Advanced Life Support Personnel Research Articles

A descriptive analysis of endotracheal intubation in a South African Helicopter Emergency Medical Service.

IntroductionHelicopter Emergency Medical Services (HEMS) exists to supplement the operations of ground-based emergency care providers, mainly in high acuity cases. One of the important procedures frequently carried out by HEMS personnel is endotracheal intubation. Several HEMS providers exist in South Africa, with a mix of advanced life support personnel, however intubation success rates and adverse events have not been described in any local HEMS operation.MethodsThis was a retrospective chart review of intubation-related data collected by a HEMS operation based in Johannesburg over a 16-month period. First-pass and overall success rates were described, in addition to perceived airway difficulty, adverse events and other data.ResultsOf the 49 cases recorded in the study period, one was excluded leaving 48 cases for analysis. Most cases (n = 34, 71%) involved young male trauma patients who were intubated with rapid sequence intubation. The first pass success rate was 79% (n = 38) with an overall success rate of 98% (n = 47). At least one factor suggesting airway difficulty was present in 29% (n = 14) of cases, with most perceived airway difficulty related to the high prevalence of trauma cases. At least one adverse event occurred in 27% (n = 13) of cases with hypoxaemia, hypotension and bradycardia most prevalent.DiscussionIn this small sample of South African HEMS intubation cases, we found overall and first-pass success rates comparable to those reported in similar contexts.

Wearable Cardioverter-Defibrillator Therapy for the Prevention of Sudden Cardiac Death: A Science Advisory From the American Heart Association.

Sudden cardiac death (SCD) accounts for >300 000 deaths in the United States annually.1 Although the majority of these deaths occur in low-risk populations2 in which aggressive interventions are not practical, some higher-risk populations have been established in whom intervention with an implantable cardioverter-defibrillator (ICD) has been shown in randomized trials to reduce mortality.3–7 Additionally, there is a population of patients who may benefit from automatic emergency cardioversion-defibrillation but are not deemed appropriate candidates for ICD implantation at the time of presentation. This group is defined by 2 populations. The first subgroup comprises those who are at perceived risk but for whom there may be optimism for clinical improvement (eg, patients soon after revascularization or those with a recent diagnosis of myocardial infarction [MI] or cardiomyopathy). Alternatively stated, the optimal management of these patients at risk (or perceived risk) during the waiting period before an ICD is indicated remains unknown. The second subgroup includes those who have a clear indication for ICD but also have a contraindication to immediate ICD placement (eg, active infection or unknown prognosis). The wearable cardioverter-defibrillator (WCD) is a device designed for patients at risk of SCD who are not immediate candidates for ICD therapy. By providing automatic therapy, the WCD does not depend on a second person to defibrillate, as required with a manual or automated external defibrillator (AED). Unlike the ICD (including both transvenous and subcutaneous devices), the WCD requires no surgical operation, can be provided for a short period of time, is temporary, and is easily removed. These characteristics of the WCD, along with safety and efficacy data presented to the US Food and Drug Administration (FDA), resulted in approval in the United States in 2002.8 Because of the increasing use of the WCD and uncertainty of indications …

Resuscitation of avalanche victims: Evidence-based guidelines of the international commission for mountain emergency medicine (ICAR MEDCOM): Intended for physicians and other advanced life support personnel

BackgroundIn North America and Europe ∼150 persons are killed by avalanches every year. MethodsThe International Commission for Mountain Emergency Medicine (ICAR MEDCOM) systematically developed evidence-based guidelines and an algorithm for the management of avalanche victims using a worksheet of 27 Population Intervention Comparator Outcome questions. Classification of recommendations and level of evidence are ranked using the American Heart Association system. Results and conclusionsIf lethal injuries are excluded and the body is not frozen, the rescue strategy is governed by the duration of snow burial and, if not available, by the victim's core-temperature. If burial time ≤35min (or core-temperature ≥32°C) rapid extrication and standard ALS is important. If burial time >35min and core-temperature <32°C, treatment of hypothermia including gentle extrication, full body insulation, ECG and core-temperature monitoring is recommended, and advanced airway management if appropriate. Unresponsive patients presenting with vital signs should be transported to a hospital capable of active external and minimally invasive rewarming such as forced air rewarming. Patients with cardiac instability or in cardiac arrest (with a patent airway) should be transported to a hospital for extracorporeal membrane oxygenation or cardiopulmonary bypass rewarming. Patients in cardiac arrest should receive uninterrupted CPR; with asystole, CPR may be terminated (or withheld) if a patient is lethally injured or completely frozen, the airway is blocked and duration of burial >35min, serum potassium >12mmolL−1, risk to the rescuers is unacceptably high or a valid do-not-resuscitate order exists. Management should include spinal precautions and other trauma care as indicated.

Basic-Level Emergency Medical Technician Administration of Fluids and Glucose via Enzyme-Assisted Subcutaneous Infusion Access

During disasters and mass-casualty incidents (MCIs), there may be insufficient numbers of advanced life support (ALS) providers to provide intravenous (IV) access to all patients requiring parenteral fluids and/or medications. Enzyme-assisted subcutaneous infusion (EASI) access, in which human recombinant hyaluronidase (HRH) augments subcutaneous fluid dispersion and absorption, may be useful when ALS resources are insufficient to meet intravascular access needs. The utility of the use of the EASI lies, in part, in its ease of placement by ALS personnel. The objectives of this study were to document the feasibility, comfort, and speed/degree of infused-glucose uptake through EASI lines placed by basic-level emergency medical technicians (EMT-Bs). Eighteen EMT-Bs instituted EASI access on each other. A total of 150 units (1 mL) of HRH were administered through the EASI line, followed by the administration of 250 mL of tracer-labeled D5W. Timed phlebotomy enabled gas chromatography/mass spectrometry characterization of glucose uptake. Enzyme-assisted subcutaneous infusion placement and comfort ratings were tracked and analyzed using non-parametric statistics and Fisher's Exact Test. In all 18 subjects, EASI access required only one attempt and was rated by the EMT-Bs as easy to accomplish. Glucose was absorbed quickly (within five minutes) in all subjects. The rate of infusion was rapid (median 393 mL/hour) and was comfortable for the recipients (median pain score 1/10). The use of EASI may be viable as a fast, simple, and reliable method for the administration of fluid and glucose by EMT-Bs.

Part 6: Electrical Therapies

The recommendations for electrical therapies described in this section are designed to improve survival from SCA and life-threatening arrhythmias. Whenever defibrillation is attempted, rescuers must coordinate high-quality CPR with defibrillation to minimize interruptions in chest compressions and to ensure immediate resumption of chest compressions after shock delivery. The high first-shock efficacy of newer biphasic defibrillators led to the recommendation of single shocks plus immediate CPR instead of 3-shock sequences that were recommended prior to 2005 to treat VF. Further data are needed to refine recommendations for energy levels for defibrillation and cardioversion using biphasic waveforms.

Intra-Arrest Transnasal Evaporative Cooling

Transnasal evaporative cooling has sufficient heat transfer capacity for effective intra-arrest cooling and improves survival in swine. The aim of this study was to determine the safety, feasibility, and cooling efficacy of prehospital transnasal cooling in humans and to explore its effects on neurologically intact survival to hospital discharge. Witnessed cardiac arrest patients with a treatment interval <or=20 minutes were randomized to intra-arrest cooling with a RhinoChill device (treatment group, n=96) versus standard care (control group, n=104). The final analysis included 93 versus 101 patients, respectively. Both groups were cooled after hospital arrival. The patients had similar demographics, initial rhythms, rates of bystander cardiopulmonary resuscitation, and intervals to cardiopulmonary resuscitation and arrival of advanced life support personnel. Eighteen device-related adverse events (1 periorbital emphysema, 3 epistaxis, 1 perioral bleed, and 13 nasal discolorations) were reported. Time to target temperature of 34 degrees C was shorter in the treatment group for both tympanic (102 versus 282 minutes, P=0.03) and core (155 versus 284 minutes, P=0.13) temperature. There were no significant differences in rates of return of spontaneous circulation between the groups (38% in treated subjects versus 43% in control subjects, P=0.48), in overall survival of those admitted alive (44% versus 31%, respectively, P=0.26), or in neurologically intact survival to discharge (Pittsburgh cerebral performance category scale 1 to 2, 34% versus 21%, P=0.21), although the study was not adequately powered to detect changes in these outcomes. Prehospital intra-arrest transnasal cooling is safe and feasible and is associated with a significant improvement in the time intervals required to cool patients.

The use of emergency medical dispatch protocols to reduce the number of inappropriate scene responses made by advanced life support personnel

Objectives. To determine whether implementation of an emergency medical dispatch (EMD) system would reduce the rate of inappropriate advanced life support (ALS) utilization, and enable more accurate identification of those patients requiring ALS care. Methods. An emergency medical services (EMS) site providing basic life support (BLS) and ALS care to a population of 200,000 served as the study site for calendar year 1996. This study compared the prospective identification of patients as ALS or BLS using EMD with that using chief complaint-based dispatch criteria. Each patient served as his or her own control. The ALS or BLS priority was assigned using both chief complaint and EMD criteria. Chief complaint-based dispatching meant that all patients with preestablished chief complaints received ALS without further triage questions, while EMD allowed the dispatchers to question callers using a scripted set of questions. The outcome measures included the number of calls categorized as ALS or BLS, the number of calls cancelled by BLS, and the number of ALS calls released to BLS care. Yates-corrected chi-square was used for statistical analysis. Results. There were 11,174 patients enrolled. The use of EMD was associated with a significant decrease in the proportion of calls designated as ALS (44.7% vs 55.8%, p < 0.0001), as well as a significant decrease in the number of ALS responses cancelled by BLS (9.2% vs 23.8%, p < 0.0001) and patients released to BLS by medical control (4.7% vs 7.3%, p < 0.0001). Conclusions. Implementation of an EMD system significantly decreased inappropriate ALS dispatching, as defined by decreased rate of ALS cancellations and BLS releases. Further study is needed to see whether other EMD dispatch models may further refine ALS dispatch. PREHOSPITAL EMERGENCY CARE 2000;4:186-189

Combination of active compression decompression cardiopulmonary resuscitation and the inspiratory impedance threshold device: state of the art.

Over the past decade, the combination of active compression decompression (ACD) cardiopulmonary resuscitation (CPR) and an impedance threshold device (ITD) has been shown to significantly increase vital organ perfusion pressures and survival rates in animals and humans. The purpose of this review article is to summarize the recent advances with this new technology. Building upon animal studies that demonstrated the benefit of the ITD used with either ACD CPR or standard CPR (S-CPR), four prospective, randomized clinical trials with ACD/ITD CPR have been recently completed. One blinded, out-of-hospital cardiac arrest trial (n = 21 patients) demonstrated that systemic blood pressures and coronary perfusion pressures were markedly higher when ACD/ITD CPR was used when compared directly with ACD CPR alone. The second blinded trial demonstrated that the combination of ACD/ITD CPR was effective with both a facemask and an endotracheal tube (n = 15 patients). A third randomized clinical trial (n = 210 patients) demonstrated that 24-hour survival rates for out-of-hospital cardiac arrest were more than 65% higher with ACD/ITD CPR than with S-CPR (P < 0.01). Neurologic function after cardiac arrest trended higher in patients with witnessed arrest who received ACD/ITD CPR than in those who received S-CPR(P < 0.07). In addition, when ACD/ITD CPR was applied later in the course of treatment, short-term survival rates were threefold higher in patients receiving ACD/ITD CPR (44%) than in those receiving S-CPR (14%)(P < 0.05). In that study, patients with the greatest chance for survival-those with witnessed cardiac arrest and an initial rhythm of ventricular fibrillation-had a 23% 24-hour survival rate with S-CPR versus a 58% 24-hour survival rate with ACD/ITD CPR (P < 0.01). It should be noted that this trial was performed in a city where an earlier study found no difference in outcomes between ACD CPR alone and S-CPR. The fourth clinical trial was a randomized, double-blinded study of 400 patients with out-of-hospital cardiac arrest treated by advanced life support personnel. All patients received ACD CPR: half were treated with a sham ITD and the other half were treated with an active ITD. Twenty-four hour survival, the primary endpoint, was 32% in the active ITD group versus 22% in the sham group (P < 0.05). On the basis of the cumulative findings of these studies, it is concluded that ACD/ITD CPR provides superior vital organ blood flow and results in significantly higher short-term survival rates than do ACD CPR alone or S-CPR. Use of the ACD/ITD CPR technology optimizes perfusion of the heart and brain during cardiac arrest and results in the highest reported survival rates of any CPR device technology. Use of this technology should be encouraged while additional studies are under way to examine the potential long-term impact of this new technology.

New equipment and techniques for airway management in trauma

A patent, unobstructed airway is fundamental in the care of the trauma patient, and is most often obtained by placing a cuffed tube in the trachea. The presence of shock, respiratory distress, a full stomach, maxillofacial trauma, neck hematoma, laryngeal disruption, cervical spine instability, and head injury all combine to increase tracheal intubation difficulty in the trauma patient. Complications resulting from intubation difficulties include brain injury, aspiration, trauma to the airway, and death. The use of devices such as the gum-elastic bougie, McCoy laryngoscope, flexible and rigid fiberscopes, intubating laryngeal mask, light wand, and techniques such as rapid-sequence intubation, manual in-line axial stabilization, retrograde intubation, and cricothyroidotomy, enhance the ability to obtain a definitive airway safely. The management of the failed airway includes calling for assistance, optimal two-person bag-mask ventilation, and the use of the laryngeal mask airway, Combitube, or surgical airway. The simulation of airway management using realistic simulator tools (e.g. full-scale simulators, virtual reality airway simulators) is a promising modality for teaching physicians and advanced life support personnel emergency airway management skills.

C ANCELLATION OF R ESPONDING ALS U NITS BY BLS P ROVIDERS : A N ATIONAL S URVEY

Objective. In many emergency medical services (EMS) systems, personnel without advanced life support (ALS) training are authorized to cancel responding ALS units before the ALS personnel arrive and examine the patient. This study was conducted to examine these cancellations in major U.S. cities. Methods. A survey was mailed to the physician medical directors of the EMS services of the 125 largest U.S. cities, with telephone follow-up of nonresponders. The survey requested information on system structure, and on policies governing cancellation of responding ALS units by non-ALS personnel. Results. Ninety-four cities responded (75%), from 35 states. Nineteen systems (20%) are all-ALS with no basic life support (BLS) tier, and these were eliminated. Of the remaining 75 systems, eight (11%) use BLS ambulances (BLS-A), 35 (47%) use BLS first responders (BLS-FR), and 32 (43%) use both. Of these 75 systems, 60 (80%) allow cancellation of responding ALS units by BLS personnel. Only 24 of these (40%) have written protocols for such cancellations, and only 12 of those (50%) involve specific medical criteria, with two (8%) relying on the best judgment of the BLS personnel with no medical criteria, and another eight (33%) allowing cancellation only for logistic reasons. Of the 60 systems that permit cancellation, 13 (22%) perform some type of medical oversight review of all such calls, 26 (43%) review some such calls (median 10%, range 2–80% for the 19 systems specifying a percentage), 15 (25%) do not review any, and six did not specify. Conclusions. Fewer than half of the surveyed EMS systems that permit non-ALS personnel to cancel responding ALS units use written protocols to guide these decisions, and only half of those protocols utilize specific medical criteria. Medical oversight review of these calls is highly variable, with many systems reviewing few or none of these cancellations.

Safety of prehospital nitroglycerin

To define changes in vital signs and cardiac rhythm in prehospital patients given sublingual nitroglycerin. A five-month prospective observational study with nitroglycerin administration as the independent variable. Five independent advanced life support services. Three hundred prehospital patients who were given nitroglycerin by advanced life support personnel for presumed myocardial ischemia or congestive heart failure; excluded were those without repeat vital signs or ECG monitoring and those given additional medications. Nitroglycerin was administered by regional emergency medical services protocols or by the order of an on-line medical command physician. Four study patients (1.3%) had adverse effects: One became asystolic and apneic for two minutes, two experienced profound bradycardia with hypotension, and one became hypotensive while tachycardic. All recovered. The 95% confidence interval for adverse effects was 0.5% to 3.4%. Mean fall in systolic blood pressure for the other 296 patients was 14 mm Hg for one dose (confidence interval, 11 to 16 mm Hg) and 8 mm Hg (confidence interval, 2 to 13 mm Hg) for a second dose. Heart rate changed minimally with nitroglycerin administration. The blood pressure drop was linearly correlated with initial systolic pressure (r = -.44; P < .001) but not correlated with number of prior doses of nitroglycerin, initial heart rate, advanced life support time interval, age, or sex. Nitroglycerin seems to be a relatively safe advanced life support drug; however, a few patients experience serious adverse effects. Most of the adverse effects we observed were bradycardic-hypotensive reactions, which appeared to be unpredictable by pretreatment characteristics. Emergency personnel should have an increased awareness of this danger when considering the use of prehospital nitroglycerin.

Physician in-field observation of prehospital advanced life support personnel: a statewide evaluation.

Direct physician observation of advanced life support (ALS) personnel is rare in a demographically diverse state. Twenty ALS agencies from throughout Arizona. A board-certified emergency physician performed on-site interviews with the emergency medical services (EMS) supervisor of each agency to approximate the number of days per year that physicians observe ALS personnel in the field. Only 11 agencies (55%) reported that physicians ever observed ALS personnel. Among all agencies, an estimated total of 84 observer-days occurred per year. The agencies staffed a total of 86 ALS units, resulting in an estimated 0.98 observer-days/unit/year (84/86). On the average, it took 3.4 ALS personnel to staff a given unit over time and the probability that an ALS provider would be on a unit on any given day was 0.29 (1/3.4). The probability of a given provider being observed during one year was approximately 0.29 (0.98 x 0.29). Thus, on the average, an ALS provider would be observed by a physician approximately once every 3.5 years (1/0.29). Among urban agencies, the "average" ALS provider would be observed once every 2.9 years. This compared to a likelihood of in-field observation of only once every 6.7 years for non-urban providers (p = .036). The skills of ALS providers in Arizona are observed by a physician in the field very infrequently. Although an uncommon occurrence in urban agencies, observation of non-urban ALS personnel occurs even less frequently. In addition, nearly one-half of the agencies surveyed never had a physician-observer. Although a variety of skills evaluation methods exist, it remains unclear whether any method is as useful as direct observation. Future investigations are needed to evaluate whether in-field physician observation impacts skills, patient care, or outcome in EMS systems.

Prehospital seizure management: Triage criteria for the advanced life support rescue team

The present study was completed to establish advanced life support (ALS) versus non-ALS triage criteria for use by ALS prehospital personnel when faced with the seizure patient, in the hope of more efficient use of ALS rescue teams. Preselected triage criteria for acuity of care based on neurological condition, vital signs, and concomitant illness/injury were tested against retrospective data (paramedic run reports) collected on 230 patients. Triage criteria sensitivity (SENS), specificity (SPEC), positive predictive value (PPV), and negative predictive value (NPV) were determined with a 95% confidence interval (CI). Point estimate of use/need of care was noted. ALS interventions were instituted in 58 patients (25%). In 57 of these cases, indication for and ALS intervention, were established on initial patient assessment (SENS, 98.28; 95% CI, 90.76 to 99.96). Of 173 patients requiring no ALS intervention on initial assessment, only 1 (0.58%) developed complications warranting ALS therapy during the course of prehospital care (SPEC, 100.00; 95% CI, 100.00 to 99.99; PPV, 100.00; 95% CI, 100.00 to 94.63; NPV, 99.42; 95% CI, 96.82 to 99.99). No inappropriate use, point estimate (PE) [ (0) (172) (0.00% to 0.01%)] or unmet need, PE [ (0) (58) (0.00% to 5.16%)] of care was noted. The data presented in this study suggest that given similar field times, after initial patient assessment by ALS personnel, it is reasonable and safe to triage seizure patients who do not require ALS intervention to non-ALS rescue teams for continuation of care and transportation.

Unexpected ALS Procedures on Non-Emergency Ambulance Calls: The Value of a Single-Tier System

AbstractBackground:In a single-tier, advanced-life-support (ALS) emergency medical service (EMS) system, ALS-trained staff in ALS-equipped vehicles respond to all ambulance calls. In some two-tier systems, basic life support (BLS) vehicles respond to calls which are determined initially to be non-emergency based on dispatcher triage. I emergency requiring ALS is discovered (or recognized) by BLS personnel, then a subsequent ALS response can be requested.Purpose:The purpose of this study was to determine the frequency of ALS care provided on ambulance calls initially dispatched as non-emergency.Setting:A single-tier, all-ALS provider, EMS system, serving an urban population of 475,000 with an annual response volume of 45,000 calls.Methods:A retrospective review of all prehospital transports initially dispatched as non-emergency from 1 January 1989 to 1 January 1990 that resulted in an ALS intervention being performed was conducted. An ALS intervention was defined as, “administration of a medication, endotracheal intubation, attempted IV insertion, and/or ECG monitoring.”Results:A total of 6,362 non-emergency calls were identified; of these 309 (5%) were upgraded to emergency while the responding unit was in route. Of 6,053 non-emergency calls remaining, 710 (11.7%) involved the provision of one or more ALS interventions. Of these, 296 (42%) received an IV, 24 (3%) a medication, and three (0.4%) were intubated. Calls that were upgraded by dispatchers required one or more interventions in 144/309 calls (46.6%). This was statistically significantly different than for the non-upgraded calls.Conclusion:Despite the use of strict dispatching protocols, 11.7% of patients prioritized as non-emergent unexpectedly received ALS care after evaluation by ALS personnel. These results add support for the use of a single-tier, ALS ambulance system.

Age-related Utilization of Advanced Life Support Services

AbstractPurpose:To investigate the relationship between age and Advanced Life Support (ALS) utilization.Population:All patients from 1 January 1987 to 31 December 1988 transported by ALS ambulances within Lebanon County, a rural/urban county of 112,000.Methods:All runs resulting in patient treatment by ALS personnel were tallied at five-year age intervals and sub-grouped by trauma- and non-trauma-related calls. Utilization rates for each age group were obtained by dividing the calls by the population of each group. Correlation with age was tested by Spearman's rank correlation. Treatment rates for age groups were calculated for the six most frequent medical etiologies. To illustrate the effect of age distributions, age rates were applied to projected state and national population distributions.Results:There was a significant correlation with age for all transports (p &lt; .01; r=.93) and for those not related to trauma (p&lt;.01; r=.98). Correlation was not detected for trauma-related responses (p&gt;.10; r=.19). Non-trauma-related case incidence varied among age groups, ranging from 1.1/1,000 for age five through nine years to 89/1,000 for age 80–84 years. Congestive heart failure, cardiac ischemia, syncope, myocardial infarction, and cardiac arrest evidenced increased incidence with age. Seizure did not. Older populations had a higher projected utilization of ALS services than did the younger age groups.Conclusion:Non-trauma ALS utilization is highly dependent on the age of the patient. Due to projected aging of the population and increased utilization of ALS by the elderly, projected utilization will increase at a rate faster than will the population. Age:rate data can be combined with population projections to estimate future need.

A Prospective Evaluation of Prehospital Patient Assessment by Direct In-field Observation: Failure of ALS Personnel to Measure Vital Signs

AbstractWe prospectively evaluated the frequency with which advanced life support (ALS) personnel fail to attempt to measure blood pressure (BP) and/or pulse (P) during prehospital patient assessment. A single in-field observer rode on ALS rescue vehicles from 20 Emergency Medical Services (EMS) agencies throughout Arizona during a one-year study (1/89–12/89). Data were collected from urban, suburban, and rural systems. Statistical evaluation was performed by Chi Square analysis with p &lt;0.05 considered significant.Among 227 patient encounters, BP and/or P measurements were omitted in 84 cases (37.0%). BP and/or P were omitted in 50.0% of children (age &lt;18 years) compared to 26.5% of adults (p=0.023). Among patients who were transported to a hospital, 19.4% had BP omitted compared to 49.1% of those not transported (p=0.00003). Seven of 58 patients in whom TVs were attempted (12.1 %) had BP omitted compared to 54 of 169 patients without IV attempts (32.0%, p=0.0055). Blood Pressure was omitted in 21.9% of patients transported Code 3 and in 24.2% of patients with Glasgow Coma Scale ≤13. Omission of BP occurred more frequently in non-urban agencies (33.9%) than in urban ones (20.0%, p=0.027).In a statewide evaluation of prehospital patient assessment, failure to measure vital signs (VS) occurred on a frequent basis. Our data indicate that a concerning lack of attention to the most basic details of patient assessment is common. It is possible that failure to measure VS might even happen more frequently during routine patient encounters without an observer present. Medical control physicians must emphasize to EMS personnel the paramount importance of careful assessment to ensure optimal patient care.

Characteristics of midsized urban EMS systems

Emergency medical services (EMS) systems in 25 midsized cities (population, 400,000 to 900,000) are described. Information describing EMS system configuration and performance was collected by written and telephone surveys with follow-ups. Responding cities provide either one- or two-tier systems. In a one-tier system, an advanced life support (ALS) unit responds to and transports all patients who use 911 to activate the system. Three types of two-tier systems are identified. In system A, ALS units respond to all calls. Once on scene, an ALS unit can turn a patient over to a basic life support (BLS) unit for transport. In system B, ALS units do not respond to all calls; BLS units may be sent for noncritical calls. In system C, a nontransport ALS unit is dispatched with a transporting BLS unit. For ALS calls, ALS personnel join BLS personnel for transport. Overall, cities staff an average of one ambulance per 51,223 population. One-tier systems average one ambulance per 53,291 compared with two-tier systems, which average one ambulance per 47,546. In the two-tiered system B, the average ALS unit serves 118,956 population. In the 60% of cities that use a one-tier system, one ALS unit serves 58,336 (P less than .0005). Overall, the code 3 response time for all cities is an average of 6.6 minutes. The average response time of two-tier systems is 5.9 minutes versus 7.0 minutes for one-tier systems (.05 less than P less than .1). These data suggest that the two-tiered system B allows for a given number of ALS units to serve a much larger population while maintaining a rapid code 3 response time.