Two-tiered Emergency Medical Services System Research Articles

A stochastic approach for designing two-tiered emergency medical service systems

Emergency medical services (EMS) systems provide out-of-hospital acute medical care and transportation to the appropriate health care provider to patients with illnesses and injuries. The objective of EMS systems is to satisfy demand requests by providing timely first care medical assistance to patients at the incident scene. This paper aims at designing a robust two-tiered EMS system while accounting for the inherent uncertainty of the demand. A two-stage stochastic programming location-allocation model is proposed to simultaneously determine the location of ambulance stations, the number and the type of ambulances to be deployed, and the demand areas served by each station. This problem is then solved efficiently using the sampling average approximation algorithm. Computational experiments highlight the performance of the proposed solution approach and its practical applicability.

Impact of Building Height and Volume on Cardiac Arrest Response Time

Emergency medical services (EMS) care may be delayed when out-of-hospital cardiac arrest (OHCA) occurs in tall or large buildings. We hypothesized that larger building height and volume were related to a longer curb-to-defibrillator activation interval. We retrospectively evaluated 3,065 EMS responses to OHCA in a large city between 2003–13 that occurred indoors, prior to EMS arrival, and without prior deployment of a defibrillator. The two-tiered EMS system uses automated external defibrillator-equipped basic life support firefighters followed by paramedics dispatched from a single call center. We calculated three time intervals obtained from the computerized dispatch report and time-synchronized defibrillators: initial 911 call to address curb arrival by first unit (call-to-curb), curb arrival to defibrillator power on (curb-to-defib on), and the combined call-to-defib on interval. Building height and surface area were measured with a validated program based on aerial photography. Buildings were categorized by height as short (<25 ft), medium (26–64 ft) and tall (>64 ft). Volume was categorized as small (<60,000 ft3), midsize (60,000–1,202,600 ft3) and large (>1,202,600 ft3). Intervals were compared using the two-tailed Mann-Whitney test. EMS responded to 1,673 OHCA events in short, 1,134 in medium, and 258 in tall buildings. There was a 1.14 minute increase in median curb-to-defib on interval from 1.97 in short to 3.11 minutes in tall buildings (p < 0.01). Taller buildings, however, had a shorter call-to-curb interval (4.73 for short vs 3.96 minutes for tall, p < 0.01), such that the difference in call-to-defib on interval was only 0.27 minutes: 6.87 for short and 7.14 for tall buildings. A similar relationship was observed for small-volume compared to large-volume building: longer curb-to-AED (1.90 vs. 3.01 minutes, p < 0.01), but shorter call-to-curb (4.87 vs. 4.05, p < 0.01); the difference in call-to-defib on was 0.18 minutes. Both taller and larger-volume buildings had longer curb-to-AED intervals but shorter 911 call-to-curb arrival intervals. As a consequence, building height and volume had a modest overall relationship with interval from call to defibrillator application. These results do not support the hypothesis that either taller or larger-volume buildings need cause poorer outcomes in urban environments.

The Impact of Heat Waves on Transport Volumes in an Urban Emergency Medical Services System: A Retrospective Review

Heat waves pose a serious public health risk to particular patient populations, especially in urban areas. Emergency Medical Services (EMS) in many urban areas constitute the first line of regional preparation and response to major heat wave events; however, little is known on heat wave operational impact to the EMS system, such as call volume or demand. To examine the effect of heat wave periods on overall urban EMS system call volume and transport volume as well as the nature of the call types. Retrospective review of all emergency medical calls to an urban, two-tiered EMS system performed over a 5-year period from 2006-2010. Heat wave days (HWD) defined as two or more consecutive days of hot weather >32.2°C (90°F) were compared with similar non-heat wave days (nHWD) of the previous year to also include two calendar days prior to and after the heat wave. National Weather Service (NWS) temperature data, daily EMS call volume data, and call type codes were collected and underwent descriptive analysis. Thirty-one HWD were identified and compared with 93 nHWD. The mean maximum temperature for HWD was 34°C (93.2°F) compared with 25.3°C (77.6°F) for nHWD (P < .001). Average daily medical emergency calls (318.4 vs 296.3, P < .001) and actual patients transported per day (247.5 vs 198.3, P < .001) were significantly higher during HWD. There was no difference in daily medical emergency call volume or EMS transports between weekdays or weekend days. No significant differences on various call types were observed between HWD and nHWD except for "heat" related calls (7.7 vs 0.5, P < .001). Emergency Medical Services call volumes were significantly increased during heat waves, however there was minimal change in the types of calls received.

Out-of-hospital cardiac arrest in denver, colorado: epidemiology and outcomes.

The annual incidence of out-of-hospital cardiac arrest (OOHCA) in the United States is approximately 6 per 10,000 population and survival remains low. Relatively little is known about the performance characteristics of a two-tiered emergency medical services (EMS) system split between fire-based basic life support (BLS) dispersed from fixed locations and hospital-based advanced life support (ALS) dispersed from nonfixed locations. The objectives of this study were to describe the incidence of OOHCA in Denver, Colorado, and to define the prevalence of survival with good neurologic function in the context of this particular EMS system. This was a retrospective cohort study using standardized abstraction methodology. A two-tiered hospital-based EMS system for the County of Denver and 10 receiving hospitals were studied. Consecutive adult patients who experienced nontraumatic OOHCA from January 1, 2003, through December 31, 2004, were enrolled. Demographic, prehospital arrest characteristics, treatment data, and survival data using the Utstein template were collected. Good neurologic survival was defined by a Cerebral Performance Categories (CPC) score of 1 or 2. During the study period, 1,985 arrests occurred. Of these, 715 (36%) had attempted resuscitation by paramedics and constitute our study sample. The median age was 65 years (interquartile range = 52-78 years), 69% were male, 41% had witnessed arrest, 25% had bystander cardiopulmonary resuscitation (CPR) performed, and 30% had ventricular fibrillation (VF) or pulseless ventricular tachycardia (VT) as their initial rhythm. Of the 715 patients, 545 (76%) were transported to a hospital, 223 (31%) had return of spontaneous circulation (ROSC), 175 (25%) survived to hospital admission, 58 (8%) survived to hospital discharge, and 42 (6%, 95% confidence interval [CI] = 4% to 8%) had a good neurologic outcome. Out-of-hospital cardiac arrest survival in Denver, Colorado, is similar to that of other United States communities. This finding provides the basis for future epidemiologic and health services research in the out-of-hospital and ED settings in our community.

Effect of Emergency Medical Technician–Placed Combitubes on Outcomes After Out-of-Hospital Cardiopulmonary Arrest

Objective. While emergency medical technicians–basic (EMT-Bs) in select emergency medical services (EMS) agencies use the Esophageal Tracheal Combitube (ETC) for the airway management of out-of-hospital cardiopulmonary arrests, the effect of this intervention on patient outcomes is not known. We compared the associations between initial EMT ETC placement and initial paramedic endotracheal intubation (ETI) on patient survival after out-of-hospital cardiopulmonary arrest. Methods. We utilized data on adult (age > 21 years), out-of-hospital cardiopulmonary arrests from a large, urban, county-based, two-tiered (EMT-B first responder, paramedic ambulance) EMS system for the years 1997–2005. EMT-Bs placed an ETC on cardiopulmonary arrest patients if they arrived before paramedics. Paramedics managed the airway primarily using ETI. We included cases in which rescuers accomplished ETC insertion or ETI on the first airway effort. We excluded cases in which an invasive airway was not used. We excluded cases with failed airway insertion or multiple airway efforts. We examined return of spontaneous circulation (ROSC), survival to hospital admission, and survival to hospital discharge. We evaluated the association between outcome and airway type (ETC vs. ETI) using multivariate logistic regression, adjusting for age, gender, bystander-witnessed arrest, bystander cardiopulmonary resuscitation (CPR), bystander automated external defibrillator (AED) use, initial electrocardiogram (ECG) rhythm, and response time. Results. Of 7,010 adult cardiopulmonary arrests, we excluded 747 cases without airway insertion and 441 cases involving failed or multiple airway efforts. Of the remaining 5,822 cardiopulmonary arrests, 4,335 (74%) received initial paramedic ETI and 1,437 (26%) received initial EMT-B ETC insertion. Compared with paramedic ETI, EMT-B ETC placement was not associated with ROSC (adjusted odds ratio [OR] 0.93; 95% confidence interval [CI]: 0.82–1.05), survival to hospital admission (adjusted OR 0.99; 95% CI: 0.86–1.13), or survival to hospital discharge (adjusted OR 1.02; 95% CI: 0.79–1.30). Conclusions. Compared with initial paramedic ETI, initial EMT-B ETC placement was not associated with patient survival after out-of-hospital cardiac arrest.

Ventricular Fibrillation in Pediatric Cardiac Arrest

After activating 9-1-1 for out-of-hospital cardiac arrest (CA), guidelines for children 1 year and older have evolved to include immediate automated external defibrillator (AED) use for witnessed arrest, and two minutes of cardiopulmonary resuscitation (CPR) followed by AED use for unwitnessed arrests. The best approach to resuscitation in a two-tiered emergency medical services (EMS) system depends in part on how likely the patient is to present with ventricular fibrillation (VF). Therefore, the authors evaluated the frequency of VF with respect to age and other characteristics to further elucidate the role of the AED among pediatric CAs. The investigation was a retrospective cohort study of EMS-treated, nontraumatic, out-of-hospital CA among persons aged 1-18 years in King County, Washington, between April 1, 1976, and December 31, 2003. The primary goal was to identify the proportion of patients presenting to EMS in VF, according to age. The association between other characteristics and the likelihood of VF was also evaluated. Finally, hospital survival according to cardiac rhythm at EMS arrival was evaluated. Ventricular fibrillation was the presenting rhythm in 17.6% of cases (48/272). The proportion presenting with VF was 7.6% (10/131) among children aged 1-7 years and 27.0% (38/141) among children aged 8-18 years (p < 0.001). In multivariable models, VF was independently associated with age 8 years and older compared with 1-7 years (odds ratio, 3.19; 95% confidence interval [CI] = 1.46 to 6.97), witnessed arrest (odds ratio, 3.33; 95% CI = 1.63 to 6.82), and cardiac etiology (odds ratio, 2.89; 95% CI = 1.32 to 6.34). Survival was 31.3% (15/48) for VF and 10.7% (24/224) for nonshockable rhythm CAs. The proportion of children aged younger than 8 years presenting with VF is low compared with older children. The greatest increase in VF proportion occurs in children older than 12 years. Based on these results, the best approach for initial EMS resuscitation in a two-tiered EMS system, CPR versus AED use, is uncertain among younger children. Inclusion of witness status into the decision process for younger children may more efficiently allocate AED use, a finding in accordance with 2005 guidelines.

Naloxone Use in a Tiered-Response Emergency Medical Services System

Objective. To examine the delivery andeffect of naloxone for opioid overdose in a tiered-response emergency medical services (EMS) system andto ascertain how much time could be saved if the first arriving emergency medical technicians (EMTs) could have administered intranasal naloxone. Methods. This was case series of all EMS-treated overdose patients who received naloxone by paramedics in a two-tiered EMS system during 2004. The system dispatches basic life support–trained fire fighter–EMTs and/or advanced life support–trained paramedics depending on the severity of cases. Main outcomes were geographic distribution of naloxone-treated overdose, severity of cases, response to naloxone, andtime interval between arrival of EMTs andarrival of paramedics at the scene. Results. There were 164 patients who received naloxone for suspected overdose. There were 75 patients (46%) initially unresponsive to painful stimulus. Respiratory rate was <10 breaths/min in 79 (48%). Death occurred in 36 (22%) at the scene or during transport. A full or partial response to naloxone occurred in 119 (73%). Recognized adverse reactions were limited to agitation/combativeness in 25 (15%) andemesis in six (4%). Average EMT arrival time was 5.9 minutes. Average paramedic arrival time was 11.6 minutes in most cases and16.1 minutes in 46 cases (28%) in which paramedics were requested by EMTs at the scene. Conclusions. There is potential for significantly earlier delivery of naloxone to patients in opioid overdose if EMTs could deliver intranasal naloxone. A pilot study training andauthorizing EMTs to administer intranasal naloxone in suspected opioid overdose is warranted.

What Are the Characteristics andOutcomes of Nontransported Pediatric Patients?

Background. The authors have demonstrated that 28% of children cared for by paramedics are not transported to hospital by ambulance. Objective. To determine the characteristics, reasons, andoutcomes for this nontransported population. Methods. This was a prospective cohort study in a single city with a two-tiered emergency medical services system. Enrolled were all children aged < 16 years assessed by paramedics but not transported to hospital over a five-month period. Data were collected from ambulance call reports, phone interviews, andhospital charts. Descriptive statistics were used. Results. Over five months, there were 345 nontransported pediatric patients with a mean age of 6 years, and58.3% were male. The dispatch priority was urgent in 68.1% of cases andprompt in 30.4% of cases. The primary problems were almost evenly split between trauma (50.7%) andmedical (45.2%) causes. Paramedics listed the following reasons for nontransport: parent will take the child to a physician (27.8%), parent will monitor the child's condition (25.8%), andno reason documented (46.4%). Phone interview was conducted with 106 parents (30.7%): 76.4% believed there was a true emergency at the time of the 9-1-1 call, 75.5% stated that the paramedics did not recommend that the child be transported to hospital by ambulance, and29.2% stated that the paramedics said ambulance transport was not necessary. Fifty-one children were seen in an emergency department (ED) within 48 hours of the 9-1-1 call. The majority (91.3%) were discharged home from the ED, while a small minority (8.7%) were admitted to hospital. No deaths were reported. Conclusions. Most nontransported children did not require immediate or urgent medical care. Both parents andparamedics gave input into the nontransport decision, andthe short-term outcome of this population appeared to be good. Paramedic documentation for the reasons for nontransport should be improved.

Cost-effectiveness of Different Advanced Life Support Providers for Victims of Out-of-hospital Cardiac Arrests

The survival rate of out-of-hospital cardiac arrest (OHCA) is only about 1.4% in Taiwan. The best configuration to achieve optimal outcomes in OHCA is still uncertain for many communities. The purpose of this study was to investigate the cost-effectiveness of two models of providing advanced life support (ALS) services, emergency medical technicians (EMTs) vs. emergency physicians (EPs), in a two-tiered emergency medical services (EMS) system. This was a prospective, observational, multicenter study comparing ALS provided by EMTs vs. EPs for the management of victims of OHCA. The study population consisted of patients experiencing OHCA of non-traumatic origin in Taipei city, Taiwan, between November 1999 and December 2000, for whom ALS was activated. We performed a cost-effectiveness analysis to determine the economic attractiveness of these two ALS provider programs. The outcome measurements were aggregate costs, survival and incremental cost per life saved. Sensitivity analyses were performed on all variables. The expected total cost per OHCA patient was 2,248.19 US$ and 832.07 US$ for the EMT and EP programs, respectively. The overall survival rate was 4.4%. The survival rate was 9.3% for the EMT program and 2.6% for the EP program. The incremental cost-effectiveness ratio (ICER) of EMTs vs. EPs was 21,136 US$ per life saved. The ICER was sensitive to hospital admission cost changes and the probability of survival to discharge in patients admitted to hospital in the EMT program. The increased survival rate of OHCA patients in the EMT program may be attributable to the services of the hospital and/or the EMT program. The use of EMTs as ALS care providers for OHCA patients in the two-tiered EMS system resulted in a reasonable cost-effectiveness ratio. EMTs could be considered as the second tier of EMS systems in urban areas in Taiwan.

The effect of pulse oximetry on emergency medical technician decision making

Objective Relatively little is known about the use of pulse oximetry in the prehospital setting. The purpose of this study was to determine how emergency medical technicians (EMTs) use pulse oximetry information to influence their decisions regarding the involvement of advanced life support (ALS) personnel in a two-tiered emergency medical services (EMS) system. Methods EMTs were trained and authorized to use pulse oximetry in predefined clinical situations. The EMTs completed a questionnaire describing the influence of the oximetry information on their decision making regarding the involvement of ALS units. Results The EMTs reported an influence on their decisions whether to involve ALS care in 35 (12%) of 302 cases. The addition of the pulse oximetry information caused the EMTs to request ALS dispatch in 11 cases, to cancel a previously dispatched ALS response in eight cases, and not to request an ALS response from the scene when they otherwise would have requested it in 16 cases. Conclusion Prehospital pulse oximetry has a measurable influence on EMT decisions concerning ALS involvement in a two-tiered EMS system. It improves system efficiency by helping to match patients to an appropriate level of care.

THE EFFECT OF PULSE OXIMETRY ON EMERGENCY MEDICAL TECHNICIAN DECISION MAKING

Objective. Relatively little is known about the use of pulse oximetry in the prehospital setting. The purpose of this study was to determine how emergency medical technicians (EMTs) use pulse oximetry information to influence their decisions regarding the involvement of advanced life support (ALS) personnel in a two-tiered emergency medical services (EMS) system. Methods. EMTs were trained and authorized to use pulse oximetry in predefined clinical situations. The EMTs completed a questionnaire describing the influence of the oximetry information on their decision making regarding the involvement of ALS units. Results. The EMTs reported an influence on their decisions whether to involve ALS care in 35 (12%) of 302 cases. The addition of the pulse oximetry information caused the EMTs to request ALS dispatch in 11 cases, to cancel a previously dispatched ALS response in eight cases, and not to request an ALS response from the scene when they otherwise would have requested it in 16 cases. Conclusion. Prehospital pulse oximetry has a measurable influence on EMT decisions concerning ALS involvement in a two-tiered EMS system. It improves system efficiency by helping to match patients to an appropriate level of care.

Do victims of an out-of-hospital cardiac arrest benefit from a training program for emergency medical dispatchers?

In this paper, we assessed the effects of a training course for emergency medical dispatchers on the handling of out-of-hospital cardiac arrest cases in the dispatch center of a two-tiered emergency medical services system. A total of 112 cardiac arrest cases were studied; 64 before and 48 after the training course. Before the course, all relevant information was obtained in 36% of cases, only partial information in 56% and no useful medical information in 8%. The corresponding figures after the training program were 62, 38 and 0%, respectively (2×3 χ2 test, P=0.01). Trends towards an increase in the percentage of cases in which a second-tier team was sent immediately after the initial call (58 vs 75%; χ2 test, P=0.06) and towards shorter overall intervals between receipt of the call and dispatch of the second-tier team (logrank test, P=0.10) were noticed. Similarly, the survival rate increased from 2% before, to 8% after the training course (χ2 test with Yates' correction, P=0.24). We conclude that our training program for emergency medical dispatchers produced some beneficial effects.

Active compression-decompression resuscitation: a prospective, randomized study in a two-tiered EMS system with physicians in the field

Improved cardiopulmonary circulation with active compression-decompression cardiopulmonary resuscitation (ACD-CPR) has been demonstrated in studies using different animal models and a small number of humans in cardiac arrest (CA). However, prehospital studies have shown both positive and no extra benefit of ACD-CPR on return of spontaneous circulation (ROSC), hospital admission and discharge rates. The aim of our prospective study was to compare standard manual CPR (S-CPR) with ACD-CPR as the initial technique of resuscitating patients with out-of-hospital CA, with respect to survival rates and neurological outcome. Patients with out-of-hospital CA treated by emergency medical services (EMS) personnel were randomly assigned to one of two groups (ACD-CPR versus S-CPR). Time intervals to key measures were documented by means of on-line tape-recording. Neurological outcome was assessed using standard scoring systems (cerebral and overall performance categories (CPC and OPC)). A total of 220 patients (S-CPR, n = 114; ACD-CPR, n = 106) were included in the study in a random order. The treatment groups were similar with respect to age, sex, time interval from collapse to CPR, defibrillation and first adrenaline medication. There was no difference between the ACD group and the standard CPR group in terms of ROSC (50.9% vs. 59.6%), hospital admission (33% vs. 33.3%), hospital discharge (16% vs. 14%), or CPC and OPC (1.82 vs. 2.13 and 2.06 vs. 2.25, respectively). Concerning complications of CPR, there was no difference between the groups. In our two-tiered EMS system with physician-staffed ambulances, ACD-CPR neither improved nor impaired survival rates and neurological prognosis in patients with out-of-hospital cardiac arrest. The new CPR technique did not increase the complications associated with the resuscitation effort.

Evaluation of a Prehospital Chest Pain Protocol

Study objectives: To evaluate the diagnostic accuracy and outcomes for patients treated by use of a prehospital chest pain protocol (CPP). Design: Consecutive case series for 1 year (1993) of prehospital nontrauma advanced life support (ALS) cases including hospital outcomes. Setting: Nonurban two-tiered emergency medical services system. Participants: Patients treated under the prehospital CPP or with hospital diagnoses of ischemic heart disease (IHD; ICD-9 between 410 and 414). Patients with cardiac arrest or dysrhythmias were excluded. Interventions: Patients were given, by standing orders, ECG monitoring, IV access, and sublingual nitroglycerin. Further therapy was guided by on-line medical direction. Results: Of 3,122 ALS nontrauma patients, 620 (20%) were treated with the CPP. All patients underwent ECG monitoring, IV access was started in 83%, and 61% received nitroglycerin. Only 55% of patients completed the entire CPP; patients who failed to complete the CPP had the same prevalence of IHD as those who completed it. When compared with hospital diagnosis of IHD, the CPP had a sensitivity of 69% (95% confidence interval [CI], 64% to 74%), a specificity of 87% (95% CI, 86% to 88%), and a positive predictive value of 42%. The positive likelihood ratio of CPP for IHD was 5.31, and the negative likelihood ratio was .36. The hospital mortality rate for all patients was 2.2%; for those with IHD, it was 1.6%. Conclusion: This prehospital ALS CPP had good diagnostic accuracy, but only half of patients completed it, and the hospital mortality rate was low. These data challenge the efficacy of the CPP. [Wuerz RC, Meador SA: Evaluation of a prehospital chest pain protocol. Ann Emerg Med November 1995;26:595-597.]

Frequency and Accuracy of Prehospital Diagnosis of Acute Stroke

This pilot study evaluated the frequency and accuracy of diagnosis of stroke made by prehospital care system dispatchers, emergency medical technicians (EMTs), and paramedics in one emergency medical services (EMS) system. In addition, the study determined patient prehospital triage and time intervals in the transport and examination of patients given a diagnosis of stroke by this EMS system. We reviewed records of 4413 consecutive prehospital records of a two-tiered EMS system for patients with potential stroke. Hospital records were obtained for patients given a diagnosis of stroke or transient ischemic attack (TIA) by an EMS dispatcher, EMT, or paramedic. The EMS system studied serves a community of 13,000 within the greater Cincinnati area. Of 4413 EMS on-scene evaluations, the diagnosis of stroke or TIA was made by an EMT or paramedic for 96 patients (2%). Of the study population (n = 86), a final hospital discharge diagnosis of stroke or TIA was made for 62 patients (72%). EMS dispatchers correctly identified 52% and paramedics 72% of these 86 patients as having sustained a stroke or TIA. Twenty-two of the 86 patients required paramedic-level interventions, which included three intubations. Of the 24 patients whose symptoms were misdiagnosed as stroke or TIA by the paramedics, 16 (19%) had acute conditions for which effective therapies are available. Prehospital personnel arrived at the scene to examine potential stroke patients in a mean of 3 minutes after the emergency 911 call was received by the dispatcher. Patients transported by basic life support units (EMTs) arrived earlier at the hospital than did those transported by advanced life support units (paramedics) (40 +/- 1 versus 45 +/- 1 minutes, P = .004). However, patients transported by advanced life support units were seen by a physician sooner after arrival at the emergency department (10 +/- 2 versus 20 +/- 4 minutes, P = .02) and underwent computed tomography of the brain sooner (47 +/- 5 versus 69 +/- 10 minutes, P = .04). Prehospital evaluation of potential stroke patients can be accomplished promptly after the EMS system is activated. Urgent evaluation and transport of potential stroke patients is justified because paramedic-level interventions are frequently required and because almost 20% of patients with potential stroke have acute medical conditions for which effective specific therapies are available.