What Is a Monophasic Defibrillator?

Cardiac defibrillator, also called electrical cardioversion machine (Figure 1), is mainly composed of defibrillation charge / discharge circuit, ECG signal amplification / display circuit, control circuit, electrocardiogram recorder, power supply and defibrillation electrode plate. One of the widely used rescue equipment in clinical practice. It applies pulse current to the heart, implements electric shock treatment, eliminates arrhythmia, and restores the heart to sinus rhythm. It has the advantages of high efficacy, fast action, simple operation, and safety compared with drugs.

Chinese name: Defibrillator
Foreign name: Automated External Defibrillator

Abbreviation: AED
Aka: Electric cardioversion

1. Defibrillator 1. How it works

Most of the general cardiac defibrillators use the RLC damping discharge method. The basic principle of charge and discharge is shown in Figure 2. The voltage converter converts the DC low voltage into a pulsed high voltage, and then charges the energy storage capacitor C after high voltage rectification, so that the capacitor obtains a certain energy storage. During the defibrillation treatment, the high-voltage relay K is controlled to operate, and the energy storage capacitor C, the inductor L, and the human body (load) are connected in series to form an RLC series resonance.

Figure 2: Basic schematic of a defibrillator

2. Defibrillator 2. Main functions

2.1 Defibrillator 2.1 Defibrillation Function

There is an energy selection switch on the instrument, and the doctor chooses the appropriate discharge energy according to the weight of the patient. Generally, the energy used for internal defibrillation cannot be greater than 50 J, and external defibrillation is between 200 and 300 J, and the maximum does not exceed 400 J.

2.2 Defibrillator 2.2 ECG Monitoring

Display the patient's heart rate and ECG waveform. A defibrillator with a diagnostic function can automatically alert to abnormal heart rhythms such as tachycardia, bradycardia, and cardiac arrest, and automatically record abnormal ECG waveforms for a few seconds.

2.3 Defibrillator 2.3 charging circuit

After selecting the energy range, press the charging button to charge the high-voltage capacitor of the defibrillator. When the predetermined value is reached, there is an audible and visual indication.

2.4 Defibrillator 2.4 discharge circuit

Each of the defibrillation electrodes has a discharge button on the left and right handles. After the defibrillation electrodes are placed, the discharge button is depressed, and the energy stored in the high-voltage capacitor releases high-voltage electrical pulses to the patient through the high-voltage relay and electrical impedance to terminate the fibrillation.

2.5 Defibrillator 2.5 Synchronous Defibrillator

The defibrillation pulse is synchronized with the QRS complex in the ECG waveform, and the discharge pulse can only appear when the R wave appears. Generally applicable to the treatment of ventricular or supraventricular tachycardia, atrial flutter, atrial fibrillation and so on.

2.6 Defibrillator 2.6 Other Features

Charge and discharge time, continuous defibrillation interval, battery working time, safety alarm, event review, voice prompt, printer, etc.

3 Defibrillator 3, classification of defibrillator

3.1 R Defibrillator 3.1 According to whether it is synchronized with the R wave

Can be divided into two types of asynchronous and synchronous defibrillators. Asynchronous defibrillators are not synchronized with the patient's own R wave during defibrillation and can be used for ventricular fibrillation or flutter. The synchronous defibrillator is synchronized with the patient's own R wave during defibrillation. It uses the human ECG signal R wave to control the distribution of current pulses, so that the shock pulse falls on the falling branch of the R wave instead of the irritable period. To avoid the occurrence of ventricular fibrillation, it is mainly used for all tachyarrhythmias except ventricular fibrillation and flutter, such as supraventricular and ventricular tachycardia.

3.2 Defibrillator 3.2 according to the position of the electrode plate

Includes internal defibrillator and external defibrillator. Internal defibrillators are electrodes that are placed in the chest to directly contact the myocardium for defibrillation.The early internal defibrillator has a simple structure and is mainly used to directly shock the myocardium during open heart surgery. Modern internal defibrillators are buried. Its structure and function are very different from early defibrillators. In addition to being able to automatically defibrillate, it can also automatically monitor, judge arrhythmias, and select treatments for treatment. External defibrillators are indirect defibrillation by placing electrodes on the chest wall. Most defibrillators currently in clinical use belong to this type.

4 Defibrillator 4, clinical application of defibrillator

4.1 Defibrillator 4.1 Preparation before Defibrillation

There are two positions where the electrode plates are placed during extracorporeal cardioversion. One is called the anterior and posterior position, that is, one electrode plate is placed on the lower subscapular region of the back; the other is placed on the left margin of the sternum between 3 and 4 intercostal levels. Some people think that this way passes more current through the heart, so that less electricity is required, and potential complications can be reduced. This method should be used for selective cardioversion. The other is an electrode plate placed on the right margin of the sternum between 2 and 3 intercostal spaces (the bottom of the heart). The other was placed in the 5th intercostal space (apical portion) within the left anterior axillary line (Figure 3). This method is quick and convenient, and is suitable for emergency shock defibrillation. The distance between the two electrode plates should not be <10 cm. The electrode plate should be pressed against the patient's skin and slightly pressurized. There should be no gaps and the edges should not be lifted. The skin on which the electrodes are placed should be coated with conductive paste, or saline gauze can be used, and even water can be used in emergency, but alcohol is absolutely prohibited, otherwise it can cause skin burns. Those who are thin and the intercostal space is significantly depressed, which causes poor contact between the electrodes and the skin, should use saline gauze, and can use more layers, which can improve the contact between the skin and the electrodes. Keep the two electrode plates dry to avoid short circuits caused by conductive paste or salt water. The electrode plate handle should also be kept dry. It cannot be contaminated by conductive paste or salt water, so as not to hurt the operator. When cardiac surgery or open-heart cardiac massage requires direct electric shock defibrillation of the heart, a proprietary small electrode plate is required, one is placed on the right ventricle surface; the other is placed on the apex, and the surface of the heart is sprinkled with physiological saline and the electrode plate Close to the ventricular wall.

The electrical energy used for cardioversion is represented by J. Charge as needed, ventricular fibrillation is 250J ~ 300J, asynchronous cardioversion. Ventricular tachycardia is 150J ~ 200J, atrial fibrillation is 150J ~ 200J, atrial flutter is 80J ~ 100J, and supraventricular tachycardia is 100J, all of which are synchronous cardioversion.

Figure 3: Common electrode placement

4.2 Defibrillator 4.2 Defibrillation in practice

(1) Quickly familiarize yourself with and check the defibrillator. The keys, knobs, and electrode pads are intact and the power is sufficient.

(2) The patient is supine, and the operator is on the right side of the patient.

(3) Quickly turn on the defibrillator, adjust the defibrillator to the monitoring position, and display the patient's heart rhythm.

(4) Quickly dry the chest skin of the patient with a dry cloth, and apply the hand-held defibrillation electrode plate with special conductive glue.

(5) Make sure that the manual defibrillation electrode plate is correctly placed on the chest. The front electrode plate is placed above the outer edge of the sternum and below the right clavicle. The outer electrode plate was placed on the left lower chest, the left side of the nipple, and the center of the electrode plate was on the anterior axillary line. The ECG wave pattern was observed and it was determined to be ventricular fibrillation.

(6) Select defibrillation energy, 200J for the first defibrillation; 200-300J for the second defibrillation; 360J for the third.

(7) Press the defibrillation charging button to charge the defibrillator.

(8) The defibrillation electrode plate is close to the chest wall, and the pressure is appropriately applied to ensure that no people around it are in direct or indirect contact with the patient.

(9) When the defibrillator displays a defibrillation signal, both hands press the two discharge buttons of the hand control electrode simultaneously to perform an electric shock.

(10) Do not remove the electrode after the discharge. Observe the heart rate after shock defibrillation. If it is still ventricular fibrillation, select the second defibrillation and the third defibrillation. Repeat steps 4-10.

4.3 Defibrillator 4.3 after defibrillation care

(1) Continue to observe heart rate, heart rhythm, breathing, blood pressure, complexion, physical condition, and the presence of embolism, and keep records at any time. Return to the ward when the condition is stable. Anticoagulant treatment before surgery. Postoperative medication is still required and anticoagulant monitoring is performed.

(2) Rest in bed for 1 to 2 days, give high calories, high vitamins, easy to digest diet, and maintain smooth stool.

(3) After cardioversion of atrial fibrillation, continue to take drugs to maintain, and observe the efficacy and adverse reactions.

(4) Health care guidance, explaining the predisposing factors to patients, such as overwork, emotional excitement, etc., to prevent recurrence.

4.4 Defibrillator 4.4 indications

(1) Ventricular fibrillation is an absolute indication of cardioversion.

(2) chronic atrial fibrillation (atrial fibrillation history within 1 to 2 years), continuous atrial flutter.

(3) Paroxysmal supraventricular tachycardia, conventional treatment is ineffective and patients with significant hemodynamic disorders or preexcitation syndrome complicated by supraventricular tachycardia and medication difficulties.

(4) Atrial flutter with 1: 1 conduction.

4.5 Defibrillator 4.5 Contraindications

(1) Chronic arrhythmias, including sick sinus syndrome.

(2) Arrhythmias caused by digitalis overdose (except ventricular fibrillation).

(3) Atrial fibrillation, atrial flutter, atrial tachycardia with high or complete conduction block.

(4) Severe hypokalemia is temporarily unsuitable for cardioversion.

(5) The left atrium is huge, the atrial fibrillation lasts for more than one year, and the long-term ventricular rate is unpleasant.

5 Defibrillator 5, performance evaluation

5.1 Defibrillator 5.1 Maximum Energy Storage

This refers to the maximum energy value stored across the energy storage capacitor before a defibrillation shock. The unit is expressed in Joules (J). It has been proved by experiments that the safe energy dose of electric shock, that is, the maximum energy storage value is preferably not more than 400J.

5.2 Defibrillator 5.2 releases electrical energy

Refers to how much power the defibrillator actually releases to the patient. This indicator is very important because it is directly related to the actual defibrillation dose. The amount of energy stored does not equal the amount that can be released to the patient. This is because when the electrical energy is released, the internal resistance of the capacitor, the skin and electrode contact resistance, and the electrode connector contact resistance all consume power, so for different patients ( (Equivalent to different release loads), the same stored electrical energy may release different electrical energy. Therefore, the amount of electrical energy released must be based on a certain load value. A load of 50 8 is usually used as the patient's equivalent resistance value.

5.3 Defibrillator 5.3 release efficiency

The ratio of released energy to stored energy is called release efficiency. Different defibrillators have different release efficiencies. The release efficiency of most defibrillators is between 50% and 80%.

5.4 Defibrillator 5.4 Maximum Energy Storage Time

The time required for the energy storage capacitor to charge to the maximum energy storage value is called the maximum energy storage time. This parameter is required to be as small as possible, because the shorter the energy storage time, the less preparation time required for rescue and treatment. However, due to the internal resistance of the power supply, this time cannot be reduced indefinitely. At present, the maximum energy storage time of most defibrillators is in the range of (10 ~ 15) s.

5.5 Defibrillator 5.5 Maximum Release Voltage

This refers to the highest voltage value on the load when the defibrillator releases energy to a certain load with the maximum energy storage value. In order to ensure safety and prevent patients from receiving excessive voltage during defibrillation shocks, the International Electrotechnical Commission stipulates that when the defibrillator is released to a 100 8 resistance load with a maximum energy storage value, the maximum voltage value on the load should not exceed 5000V.

6 Defibrillator 6, maintenance of defibrillator

The maintenance and cleaning of the defibrillator include the following aspects:

6.1 Defibrillator 6.1 Cleaning the recorder print head

If the printed ECG strips are too light or uneven, clean the print head with a cotton ball moistened with alcohol to remove the remaining paper scraps.

6.2 Defibrillator 6.2 Maintenance Battery

The defibrillator can be powered by AC or battery. After the battery is installed in the defibrillator, it should be charged for 24 hours to ensure that the battery reaches its full capacity. Usually, the instrument should be connected to the AC power supply to force the battery to be fully charged after each use. Will reduce battery capacity and life. If the defibrillator is stored for more than one month without AC power, first charge the battery for 48 hours, then remove it from the instrument and store it in a cool, dry place, but it should not be stored below zero degrees Celsius. Charge the stored battery at least 24 hours every 6 months to ensure that the battery is not completely discharged during storage. When the battery is removed from the instrument, it should be marked on the instrument immediately. AC power is required to work.

Leaving the battery uncharged for too long can cause permanent damage to the battery. Therefore, check the battery capacity at least once every 6 months. The sealed lead-acid new battery can provide a minimum of 2.5 hours of monitoring time. When 5 cannot provide a minimum of 2.5 hours of monitoring time, or the battery cannot provide 10 minutes of "battery voltage" This battery needs to be replaced during the "low" warning time.

6.3 Defibrillator 6.3 Cleaning the outer surface

Keep the exterior of the instrument free of dust, and thoroughly remove the extraneous glue on the defibrillation electrodes. Use a non-corrosive detergent such as soapy water and chlorine bleach to clean the exterior. Do not let any liquid enter the interior of the instrument. Do not use strong Solvents such as acetone or acetone-based compounds can easily crack the display. Be very careful when cleaning. Do not steam or gas fumigate the monitoring leads and defibrillation electrodes.

7 Defibrillator 7, new progress of ECG defibrillator

The new generation of ECG defibrillator has the characteristics of small size and multi-function. When processing ECG data, it can capture up to 8 hours of continuous ECG waveforms and events (including drugs and treatment marks) and store them in its memory. Or 50 optional 12-lead ECG reports can be stored on an optional removable data card. The "event summary report" can be printed out and transferred to a data management software running on a computer to compile, edit, and other data, and can be shared and archived. When processing the patient's data, the data card can be removed from Remove the defibrillator and insert another defibrillator to display the original ECG waveform and data. Due to the high degree of intelligence of the defibrillator's self-test and operation test, the results automatically stored in memory can keep the latest ECG waveform inspection records.

The new defibrillator can be used in a variety of environments. The patient cable will automatically start ECG monitoring when connected to the defibrillator. Digital measurement results, waveforms and alarm indicators can quickly find the information doctors need. Measurement results And the waveform can be freely customized by the physician. At the same time, the new ECG defibrillator has a new technology of bi-phase waveform. The new generation of defibrillator uses bi-phase wave to display the ECG waveform signal, whether it is in the defibrillation effect or reducing the heart after defibrillation. In terms of insufficiency, it has a very important role. And the new ECG defibrillator also has the function of impedance compensation. When measuring the impedance of the chest wall, a low-energy shock can be issued according to the individual physical conditions of the patient. And can be quickly charged. Quickly charge to a maximum energy of 200J within 3s to perform ECG defibrillation on a critically ill heart patient. In addition, the new ECG defibrillator also has the function of non-invasive pulsation: the new defibrillator uses a single-phase truncated exponential pulsation. The 40ms pulse width of the pacemaker is constant, but the frequency and output power are adjustable.

With the continuous advancement of high-tech medical equipment, ECG emergency equipment has been greatly developed; the technology used in ECG defibrillators is becoming more advanced, and the current ECG defibrillator has more functions. : (1) There are many accessories, but the weight is still very light and easy to carry. (2) The defibrillator provides a training program for self-mastery, which can run a simulation program of actual operation and test your own understanding of mastery. (3) Provides a quick reference card to make the key functions and operations of the device clear at a glance, so that doctors can quickly grasp the operation items, and make the ECG defibrillator intelligent and multifunctional.

Defibrillator References:

[1] Cui Liang, Cui Yan, Huang Tao. Quality Control of Cardiac Defibrillator / Defibrillator [J]. China Medical Equipment, 2011, 8 (7): 54 ~ 55.

[2] American Heart Association. ECC Guidelines [M]. 2000, 102.

[3] Wang Guohong, Zheng Fuqiang. Overview and technical progress of defibrillators [J]. Medical Equipment Information, 2006, 21 (5): 37 ~ 38.

[4] Chen Kang. Overview and new development of ECG defibrillator [J]. China Medical Devices Information, 2005, 11 (6): 27 ~ 32.