# I have an ALS question.



## BBFDMedic28 (Nov 9, 2007)

Just for my own knowledge. Can Someone explain the difference between Biphasic and monophasic defibrillators?


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## KEVD18 (Nov 9, 2007)

if i understand correctly(and if i dont someone will be along to correct me):

monophasic- total "dose" of electricity moves from one pad or paddle to the other in one phase or step

biphasic- half of the dose goes from pad a to pad b, the other half from pad b to pad a. the goal here to reduce the amount of heating or cooking type action that takes place during a shock


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## EMS14 (Nov 9, 2007)

*<Moderator Note: User states this information may not be correct>*

That is the way I understand it as well.
Monophasic from one pad to the other and biphasic is from both pads and "meets in the middle" so to speak.


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## skyemt (Nov 9, 2007)

ems14,

in biphasic, the charge does not eminate from both pads and "meet in the middle"... it travels in one direction for a specified period of time, and then the flow reverses in the negeative direction for the duration.


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## nsom9ac (Nov 9, 2007)

going on what skyemt said .... don't know if there's any truth to it, but i've heard that in biphasic the initial energy is much lower and is intended to decrease the resistance so when the 2nd surge is released it doesn't have to be as high to give the same amount to the target tissue.


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## EMS14 (Nov 9, 2007)

I am truly sorry for the incorrect information, I was just going off what I thought I remembered from my Basic class.


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## EMS14 (Nov 9, 2007)

I would really like to delete my post number 3 but I am unable to, the edit button does not show up. So everyone can disregard it, and if an admin reads this they can delete it.


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## Asclepius (Nov 11, 2007)

So let's talk about the biphasic equivalents. Our protocols simply say "or biphasic equivalent" without any explanation as to what those settings should me. So, for mononphasic it is 200j, 300j, 360j. But biphasic is not stacked...I believe it should be 200j and remain there. What about cardioversion settings? What should they be? Is there some kind of mathematical equation to figure out the equivalents?


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## nsom9ac (Nov 11, 2007)

Asclepius said:


> So let's talk about the biphasic equivalents. Our protocols simply say "or biphasic equivalent" without any explanation as to what those settings should me. So, for mononphasic it is 200j, 300j, 360j. But biphasic is not stacked...I believe it should be 200j and remain there. What about cardioversion settings? What should they be? Is there some kind of mathematical equation to figure out the equivalents?



well if you're talking about defib, the new acls calls for all shocks to be at 360 or biphasic equivalent (which i've also been told to use 200). as far as c-version settings go, i've asked the question before more than once and got a less than comforting unsure answer. however, at the service i work at we use the same settings as monophasic. 100-200-300-360 except a-fib/a-flutter start at 50 after contacting med control.


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## ffemt8978 (Nov 12, 2007)

I believe our biphasics are set to deliver 150 joules on every shock, and our two saves both occurred with these units/settings (including one guy who was shocked 9 times on scene)


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## Rangat (Nov 12, 2007)

Biphasic does require less energy to fully depolarize the cells. This reduces damage to the cardiovascular conduction system. It switches current direction halfway through the delivery time.

Lots of research is being done on a Triphasic defibrillator.

Energy settings for monophasic is usually 360J. And nothing is stacked any more. The myocardium needs to be prepared for defibrillation. This is done through CPR.

For Biphasic the setting is usually 200J as mentioned, but it is manufacturer specific. One unfortunately needs to look up the specific settings.

This is where you may start: http://www.resuscitationcouncil.co.za/AlgPage5.pdf


Hope this was what you wanted to know. Tell us if you know more?


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## byun01 (Jan 10, 2008)

*How biphasic defibrillators work...*

Hello Hello,

Here is an explanation of how biphasic defibrillators work from what I can gather.  A quick summary:  It's common knowledge, that humans have resistance a defibrillator. In the old days, the only way to bypass this resistance was to increase the energy (200, 300, 360).  The question arises how do you reduce resistance?  Well resistance can come from not only the human body, but also the machine and pads (hence why we placed gel on the end of the paddles).    With new technology there are other ways to change the resistance by altering the machine.  What follows is a sort of complicated explanation.

To understand how defibrillation terminates life-threatening dysrhythmias, a basic knowledge of physics is needed to understand how energy works.  Electrical output of defibrillators is expressed in terms of energy, which units are in joules.  Joules describes the power (watts) and the length of time it is applied (milliseconds).  Therefore energy equals power and duration shown in this equation (a): Joules = watts x sec.  Note that a watt equals current (amps) and the voltage (volts).  Current is what defibrillates the heart.  Voltage is what pushes the current into the heart.  Therefore energy is showed in this equation (b): Joules = current x voltage x duration.  The amount of current delivered depends on impedance or resistance to flow shown in this equation (c) or also known as Ohm’s Law: Current = Voltage / Resistance (in ohms).  If we combine equations (b) and (c), we get equation (d): energy in joules = (voltage2/resistance)(duration).  Duration is important because it determines the length of time a current is given, determining the waveform of the defibrillation.  
Finding a balance between impedance and effective defibrillation is important.  As the Philips website best puts it: 
Think of administering medicine to a patient: The objective is to provide a dose of the correct medicine to quickly and effectively treat a condition. The dose must be properly measured and delivered over a prescribed period of time. The dose must be large enough to be therapeutic but not so large as to be harmful. With too little, the dose may be ineffective; with too much there are risks of an overdose. In critical situations, it is important to get the dose right the first time without having to try several experimental doses. (Philips)   
Impedance is a problem that is different depending on the situation.  Only so much can be done by the operator to reduce resistance, albeit important.  The operator can ensure proper placement and pressure of the paddles, use electrode gel, gel pads, or electrode paste, remove hair, and clean the area.  The remaining resistance offered by the patient, depending on their body size, bone structures, skin, and health conditions, is constant.  According to Medtronic, peak current needs to be looked at to gauge the relative risk associated with shocking a patient (Medtronic).  Peak current is the maximum current flow and as a result has the greatest chance of damaging the heart.  A damaged heart can do more harm to an already injured heart that may have occurred from Cardiopulmonary resuscitation, acute myocardial infarction, and cell death secondary to hypoxemia.  Finding this balance is important for post-resuscitation and as a result is on the minds of every developer of defibrillators. 
	New studies show that biphasic defibrillators are more effective, even at lower energies, in producing spontaneous circulation than the past monophasic defibrillators.  ‘In the recent human study, the biphasic shock defibrillation rate for long-duration VF was 82% (55/67), which was significantly higher than the monophasic shock defibrillation rate of 66% (108/164)’ (AHA).  But to understand biphasic defibrillators, a quick look at monophasic defibrillators is needed.  The defibrillation given by monophasic defibrillators produces a current flow in one direction producing a damped sine waveform or half sinusoidal.  According to Philips, early defibrillators, due to inefficiencies in technology, had only one way of overcoming impedance and that was by escalating the joules.  By escalating the energy, monophasic defibrillators increased the current, increasing the probability of success.  Note in equation (d), energy in joules = (voltage2/resistance)(duration), if resistance and duration remain constant due to technological limits and resistance is high, the only way for monophasic defibrillators to overcome resistance is by increasing the voltage, increasing the current.    The American Heart Association recommends escalating energy levels of 200, 200-300, 360J.  
	Biphasic defibrillators and new technology allows better control of manipulating energy.  Current flows positively and negatively which changes the waveform into a sinusoidal shape.  Current goes from one pad to another and then reverses going the opposite direction.  The manufacturer of biphasic defibrillators can manipulate this waveform by increasing or decreasing the duration and shape.  They can also manipulate voltage and resistance.  With this new technology, many manufacturers have chosen different approaches to tackle the problem associated with impedance and effective energy settings.
	The HeartStart MRx ALS Monitor/Defibrillator is a product developed by Philips.  The energy settings they recommend is 150J for 3 stacked shocks for ventricular fibrillation.  Philips claims that a proper adapting waveform is crucial to achieving successful defibrillation.  Using technology as an advantage, the Philips’ Smart Biphasic waveform adjusts to a patient’s impedance by changing the waveform.  According to the Philips’ website, a patient’s impedance ranges anywhere from 25-180 ohms.  “In the case of high impedance patients, the waveform lengthens to deliver adequate energy. For low impedance patients, the defibrillator delivers somewhat higher peak currents to compensate for the possible effects of shunting” (Philips).  Recall that waveform is current flow in relation to time.  Referring to equation (d), energy in joules, voltage, and resistance are constant, while Philips manipulates duration.  Essentially, the higher the impedance, the greater the duration will be, and the lower the impedance, the lesser the duration will be.
	The M series Monitor/Defibrillator is a product produced by Zoll.   The manufacturers recommended energy settings are 120, 150, 200J for ventricular defibrillation.  Zoll claims that the waveform’s shape and duration must stay the same regardless of patient impedance to ensure a constant current shock.  Since resistance is a factor of both the patient and the defibrillator, impedance is “controlled” by changing the defibrillator’s internal resistors and results in Zoll’s Rectilinear Biphasic waveform.  Within patient impedance parameters, Zoll’s waveform is a constant current for the beginning of the duration.  Zoll has increasing energy levels providing another way to overcome patient impedance.  Referring to equation (d) again, duration is constant, while voltage and resistance are manipulated.  The higher the impedance of the patient, the higher the voltage and lesser the internal resistors will be and vice versa.  
	Lifepak 12 Defibrillator/Monitor is produced by Medtronic Physio-Control.  The recommended joules setting are exactly the same as the current American Heart Association recommendation for monophasic defibrillators.  They are 200, 300, 360J for a v-fib or pulseless v-tach arrest.  Nonetheless, even though the energy settings are the same, there is a whole different concept behind the energy delivered.  Increasing energy level shocks and changing the waveform is how Medtronic deals with impedance.  According to Medtronic, increasing energy levels increase the delivered current to the heart by around 25% to 30% as opposed to a set energy level, which would only increase the current delivered by 5% (Walker par 7).  Subsequent and rapid one after another shock decreases resistance.  Therefore, the current delivered by a second shock would be a higher than the first shock current.  Resistance relatively remains constant, while voltage and duration are increased or decreased depending on the impedance.  The duration is increased for patience with greater impedance.  The waveform is called a biphasic truncated exponential waveform.


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