older children (9 to 18 years old) had an incidence of an initial shockable rhythm similar to that of adults (32%) TABLE 9.7 PRESENTING RHYTHM IN PEDIATRIC PATIENTS WITH OUT-OFHOSPITAL CARDIOPULMONARY ARREST AND IN-HOSPITAL CARDIOPULMONARY ARREST (%) Defibrillation is the asynchronous delivery of a shock to the myocardium in an attempt to produce simultaneous depolarization of a critical mass of myocardial cells to allow spontaneous repolarization and the resumption of a perfusing cardiac rhythm Most defibrillators deliver biphasic wave forms, allowing for successful defibrillation at a lower energy of 150 J Standard adult paddles, to 13 cm in diameter and pediatric paddles 4.5 cm in diameter, are available with most defibrillators The correct paddle size is that which makes complete uniform contact with the chest wall The large paddle can usually be used for infants older than year of age and/or weighing more than 10 kg Larger paddle surfaces result in decreased intrathoracic impedance and optimize the energy reaching the myocardium Electrode paste decreases impedance and prevents skin injury Paddles are applied anteriorly at the right upper chest below the clavicle and to the left of the nipple in the anterior axillary line directly over the heart; they are applied with pressure and should never touch each other Most defibrillators also have disposable hands-free adhesive pads that allow both rhythm recognition and shock delivery These can be applied in the same location on the arrested child, or