How to Identify Monophasic vs Biphasic Defibrillator

With the popularization of emergency rescue knowledge, many of you may know that defibrillation is the defibrillation of a patient by discharging electricity to restore their heart rhythm. However, when purchasing defibrillation, you may be troubled by the different types and discharge energy. In the early days, there were only monophasic wave defibrillators, and then, with the development of technology, biphasic defibrillators gradually became mainstream. Usually, there is no significant difference between the two in appearance, so how can we distinguish between monophasic and biphasic defibrillators?

Definition of electrical defibrillation

Electrical defibrillation is a method of terminating ectopic rhythms and re-establishing sinus rhythm by using a defibrillator to release a high-energy electrical pulse through the myocardium, which simultaneously depolarizes the myocardium. The defibrillator energy setting provides the minimum effective energy required to terminate ventricular fibrillation, and classical defibrillation (successful shock) is defined as the termination of ventricular fibrillation for at least 5 seconds after the shock.

How defibrillators work

Defibrillation uses electricity to help restart the heart. An electric current is passed through the heart, depolarizing the heart muscle with a strong current high-energy pulse. When the sinus node sends the next electrical signal, it drives the heart muscle to beat again, restoring normal sinus rhythm.

The method of removing arrhythmia and restoring sinus rhythm by passing a stronger pulse of electricity through the heart is called defibrillation or electrical cardioversion. Both pacing and defibrillation utilize exogenous electrical currents to treat arrhythmia, and both are recent methods.

Monophasic vs biphasic defibrillator

A monophasic defibrillator is half a positive wave, while a biphasic defibrillator is a full positive wave. Monophasic defibrillators generally have a maximum discharge energy of 360 J, and biphasic defibrillators generally have a maximum charge of 200 J. In our past knowledge of defibrillator shock energy, we tend to think that a higher shock energy will be better and that the resuscitation rate will be higher, but this is not the case. It is reported that the complication rate is 6% when the shock energy is 150J and up to 30% when it is greater than 300J; therefore, high-energy shock should be avoided as much as possible.

In contrast to the monophasic wave technology used in monophasic defibrillators, biphasic waves exhibit superior defibrillation characteristics due to their low peak current and long effective current duration, resulting in a high defibrillation success rate and little cardiac damage. Most defibrillators on the market today use biphasic defibrillation.

Monophasic defibrillator

Monophasic waveforms are unipolar transmitter currents divided into monophasic impedance sine waves and spike waves. Monophasic impedance sine wave means that the current changes gradually from the peak of the pulse to 0 in a sinusoidal shape; monophasic sharp wave means that the current drops directly from the peak of the pulse to 0, resulting in a single-peaked current wave.

Monophasic defibrillators have two main disadvantages:

1. The defibrillation energy is relatively high, 360 J, which can cause some damage to the patient's myocardial function;

2. The defibrillator cannot change with the size of the patient's transthoracic resistance and does not have an automatic adjustment function, which makes the defibrillation effect less desirable in patients with high transthoracic impedance.

Biphasic defibrillator

A biphasic wave is a discharge in which the direction of current flow has positive and negative phases and is categorized as a single-peaked biphasic wave or a linear biphasic wave. Biphasic waves are safer than unidirectional waves and have equal or greater efficiency in terminating ventricular fibrillation. The advantage of bi-directional waves is that the unidirectional wave ends the cardiac disturbing clutter and gives a guided wave in one direction. This guided wave is close to the normal electrical signal of the heart and, therefore, more effective in stimulating the heart to function normally.

The defibrillation energy of 150J to 200J for biphasic waveforms can achieve similar or even higher success rates than 360J for monophasic waveforms.

Biphasic defibrillators have the following advantages.

1. It can change with the size of the patient's transthoracic impedance, and the success rate of the first defibrillation shock will be higher;

2. The discharge energy is small, the current is low, and the damage to the patient's myocardial function is not so great that subsequent shocks can be selected at the same or increasing energy levels.

How to tell if defibrillator is monophasic or biphasic

Monophasic defibrillators generally have a maximum discharge energy of 360J, while biphasic defibrillators generally have a maximum charge of 200J.

How is the energy adjusted for bi-directional and uni-directional waves?

First shock defibrillation: 360J for monophasic defibrillation, 120-200J for biphasic defibrillation or the energy recommended by the device manufacturer.

Subsequent shock energy: 360J for monophasic defibrillation. The same or higher energy can be used for biphasic defibrillation.

How to use biphasic defibrillator

1. Preparation of materials:

   Defibrillator, electrically conductive paste, instruments and medicines needed for resuscitation, such as oxygen, simple respiratory airbag, suction supplies, tracheal intubation supplies, cardiac monitoring equipment, emergency vehicle, etc.

2. Position the patient in a flat position.

3. Quickly dry the patient's chest skin, and the electrode plate coated with special conductive paste is evenly distributed on the two electrode plates.

4. Choose defibrillation energy, monophasic wave defibrillation with 360 J, biphasic wave with 150-200 J. If the operator is unfamiliar with the defibrillator, the energy selection of 200 J. Confirms the state of electrical resuscitation for the asynchronous mode.

5. The electrode plates are placed in the correct position and are in close contact with the skin.

   Apical part of the heart (APEX): the lateral wall of the left breast (4th and 5th intercostal space in the left mid-axillary line or posterior axillary line)

   The bottom of the heart (STERNUM): Anteriorly right chest, under the clavicle (the right edge of the sternum between the 2nd and 3rd ribs), two electrode plate nails spaced 10 CM.

6. Electrode plate pressure is appropriate; observe whether the ECG wave is ventricular fibrillation.

7. Ensure that the surrounding personnel did not have direct or indirect contact with the patient.

8. Discharge defibrillation by pressing both thumbs at the same time.

9. Defibrillation is successful; the patient returns to sinus heart rate and removes the electrode plate.

10. Clean the electrode plate.

11. Closely observe the changes in vital signs and continue to do a good job of follow-up treatment; if the patient's condition is stable, wipe the skin.

12. Turn off the machine.

Precautions for biphasic defibrillator

1. To ensure safety in operation, remove the bedrail and other metal objects;

2. Conductive paste is applied evenly to avoid localized skin burns;

3. Master the handle pressure (11 ~ 14Kg);

4. Keep the electrode plates clean and spaced >10cm apart;

5. To be able to accurately time, the record should be based on a clock;

6. Avoid ulcerated or wound areas;

7. Avoiding built-in pacemaker parts (spacing >10cm);

8. Mischarging shall be discharged on the defibrillator, not into the air, and the two electrode plates shall not be struck against each other;

9. Avoid high oxygen environment as much as possible;

10. Defibrillation during CPR should be discharged at the end of the patient's expiration to reduce the trans-thoracic actuation electrical impedance.

Maintenance and care of defibrillator

1. Ensure that the instrument is neat, dry and complete, with complete supplies, and no other items shall be placed on the instrument;

2. Check the performance of the instrument and the lead wires are free of scratches, abrasion and folding;

3. Clean the lead wires and electrode plates after use, pay attention to the protection of the screen, and forbid the use of rough cloth to wipe the screen;

4. Each time after charging promptly, more than a week without re-charging;

Conclusion

The ideal defibrillator should be able to achieve defibrillation while minimizing the side effects of strong shocks. When choosing a monophasic or biphasic defibrillator, we try to avoid too much energy. Biphasic low-energy defibrillation minimizes the defibrillation energy while achieving the defibrillation effect, thus reducing the harm to the patient from the high current released by the defibrillator.