shown that these limits are often exceeded in the prehospital environment. We exposed four different drugs to temperatures of -20 degrees C (-6 degrees F) and 70 degrees C (150 degrees F) and subsequently performed assays to determine their respective chemical stability compared with that of control samples. We determined that no significant difference in chemical structure occurred between the standard sample and the four drugs exposed to extreme temperatures (P > .05). This information has obvious implications in making further recommendations for drug storage. More work to determine bioactivity of temperature-exposed drugs may show results with implications for success in prehospital cardiac resuscitation.

The patient with an automatic implantable cardioverter defibrillator

Sudden cardiac death is the leading cause of death in the United States. A relatively new technology used to treat ventricular dysrhythmias that lead to sudden cardiac death is the automatic implantable cardioverter defibrillator. This device uses patches on the heart to deliver an energy current to convert lethal dysrhythmias. The nurse practitioner can expect to encounter these devices when seeing patients for a variety of diagnoses. This article will serve as a resource for clinical management and patient education.

Initiation of resuscitation in patients with prehospital bradyasystolic cardiac arrest in Helsinki

The factors influencing the decision to initiate resuscitation in prehospital cardiac arrest patients encountered in bradyasystole due to presumed heart disease were studied. For this purpose, the characteristics and circumstances of arrest of the patients encountered in asystole and electromechanical dissociation, seen by a physician-staffed prehospital emergency care unit in a tiered emergency medical system, were reviewed. During the study period, resuscitation was initiated in 83 bradyasytolic patients. The characteristics of these patients were compared with those of 72 patients in asystole or electromechanical dissociation declared dead on the scene without resuscitation. The presence of EMD was the most important factor influencing the decision to resuscitate (P less than 0.001), even if the arrest was unwitnessed, while the patient's age was of less importance. For the patients with a witnessed arrest, the delay before treatment was initiated also affected the decision. Successful resuscitation and survival of the patients was similar to earlier reports. The results provide guidelines in the decision making of initiation of resuscitation when developing our emergency care system into one with non-physicians as advanced life support providers.

Algorithm use in the treatment of pre-hospital ventricular fibrillation: an analysis of 160 cases

In a series of 160 consecutive patients with pre-hospital ventricular fibrillation, outcomes were improved if base-station personnel precisely followed the initial 7 steps of standard VF algorithms. This improvement reached statistical significance regarding survival to hospital discharge (17% vs. 6%, P less than 0.05), and reflected a very strong trend with regard to initial resuscitation and admission to hospital (31% vs. 18%, 0.05 less than P less than 0.10). These measures of outcome were even more strongly related to field time, such that patients treated in the field for less than 15 min did far better than patients treated longer. While concordance with algorithms did not independently diminish field time in this study, this probably reflects the fact that paramedics had to establish base hospital contact and receive orders from base personnel in all patients; thus it is probable that allowing paramedics to treat patients in VF, using precise protocols, without prior communication with a base hospital, would diminish field time, and this might lead to even further improvement in patient outcome.

Decision making to cease or to continue cardiopulmonary resuscitation (CPR). The Cerebral Resuscitation Study Group

CPR should be initiated in any patient who has a cardiac arrest. This might improve overall outcome but implies that CPR is started in patients without any virtual chance for long-term survival (LTS). The aim of this study is, by analysing retrospectively 2713 out-of-hospital cardiac arrests (CA), to identify indices which might be of help in the decision making to continue or to discontinue CPR. In an important number of unsuccessful CPR attempts ALS-time did not exceed 20 min. This occurred more frequently in subgroups where limited chances of LTS are expected on clinical grounds. The decision to cease CPR might have been based on other clinical and/or ethical parameters which were not recorded in the registry. This behavior results in a "self-fulfilling prophecy". A subset of patients with limited chances for LTS (0/405) can be identified: patients in electromechanical dissociation (EMD) or asystole on arrival of the mobile intensive care unit (MICU) team, without pupil reaction to light during CPR and with inefficient cardiac massage by the MICU (405/2713). Other patients in EMD or asystole without pupil reaction to light during CPR (1373/2713) but with efficient ECC should be resuscitated for more than 30 min, especially if the patient is gasping during CPR (LTS 27/1373). Patients in EMD or asystole on arrival of the MICU with pupil reaction to light during CPR (236/2713) should have an ALS-time of at least 45 min (LTS 42/236). Cardiac arrests in ventricular fibrillation (VF) (699/2713) should be resuscitated for at least 45 min, especially when gasping during CPR (LTS 119/699).

Out-of-hospital cardiac arrest: a six-year experience in a suburban-rural system

All out-of-hospital cardiac arrest advanced life support (ALS) trip sheets were collected from January 1980 through December 1985 for this suburban-rural system. Information was extracted according to a uniform reporting format. In our study, 18% of patients with early CPR (less than four minutes) and early ALS (less than ten minutes) survived to hospital discharge, compared with 7% with early CPR and late ALS, 6% with late CPR and early ALS, and 3% with both occurring late. Although 75% of the survivors had ventricular tachyarrhythmias as initial rhythms, bradyasystolic arrests were not uniformly lethal, even with long CPR and ALS times. This study supports the need for early CPR in the prehospital care of potential sudden-death victims. We recommend, with qualification, this reporting format to emergency medical services systems to describe their cardiac arrest experience.

Clinical prediction rules. Applications and methodological standards

The objective of clinical prediction rules is to reduce the uncertainty inherent in medical practice by defining how to use clinical findings to make predictions. Clinical prediction rules are derived from systematic clinical observations. They can help physicians identify patients who require diagnostic tests, treatment, or hospitalization. Before adopting a prediction rule, clinicians must evaluate its applicability to their patients. We describe methodological standards that can be used to decide whether a prediction rule is suitable for adoption in a clinician's practice. We applied these standards to 33 reports of prediction rules; 42 per cent of the reports contained an adequate description of the prediction rules, the patients, and the clinical setting. The misclassification rate of the rule was measured in only 34 per cent of reports, and the effects of the rule on patient care were described in only 6 per cent of reports. If the objectives of clinical prediction rules are to be fully achieved, authors and readers need to pay close attention to basic principles of study design.

Sensitivity, accuracy, and safety of an automatic external defibrillator

An automatic external defibrillator (AED) was used by paramedics to detect ventricular fibrillation and deliver countershocks in 39 people with out-of-hospital cardiac arrests. The AED identified and delivered at least 1 countershock to 13 of the 16 people in ventricular fibrillation (81% sensitivity). The AED responded correctly to all 21 of the non-ventricular-fibrillation rhythms (8 other electrical rhythms, 13 asystole) with no countershocks (100% specificity). In 2 patients the rhythm could not be assessed. The device caused no injuries to patients or personnel. The performance of the AED was also analysed by considering each 15 s segment of ventricular fibrillation as a separate challenge; the device delivered a countershock in 19 of 29 such segments (66%).

External non-invasive cardiac pacing: a comparative hemodynamic study of two techniques with conventional endocardial pacing

Out-of-hospital therapy for cardiac arrest due to bradyarrhythmias or asystole is pharmacologic and the outcome is uniformly dismal. Optimal therapy for the latter disturbances may be artificial cardiac pacing, but conventional invasive pacing techniques are not employed or are of limited value in the out-of-hospital and emergency department setting. This investigation compared the hemodynamic effects of two techniques of non-invasive external pacing: 1) transcutaneous transthoracic pacing (TTP) and 2) tongue-to-epigastrium pacing (TEP), with conventional transvenous right ventricular endocardial pacing (RVEP) in a closed-chest, chronic heart block canine model. All techniques significantly increased (p less than .001) cardiac output (CO). However, CO and mean arterial pressure (MAP) measured during external pacing with either non-invasive technique were significantly greater than that during RVEP (p less than .001). TEP produced vigorous skeletal muscle stimulation and, in the canine model, it produced contraction resulting in impaired ventilation, hypoxemia, and a decrease in systemic vascular resistance. TTP in this model resulted in improved MAP and CO when compared with control and RVEP values and did not affect arterial or mixed venous blood gas values. Thus, this study demonstrates that noninvasive TTP is comparable to RVEP in its hemodynamic effects. TTP may offer definitive non-invasive therapy for a subset of victims of out-of-hospital cardiac arrest.

Resuscitation time in ventricular fibrillation--a prognostic indicator

Length of resuscitation in prehospital ventricular fibrillation patients was studied to define its relationship to survival. Five hundred sixty-five patients presenting with the initial rhythm of ventricular fibrillation to the Milwaukee County Paramedic System between January 1978 and April 1982 were resuscitated successfully. Pediatric patients and patients with trauma, poisoning, and drowning were excluded. Of the 565 resuscitated patients, 262 (46%) were discharged alive and 303 (54%) died during hospitalization. For all 565 patients the resuscitation time and times from arrival of paramedics until the first sustained pulse were plotted against survival to define a curve. The curve demonstrated rapidly declining survival rates for resuscitation time up to 20 minutes; thereafter, survival declined more gradually with respect to resuscitation time. The mean resuscitation time for those eventually discharged alive was 12.6 minutes, which was statistically shorter (P less than .0001) than the mean resuscitation time of 23.9 minutes for those who eventually died. The overall survival curve of witnessed arrest patients was not statistically different from that of unwitnessed patients. The survival curve of those patients receiving bystander cardiopulmonary resuscitation (CPR) was similar to the curve of those who received no CPR. We conclude that resuscitation time is a heretofore undefined significant predictor of survival of resuscitated prehospital ventricular fibrillation patients.