Experience with the use of automated external defibrillators in out of hospital cardiac arrest

Sensitivity and specificity of two different automated external defibrillators

AIM

The aim was to investigate the clinical performance of two different types of automated external defibrillators (AEDs).

METHODS

Three investigators reviewed 2938 rhythm analyses performed by AEDs in 240 consecutive patients (median age 72, q1-q3=62-83) who had suffered cardiac arrest between January 2011 and March 2015. Two different AEDs were used (AED A n=105, AED B n=135) in-hospital (n=91) and out-of-hospital (n=149).

RESULTS

Among 194 shockable rhythms, 17 (8.8%) were not recognized by AED A, while AED B recognized 100% (n=135) of shockable episodes (sensitivity 91.2 vs 100%, p<0.01). In AED A, 8 (47.1%) of these episodes were judged to be algorithm errors while 9 (52.9%) were caused by external artifacts. Among 1039 non-shockable rhythms, AED A recommended shock in 11 (1.0%), while AED B recommended shock in 63 (4.1%) of 1523 episodes (specificity 98.9 vs 95.9, p<0.001). In AED A, 2 (18.2%) of these episodes were judged to be algorithm errors (AED B, n=40, 63.5%), while 9 (81.8%) were caused by external artifacts (AED B, n=23, 36.5%).

CONCLUSIONS

There were significant differences in sensitivity and specificity between the two different AEDs. A higher sensitivity of AED B was associated with a lower specificity while a higher specificity of AED A was associated with a lower sensitivity. AED manufacturers should work to improve the algorithms. In addition, AED use should always be reviewed with a routine for giving feedback, and medical personnel should be aware of the specific strengths and shortcomings of the device they are using.

Reducing ambulance response times using geospatial-time analysis of ambulance deployment

OBJECTIVES

This study aimed to determine if a deployment strategy based on geospatial-time analysis is able to reduce ambulance response times for out-of-hospital cardiac arrests (OOHCA) in an urban emergency medical services (EMS) system.

METHODS

An observational prospective study examining geographic locations of all OOHCA in Singapore was conducted. Locations of cardiac arrests were spot-mapped using a geographic information system (GIS). A progressive strategy of satellite ambulance deployment was implemented, increasing ambulance bases from 17 to 32 locations. Variation in ambulance deployment according to demand, based on time of day, was also implemented. The total number of ambulances and crews remained constant over the study period. The main outcome measure was ambulance response times.

RESULTS

From October 1, 2001, to October 14, 2004, a total of 2,428 OOHCA patients were enrolled into the study. Mean ± SD age for arrests was 60.6 ± 19.3 years with 68.0% male. The overall return of spontaneous circulation (ROSC) rate was 17.2% and survival to discharge rate was 1.6%. Response time decreased significantly as the number of fire stations/fire posts increased (Pearson χ(2) = 108.70, df = 48, p < 0.001). Response times for OOHCA decreased from a monthly median of 10.1 minutes at the beginning to 7.1 minutes at the end of the study. Similarly, the proportion of cases with response times < 8 minutes increased from 22.3% to 47.3% and < 11 minutes from 57.6% to 77.5% at the end of the study.

CONCLUSIONS

A simple, relatively low-cost ambulance deployment strategy was associated with significantly reduced response times for OOHCA. Geospatial-time analysis can be a useful tool for EMS providers.

Knowledge and attitudes towards cardiopulmonary resuscitation and defibrillation amongst Asian primary health care physicians

Objective

To assess the knowledge and attitudes of local primary health care physicians in relation to cardiopulmonary resuscitation (CPR) and defibrillation.

Methods

We conducted a survey on general practitioners in Singapore by using a self-administered questionnaire that comprised 29 questions.

Results

The response rate was 80%, with 60 of 75 physicians completing the questionnaire. The average age of the respondents was 52 years. Sixty percent of them reported that they knew how to operate an automated external defibrillator (AED), and 38% had attended AED training. Only 36% were willing to perform mouth-to-mouth ventilation during CPR, and 53% preferred chest compression-only resuscitation (CCR) to standard CPR. We found those aged <50 years were more likely to be trained in basic cardiac life support (BCLS) (P < 0.001) and advanced cardiac life support (P = 0.005) or to have ever attended to a patient with cardiac arrest (P = 0.007). Female physicians tended to agree that all clinics should have AEDs (P = 0.005) and support legislation to make AEDs compulsory in clinics (P < 0.001). We also found that a large proportion of physicians who were trained in BCLS (P = 0.006) were willing to perform mouth-to-mouth ventilation.

Conclusion

Most local primary care physicians realize the importance of defibrillation, and the majority prefer CCR to standard CPR.

Geographic-Time Distribution of Ambulance Calls in Singapore: Utility of Geographic Information System in Ambulance Deployment (CARE 3)

Introduction: Pre-hospital ambulance calls are not random events, but occur in patterns and trends that are related to movement patterns of people, as well as the geographical epidemiology of the population. This study describes the geographic-time epidemiology of ambulance calls in a large urban city and conducts a time demand analysis. This will facilitate a Systems Status Plan for the deployment of ambulances based on the most cost-effective deployment strategy. Materials and Methods: An observational prospective study looking at the geographic-time epidemiology of all ambulance calls in Singapore. Locations of ambulance calls were spot-mapped using Geographic Information Systems (GIS) technology. Ambulance response times were mapped and a demand analysis conducted by postal districts. Results: Between 1 January 2006 and 31 May 2006, 31,896 patients were enrolled into the study. Mean age of patients was 51.6 years (S.D. 23.0) with 60.0% male. Race distribution was 62.5% Chinese, 19.4% Malay, 12.9% Indian and 5.2% others. Trauma consisted 31.2% of calls and medical 68.8%. 9.7% of cases were priority 1 (most severe) and 70.1% priority 2 (moderate severity). Mean call receipt to arrival at scene was 8.0 min (S.D. 4.8). Call volumes in the day were almost twice those at night, with the most calls on Mondays. We found a definite geographical distribution pattern with heavier call volumes in the suburban town centres in the Eastern and Southern part of the country. We characterised the top 35 districts with the highest call volumes by time periods, which will form the basis for ambulance deployment plans. Conclusion: We found a definite geographical distribution pattern of ambulance calls. This study demonstrates the utility of GIS with despatch demand analysis and has implications for maximising the effectiveness of ambulance deployment. Keywords: Demand analysis, Despatch, Emergency Medical Services

Out-of-hospital cardiac arrests occurring in primary health care facilities in Singapore

OBJECTIVES

To study out-of-hospital cardiac arrests (OHCA) occurring in primary healthcare facilities (HCF) in Singapore and to compare these with arrests occurring in the community.

METHODS

This prospective observational study was part of the Cardiac Arrest and Resuscitation Epidemiology (CARE) project. Included were all patients with OHCA occurring in HCF. Patient characteristics, cardiac arrest circumstances, EMS response and outcomes were recorded according to the Utstein style.

RESULTS

From 1 October 2001 to 14 October 2004, the data from 2428 subjects were received of which 138 patients were OHCA occurring in HCF. This is an incidence of 1.12/100,000 population per year and constituted 6.0% of all OHCA. Arrest occurring in HCF were more likely to be witnessed (p<0.01), or have bystander CPR (p<0.01). The HCF group was also more likely to receive CPR with both compression and ventilation (p<0.01) and have a non-trauma cause of arrest (p=0.03). HCF arrests also had a shorter collapse to call (EMS number) than the non-HCF group (HCF 1.54min versus non-HCF 5.36min, p=0.01). However, no HCF patient received defibrillation prior to EMS arrival. HCF patients were more likely to have return of spontaneous circulation at any time (p=0.05), survival to hospital admission (p<0.01) and survival to discharge (p<0.01) compared to non-HCF patients.

CONCLUSION

This study suggests that primary health care providers do have an important role locally in managing out-of-hospital cardiac arrest. We propose an initiative to encourage early defibrillation by primary health care providers.

Teaching basic life support to nurses

BACKGROUND AND OBJECTIVE

Every member of healthcare personnel should be able to perform basic life support including defibrillation (CPR-D). The biggest cost of implementation is training and these costs need to be reduced. The purpose of this randomized study was to evaluate the applicability of distance learning as a method to teach CPR-D.

METHODS

Nurses (n = 56) working in a geriatric hospital were randomized into three groups. The first group was given the Internet-based CPR-D course and the second was given a traditional, small-group CPR-D course. A third group without specific training in CPR-D served as a control group. An objective structured clinical examination (OSCE) was performed 2 weeks after the courses with a manikin patient having a cardiac arrest.

RESULTS

The median score of all participants was 31/49 (range 21-38). The reliability of the checklist was adequate (Cronbach alpha 0.77). Nurses receiving traditional CPR-D performed better than those receiving the Internet-based course (median score 34 vs. 28, P < 0.05) and the control group (median score 34 vs. 26, P < 0.0001). Nurses receiving Internet-based course performed similarly as the control group (median score 28 vs. 26, ns).

CONCLUSIONS

Distance learning cannot substitute for traditional small-group learning.

Resuscitation of out-of-hospital cardiac arrest by Asian primary health-care physicians

AIM

To assess the experience, knowledge and attitudes of local primary health-care doctors towards resuscitation in out-of-hospital cardiac arrest.

METHODS

We conducted a survey of general practitioners (GPs) working in both private and public sectors. The survey consisted of 29 questions and was self-administered.

RESULTS

Response rate was 78.8% with 66 public practice doctors and 23 from private practice. Average ages were 39.8 years (private) and 35.5 years (public) with mean years of practice being 15.1 (private) and 11.4 (public). 47.8% of private and 69.7% of public doctors had been advanced cardiac life-support (ACLS) trained. 13.0% of private and 10.6% of public had witnessed a cardiac arrest in their clinics in the past year. 92.3% of public and 26.1% of private doctors had defibrillators in their clinics (P < 0.01, OR = 34.0, 95% CI = 9.2-125.2). 83.3% (public) versus 52.2% (private) (P < 0.01 OR = 4.6, 95% CI = 1.6-13.0) agreed that all clinics should have defibrillators. 59.1% (public) and 34.8% (private) would support legislation for defibrillators in clinics (P = 0.04, OR = 2.7, 95% CI = 1.01-7.3). Reasons given for not buying defibrillators included 'too expensive' (70.6%) and 'unsure how to use' (5.9%). 66.0% would consider buying a defibrillator if the cost was less than Singapore 3000 dollars (1400 Euro). 69.6% (private) and 63.6% (public) were interested in participating in a GP defibrillation project.

CONCLUSION

Primary care physicians do see themselves as having an important role in resuscitation. We propose a local initiative to equip, educate and encourage defibrillation by GPs in our community.

Effect of digital cellular phones on tachyarrhythmia analysis of automated external defibrillators

OBJECTIVES

Emergency services personnel, family members, laypersons or patients often carry and use mobile phones on sites of emergencies. As there are reported effects on implanted pacemakers and cardioverter defibrillators, the influence of digital cellular phones on automated external defibrillators was studied.

METHODS

Twelve automated external defibrillator models were bench tested for their correct decision to or not to advise a shock, while being exposed to electromagnetic interference from a handheld cellular phone with 2 W or a portable cellular phone with 8 W transmitting power. The phones were programmed by a special subscriber identity module card to maximum output power with a carrier frequency of 906.2 MHz. The tests were conducted with a burst frequency of 217 Hz in speech mode and 2-8 Hz in discontinuous transmitting exchange mode. The sensitivity and specificity of electrocardiogram analysis systems were tested, with shockable and non-shockable rhythms provided by an electrocardiogram simulator and on two human subjects with normal sinus rhythm.

RESULTS

A total of 8640 tests were recorded, each automated external defibrillator was tested a total of 720 times. The automated external defibrillators demonstrated a sensitivity of 100% and a specificity of 100%, representing a positive likelihood ratio of 8641 and a negative likelihood ratio of 0.000. In this setting all automated external defibrillators analysed correctly even under worst-case testing conditions, and performed excellently without any single failure. In some devices, voice prompts were distorted beyond comprehension, as the coil of the automated external defibrillator speaker received the pulsed signals.

CONCLUSION

Shock advisory systems of automated external defibrillators are not susceptible to electromagnetic interference of 900 MHz cellular phones. Voice prompts, however, could be distorted by the operation of nearby digital mobile phones. During automated external defibrillator training this issue needs to be addressed.

Susceptibility of automated external defibrillators to train overhead lines and metro third rails

INTRODUCTION

Immediate accessibility to automated external defibrillators (AED) is recommended for highly frequented public areas. In train terminals and metro stations electromagnetic interference (EMI) is present. In preparation for a public access defibrillation (PAD) programme in this environment possible effects on AED safety and accuracy were studied.

METHODS

In typical public transportation settings 11 different AED models were bench tested for their sensitivity and specificity of ECG analysis with shockable and nonshockable rhythms provided by an ECG simulator. The devices were exposed to the electromagnetic interference of a rail system operating with 15 kV alternating current (ac) with a frequency of 16 2/3 Hz and a subway system powered with 750 V direct current (dc). AED cables were setup parallel and perpendicular to the tracks, the tests were carried out at 3 m distance from the rails in an empty station and with incoming trains.

RESULTS

A total of 5280 tests were recorded, each device was tested a total of 480 times. Fifteen kilovolts 16 2/3 Hz ac interfered more than 750 V dc with the tachyarrhythmia detection systems (P < 0.0001). An AED setup with electrode cables perpendicular to track and power line reduced interference (P < 0.0001), while incoming trains had no significant effect on ECG analysis (P = 0.19). Depending on the AED model, sensitivity ranged from 60 to 100% and specificity from 54 to 100%, representing a positive likelihood-ratio from 1.3 to 241 and a negative likelihood-ratio from 0.7 to 0.0. In the public transportation setting tested, four AED models were unsuitable for automated defibrillation as these devices demonstrated an unacceptable performance in respect of accuracy and safety. In the train setting two devices performed with an accuracy of 57 and 65%. One AED recommended shocks for sinus rhythm at normal frequency. In the metro setting one AED did not advise shocks for ventricular tachycardia.

CONCLUSION

Shock advisory systems of some AED models are susceptible to electromagnetic interference, especially in terminals with 15 kV 16 2/3 Hz ac power supplies. Interference is minimized, if patient position is parallel and electrode cables are perpendicular to overhead line. The choice of AED model for train or metro stations depends on its lack of susceptibility to typical electromagnetic interference.

Does attendance at an immediate life support course influence nurses’ skill deployment during cardiac arrest?

OBJECTIVE

To determine if attendance at a Resuscitation Council (UK) immediate life support (ILS) course influenced the skill deployment of nurses at a subsequent cardiac arrests.

METHODS

Data from all cardiac arrests occurring in two 12-month periods (before and 12 months after ILS course implementation) were collected. Semi-structured interviews were conducted with a sample of nurses who had completed ILS training within the past 12 months and who had subsequently attended a cardiac arrest.

RESULTS

There were 103 patients defibrillated (after ILS implementation). Only one ward nurse defibrillated prior to the arrival of the crash team. There were 99 laryngeal mask airways (LMAs) inserted during the same period. Ward nurses performed two of these, one with the supervision of the resuscitation officer (RO). The interviews revealed that although many nurses felt confident after the course most felt that as time passed their confidence reduced to such a degree that they would not use their skills without supervision. Attendance at cardiac arrest soon after the course appeared to be a key element in maintaining confidence levels.

CONCLUSION

ILS training alone may be insufficient to increase deployment of these skills by nurses who are not cardiac arrest team members. A more supportive approach, involving individual coaching of these individuals may need to be considered.

Public access defibrillation

Very early defibrillation, within the first few minutes of VF cardiac arrest, results in significantly improved survival rates [1,10-12,34]. Most EMS systems cannot consistently provide defibrillation within the first few minutes following cardiac arrest. Defibrillation within the first few minutes following collapse is potentially achievable through the use of AEDs and PAD [9-14,62]. The delivery of defibrillation with AEDs has been made more efficient through the use of impedance-compensated defibrillation, larger pad sizes, and biphasic waveforms [34]. The technology is simple and easy to use. Preliminary cost-effectiveness analysis indicates that PAD and first-responder defibrillation are economically as attractive as other interventions in cardiac arrest [44]. Effective PAD requires significant investment in time, energy, informed planning, and rigorous quality improvement; however, the benefits are enormous. Reported VF survival rates can approach 50% or higher [11,12,62]. PAD provides the potential opportunity to transform cardiac arrest into a survivable event for most victims by making the community the ultimate coronary care unit.

Automated external defibrillation as part BLS: implications for education and practice

The latest Adult Basic Life Support (BLS) guidelines support the inclusion of the use of the automated external defibrillator (AED), as part of basic life support (BLS). Emphasis on the provision of early defibrillation as part of BLS acknowledges the importance of this manoeuvre in the successful termination of ventricular fibrillation. The ramifications of such changes for both first responders and organisations implementing the guidelines should not be underestimated. Issues relating to resourcing, content and duration of training and retraining, auditing and evaluation require further exploration. To consider these issues now seems particularly pertinent, given the recent launch of the UK Government's paper on public health, 'Saving Lives-Our Healthier Nation' which seeks to deploy AEDs in busy public places for use by trained members of the lay public. Additionally, defibrillation has been identified as one of the key competencies that all trained nurses and other health care providers should be able to undertake. This paper will consider the background to the current guideline changes, analyse the wider implications of translating the recommendations into practice, and offer possible solutions to address the issues raised. Whilst the analysis is particularly pertinent to the United Kingdom, many of the issues raised have international importance.

Do nurses and physiotherapists require training to use an automated external defibrillator?

Healthcare staff with the duty to perform CPR should also be capable of using an automated external defibrillator (AED). We investigate whether nurses and physiotherapists can use an AED without prior training. Subjects were tested on a manikin during a cardiac arrest scenario. All 15 untrained subjects could deliver a shock with an AED in 68.8+/-29.2 s (time+/-S.D., range, 40-169 s). Most failed to position the pads correctly (53%) or follow correct safety procedures (67%). After a standardised training session, the time to deliver a shock improved significantly to 48.5+/-5.5 s (range, 41-61 s, P<0.01) and all subjects placed the pads correctly and followed a safe defibrillation procedure. This study shows that nurses and physiotherapists, with no previous AED training, can deliver a shock with an AED. Training improves speed of shock delivery, correct pad placement and safety. This study suggests that it is feasible to train healthcare professionals to use an AED with relatively little training. This should allow rapid deployment of AEDs in those areas of the hospital where cardiac arrests are infrequent and staff do not have rhythm recognition skills.

Bystander cardiopulmonary resuscitation in prehospital cardiac arrest patients in Singapore

INTRODUCTION

The chain of survival emphasizes the importance of the four links associated with survival after cardiac arrest (CA). The involvement of laypersons has been increasing over the years. They have been contributing toward "early access," "early cardiopulmonary resuscitation" (CPR), and, of late, "early defibrillation," with the advent of automated external defibrillators (AEDs). Bystander CPR rates are difficult to assess due to the lack of formal documentation.

OBJECTIVE

To assess the bystander CPR rate for CA patients brought to the emergency department (ED) of an urban, tertiary teaching hospital in the central part of Singapore, over a period of 12 months.

METHODS

This was a retrospective cohort study carried out from May 1, 1999, to April 30, 2000. "Bystander CPR" refers to an attempt to perform basic CPR by someone who is not part of an organized emergency response system. In general, this refers to the person who witnesses the arrest.

RESULTS

There were 155 adult patients with CA who satisfied the inclusion criteria over the 12-month period. The median age was 62.1 +/- 6.4 years, and the majority of patients were brought in by ambulances (126, or 81.3%). There were 142 (91.6%) non-trauma and 13 (8.4%) trauma CAs. Most patients had the CA at home (96, or 61.9%), and the most common initial rhythm at presentation upon the arrival of the paramedics was ventricular fibrillation (VF) (50 patients, or 32.2%). The bystander CPR rate was 20.0% (i.e., 31 of the 155 patients). A total of 32 (20.6%) patients had return of spontaneous circulation (ROSC, defined as the return of a palpable pulse) and 31 (96.9%, or 31/32) of them were those who had some form of bystander CPR performed. Of these 31 who had bystander CPR, four (12.9%) were subsequently admitted to the intensive care unit (ICU), while among those who did not have bystander CPR, all had death pronounced in the ED. Of the four patients admitted to the ICU, three (3 of 4, or 75.0%; or 3 of 155 CA patients, or 1.9%) were subsequently discharged alive from the hospital.

CONCLUSION

The bystander CPR rate for prehospital CA was 20.0%. About 12.9% (4 patients) of those who had bystander CPR were admitted to the ICU, compared with none from the group that did not receive any form of bystander CPR. Three patients (1.9% of all prehospital CAs) were discharged alive from the hospital.

Automatic external defibrillators: changing the way we manage ventricular fibrillation

OBJECTIVE

To discuss recent developments in automatic defibrillation and to review the evidence that first-responders equipped with automatic external defibrillators (AEDs) improve survival from out-of-hospital cardiac arrest.

DATA SOURCES

MEDLINE search from 1966 to 1999 (articles in English only) and examination of bibliographies.

STUDY SELECTION

Published studies of out-of-hospital cardiac arrest and first-responders equipped with AEDs. Studies had to have a control group and to report survival to hospital discharge from ventricular fibrillation (VF).

DATA EXTRACTION

Six studies met the selection criteria (two prospective randomised trials, two prospective controlled trials, and one cohort study and one retrospective study, both with historical controls).

DATA SYNTHESIS

A random effects meta-analysis of odds ratios for survival from VF.

CONCLUSIONS

Meta-analysis suggests that equipping first-responders with AEDs increases the probability of survival to hospital discharge after out-of-hospital cardiac arrest (odds ratio, 1.74; 95% CI, 1.27-2.38; P < 0.001). However, most of the studies lacked sufficient power to draw definitive conclusions. Until the impact of wide deployment of AEDs is fully understood, first-responder defibrillation in Australia should only occur as part of coordinated multicentre research studies.