Defibrillator (ppt)

1. Defibrillator

2. OBJECTIVE 1. Define defibrillation. 2. Describe Need and history of defibrillation. 3. Describe the principle and mechanism of defibrillation. 4. Types and classes of defibrillator 5. Describe the Automated external defibrillator 6. Identify the precautions and risk 7. Troubleshooting of defibrillator

3. defibrillator

4. Introduction Definition: Defibrillation is a process in which an electronic device sends an electric shock to the heart to stop an extremely rapid, irregular heartbeat, and restore the normal heart rhythm. Defibrillation is a common treatment for life threatening cardiac dysrhythmias , ventricular fibrillation, and pulse less ventricular tachycardia.

5. NEED FOR A DEFIBRILLATOR Ventricular fibrillation is a serious cardiac emergency resulting from asynchronous contraction of the heart muscles. Due to ventricular fibrillation, there is an irregular rapid heart rhythm. Fig. Ventricular fibrillation Fig. Normal heart beat

6. Ventricular fibrillation can be converted into a more efficient rhythm by applying a high energy shock to the heart. This sudden surge across the heart causes all muscle fibres to contract simultaneously. The instrument for administering the shock is called a DEFIBRILLATOR. Possibly, the fibres may then respond to normal physiological pace making pulses. NEED FOR A DEFIBRILLATOR

7. Defibrillation is performed to correct life-threatening fibrillations of the heart, which could result in cardiac arrest. It should be performed immediately after identifying that the patient is experiencing a cardiac emergency, has no pulse, and is unresponsive. Purpouse of defibillation

8. History Of Defibrillation Defibrillation was invented in 1899 by Prevost and Batelli, two Italian physiologists. They discovered that electric shocks could convert ventricular fibrillation to sinus rhythm in dogs.The first case of a human life saved by defibrillation was reported by Beck in 1947 .

9. Principle Of Defibrillation Energy storage capacitor is charged at relatively slow rate from AC line . Energy stored in capacitor is then delivered at a relatively rapid rate to chest of the patient. Simple arrangement involve the discharge of capacitor energy through the patient’s own resistance.

10. Principle Of Defibrillation Fig: Schematic diagram of a defibrillator

11. Principle Of Defibrillation The discharge resistance which the patient represents as purely ohmic resistance of 50 to 100Ω approximately for a typical electrode size of 80cm2. This particular waveform Fig is called ‘ Lown ’ waveform. The pulse width of this waveform is generally 10 ms.

12. energy (joules) charge (coulombs) current (amps) pulse duration defibrillation occurs no defibrillation Defibrillator Strength Duration Curve

13. minimum defibrillation energy occurs for pulse durations of 3 - 10 ms (for most pulse shapes). pulse amplitude in tens of amperes (few thousand volts). Strength Duration Curve

14. Strength Duration Curve intrinsic characteristics of patient patient’s disease duration of arrhythmia patient’s age type of arrhythmia (more energy required for v. fib.) operator selects energy delivered: 50-360 joules, depends on:

15. Fibrillations cause the heart to stop pumping blood, leading to brain damage. Defibrillators deliver a brief electric shock to the heart, which enables the heart's natural pacemaker to regain control and establish a normal heart rhythm. Mechanism

16. POWER OF DEFIBRILLATION Higher voltages are required for external defibrillation than for internal defibrillation. A corrective shock of 750-800 volts is applied within a tenth of a second. That is the same voltage as 500-533 no of AA batteries!

17. Normal Cardiac Conduction ECG tracing Electrical pattern

18. Cardiac Arrest Occulsion of the coronary artery leads to ischemia Ischemia leads to infarct which causes interruption of normal cardiac conduction Infarct = VF/VT

19. Shockable Rhythms Ventricular Fibrillation Ventricular Tachycardia

20. DEFIBRILLATOR ELECTRODES Types of Defibrillator electrodes:- Spoon shaped electrode Applied directly to the heart. Paddle type electrode Applied against the chest wall Pad type electrode Applied directly on chest wall

21. DEFIBRILLATOR ELECTRODES fig: Electrodes used in defibrillator (a) a spoon shaped internal electrode that is applied directly to the heart. (b) a paddle type electrode applied against the anterior chest wall.

22. Fig.- Pad electrode DEFIBRILLATOR ELECTRODES

23. ELECTRODE PLACEMENT OF AED Anterior electrode pad Apex electrode pad Fig: anterior –apex scheme of electrode placement

24. Classes of discharge waveform Monophasic pulse or waveform Bi- phasic pulse or waveform

25. Classes of discharge waveform There are two general classes of waveforms: mono- phasic waveform Energy delivered in one direction through the patient’s heart Biphasic waveform Energy delivered in both direction through the patient’s heart

26. Classes of discharge waveform Fig:- Generation of bi- phasic waveform

27. Classes of discharge waveform The biphasic waveform is preferred over monophasic waveform to defibrillate. Why????? A monophasic type, give a high-energy shock, up to 360 to 400 joules due to which increased cardiac injury and in burns the chest around the shock pad sites. A biphasic type, give two sequential lower- energy shocks of 120 - 200 joules, with each shock moving in an opposite polarity between the pads.

28. TYPES OF DEFIBRILLATORS Internal External 28

29. TYPES OF DEFIBRILLATORS Internal defibrillator Electrodes placed directly to the heart e.g..-Pacemaker External defibrillator Electrodes placed directly on the heart e.g..-AED

30. For each minute elapsing between onset of ventricular fibrillation and first defibrillation, survival decreases by 10%. defibrillators should be portable, battery operated, small size. energy in defibrillators usually stored in large capacitors. total energy stored in capacitor: V c = capacitor voltage External Defibrillators

31. External Defibrillator power supply energy storage patient ECG monitor timing circuitry gate charge discharge standby switch is under operator control applies shock about 20 ms after QRS complex, avoids T-wave

32. AUTOMATIC EXTERNAL DEFIBRILLATOR

33. AED is a type of external defibrillation process. AUTOMATIC EXTERNAL DEFIBRILLATOR AED is a portable electronic device that auto- matically diagnoses the ventricular fibrillation in a patient. Automatic refers to the ability to autonomously analyse the patient's condition.

34. AEDs require self-adhesive electrodes instead of hand held paddles. AUTOMATIC EXTERNAL DEFIBRILLATOR The AED uses voice prompts, lights and text messages to tell the rescuer what steps have to take next .

35. WORKING OF AED Turned on or opened AED. AED will instruct the user to:- Connect the electrodes (pads) to the patient. Avoid touching the patient to avoid false readings by the unit. The AED examine the electrical output from the heart and determine the patient is in a shock able rhythm or not

36. WORKING OF AED When device determined that shock is warranted, it will charge its internal capacitor in preparation to deliver the shock. When charged, the device instructs the user to ensure no one is touching the victim and then to press a red button to deliver the shock. Many AED units have an 'event memory' which store the ECG of the patient along with details of the time the unit was activated and the number and strength of any shocks delivered.

37. PRECAUTIONS The paddles used in the procedure should not be placed:- on a woman's breasts over an internal pacemaker patients. Before the paddle is used, a gel must be applied to the patient's skin

38. Skin burns from the defibrillator paddles are the most common complication of defibrillation. Other risks include injury to the heart muscle, abnormal heart rhythms, and blood clots. Risk in defibrillation

39. Troubleshooting Attach the external and internal paddles if the monitor reads, "No paddles." Check to ensure that the leads are securely attached if the monitor reads, "No leads.“ Connect the unit to AC power if the message reads, "Low battery." Verify that the Energy Select control settings are correct if the defibrillator does not charge.

40. Change the electrodes and make sure that the electrodes adapter cable is properly connected if you receive a message of "PACER FAILURE." Restart the pacer. Close the recorder door and the paper roll if the monitor message reads, "Check recorder”. Troubleshooting

41. References Willis A Tacker , “External Defibrillators,” in The Biomedical Engineering Handbook, J. Bronzino ( ed ) CRC Press, 1995. www.google.com en.wikipedia.org/wiki/ Defibrillation http://www.slideworld.org/viewslides.aspx/defibrillator