Defibrillation delivers a controlled electrical shock to the heart to interrupt a lethal, chaotic rhythm, such as ventricular fibrillation, allowing the heart’s natural pacemaker to restart a normal beat. While the fundamental concept is straightforward, the procedure becomes complex when special patient conditions or environmental factors are present. Recognizing these unique circumstances is necessary to ensure the shock is both effective for the patient and safe for the rescuers. Specialized protocols deviate from the standard adult approach to maximize the chance of success.
Defibrillation Around Internal Devices and Implants
Implanted medical devices, such as pacemakers and implantable cardioverter-defibrillators (ICDs), require modified pad placement to prevent damage to the device electronics. These devices are typically placed beneath the skin in the upper chest. Placing an external defibrillation pad directly over the device may cause it to malfunction or sustain physical damage from the high energy shock.
Rescuers should visually identify the location of the implanted device, often visible as a small bulge. The defibrillation pad must be positioned at least one inch (eight centimeters) away from the device generator to minimize electrical interference and potential damage. If the standard anterior-lateral pad placement is too close, an alternative position, such as the anterior-posterior placement, should be used. This directs the electrical current through the heart without passing directly through the implanted hardware.
Metal implants, such as sternal wires or internal fixation plates, are generally not a primary concern for external shock effectiveness. The current’s main pathway is between the pads, through the heart muscle. While sternal wires can rarely cause electrical noise in patients with a subcutaneous ICD (S-ICD), the focus remains on proper pad-to-skin contact. The metal itself does not typically alter the procedure.
Adjustments for Physical and Environmental Factors
Environmental conditions and the patient’s physical state can complicate defibrillation effectiveness and safety. A patient experiencing severe hypothermia (below 30°C/86°F) may have a heart resistant to electrical shock. Guidelines suggest attempting up to three shocks if a shockable rhythm is present. If the rhythm persists, further shocks are withheld until rewarming efforts raise the core temperature above 30°C. The focus shifts to continuous cardiopulmonary resuscitation (CPR) and active rewarming, as electrical instability may resolve when the body temperature rises.
Moisture on the patient’s skin or pooling water can create a pathway for the electrical current to travel across the skin instead of through the heart. This increases electrical resistance, making the shock ineffective and posing a safety risk. Before delivering a shock, the patient’s chest must be dried to ensure proper pad adherence and current direction through the body. Defibrillation is safe on wet or metal surfaces, provided pads are applied correctly and no one touches the patient during shock delivery.
Excessive chest hair prevents direct pad contact with the skin, significantly increasing transthoracic impedance. This higher resistance means less electrical current reaches the heart, reducing shock success and potentially causing burns due to arcing. If hair prevents pad adhesion, it must be quickly removed using a razor or by applying and rapidly ripping off the first set of pads to remove the hair.
A large body habitus or increased anterior-posterior chest diameter increases transthoracic impedance because the heart is further from the external pads. For patients with a large chest, the standard anterior-lateral pad placement may be less effective. Using an alternative, such as the anterior-posterior position (one pad front, one pad back), is often necessary to ensure the heart lies directly in the current path. Applying firm pressure to the chest wall during the shock may also be used to reduce the distance to the heart and lower impedance.
Special Protocols for Pediatric and Pregnant Patients
Defibrillation protocols for children differ significantly from adults due to their smaller size and unique physiology. The energy dose must be calculated based on the child’s weight to prevent myocardial damage while remaining effective. The initial shock energy is typically two joules per kilogram of body weight, and subsequent shocks may increase to four joules per kilogram.
Appropriately sized pads are a strict requirement. Pediatric pads are designed to attenuate the energy delivered by an automated external defibrillator (AED) and must be used for children under eight years old or weighing less than 25 kilograms. Pad placement is often modified to the anterior-posterior position to ensure the pads do not touch, which would otherwise create a short circuit. If pediatric pads are unavailable, adult pads can be used, provided they are placed without overlapping.
For a pregnant patient in cardiac arrest, the primary goal is to restore the mother’s circulation, which ensures fetal well-being. If the uterus is palpable at or above the navel (gestation of 20 weeks or more), left lateral tilt or manual uterine displacement is required. The uterus must be pushed manually to the patient’s left side, or the patient’s right hip can be elevated by 15 to 30 degrees, to relieve pressure on the inferior vena cava and aorta. This pressure restricts blood return to the heart, making CPR and defibrillation ineffective. Standard adult energy levels and pad placement are used for the defibrillation shock, as the mother’s body provides sufficient insulation for the fetus.
Ensuring Safety for Rescuers and Bystanders
The high-energy discharge necessitates strict safety measures to protect everyone nearby. Before the shock is delivered, the operator must ensure no one is in direct or indirect contact with the patient, the bed, or connected equipment. This includes personnel performing chest compressions or managing the airway.
Clear, loud verbal commands, typically “Charging,” followed by “Clear!” are mandatory to warn all personnel to step away and break contact. The operator must visually confirm the patient is entirely clear before pressing the shock button. Once the shock is delivered, it is safe to immediately touch the patient to resume CPR, as the electrical charge does not remain in the body.