Is the orientation of the apical defibrillation paddle of importance during manual external defibrillation?
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).where 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.
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Cited by (27)
European Resuscitation Council Guidelines 2021: Adult advanced life support
2021, ResuscitationCitation Excerpt :Either pad can be placed in either position (apex or sternal). An observational study in patients undergoing elective cardioversion with external defibrillator paddles showed that transthoracic impedance was lower when the paddle was orientated in a cranio-caudal direction.126 Consider shaving the chest if it is very hairy and the electrodes will not stick firmly.
European Resuscitation Council Guidelines for Resuscitation 2015. Section 3. Adult advanced life support.
2015, ResuscitationCitation Excerpt :It does not matter which electrode (apex/sternum) is placed in either position. The long axis of the apical paddle should be orientated in a cranio-caudal direction to minimise transthoracic impedance.438 Atrial fibrillation is maintained by functional re-entry circuits anchored in the left atrium.
Analysis of transthoracic impedance during real cardiac arrest defibrillation attempts in older children and adolescents: Are stacked-shocks appropriate?
2010, ResuscitationCitation Excerpt :One of the major determinants of current flow is transthoracic impedance. TTI is dependent on multiple patient and care delivery factors: body weight, body surface area, chest size, fat, hypothermia, variations in patient fluid status (pulmonary edema, heart failure, edema, etc.), paddle/pad size, paddle force and skin contact, pad orientation and number of prior shocks given.16–26 Defibrillation success is affected mainly by TTI and energy dose delivered, though various other patient and equipment factors also affect the response to defibrillation attempts.
European Resuscitation Council Guidelines for Resuscitation 2010 Section 3. Electrical therapies: Automated external defibrillators, defibrillation, cardioversion and pacing
2010, ResuscitationCitation Excerpt :Transthoracic impedance has been shown to be minimised when the apical electrode is not placed over the female breast.63 Asymmetrically shaped apical electrodes have a lower impedance when placed longitudinally rather than transversely.64 Atrial fibrillation is maintained by functional re-entry circuits anchored in the left atrium.
Part 10: Paediatric basic and advanced life support: 2010 International consensus on cardiopulmonary resuscitation and emergency cardiovascular care science with treatment recommendations
2010, ResuscitationCitation Excerpt :Transthoracic impedance was increased in one adult LOE 5267 study by placing the pads too close together and in one LOE 5260 study when the pads were placed over the female breast. Additionally, one adult LOE 5268 study showed that placing the apical pad in a horizontal position lowers transthoracic impedance. There is insufficient evidence to alter the current recommendations to use the largest size paddles/pads that fit on the infant or child's chest without touching each other or to recommend one paddle/pad position or type over another.
Physical principles of defibrillators
2009, Anaesthesia and Intensive Care Medicine