weighed heavily in the survival from VF. We do not known how many of the 23 survivors who benefitted from prehospital defibrillation were in this EMT-witnessed group. Obviously those patients who experienced an EMTwitnessed arrest, were defibrillated immediately, and regained a spontaneous circulation were the direct beneficiaries of this intervention. At the same time, such patients comprise a rather select group among those with out-ofhospital VF, in this study a somewhat surprisingly large 8.5% of those with VF. Ten survivors experienced impaired cerebral performance. EKen if~ this includes all three patients with electromechanical dissociation, there still remain seven "survivors" of VF with cerebral impairment. Whether patients with neurologic impairment after cardiorespiratory arrest and resuscitation should be considered "survivors" is certainly open to serious question.
We believe these observations on this experience must be taken into account in an attempt to define the presumed benefits of early defibrillation conferred on patients in this published experience. We have been, and remain, advocates of the development and implementation of early defibrillation programs, but we believe it is mandatory to scrutinize available data very carefully in quantitating the benefits of this treatment in a variety of prehospital environments.
Roger D White, MD Department of Anesthesiology Larry F Vukov, MD Department of Medicine Mayo Medical School and Mayo Clinic Rochester, Minnesota
D a t a C o l l e c t i o n & O b s e r v e r Bias To the Editor: Drs Jones, Nesper, and Alcouloumre reported the results of a prospective examination of prehospital intravenous line placement in "Prehospital Intravenous Line Placement: A Prospective Study" [March 1989;18:244246]. Although the authors did not subject their data to statistical analysis, they did report rates. It is our conclusion that an incorrect denominator was used to determine the IV line start success rate. The denominator used was identified in the following excerpt from the paper: "All data forms that were returned and that included an IV line attempt (except those performed by a paramedic trainee) were entered into the study." The total number of IV line attempts, not the number of data forms returned, by the observed paramedic units during the period of the study would have been the correct denominator. One can imagine a worst-case scenario in ~which wellmeaning but biased observers return only data forms for IV line attempts that proceed quickly and successfully.
Roland W Petri, MD Stanford University Stanford, California Robert Wears, MD University of Florida Jacksonville In Reply: We appreciate the comments by Drs Petri and Wears in regard to our study. The language used in the methods section may have misled them to make an erroneous in-
ference. Because the data forms included some information that was obtained by observers in advance of the IV attempt (age, chief complaint, time of arrival, initial vital signs), many data forms were initiated on patients who ultimately did not have an IV line attempted. Because the true denominator was the number of IV attempts, only the patients on whom an IV line was attempted were included in the study. Alternately, we could have stated that "all data forms that were returned that did not include an IV attempt were not entered into the study." Although any unblinded observational study like ours is potentially subject to observer bias, we disagree with their inference that it did occur. Paramedics were the only personnel starting the IV lines in the study, and none of our observers were paramedics. Most of the observers were medical students who were unaware of the controversy surrounding prehospital line placement, and they were not routinely informed of the underlying purpose of the study. Finally, given their distinct observer status, we believe it is unlikely that observers gained any individual benefit by biasing the outcome.
Stephen E Jones, MD LAC/USC Medical Center Los Angeles, California Timothy P Nesper, MD Riverside General Hospital~University Medical Center Riverside, California Eric Alcouloumre, MD Hoag Memorial Hospital Newport Beach, California
C o s t - E f f e c t i v e n e s s : A s s e r t e d , Not S h o w n To the Editor: Cwinn and colleagues asserted cost-effectiveness for their approach to providing emergency medical services at 19:5 May 1990
Denver's Stapleton International Airport in their article, "Prehospital Care at a Major International Airport" [Octo-
Annals of Emergency Medicine
614/173
CORRESPONDENCE
ber 1988;17:1042-1048]. While their report does demonstrate the efficiency of their approach, it does not provide evidence to support the conclusion of cost-effectiveness beyond their assertion. Cost-effectiveness is a form of economic analysis that may be applied to many endeavors, including health care. It depends on an analysis of both costs and the consequences of the program. Defined objectives are evaluated for evidence of improvement while at the same time no change (worsening) occurs in other measures. If worsening occurs, then an analysis of trade-offs must be included. 1 For example, if Cwinn and colleagues had sought a reduction in unnecessary trips to the airport with no concomitant deterioration in patient outcomes as their objectives yet had found increased morbidity of a subset of patients because of delayed transport, then a trade-off analysis
would be required. The authors apparently achieved their objectives, and while I don't doubt that the cost-effectiveness analysis was conducted by the authors, no cost data were presented. Thus, cost-effectiveness was simply asserted, not demonstrated. Given the growing scrutiny of health care services by all levels of government and other interested parties, it behooves us to document fully our assertions of cost-benefit or cost-effectiveness in new health care programs.
Steven J Davidson, MD, MBA, FACEP Philadelphia EMS Philadelphia, Pennsylvania 1. Drummond ME Stoddart GL, Torrance GW: Cost effectiveness analysis, in: Methods for the Economic Evaluation of Health Care Programme& Oxford, UK, Oxford Medical Publications, 1987, p 74-111.
Lung Function C o m p r o m i s e d by Spinal I m m o b i l i z a t i o n To the Editor: Bauer and Kowalski, in their article, "Effect of Spinal Immobilization Devices on Pulmonary Function in the Healthy, Nonsmoking Man" [September 1988;17:915-918], described for the first time reductions of pulmonary function volumes caused by spinal immobilization devices. They noted that these findings need documentation in the clinical setting. We report a case of compromised lung function caused by spinal immobilization of a multiple trauma patient. A 17-year-old man presented to a rural hospital with facial lacerations, left lung contusions, fracture of the distal left humerus with radial nerve palsy, and tearing of the ascending colonic mesentery following an automobile accident. On admission, his vital signs were blood pressure of 120/70 m m Hg; pulse, 78; respirations 26; and temperature, 37.1 C; and he was alert. Arterial blood gases on room air revealed PO2, 87 m m Hg; Pcoz, 42 m m Hg; pH, 7.39; and HCO3, 20 mEq/L. Oxygen was given at 10 L/min by a nonrebreather mask. An XP-1 cervical collar with short board and chest straps was applied in the emergency department for cervical stabilization after the first arterial blood gas because all available cervical collars in the department were in use. During the next hour the patient became combative, less alert, and more tachycardic. A repeat arterial blood gas revealed POz, 47 m m Hg; Pcoz, 48 m m Hg; pH, 7.29; and I-tCO3, 20 mEq/L. A defective wall outlet for oxygen was discovered. The patient was given the oxygen through a new outlet and the XP-1 device was removed. Thirty minutes later the arterial blood gases revealed POz, 206 m m Hg; Pco z 39 m m Hg; pH, 7.34; and HCO 3 21 mEq/L. The patient became less combative and more alert. He was taken to surgery and made an uneventful recovery. This case demonstrates the deleterious effect of spinal i m m o b i l i z a t i o n devices on p u l m o n a r y function of the multiple trauma patient. Although the i m p r o v e m e n t of oxygenation in this case was undoubtedly the result of the application of oxygen, the reduction of the P c o z c o r r e 174~15
sponded with the increased ventilation that followed removal of the device. Also, alveolar hypoventilation followed the application of the device. Other studies have d o c u m e n t e d the effect of chest strapping on pulmonary mechanics. Significant findings include a reduction of outward chest recoil, a decrease of both chest wall and lung compliance, an increase of the work of breathing due to increased resistance of the chest wall to distention, and an uneven distribution of pulmonary gas flow. These alterations of pulmonary mechanics result in significant reductions in vital capacity, total lung capacity, functional residual capacity, and respiratory volume. Thus, the n o r m a l strapped r e s p i r a t o r y s y s t e m closely resembles the respiratory system of a markedly obese subject, t-s These abnormalities caused by restricted breathing at low volumes persist after the strapping is removed until the subjects resume breathing at normal total lung capacity. 6 Because victims of multiple trauma often have thoracic cage and proximal airway abnormalities, central hypoventilation caused by central nervous system trauma, and pulmonary shunting caused by lung contusions, it seems that prolonged application of the extrication devices may present a risk to the patient. Because these apparatuses are useful for extrication, we recommend immediate loosening of the chest straps following extrication and immobilization. In addition, the patient should be encouraged to breathe deeply because alterations of p u l m o n a r y mechanics persist at low-volume breathing until normal total lung capacity is reached. Mark Walsh, MD, FACEP South Bend, Indiana Terry Grant Sam Mickey Elizabeth City, North Carolina 1. DeTroyer A: Mechanics of the chest wall during restrictive thoracic strapping. Respiration 1980139:241-250.
Annalsof EmergencyMedicine
19:5 May 1990
We believe these observations on this experience must be taken into account in an attempt to define the presumed benefits of early defibrillation conferred on patients in this published experience. We have been, and remain, advocates of the development and implementation of early defibrillation programs, but we believe it is mandatory to scrutinize available data very carefully in quantitating the benefits of this treatment in a variety of prehospital environments.
Roger D White, MD Department of Anesthesiology Larry F Vukov, MD Department of Medicine Mayo Medical School and Mayo Clinic Rochester, Minnesota
D a t a C o l l e c t i o n & O b s e r v e r Bias To the Editor: Drs Jones, Nesper, and Alcouloumre reported the results of a prospective examination of prehospital intravenous line placement in "Prehospital Intravenous Line Placement: A Prospective Study" [March 1989;18:244246]. Although the authors did not subject their data to statistical analysis, they did report rates. It is our conclusion that an incorrect denominator was used to determine the IV line start success rate. The denominator used was identified in the following excerpt from the paper: "All data forms that were returned and that included an IV line attempt (except those performed by a paramedic trainee) were entered into the study." The total number of IV line attempts, not the number of data forms returned, by the observed paramedic units during the period of the study would have been the correct denominator. One can imagine a worst-case scenario in ~which wellmeaning but biased observers return only data forms for IV line attempts that proceed quickly and successfully.
Roland W Petri, MD Stanford University Stanford, California Robert Wears, MD University of Florida Jacksonville In Reply: We appreciate the comments by Drs Petri and Wears in regard to our study. The language used in the methods section may have misled them to make an erroneous in-
ference. Because the data forms included some information that was obtained by observers in advance of the IV attempt (age, chief complaint, time of arrival, initial vital signs), many data forms were initiated on patients who ultimately did not have an IV line attempted. Because the true denominator was the number of IV attempts, only the patients on whom an IV line was attempted were included in the study. Alternately, we could have stated that "all data forms that were returned that did not include an IV attempt were not entered into the study." Although any unblinded observational study like ours is potentially subject to observer bias, we disagree with their inference that it did occur. Paramedics were the only personnel starting the IV lines in the study, and none of our observers were paramedics. Most of the observers were medical students who were unaware of the controversy surrounding prehospital line placement, and they were not routinely informed of the underlying purpose of the study. Finally, given their distinct observer status, we believe it is unlikely that observers gained any individual benefit by biasing the outcome.
Stephen E Jones, MD LAC/USC Medical Center Los Angeles, California Timothy P Nesper, MD Riverside General Hospital~University Medical Center Riverside, California Eric Alcouloumre, MD Hoag Memorial Hospital Newport Beach, California
C o s t - E f f e c t i v e n e s s : A s s e r t e d , Not S h o w n To the Editor: Cwinn and colleagues asserted cost-effectiveness for their approach to providing emergency medical services at 19:5 May 1990
Denver's Stapleton International Airport in their article, "Prehospital Care at a Major International Airport" [Octo-
Annals of Emergency Medicine
614/173
CORRESPONDENCE
ber 1988;17:1042-1048]. While their report does demonstrate the efficiency of their approach, it does not provide evidence to support the conclusion of cost-effectiveness beyond their assertion. Cost-effectiveness is a form of economic analysis that may be applied to many endeavors, including health care. It depends on an analysis of both costs and the consequences of the program. Defined objectives are evaluated for evidence of improvement while at the same time no change (worsening) occurs in other measures. If worsening occurs, then an analysis of trade-offs must be included. 1 For example, if Cwinn and colleagues had sought a reduction in unnecessary trips to the airport with no concomitant deterioration in patient outcomes as their objectives yet had found increased morbidity of a subset of patients because of delayed transport, then a trade-off analysis
would be required. The authors apparently achieved their objectives, and while I don't doubt that the cost-effectiveness analysis was conducted by the authors, no cost data were presented. Thus, cost-effectiveness was simply asserted, not demonstrated. Given the growing scrutiny of health care services by all levels of government and other interested parties, it behooves us to document fully our assertions of cost-benefit or cost-effectiveness in new health care programs.
Steven J Davidson, MD, MBA, FACEP Philadelphia EMS Philadelphia, Pennsylvania 1. Drummond ME Stoddart GL, Torrance GW: Cost effectiveness analysis, in: Methods for the Economic Evaluation of Health Care Programme& Oxford, UK, Oxford Medical Publications, 1987, p 74-111.
Lung Function C o m p r o m i s e d by Spinal I m m o b i l i z a t i o n To the Editor: Bauer and Kowalski, in their article, "Effect of Spinal Immobilization Devices on Pulmonary Function in the Healthy, Nonsmoking Man" [September 1988;17:915-918], described for the first time reductions of pulmonary function volumes caused by spinal immobilization devices. They noted that these findings need documentation in the clinical setting. We report a case of compromised lung function caused by spinal immobilization of a multiple trauma patient. A 17-year-old man presented to a rural hospital with facial lacerations, left lung contusions, fracture of the distal left humerus with radial nerve palsy, and tearing of the ascending colonic mesentery following an automobile accident. On admission, his vital signs were blood pressure of 120/70 m m Hg; pulse, 78; respirations 26; and temperature, 37.1 C; and he was alert. Arterial blood gases on room air revealed PO2, 87 m m Hg; Pcoz, 42 m m Hg; pH, 7.39; and HCO3, 20 mEq/L. Oxygen was given at 10 L/min by a nonrebreather mask. An XP-1 cervical collar with short board and chest straps was applied in the emergency department for cervical stabilization after the first arterial blood gas because all available cervical collars in the department were in use. During the next hour the patient became combative, less alert, and more tachycardic. A repeat arterial blood gas revealed POz, 47 m m Hg; Pcoz, 48 m m Hg; pH, 7.29; and I-tCO3, 20 mEq/L. A defective wall outlet for oxygen was discovered. The patient was given the oxygen through a new outlet and the XP-1 device was removed. Thirty minutes later the arterial blood gases revealed POz, 206 m m Hg; Pco z 39 m m Hg; pH, 7.34; and HCO 3 21 mEq/L. The patient became less combative and more alert. He was taken to surgery and made an uneventful recovery. This case demonstrates the deleterious effect of spinal i m m o b i l i z a t i o n devices on p u l m o n a r y function of the multiple trauma patient. Although the i m p r o v e m e n t of oxygenation in this case was undoubtedly the result of the application of oxygen, the reduction of the P c o z c o r r e 174~15
sponded with the increased ventilation that followed removal of the device. Also, alveolar hypoventilation followed the application of the device. Other studies have d o c u m e n t e d the effect of chest strapping on pulmonary mechanics. Significant findings include a reduction of outward chest recoil, a decrease of both chest wall and lung compliance, an increase of the work of breathing due to increased resistance of the chest wall to distention, and an uneven distribution of pulmonary gas flow. These alterations of pulmonary mechanics result in significant reductions in vital capacity, total lung capacity, functional residual capacity, and respiratory volume. Thus, the n o r m a l strapped r e s p i r a t o r y s y s t e m closely resembles the respiratory system of a markedly obese subject, t-s These abnormalities caused by restricted breathing at low volumes persist after the strapping is removed until the subjects resume breathing at normal total lung capacity. 6 Because victims of multiple trauma often have thoracic cage and proximal airway abnormalities, central hypoventilation caused by central nervous system trauma, and pulmonary shunting caused by lung contusions, it seems that prolonged application of the extrication devices may present a risk to the patient. Because these apparatuses are useful for extrication, we recommend immediate loosening of the chest straps following extrication and immobilization. In addition, the patient should be encouraged to breathe deeply because alterations of p u l m o n a r y mechanics persist at low-volume breathing until normal total lung capacity is reached. Mark Walsh, MD, FACEP South Bend, Indiana Terry Grant Sam Mickey Elizabeth City, North Carolina 1. DeTroyer A: Mechanics of the chest wall during restrictive thoracic strapping. Respiration 1980139:241-250.
Annalsof EmergencyMedicine
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