TechNation: Biomed 101 - Defibrillators Need to be Maintained Properly

Defibrillators are used by medical staff to apply a momentary electrical shock across a patient’s heart muscle with the goal of ending fibrillation (defibrillation) and restoring a normal sinus rhythm (NSR). Defibrillators are utilized to diagnose and treat potentially deadly heart conditions, so it is critical that you keep them in perfect operational condition.

CLINICAL APPLICATION

Heart rhythms are regulated by an internal pacemaker called the sinoatrial node (SA node) that is located in the right atrium of the heart. Failure of the SA node to produce an NSR can lead to various arrhythmias, such as Atrial Fibrillation (A-Fib) or Ventricular Fibrillation (V-Fib). Defibrillators are useful to resolve both conditions.

A-Fib: During this arrhythmia, the two upper chambers (the atria) beat rapidly and irregularly, resulting in poor blood circulation to the body. This condition can be remedied with a defibrillator through synchronized cardioversion, where an electrical shock is applied to the heart precisely during the “R” portion of the QRS complex.

V-Fib: This arrhythmia is characterized by the uncoordinated fluttering of the two lower chambers of the heart (the ventricles). This condition is extremely dangerous because no blood is transported through the circulatory system. V-fib requires an immediate unsynchronized shock across the heart to restore NSR.

It is important to note that defibrillators are not effective during the absence of electrical activity in the heart commonly known as “asystole” or “flatline.” There must be some electrical activity in the heart for a defibrillator to be effective.

DEFIBRILLATOR BASICS

Defibrillators have two hard paddles or adhesive pads that are placed across the patient’s chest. The paddles are labeled as “Sternum” and “Apex.” They are applied across the patient’s chest and provide a pathway to guide the corrective extrinsic electrical shock. In the most basic terms, defibrillators charge an internal capacitor to a set voltage, and deliver the prescribed energy in Joules (J). This is the standard unit of measurement for delivered energy during defibrillation. One joule of electrical energy is equal to the work done when a current of one ampere is passed through a resistance of one ohm for one second. To deliver the correct amount of current across the heart muscle, the defibrillator voltage is varied in accordance to the impedance in the patient’s chest. Ohms law states that Current=Voltage/Impedance.

SIZE MATTERS

Defibrillator supplies and settings are divided between two categories, Adult and Pediatric. The power of the therapeutic shock is determined by patient weight. The 2010 AHA Guidelines state that, “with a manual defibrillator (monophasic or biphasic), use a dose of 2 J/kg for the first attempt and 4 J/kg for subsequent attempts.” In order to account for the physiologic differences between an adult and child, either pediatric specialty paddles or pediatric electrode pads are used. Pediatric electrode pads often have internal circuitry that acts as a safety feature to limit shock magnitude.

PREVENTIVE MAINTENANCE

It is extremely important that you follow the manufacturer’s guidelines while performing a PM or repair on any defibrillator. Perform and document all of the function checks in the interval as specified in the technical guidance for the model of defibrillator you have. This is one particular device that it is wise to keep records of test results.

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