There must be enough current to reach the heart to defibrillate stop the lethal rhythm , but not so much peak current remember, the peak is one part of the current waveform that you risk damaging the heart. Biphasic waveforms adjust for impedance by varying the characteristics of their waveforms, and are intended to ensure that high-impedance persons will have the same chance for survival as those who are of low impedance.
Clinical studies demonstrate the success of low-energy biphasic waveforms, but they are reliant on many factors that affect the chance of defibrillation success: time elapsed before the first shock is given, placement of electrode pads, the person's impedance level and certain health conditions.
The objective in defibrillation is to achieve the highest efficacy with the lowest energy and current. Biphasic waveforms could improve therapy and affect outcomes when compared to monophasic waveforms. Although the latest research shows biphasic defibrillation to be more effective than monophasic, international guidelines state that the care given using monophasic devices is neither unsafe nor ineffective.
Significant research into the safety, efficacy and success in terminating episodes of VF has been completed since the release of these guidelines. Biphasic waveforms are now becoming more popular for use in external defibrillators, due in part to these studies demonstrating improvements in patient care. Correlation of studies performed in-hospital may be difficult in out-of-hospital SCA. The out-of-hospital scenario is significantly different from the in-hospital time to delivery of the first shock.
Out-of-hospital VF is most often due to myocardial ischemia, frequently in the absence of CPR, within a rapidly developing hypoxia and acidosis. Resuscitations are dynamic events with multiple rescuers and interventions and intermediate outcomes. Defibrillation has several outcomes: persistent VF or conversion to a perfusing rhythm, asystole or pulseless electrical activity.
Furthermore, patients who have had defibrillation may later refibrillate and require more shocks. Shock delivery and outcome occur in combination with many other interventions, such as CPR and the arrival of ACLS personnel who provide endotracheal intubation and intravenous medications. Clinical treatment data are difficult to correlate with data recorded by the event documentation components of the biphasic defibrillator.
Biphasic defibrillation waveforms increase the rate of successful conversion of ventricular fibrillation, reduce the myocardium's exposure to high peak current and have the potential to improve outcomes. Emerging data show that postshock dysfunction, cellular injury, transmembrane effects, recovery time and skin effects are reduced and outcomes improved with clinically relevant defibrillation energies.
Several factors will optimize the application of biphasic defibrillators in EMS systems. Great training and patient preparation for defibrillation will improve outcomes in the use of this tool. The EMS system can minimize the time from accessing the patient to delivery of the first shock with training and review of the defibrillator, easy access to all needed equipment and supplies including a razor and electrodes , preconnection of the multifunction pads, if available, and rapid patient assessment.
Impedance may be increased in patients with a large chest, air in the lungs, chest hair and flaky dry skin. Reducing impedance can help improve the efficacy of biphasic defibrillation. Sign in. EMS World Expo. Current Issue. Issue Archives. Start Print Subscription. Renew Print Subscription. Start Digital Subscription.
Patient Care. Expo on Demand. CE Articles. Online Product Guide. Contact Us. Advisory Board. About Us. Copied to clipboard. Evolution of Defibrillation The common use of defibrillation technology to treat ventricular fibrillation or ventricular tachycardia VT is a relatively new phenomenon, having been developed only 50 years ago. Monophasic Defibrillation Successful defibrillation depends on the defibrillator's ability to generate sufficient current flow through the heart.
Biphasic Defibrillation Unlike conventional monophasic defibrillators, biphasic defibrillators deliver current in two directions. Reducing Myocardial Damage in Defibrillation The potential side effects of defibrillation include cell membrane damage, postshock dysrhythmias and postdefibrillation ST-segment depression on the electrocardiogram.
Increasing Efficacy and Reducing Post-Resuscitation Complications As demonstrated in the figures, a wave of electrical current has a shape that can be drawn as a "waveform," showing how the flow of current changes over time during the defibrillation shock. More current may be delivered by increasing the energy selected on the defibrillator. Clinical Efficacy of Biphasic Defibrillation for EMS The objective in defibrillation is to achieve the highest efficacy with the lowest energy and current.
Challenges for EMS Biphasic defibrillation waveforms increase the rate of successful conversion of ventricular fibrillation, reduce the myocardium's exposure to high peak current and have the potential to improve outcomes. Multicenter, randomized, controlled trial of J biphasic shocks compared with to J monophasic shocks in the resuscitation of out-of-hospital cardiac arrest victims. Circulation —87, Prospective, randomized comparison of rectilinear biphasic waveform shock versus truncated exponential biphasic waveform shock for transthoracic cardioversion of atrial fibrillation.
JACC 41 6 : A, Comparison of six clinically used external defibrillators in swine. Resuscitation 57 1 —83, Apr Ischemically induced ventricular fibrillation VF : A comparison of fixed and escalating energy defibrillation.
Acad Emerg Med , Biphasic and monophasic shocks for transthoracic defibrillation: A meta analysis of randomised controlled trials. Resuscitation 58 1 :9—16, Jul Transthoracic biphasic waveform defibrillation at very high and very low energies: A comparison with monophasic waveforms in an animal model of ventricular fibrillation.
Resuscitation 54 2 —, Aug Escalating energy is more effective than fixed energy defibrillation for ischemically induced ventricular fibrillation. Comparison of a novel rectilinear biphasic waveform with a damped sine wave monophasic waveform for transthoracic ventricular defibrillation. ZOLL Investigators. J Am Coll Cardiol —, Comparison of the efficacy and safety of two biphasic defibrillator waveforms for the conversion of atrial fibrillation to sinus rhythm. Amer Joun Card 92 7 —14, Do clinically relevant transthoracic defibrillation energies cause myocardial damage and dysfunction?
Resuscitation 59 1 —70, Oct First responders and paramedics who may arrive first on-scene were randomized daily to use either monophasic shocks J, J, and J or biphasic shocks J, J, and J for patients with initial rhythms of ventricular fibrillation.
Survival to discharge was 27 percent and 33 percent, respectively -- not a significant difference. This study was severely underpowered to detect differences in survival. However, the higher rates of conversion and ROSC for the biphasic defibrillation waveform support its theoretical advantages and provide a sound basis for a larger mortality trial. In the meantime, if forced to choose, there seems to be no disadvantage -- and potentially some real advantage -- to using biphasic defibrillators over monophasic models.
Schneider T et al. Multicenter, randomized, controlled trial of J biphasic shocks compared with J to J monophasic shocks in the resuscitation of out-of-hospital cardiac arrest victims. During the positive peak, the current moves from electrode A to electrode B and vice versa during negative peak, i. This allows rescuers to immediately select the correct mode, which then enables the device to do its job with even greater efficacy. The exact shape of the current delivery is determined by factors such as the current, energy of direction, and duration of delivered energy.
What makes biphasic devices so important is that they adjust for patient impedance through varied characteristics of the waveforms to make sure that high- and low-impedance patients have the same chances of survival.
Besides the main difference in the current flow, biphasic AED also differ from monophasic devices because they achieve the same effect but with a lower number of joules. Therefore, what we can see here is that the higher efficacy can be achieved with biphasic AEDs as opposed to the monophasic ones when they are with the equal level of delivered average energy. In order to achieve better resuscitation outcomes for patients who are typically difficult to defibrillate, such as those with obesity or higher impedance, Mindray has developed the J biphasic technology and integrated it into the AED devices to increase the termination rates of refibrillation.
The very first defibrillators were monophasic devices, and they have been used for a long time until the invention of biphasic defibrillators. But it is impossible not to wonder about the quality of these defibrillators when compared side by side. Are biphasic AED defibrillators really better? They are not just trendy in the healthcare industry, lightweight, and easy to spot, but biphasic machines really are better than their older counterparts.
Reasons for the supreme position of biphasic machines are numerous, including the above-mentioned fact that the biphasic AEDs can achieve higher efficacy but with the equal or even lower amount of delivered energy. At the same time, they also produce less impairment of cardiac function, which is always important.
Another benefit of biphasic defibrillators is that they normally do not produce other negative effects such as skin burns, which can happen with their monophasic counterparts. Moreover, since they require a lower amount of energy to produce the same effects, biphasic AED machines are usually lighter, smaller, less demanding on batteries, and require lower maintenance than monophasic defibrillators. On the flip side, monophasic devices can be quite bulky and impractical to handle in hectic situations.
As the technology keeps progressing alongside science, biphasic machines are becoming more versatile and practical in terms of features and options they provide to rescuers.
Although monophasic and biphasic machines are successful in performing defibrillation, the latter is considered a better option. They are more convenient, accurate, effective, and cost less and are able to prevent further damage to the heart.
Biphasic machines require relatively lower peak current in order to lower the risk to heart damage, and are able to adjust impedance to work equally on different types of patients. Biphasic devices are going to completely take over the world as many companies stopped producing their older counterparts.
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