1. Madias C, Maron BJ, Supron S, et al. Cell membrane stretch and Chest blow-induced ventricular fibrillation: Commotio cordis. J Cardiovasc Electrophysiol 2008;19:1304-9.
2. Lakkireddy D, Wallick D, Ryschon K, et al. Effects of cocaine intoxication on the threshold for stun gun induction of ventricular fibrillation. J Am Coll Cardiol 2006;48:805-11.
3. Nanthakumar K, Billingsley I, Masse S, et al. Cardiac electrophysi- ological consequences of neuromuscular incapacitating device dis- charges. J Am Coll Cardiol 2006;48:798-804.

The utility of flow-limited automated mechanical ventilation during airborne hoist rescue missions

To the Editor,

Prehospital rescue operations are often challenging events demanding highly trained professional personnel and proper equipment [1]. These events may be compli- cated by the setting of geographically inaccessible areas that demand airborne hoist rescue, in particular for patients requiring continuous mechanical ventilation. The only operational aeromedical program in Israel compatible with hoist rescue missions is the Air Force Rescue and Aeromedical Evacuation Unit (RAEU). Each RAEU team consists of a flight surgeon and a flight paramedic joined by 3 rescue operators. When a hoist rescue is initiated, the flight physician and 2 rescue operators descend to the patient and complete Urgent treatment and proper affixation to a rescue stretcher and to the winch. The patient and one rescue operator are then elevated to the helicopter followed by the elevation of the flight physician and the second rescue operator. During this procedure, the monitoring of the patient is minimal; and the focus is to the safe execution of the hoist. Upon entering the aircraft, full monitoring and care of the patient are resumed. Immediately after the hoist rescue, the patient is transported straight to a trauma center. Until 2005, the only operational option for RAEU teams to ventilate a patient during hoist rescue was by manual ventilation with a bag-valve ventilation device. To improve ventilation execution during hoist rescues, the RAEU chose to use the Oxylator EM-100 (CPR Medical Devices Inc, Toronto, Canada) [2]. This is a relatively small (57 mm x 108 mm), lightweight (0.25kg), and easy-to-use flow- limited resuscitator. It is dependent on Compressed air or oxygen supply (45-80 psi) and has both manual and automatic modes. Flow pressure limit can be adjusted between 25 and 50 cm H₂O. This portable ventilator allows the rescue operator to focus completely on manipulation of the winch during the hoist.

We reviewed 5 hoist rescue missions in which mechanical ventilation using the Oxylator (ventilator) was undertaken. Data were retrieved from the computerized database of the RAEU (Microsoft Access 2002 software on an SQL server) and the Air Force Command and Control Headquarters logs. All rescued patients were male aged 16

to 55 (mean, 23.6; median, 22) years. Four patients sustained blunt trauma injuries, and one suffered from Heat stroke. The clinical characteristics of the patients and main Prehospital interventions are summarized in Table 1. All patients were connected to the ventilator immediately after securing the airway, before the hoist rescue. The ventilator was set to the automated mode with pressure limit values between 25 and 30 cm H₂O. The ventilator was connected to a portable oxygen tank (D cylinder, minimal pressure of 2200 psi). The duration of ventilation with the ventilator was 7 to 13 (mean, 10.5; median, 10) minutes. After completing the hoist rescue and placing the patients in the helicopter, the ventilator was removed; and ventilation was resumed manually with a bag-valve device (AMBU Mark III; AMBU Corporate, Ballerup, Denmark) for the remaining period of the aeromedical evacuation. Patients were continuously monitored (ETCO₂, pulse, and oxygen saturation) throughout the mission (Nonin 9847 CO2 Detector Pulse oximeter; Nonin Medical Inc, Minneapolis, MN, and the Propaq Encore 206EL; Welch Allyn Inc, Skaneateles falls, NY). Recordings were retrieved before the hoist elevation, immediately after the hoist (before removing the ventilator), and every 5 to 10 minutes during the aeromedical transport. The vital signs of the patients are presented in Table 2. Time from injury to the initiation of the hoist rescue was 60 to 130 (mean, 83; median, 70) minutes. The time of total prehospital mechanical ventila- tion (ground and airborne) was 35 to 65 (mean, 49; median, 50) minutes, and time of airborne evacuation was 15 to 24 (mean, 19; median, 18) minutes. During airborne evacua- tion and upon arrival to the hospital, all patients were hemodynamically and respiratorily stable. Interventions in the hospital and outcome are presented in Table 1. Mechanical ventilation during the hoist procedure was uncomplicated in 4 patients. Technical difficulty was reported in 1 patient (no. 2). In this particular case, obstruction of airflow was detected soon after the connection of the ventilator and before the lift. A distinctive rapidly repetitive sound of air release from the exhaust port was heard pointing to an airflow fault. This was caused by a folding of the external segment of the endotracheal tube due to malposition of the ventilator. The problem was identified immediately and corrected by repositioning the device and securing it in a new position with a band. No deterioration of vital signs was observed in any of the patients during ventilation with the device or immediately after its disconnection to resume manual ventilation.

The need for automated ventilation during hoist rescue originates from operational limitations and risks. In the present report, we provide our initial experience with mechanical ventilation using a small mobile flow-limited resuscitator during hoist rescue missions. The ventilation with the ventilator served as a bridge between manual ventilation on the ground and manual ventilation in the helicopter, permitting the operator to concentrate on the completion of a safe and successful hoist. Ventilation

Table 1 Study patients’ clinical characteristics, hospital interventions, and outcome

Patient 1 Patient 2 Patient 3 Patient 4 Patient 5

Age (y) 16 22 17 28 55

Sex Male Male Male Male Male

Prior health status Healthy Healthy Healthy Healthy Psychiatric disorder

Mechanism of injury Trauma, fall during hiking Trauma, fall during

mountain climbing

Trauma, fall during air-gliding Trauma, fall during hiking Heat stroke during hiking

Main medical diagnosis

Intracranial bleeding and edema, skeletal fractures, lung contusion, Retroperitoneal hematoma

Brain contusion, skeletal fractures, lung contusion, kidney blast

Intracranial bleeding, skeletal fractures, lung contusion

Intracranial bleeding, skeletal fractures, pelvic bleeding, lung contusion

Severe heat stroke with core temperature of 42.5?C, seizures

Level of consciousness before sedation

GCS 6 GCS 3 GCS 3 GCS 7 Coma

ISS 57 22 50 41 NA

Main prehospital interventions

Endotracheal intubation, oxygenation, ventilation, midazolam & ketamine sedation, IV fluid, affixation

Endotracheal intubation, oxygenation, ventilation, midazolam & ketamine sedation, IV fluid, affixation

Endotracheal intubation, oxygenation, ventilation, midazolam & ketamine sedation, IV fluid, affixation

Endotracheal intubation, oxygenation, ventilation, midazolam & ketamine sedation, IV fluid, affixation

Laryngeal mask insertion, oxygenation, ventilation, midazolam & ketamine sedation, IV fluid, affixation

Prehospital ground treatment provider

Other ground team Other ground team Other ground team RAEU team RAEU team

Main interventions in hospital

Craniotomy, ICP catheter, internal fracture fixation

External fracture fixation Craniotomy, ICP catheter,

internal fracture fixation

Iliac artery embolization, internal fracture fixation

external cooling

Outcome Discharged to rehabilitation with cognitive and motor impairment

Discharged to his home without major complications

Discharged to rehabilitation with cognitive and motor impairment

Discharged to his home without major complications

Pronounced dead shortly after arrival to the ED

NA indicates not applicable; ED, emergency department; IV, intravenous; GCS, Glasgow coma scale; ISS, injury severity score; ICP, intracranial pressure.

524

Correspondence

Table 2 Vital signs of patients in the prehospital phase: before, a during, b and after c mechanical ventilation
		Patient 1	Patient 2	Patient 3	Patient 4	Patient 5
SO2 (%)	Prior	98	98	97	92	97
	During	98	98	98	95	95
	After	98	98	97	95	97
ETCO2 (mm Hg)	Prior	40	35	40	40	35
	During	40	35	40	35	35
	After	40	35	35	35	35
Pulse (/min)	Prior	90	110	60	100	140
	During	100	102	60	105	145
	After	105	100	60	108	145
a Within 2 minutes before connecting the ventilator, during manual ventilation. b Immediately after the hoist elevation, inside the helicopter, before removing the ventilator. c Five minutes after removing the ventilator and restarting manual ventilation.

during these critical missions was successful as suggested by the stable monitoring parameters observed. We faced only one technical problem (kink of the endotracheal tube), but this was easily identified and corrected without apparent clinical implications. This observation suggests that strict attention and optimal positioning and fixation of the ventilator should be undertaken before starting the elevation to the helicopter.

The number of published studies that evaluated the utility of the ventilator is limited; and to the best of our knowledge, none reported its utility or any other automated ventilator in hoist rescue missions. Osterwalder and Schuhwerk [3] performed a randomized crossover study comparing a bag-valve device and the ventilator for ventilating a manikin with unprotected airway. The ventilator showed better results with significantly less events of gastric inflation and better minute ventilation values [3]. These results, however, were not found by Barnes et al [4]. In another study, Noordergraaf et al [5] tested the ventilator in a clinical prospective controlled study. In this study, firemen First responders ventilated 104 patients during anesthesia in an operating room setup. The ventilator improved significantly the ability to achieve and maintain normocapnia, even when the responders were distracted, compared with the results achieved by the same personnel with a bag-valve device [5]. On the other hand, the same authors found the ventilator inferior to bag-valve device in maintaining normocapnia in 40 patients ventilated under anesthesia by medical professionals [6]. In the setting of hoist rescue missions, such as our own experience, the ventilation on the winch is not performed by professional medical personnel, but rather by rescue operators. Thus, the use of the ventilator can ensure continuous efficient ventilation. We did not observe any alterations in the parameters of ETCO₂, oxygen saturation, and pulse rate from the beginning of the automated ventilation until the conversion to bag-valve device use.

Although the ventilator can be used for the remaining period of the evacuation, this practice was not used. Compared with hoist elevation, manual ventilation with a

bag-valve device during aeromedical transport is relatively safe; and it is executed by professional medical personnel under less demanding conditions with improved monitoring and easier access to the patient. Yet, different modes of ventilation during aeromedical transport should be further studied.

In conclusion, our experience with automated ventilation suggests that this type of ventilation is efficient for ventilating adult patients with protected airway during the short periods of hoist rescue and facilitates a smoother rescue operation.

Ophir Lavon MD Dan Hershko MD

Israeli Air Force Rescue and Aeromedical Evacuation Unit

Israel Defense Forces PO Box 13289, Nesher 36760, Israel

E-mail address: [email protected]

Erez Barenboim MD

Israeli Air Force Surgeon General Headquarters

Israel Defense Forces, Israel

doi:10.1016/j.ajem.2010.02.001

References

1. Wayne MA, Delbridge TR, Ornato JP, et al. Concepts and application of prehospital ventilation. Prehosp Emerg Care 2001;5:73-8.
2. Lindsey J. The oxylator: an innovative oxygen delivery device. JEMS 2004;29:100-2.
3. Osterwalder JJ, Schuhwerk W. Effectiveness of mask ventilation in a training mannikin. A comparison between the Oxylator EM-100 and the bag-valve device. Resuscitation 1998;36:23-7.
4. Barnes TA, Catino ME, Burns EC, et al. Comparison of an oxygen- powerED flow-limited resuscitator to manual ventilation with an adult 1,000-mL self-inflating bag. Respir Care 2005;50:1445-50.
5. Noordergraaf GJ, van Dun PJ, Kramer BP, et al. Can first responders achieve and maintain normocapnia when sequentially ventilating with a bag-valve device and two oxygen-driven resuscitators? A controlled clinical trial in 104 patients. Eur J Anaesthesiol 2004;21:367-72.

526 Correspondence

1. Noordergraaf GJ, Van Dun PJ, Schors MP, et al. Efficacy and safety in patients on a resuscitator, Oxylator EM-100, in comparison with a bag- valve device. Am J Emerg Med 2004;22:537-43.

Adenosine-induced cardiopulmonary arrest in a patient with Paroxysmal supraventricular tachycardia—

a response

To the Editor,

We read with interest the case report of Walsh et al in September’s issue of the American Journal of Emergency Medicine, “Adenosine-induced cardiopulmonary arrest in a patient with paroxysmal supraventricular tachycardia” [1] (SVT). We recently found success in using the ?-agonist metaraminol to terminate SVT.

An otherwise fit 64-year-old man underwent a laparotomy and colostomy for Crohn disease and associated malignancy. After an uncomplicated general anesthetic, the patient’s heart rate suddenly increased from 70 to 150 beats per minute. A 12-lead electrocardiogram confirmed an atrioventricular nodal reentry tachycardia with a rate of 150 beats per minute. Carotid massage was performed with no effect. Adenosine 6 mg was given as a rapid bolus followed by a large flush, after which the systolic blood pressure dropped significantly to 70 mm Hg. At this point, we decided to sedate the patient for synchronized electrical cardioversion. However, we first administered an Intravenous bolus of

0.5 mg of metaraminol to attempt to increase the patient’s blood pressure, after which the tachyarrhythmia suddenly terminated and systolic blood pressure returned to 120 mm Hg. A further 12-lead electrocardiogram showed no evidence of ischemia or aberrant pathway, and the patient’s subse- quent recovery was uneventful.

Metaraminol is a sympathomimetic amine, having direct and indirect agonist effects at predominantly ?-adrenorecep- tors, thus causing a vasopressor effect [2]. The use of metaraminol for termination of SVT has previously been described as a subcutaneous regimen [3], and other ?-agonists such as phenylephrine have also been used [4]. The proposed mechanism is that, by raising the blood pressure, they cause stimulation of carotid sinus and aortic baroreceptors with consequent reflex vagal stimulation. It has also been proposed that the increase in blood pressure improves Coronary blood flow, reversing any ischemia that may be causing the arrhythmia [4].

Metaraminol has many properties that may make it preferable to adenosine, including absence of bronchospasm, chest pain, and hypotension. Metaraminol can be given peripherally, has no significant Drug interactions, and has a longer half-life than adenosine, making it easier to administer. In the case reported by Walsh et al [1], metaraminol would have been far less likely to lead to cardiopulmonary arrest. As such, we propose that metaraminol could be

considered as part of the management of SVT, particularly if the patient is hypotensive.

Nigel S. Jenkins MB BS, MA

Department of Anaesthetics

Ysbyty Gwynedd LL57 2PW Bangor, UK

Mark Knights Mb ChB

Department of Anaesthetics

Morriston Hospital Swansea, UK

Carsten Eickmann State Exam Med, DA

Department of Anaesthetics

Ysbyty Gwynedd LL57 2PW Bangor, UK

Mark Payne MB BS

Department of Cardiology

Ysbyty Gwynedd Bangor, UK

doi:10.1016/j.ajem.2010.02.020

References

1. Walsh RC, Felice KL, Meehan TJ, Stull BW, Schumann HM, Zautcke JL. Adenosine-induced cardiopulmonary arrest in a patient with paroxysmal supraventricular tachycardia. Am J Emerg Med 2009;27: 901.
2. Sasada M, Smith S. Drugs in anaesthesia & intensive care. 2nd ed. Oxford University Press; 1997.
3. Bowers D. Metaraminol in the treatment of paroxysmal supraventricular tachycardia. Can Med Assoc J 1968;99:868.
4. Jacobson L, Turnquist K, Masley S. Wolff-Parkinson-White syndrome. Termination of paroxysmal supraventricular tachycardia with phenyl- ephrine. Anaesthesia 1985;40(7):657-60.

A response to a letter regarding the case report “Adenosine-induced cardiopulmonary arrest in a patient with paroxysmal supraventricular tachycardia“

To the Editor,

We would like to comment upon the response generated by our original case report, “Adenosine-induced cardiopul- monary arrest in a patient with paroxysmal supraventricular tachycardia.” Although we are grateful for the attention our report has generated, we have some concerns regarding the specifics of the query.

The authors have an excellent case report themselves that likely deserves some consideration to be published on its own and not as part of a letter discussing our report. Not only are the pharmaceuticals involved in both of these cases