Dean Hess

An Analysis of Invasive Airway Management in a Suburban Emergency Medical Services System

INTRODUCTION Airway management is the most critical and potentially life-saving intervention performed by emergency medical service (EMS) providers. Invasive airway management often is required in non-cardiac-arrest patients who are combative or otherwise uncooperative. The success of prehospital invasive airway management in this patient population was evaluated. METHODS A retrospective review was undertaken of the records of all such patients requiring endotracheal intubation over a three-year period (1987-1989). The study population included 278 patients enrolled by five advanced life support (ALS) units serving a suburban population of 425,000. Field trip sheets were reviewed for diagnosis, intubation method and success, number of intubation attempts, provider experience, reasons for unsuccessful intubations, and complications. RESULTS A total of 394 invasive airway management attempts were performed on 278 patients. The overall successful intubation rate was 75% (41% orotracheal, 52% nasotracheal, 7% other or unknown). The most common diagnoses were COPD and pulmonary edema (30%) and trauma (24%). Experienced providers were successful on the first attempt in 57% of cases compared to 50% by inexperienced providers (p=.24). Multiple intubation attempts were required in 33% of the patients. There was no statistically significant difference in success rates between the orotracheal and nasotracheal methods (p=.51). The most common reason for unsuccessful intubation was altered level of consciousness. Complications occurred with 7% of successful attempts and in 18% of unsuccessful attempts (p less than .001). Forty-six percent of the patients who were not intubated successfully in the field and required intubation in the emergency department (ED) received a neuromuscular blocking agent prior to successful intubation. CONCLUSION Prehospital providers can intubate a high but improvable proportion of non-cardiac-arrested patients by both the orotracheal and nasotracheal routes. The use of pharmacologic adjuncts to facilitate the prehospital intubation of selected, non-cardiac-arrested patients is a promising adjunct that needs further evaluation.

Ventilatory volumes using mouth-to-mouth, mouth-to-mask, and bag-valve-mask techniques

The volumes delivered to a resuscitation manikin were compared using four ventilatory techniques: mouth-to-mouth, mouth-to-mask, one-person bag-valve-mask, and two-person bag-valve-mask. The effects of experience and sex of the rescuer on the resuscitation volume delivered were also evaluated. The volume delivered using the one-person bag-valve-mask technique was significantly less than that using the other three techniques (P less than 0.001). The experience and sex of the rescuer made no significant difference in the volume delivered using any of the techniques. As compared with the one-person technique, bag-valve-mask ventilatory volume improved significantly when it was performed as a two-person technique. The mean volumes delivered using mouth-to-mouth and mouth-to-mask ventilation were lower than those recommended by the American Heart Association. Emphasis must be placed on ventilation with an adequate volume when these techniques are taught. When mouth-to-mouth and mouth-to-mask ventilation are taught, a spirometer should be used with the manikin so that the rescuer can learn how to estimate an adequate expired volume.

One-year survival after prehospital cardiac arrest: The Utstein style applied to a rural-suburban system☆

To evaluate the recently published Utstein algorithm (Ann Emerg Med 1991;20:861), the authors conducted a retrospective review of all advanced life support (ALS) trip sheets and hospital records of patients with prehospital cardiac arrests between January 1988 and December 1989. Telephone follow-up was used to determine 1-year survival rates. Of 713 arrests in the 24-month study period, 601 were of presumed cardiac etiology. Approximately 599 of these charts were available for analysis. One hundred ninety-three (32.2%) of these had return of spontaneous circulation (ROSC), 36 (6.0%) survived to hospital discharge, and 24 were alive at 1-year follow-up (4.0% of total or 67% of survivors to discharge). The Utstein style was found to be a useful algorithmic format for reporting prehospital cardiac arrest data in a manner that should allow direct comparison between emergency medical service (EMS) systems. Existing prehospital record-keeping practices (trip sheets) are easily adapted to this style of data collection, although certain data for the template (eg, resuscitations not attempted and alive at 1-year) are more difficult to ascertain. Additionally, the authors report their own experience during a 2-year period, including data that suggest that the majority of patients with cardiac arrest who survive to hospital discharge are still alive at 1 year.

An evaluation of pulse oximetry in prehospital care

STUDY OBJECTIVES We performed this study to evaluate the accuracy of pulse oximetry oxygen saturation (SpO2) against direct measurements of arterial oxygen saturation (SaO2) in the field. DESIGN Prospective, cross-sectional, paired measurements of SpO2 against SaO2. SETTING This evaluation was done in the prehospital setting. INTERVENTIONS A pulse oximeter with digital probe was used to measure SpO2 in 30 patients. Arterial blood gases were drawn in the field while the pulse oximeter was in use, and oxygen saturation (HbO2) was measured by CO-oximetry. MAIN RESULTS There was no significant difference between SpO2 (94.6 +/- 5.4%) and HbO2 (94.9 +/- 5.1%) (P = .495, beta less than .2). There was a strong correlation between SpO2 and HbO2 (r = .898). The bias between SpO2 and HbO2 was -0.3, with a precision of 2.4. When SpO2 was 88% or more, HbO2 was 90% or more in every case. Mean carboxyhemoglobin was 1.3 +/- 0.9%, and mean methemoglobin was 0.9 +/- 0.3%. There was no significant difference between the pulse oximeter heart rate and the ECG heart rate (P = .223, beta less than .2). CONCLUSION We conclude that pulse oximetry is sufficiently accurate to be useful in the field when SpO2 is more than 88%. It is potentially useful in patients with clinical signs of acute hypoxemia and in patients receiving interventions that may produce acute hypoxemia. Further work is needed to evaluate the accuracy of pulse oximetry in the settings of elevated carboxyhemoglobin, methemoglobin, and very low saturations.

Noninvasive transcutaneous cardiac pacing in prehospital cardiac arrest

This study evaluated the efficacy of prehospital external cardiac pacing in cardiac arrest patients. From October 1984 to June 1985, 91 patients were paced. Mean time from cardiac arrest to advanced life support (ALS) intervention in this metropolitan-rural ALS system was 14.5 minutes. Electrical capture occurred in 85 (93%), mechanical capture (pulses) occurred in ten (11%), and a measurable blood pressure occurred in three (3%) of the 91 patients. Despite a high rate of electrical capture, palpable pulses were produced only in 11%, and no patients survived to be discharged from the hospital. There was no difference in the frequency of electrical capture, palpable pulses, or outcome for patients receiving pharmacologic intervention before or after pacing. Likewise there was no difference in the frequency of electrical capture, palpable pulses, or outcome for patients receiving ALS therapy within or after ten minutes of their arrest. Although we found that external cardiac pacing was easily used in the prehospital setting, pacing did not result in any increase in survival in cardiac arrest patients.

Early defibrillation program: Problems encountered in a rural/suburban EMS system

Many studies have shown improved survival of cardiac arrest patients by the use of early defibrillation (EMT-D) in the field. This prospective study was the first in Pennsylvania and was undertaken to determine if an EMT-D program would be successful in our suburban/rural setting. One hundred two EMTs were trained to use a semi-automatic defibrillator and data were collected over 16 months. There were 96 cardiac arrests, with only 33 patients (34%) presenting with initially treatable dysrhythmias--ventricular fibrillation (VF) or tachycardia (VT). Twenty-three patients (24%) were admitted to the hospital; survival to hospital discharge occurred in only 5 patients (5.2%). Survival to hospital admission was higher among VF/VT presenting rhythms (36%) than for those with other rhythms (17%, P = 0.07), but survival to discharge among VF/VT rhythms (9%) was not statistically different from other rhythms (3%, P = 0.45). Among VF/VT patients, survival to discharge was correlated with shorter call to first defibrillation intervals. Mean call to response interval was longer than in other reported studies (7.2 +/- 4.3 minutes). In addition, there was a high drop-out rate of EMT participants, no central/uniform early access system (that is, 911), and a lower rate of CPR than reported in other studies. It is concluded that introduction of an EMT-D program without careful analysis of systems response factors will not lead to the improved cardiac arrest survival percentages that have previously been reported.

Variability of blood gases, pulse oximeter saturation, and end-tidal carbon dioxide pressure in stable, mechanically ventilated trauma patients

We evaluated the short-term variability of Pao 2, Paco 2, pulse oximeter saturation (Spo 2), and end-tidalPco 2 (Petco 2) in mechanically ventilated trauma patients. All patients were stable and undisturbed during the evaluation periods. Blood gases were obtained from an arterial catheter 4 times at 20-minute intervals.Spo 2 andPetco 2 were recorded when the blood gases were obtained. Fifty evaluations were made in 26 patients; 24 patients were evaluated twice, with ≥24 hours between evaluation periods. Variability was expressed as coefficient of variation (%CV) for each evaluation period. The median %CVs were 3.6% for Pao 2 (95th percentile = 9.8%), 0.5% forSpo 2 (95th percentile = 1.4%), 2.8% for Paco 2 (95th percentile = 7.4%), and 2.4% forPetco 2 (95th percentile = 7.1%). The overall correlation between Paco 2 andPetco 2 wasr=0.80, and the mean difference between Paco 2 andPetco 2 was 0.9±3.6 mm Hg. The variability ofPetco 2 was similar to the variability of Paco 2. However, the variability of Pao 2 was considerably greater than that ofSpo 2, which was probably related to the shape of the oxyhemoglobin dissociation curve and the relatively high saturations of the patients in this study. Variability of blood gases,Spo 2, andPetco 2 should be considered when these values are clinically interpreted.We evaluated the short-term variability of Pao2, Paco2, pulse oximeter saturation (Spo2), and end-tidalPco2 (Petco2) in mechanically ventilated trauma patients. All patients were stable and undisturbed during the evaluation periods. Blood gases were obtained from an arterial catheter 4 times at 20-minute intervals.Spo2 andPetco2 were recorded when the blood gases were obtained. Fifty evaluations were made in 26 patients; 24 patients were evaluated twice, with ≥24 hours between evaluation periods. Variability was expressed as coefficient of variation (%CV) for each evaluation period. The median %CVs were 3.6% for Pao2 (95th percentile = 9.8%), 0.5% forSpo2 (95th percentile = 1.4%), 2.8% for Paco2 (95th percentile = 7.4%), and 2.4% forPetco2 (95th percentile = 7.1%). The overall correlation between Paco2 andPetco2 wasr=0.80, and the mean difference between Paco2 andPetco2 was 0.9±3.6 mm Hg. The variability ofPetco2 was similar to the variability of Paco2. However, the variability of Pao2 was considerably greater than that ofSpo2, which was probably related to the shape of the oxyhemoglobin dissociation curve and the relatively high saturations of the patients in this study. Variability of blood gases,Spo2, andPetco2 should be considered when these values are clinically interpreted.

Comparison of six methods to calculate airway resistance during mechanical ventilation in adults

Objective. A variety of methods are used to calculate indices of lung mechanics. We conducted this study to compare 6 methods of calculating airway resistance.Methods. Data were recorded from 20 adult mechanically ventilated patients. All were relaxed and breathing in synchrony with the ventilator, and an end-inspiratory pause sufficient to produce a pressure plateau (0.5–1.5 s) was used. Pressure and flow rate were measured at the proximal airway using a calibrated lung mechanics analyzer (VenTrak, Med Science, St Louis, MO). Flow rate, pressure, and volume were printed simultaneously. Airway resistance was calculated using 6 methods: Suter, Krieger, Neergard, Bergman, Comroe, and Jonson.Results. Mean calculated resistances (± SD) (cm H2O/L/s) were 11.7 ± 4.8 (Suter method), 13.3 ± 5.0 (Krieger method), 14.9 ± 5.3 (Neergard method), 25.0 ± 6.6 (Bergman method), 24.7 ± 6.4 (Comroe method), and 26.9 ± 4.8 (Jonson method). By repeated measures analysis of variance, these differences were significant (p < 0.001). Using Scheffe analysis, no difference was found between the calculations using the Bergman, Comroe, and Jonson methods; these were significantly greater than the other 3 methods (p < 0.05).Conclusions. Methods that evaluate expiratory resistance (Comroe, Bergman, and Jonson) produce higher values than methods that evaluate inspiratory resistance (Suter and Neergard) or a combination of inspiratory and expiratory resistance (Krieger). Because of these differences, investigators should clearly describe their calculations when reporting airway resistance values.RésuméObjectifs. De nombreuses méthodes sont utilisées pour calculer des indices de mécanique respiratoire. Nous avons réalisé une étude afin de comparer 6 méthodes de calcul de la résistance des voies aériennes.Méthodes. Les paramètres respiratoires de 20 patients adultes sous ventilation mécanique ont été enregistrés. Tous les patients étaient calmes et ne présentaient aucun asynchronisme avec le respirateur. Une pause en fin d’inspiration, suffisante pour entrainer un plateau de pression (durée 0,5 – 1,5s), était appliquée. La pression et le débit étaient mesurés au niveau des voies aériennes proximales par l’intermédiaire d’un analyseur calibré de mécanique respiratoire (Ventrak, Med Science, St Louis, MO). Les courbes de débit, pression et volume étaient imprimées simultanément. La résistance des voies aériennes a été calculée selon 6 méthodes: Suter, Krieger, Neergard, Bergman, Comroe, et Jonson.Résultats. Les résistances calculées (moyenne ± écarts-type) (cm H2O/L/s) ont été 11,7 ± 4,8 (méthode de Suter), 13,3 ± 5,0 (méthode de Krieger), 14,9 ± 5,3 (méthode de Neergard), 25,0 ± 6,6 (méthode de Bergman), 24,7 ± 6,4 (méthode de Comroe), et 26,9 ± 4,8 (méthode de Jonson). L’analyse de la variance a révélé une différence significative entre toutes ces méthodes (p < 0,001). L’analyse de Scheffe n’a retrouvé aucune différence significative entre les résultats issus des méthodes de Bergman, Comroe, et Jonson; ceux-ci sont significativement plus élevés qu’avec les 3 autres méthodes (p < 0.05).Conclusions. Les méthodes évaluant la résistance expiratoire (Comroe, Bergman, et Jonson) conduisent à des valeurs plus élevées que les méthodes évaluant la résistance inspiratoire (Suter et Neergard) ou une combinaison de la résistance expiratoire et inspiratoire (Krieger). En raison de ces différences, les investigateurs devraient clairement décrire les calculs utilisés lorsque sont présentés des valeurs de résistance des voies aériennes.KurzfassungZiel. Eine Reihe von Methoden werden zur Berechnung von Merkmalen der Lungenmechanik verwendet. Wir führten diese Untersuchung mit dem Ziel durch, 6 Methoden zur Berechnung des Atemwegewiderstands zu vergleichen.Methoden. Die Daten von 20 erwachsenen, künstlich beatmeten Patienten wurden aufgezeichnet. Alle waren relaxiert und atmeten synchron zum Beatmungsgerät, und eine endinspiratorische Pause, ausreichend zur Ausbildung eines Druckplateaus (0,51, 5 sec), wurde angewendet. Druck und Flowrate wurden am proximalen Luftweg mit einem kalibrierten Lungenmechanik-Monitor (VenTrak, Med Science, St Louis, Mo) gemessen. Gleichzeitig wurden Flowrate, Druck und Volumen ausgedruckt. Der Atemwegewiderstand wurde nach 6 Methoden berechnet: nach Suter, Krieger, Neergard, Bergman, Comroe und Jonson.Ergebnisse. Die berechneten mittleren Widerstánde (± SD) (cm H22O/1/sec) betrugen 11,7 ± 4,8 (Suter-Methode ), 13,3 ± 5,0 (Krieger-Methode), 14,9 ± 5,3 (Neergard-Methode), 25,0 ± 6,6 (Bergman-Methode), 24,7 ± 6,4 (Comroe-Methode), und 26,9 ± 4,8 (Jonson-Methode). In der Varianzanalyse der wiederholten Messungen waren diese Unterschiede signifikant (p < 0,001). Mit Hilfe der Scheffe-Analyse wurden zwischen den Berechnungen nach den Methoden von Bergman, Comroe und Jonson keine Unterschiede festgestellt; diese waren signifikant größer als die drei anderen Methoden (p < 0,05).Schlußfolgerung. Methoden zur Beurteilung des exspiratorischen Widerstandes (Comroe, Bergman und Jonson) ergeben höhere Werte als Methoden zur Beurteilung des inspiratorischen Widerstandes (Suter und Neergard) oder der Kombination von inspiratorischem und exspiratorischem Widerstand (Krieger). Auf Grund dieser Unterschiede sollten Forscher bei der Veröffentlichung von Werten des Atemwegewiderstands ihre Berechnungen eindeutig beschreiben.ResumenObjetivo. Existe una variedad de métodos para calcular índices de mecánica pulmonar. Este estudio comparó 6 diferentes métodos para calcular resistencia de vía aérea.Métodos. Se colectó información de 20 pacientes adultos ventilados mecánicamente. Todos estaban relajados y ventilando en forma sincrónica con el respirador. Se usó pausa de fin de inspiración suficiente para producir presión de plateau durante 0.5 a 1.5 segundos. Se midió presión y flujo en la vía aérea proximal usando un analizador calibrado de mecánica pulmonar (VenTrak, MedScience, St Louis, MO). Flujo, presión y volumen fueron impresos en forma simultánea. La resistencia de la vía aérea se calculó usando seis métodos: Suter, Krieger, Neergard, Bergman, Comroe, yjonson.Resultados. Las resistencias promedio calculadas (± DS) (cm H2O/L/ seg) fueron 11.7 ± 4.8 (Método de Suter), 13.3 ± 5.0 (Método de Krieger), 14.9 ± 5.3 (Método de Neergard), 25.0 ± 6.6 (Método de Bergman), 24.7 ±6.4 (Método de Comroe), y 26.9 ±4.8 (Método de Jonson). Estas diferencias fueron significativas usando análisis de varianza para muestras repetidas (p < 0.001). No se detectó diferencias al usar análisis de Scheffé entre los cálculos usando las técnicas de Bergman, Comroe y Jonson; estas tres fueron significativamente mayores que los otros tres métodos (p < 0.05).Conclusiones. Los métodos de evaluación de la resistencia expiratoria de Comroe, Bergman y Jonson producen valores más altos que los métodos que evalúan la resistencia inspiratoria de Suter y Neergard o la combinación inspiratoria-expiratoria de Krieger. Debido a la existencia de estas diferencias, los investigadores deberían especificar claramente el método usado al reportar valores de resistencia de vía aérea.

Prehospital administration of inhaled metaproterenol

STUDY OBJECTIVES We conducted a study of the prehospital use of inhaled metaproterenol. DESIGN, SETTING, TYPE OF PARTICIPANTS, AND INTERVENTIONS: Advanced life support (ALS) providers were trained with a standardized curriculum to identify patients likely to benefit from prehospital inhaled metaproterenol administration. Unit doses of metaproterenol were used in a small-volume nebulizer. We prospectively included 122 patients in an initial study (71 men; age, 63 +/- 19 years) to evaluate the safety and effectiveness of metaproterenol in the field, and 150 patients (including the original 122) in an additional study to evaluate patient selection criteria. MEASUREMENTS AND MAIN RESULTS The treatments resulted in an increase in peak flows, a decrease in respiratory rates, and no change in heart rates. In 62% of patients, the increase in peak flow exceeded 15%. Wheezing improved in 59% of the patients, worsened in 4%, and did not change in the remainder. Air entry by auscultation improved subjectively in 59% of patients. Mild tremor occurred in 8% of patients, moderate tremor occurred in 1%, and no tremor occurred in the remainder. Significant dysrhythmias did not occur. CONCLUSIONS ALS providers correctly identified patients for this therapy. No technical problems were encountered in the field with this treatment approach. We conclude that ALS providers can be taught to identify patients likely to benefit from inhaled metaproterenol, that inhaled metaproterenol can be administered in the field, and that metaproterenol is both safe and effective when used in the prehospital setting.