Pediatric cardiac arrest, while infrequent compared to adult cases, requires immediate and specific intervention. Most pediatric arrests result from progressive respiratory failure or shock, but some are caused by a sudden electrical problem in the heart. When the heart’s electrical system malfunctions severely, a controlled dose of electricity can restore a normal rhythm. This electrical therapy depolarizes the heart muscle simultaneously, resetting chaotic activity so the heart’s natural pacemaker can take over. The precise amount of energy needed is determined by the child’s weight and the specific type of electrical malfunction.
Defining Pediatric Electrical Therapy: Defibrillation vs. Cardioversion
Electrical therapy for children involves two distinct procedures, each treating a different category of abnormal heart rhythm. The fundamental difference lies in whether the electrical shock is delivered randomly or timed to a specific point in the heart’s cycle. This distinction dictates the energy level used and the rhythm being treated.
Defibrillation involves delivering an immediate, unsynchronized electrical shock to the chest. This procedure is reserved for chaotic, life-threatening rhythms where the heart muscle is quivering ineffectively, such as ventricular fibrillation (V-fib) or pulseless ventricular tachycardia (pVT). These are considered “shockable” rhythms in a child who is pulseless and requires cardiopulmonary resuscitation (CPR). The goal is to stop all electrical activity, allowing the heart’s natural conduction system to restart with a functional rhythm.
Cardioversion, by contrast, is a synchronized shock used to treat organized, rapid heart rhythms when the child still has a pulse but is showing signs of instability. Rhythms commonly treated include supraventricular tachycardia (SVT) or ventricular tachycardia (VT) with a pulse. The device times the shock to avoid the heart’s vulnerable repolarization period, specifically the T-wave. This precise timing prevents the controlled shock from degenerating the organized rhythm into a chaotic one.
Energy Requirements for Unsynchronized Defibrillation
When a child experiences a pulseless shockable rhythm, the energy dose for unsynchronized defibrillation is calculated based on their body weight in kilograms (kg). Current Pediatric Advanced Life Support (PALS) guidelines recommend starting with a low dose for the first attempt. The initial shock should be set to 2 Joules per kilogram (2 J/kg). This weight-based calculation ensures the energy is scaled appropriately for the child’s size.
If the first shock fails to restore a normal rhythm, the energy level must be increased for subsequent attempts. The dose for the second and all following shocks is doubled to 4 J/kg. This escalation recognizes that the initial dose may not have been sufficient to fully depolarize the heart muscle.
While 4 J/kg is the standard for repeat shocks, some guidelines permit further escalation up to a maximum of 10 J/kg. The energy delivered should never exceed the maximum adult dose available on the device, regardless of the child’s calculated weight. Rapid, accurate calculation of the dose is necessary, as delayed defibrillation significantly reduces the chance of survival.
Energy Requirements for Synchronized Cardioversion
The energy requirements for synchronized cardioversion are substantially lower than for unsynchronized defibrillation. This is due to the organized nature of the rhythm being treated and the precise timing of the shock. The initial dose for synchronized cardioversion is set between 0.5 and 1.0 J/kg.
The lower energy level is sufficient to interrupt the re-entry circuit causing the rapid rhythm while minimizing the total energy delivered. If the first synchronized shock is unsuccessful, the energy level is increased for the next attempt. The subsequent dose is escalated to 2 J/kg.
The synchronization feature is a procedural safeguard used for this therapy. The device analyzes the child’s electrocardiogram (ECG) and delivers the electrical current exactly on the peak of the QRS complex. This timing is essential to avoid the T-wave, the period when the heart muscle is vulnerable to developing ventricular fibrillation.
Technical Considerations: Patient Size and Electrode Placement
Beyond the calculation of the energy dose, the physical components of electrical therapy, namely the electrodes, require careful consideration. Selecting the correct electrode pad size ensures effective current delivery while preventing electrical arcing or burns. Pediatric-specific pads are recommended for children under 8 years of age or those weighing less than 25 kilograms (55 pounds).
These pediatric pads are designed with an energy attenuator, which reduces the total electrical output from the defibrillator to an appropriate level for a child. Using adult pads on a small child without an attenuator could result in the delivery of a dangerously high energy dose.
The pads must be placed on the child’s chest to ensure the electrical current passes directly through the heart. Two common placement configurations are the anterolateral and the anteroposterior positions. A crucial safety point for any placement is ensuring the edges of the pads do not touch or overlap, which requires a minimum separation of approximately 3 centimeters.
Anterolateral Position
The anterolateral position involves placing one pad to the right of the upper sternum and the second pad on the left side of the chest, slightly below the nipple line.
Anteroposterior Position
The anteroposterior configuration places one pad on the front of the chest and the other on the back, just below the shoulder blade.