What is the optimal paddle force for defibrillation?

Introduction

Firm paddle pressure during defibrillation is important to minimize transthoracic impedance (TTI) and optimize trans-myocardial current. Previous European Resuscitation Council (ERC) guidelines recommended that 12 kg force should be used [1] and the more recent International Liaison Committee on Resuscitation (ILCOR) guidelines recommend 'firm' pressure [2]. The actual relationship between force and transthoracic impedance has not been established.

Methods

55 patients (36 male, 19 female) undergoing general anaesthesia for cardiac surgery were investigated. Male chests were shaved. A pair of gel pads and paddles were placed in the anterior-apical position according to the ILCOR guidelines. The endotracheal tube was opened to air and paddles instrumented with force sensors were applied to the chest wall with progressive force to a maximum of 12 kgf. The resultant TTI was recorded at 10 measurements per second to a hard drive.

Results

Light pressure results in a high TTI that rapidly decreases as paddle force increases (Fig. 1). An 18.7% fall in overall TTI occurs when applying force from 0.5 to 6.0 kg. Increasing paddle force from 6 to 12 kg results in a further decrease in TTI of 3.2%.

Figure 1

The relationship between force and mean TTI for 55 patients.

Conclusion

A minimum of 6 kg force applied to each paddle is necessary to achieve 83% of the overall decrease in TTI seen at 12 kgf. Further decrease in TTI as force is applied in excess of 6 kgf is small and a force of 12 kgf only reduces TTI by a further 3.2% compared with TTI at 6 kgf. The additional clinical benefit of applying 12 kgf as opposed to 6 kgf is questionable.