Elsevier

Resuscitation

Volume 56, Issue 1, January 2003, Pages 15-18
Resuscitation

Is the orientation of the apical defibrillation paddle of importance during manual external defibrillation?

https://doi.org/10.1016/S0300-9572(02)00290-3Get rights and content

Abstract

Objective: Transthoracic impedance (TTI) is a factor determining the magnitude of the transmyocardial current during external defibrillation. Minimising TTI increases the chances of successful defibrillation. Most external defibrillation paddles are rectangular in shape and can, therefore, be placed in a transverse or longitudinal orientation. The apical paddle is often placed in a transverse orientation. This may theoretically result in a higher TTI than a longitudinal orientation because of poorer contact at the lateral paddle edges. We compared TTI with the apical paddle in both a transverse and longitudinal orientation. Materials and methods: Twenty sequential anaesthetised patients were studied. A pair of defibrillator paddles were instrumented to measure paddle force. TTI was recorded pre-operatively at end-expiration with the apical paddle in both longitudinal and transverse orientations. The sternal paddle was placed in a longitudinal orientation for all measurements. Results: TTI decreased in both transverse and longitudinal orientations as paddle force increased. Transverse paddle orientation resulted in a significantly (P<0.01) higher TTI than longitudinal orientation at all paddle forces below 12 kg force. Conclusion: The longitudinal orientation of a rectangular defibrillation paddle provides a lower TTI than orientation horizontally.

Sumàrio

Objectivo: A impedância transtorácica (ITT) é um factor determinate na magnitude da corrente transmiocárdica durante desfibrilhação externa. Minimizar a ITT aumenta a probabilidade de desfibrilhação eficaz. A maioria das pás externas de desfibrilhação são rectangulares e podem por isso ser colocadas numa orientação transversal ou longitudinal. A pá apical é muitas vezes colocada numa posição transversal. Em teoria, isto pode resultar numa ITT maior que numa orientação longitudinal devido ao pior contacto nos bordos laterais da pá. Comparamos a ITT com a pá apical nas orientações transversal e longitudinal. Materiais e métodos: Foram estudados vinte doentes seguidos, anestesiados. Um par de pás de desfibrilação foram preparadas para medir a força aplicada. A ITT foi medida no pré-operatório, no final da expiração com a pá apical nas orientações longitudinal e transversal. A pá esternal foi colocada longitudinalmente em todas as medições. Resultados: A ITT diminuiu em ambas as orientações á medida que a força aplicada na pá era aumentada. A orientação transversa da pá resultou numa ITT significativamente maior (P<0.01) que a orientação longitudinal para forças até 12 kg. Conclusão: A orientação longitudinal de uma pá rectangular de desfibrilação resulta numa ITT menor que a orientação transversa.

Resumen

Objetivo: La impedancia transtorácica (TTI) es un factor determinante de la magnitud de corriente transmiocárdica durante la desfibrilación externa.. El minimizar la TTI aumenta la posibilidad de desfibrilación exitosa. La mayorı&#x0301;a de los electrodos de desfibrilación externa son de forma rectangular y, pueden ser ubicadas con orientación transversal o longitudinal. La paleta apical es frecuentemente ubicada con orientación transversal. Esto podrı&#x0301;a teóricamente resultar en más alta TTI que en orientación longitudinal por el menor contacto en los bordes de la paleta. Comparamos la TTI con la paleta apical en ambas orientaciones, transversa y longitudinal. Materiales y métodos: Se estudiaron 20 pacientes anestesiados consecutivos. Se instrumentaron un par de paletas de desfibrilación para medir la la fuerza de la paleta. Se registró la TTI preoperatorio a final de espiración con la paleta apical tanto en orientación longitudinal y transversal. La paleta esternal fue ubicada en orientación longitudinal para todas las medidas. Resultado: La TTI disminuyó en ambas orientaciones a medida que aumentaba la fuerza aplicada sobre la paleta. La orientación transversa de la paleta resultó en TTI significativamente mas alta (P<0.01) que en orientación longitudinal en todas las fuerzas bajo 12 kg. Conclusión: La orientación longitudinal de una paleta de desfibrilación provee una menor impedancia que la orientación horizontal.

Introduction

Successful defibrillation is achieved by the passage of a transthoracic electrical current between two external electrodes, resulting in a transmyocardial current of sufficient magnitude to defibrillate a critical mass of myocardium [1]. Since current guidelines for external defibrillation specify the delivery of a fixed amount of energy [2], the magnitude of this current (Im) is determined by transthoracic impedance (TTI).ImEZwhere Im is the peak discharge current; Z is the TTI and E is the electrical energy.

High TTI decreases transmyocardial current and reduces the chances of successful defibrillation. Therefore, measures that minimise TTI should improve the success of defibrillation [3], [4].

Although intrinsic factors determining TTI such as lung volume and thoracic size are fixed, several extrinsic factors such as paddle force, coupling agent and paddle position are variable and dependent upon the operator during defibrillation [5], [6]. Paddle orientation as a factor affecting TTI has not previously been studied. Most external defibrillation paddles are rectangular in shape, allowing them to be placed in a longitudinal (cranio-caudal) or transverse orientation (Fig. 1). Although we believed the sternal paddle to be generally placed in a longitudinal position, a small survey in our institution of doctors involved in defibrillation showed that numbers were equally divided between those who would place the apical paddle in a transverse or longitudinal orientation (n=50). Current guidelines do not specify as to the optimal orientation and we are not aware of any studies which have compared the TTI between the two.

We, therefore, undertook a study to compare TTI with the apical paddle placed in the longitudinal and transverse planes, across a range of paddle forces.

Section snippets

Methods

Following approval by our local Ethics Committee, we obtained informed written consent from 20 sequential patients undergoing elective cardiac surgery. Patients who had undergone previous cardiac surgery were excluded from this study because thoracotomy has been shown to decrease TTI and may also affect thoracic compliance. All men with hirsute chests were shaved the night before their surgery.

Routine medication was continued until the morning of surgery. Patients received lorazepam 1–2 mg

Results

Twenty subjects were recruited to the study (13 male, seven female). Randomisation of the orientation of the apical paddle for the initial reading resulted in ten subjects studied with the defibrillation paddle initially placed in the longitudinal orientation. The remaining ten subjects were randomised to the opposite order.

The results of the study are summarised in Table 1 and Fig. 2. TTI decreased in both apical and longitudinal orientations as paddle force increased. The difference in

Discussion

Longitudinal orientation of the apical defibrillation paddle compared with transverse orientation results in a lower TTI at all paddle forces between 1 and 12 kg force. We believe that this has not been documented previously.

The median value of paddle force applied to both apical and sternal paddles during defibrillation is 6 kg force [8]. At this force, overall TTI is increased by 3.9 Ω (5.0%) using a transverse rather than longitudinal apical paddle orientation (P<0.001). Although this study

Acknowledgements

This research was funded by the Nuffield Fund of the Royal College of Anaesthetists. We thank Steve Clitheroe for his technical assistance.

References (9)

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