Manual Defibrillators, Automatic External Defibrillators, Cardioversion, and External Pacing Key Points Defibrillators: - know the definition & electrical value of a joule - monophasic vs biphasic types: - differences in output - know typical voltage and current values - advantages of biphasic - AED s - how they differ from full-function defibrillators - cardioversion - what it is, what it is not, and how a defibrillator is used for it - external pacers in defibrillators: - asynchronous and synchronous D. J. McMahon 141001 cewood rev 2017-10-04 local manufacturers on parade; Museum of History & Industry (MOHAI)
joule: Unit of energy or work: 1 Newton through a distance of 1 meter or James P Joule 1 amp through 1 ohm for 1 second Mathematically, the joule can be defined both ways, but the convention is to use joules for energy, and newton-meters for torque. One joule = one watt-second = ~ 0.24 calorie = ~ 0.74 foot-pound Essential monophasic defibrillator with switch A in this position, defibrillation is happening, (not charging) Coil The Lown waveform: Monophasic, damped
Basic Lown waveform creation Specific Lown waveform creation Energy in the capacitor : U = ½ CV p 2 Biphasic defibrillation: > 1990 s improvement in defib circuitry. > Achieves defibrillation in fewer attempts, using lower energies in each attempt. > Less time delay in salvaging a cardiac crisis, and less damage to the heart. > became biphasic truncated exponential (BTE) waveform (Physio Control and Philips)
Current & Time at Various Patient Impedances Insulated Gate Bipolar Transistor (IGBT): - Combines an isolated gate FET for the input, and a bipolar power transistor as a switch, in a single device. - Has the gate-drive characteristics of a MOSFET and the high-current and low-saturation-voltage capability of a bipolar transistor. - Used in medium- to high-power applications. Test loads are 50Ω
Some manufacturers of biphasic defibs provide a maximum energy of 200 joules, while many provide a maximum of 360 joules.
Pads have replaced paddles in most applications of defibrillators. Pads assure a better contact with the patient s skin, so resistive losses are minimized. They are also safer for the user. Paddles, internal as well as external, are still used in specific clinical areas (O.R., PACU, etc.) Defib voltages are very brief, but very high and potentially lethal! paddles pads spoons for OR Correct placement of the pads or paddles is important
Internal paddles for use in open-heart surgery: 2010 AHA Guidelines for pediatric defibrillation: With a manual defibrillator use a dose of 2 J/kg for the first attempt, and 4 J/kg for subsequent attempts. Placed directly on the heart to re-start the beat. Defibrillator limits energy to them at 50 joules. ECG Input Protection from Defibrillator Pulses: NE2H lamps
Automatic External Defibrillators (AED s) > Semi-automated defibs that analyze cardiac status and deliver therapeutic shock as indicated, using a pre-set algorithm and voice commands. > Intended for non-clinical settings, for use by non-clinicians. > Typical biomed maintenance consists of a functional check and a battery check. Conductive gel left on paddles from a previous use. Typical block diagram for an AED
Defibs for Cardioversion (this is not defibrillation!) > The use of a small energy pulse from a defibrillator to convert a non-lethal arrhythmia (e.g. atrial flutter) to a normal sinus rhythm > Delivers a pulse about 30ms after the peak of the R-wave, synchronized by the defibrillator > Modern units can discriminate the R-wave from the T-wave or noise spikes Timing of cardioversion pulse Defibs as External Pacemakers Defibrillators can be used as temporary external pacemakers for patients with bradycardia or other issues. Pacing is either synchronous or asynchronous : In Synchronous pacing ( Demand mode): pacer fires only when no complex is sensed for a predetermined amount of time. Do NOT cardiovert across the T-wave! In Asynchronous pacing: pacer fires at a fixed rate at preset intervals, independent of cardiac activity. ( not synchronized means the pacemaker leads and the heart follows)
Typical external pacemakers deliver a 40-millisecond impulse for each beat. The average current necessary for external pacing is from 45-100 ma, depending on the cardiac status. In pacing, the same defibrillator electrodes are used.
Major Makers of full-function Defibrillators and AEDs: October, 2014 Test equipment: Defibrillator Analyzers BC Biomedical Fluke Biomedical http://testequipmentandtools.com/acatalog/bc_online_store_defibrillator_analyzers_5.html http://assets.fluke.com/demos/biomedical/impulse/3035532_impulse_demo.html