- 1. 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
2. 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. 3. 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 fibrillationFig.
Normal heart beat 4. 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. Possibly, the fibres may then respond
to normal physiological pace making pulses. The instrument for
administering the shock is called a DEFIBRILLATOR. 5.
Defibrillation is performed to correct lifethreatening
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. 6. Defibrillation was invented in 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 . 7. 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 patients own resistance. 8. Fig: Schematic diagram of a
defibrillator 9. The discharge resistance which the patient
represents as purely ohmic resistance of 50 to 100 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. 10. current (amps)defibrillation occursno
defibrillationpulse duration 11. minimum defibrillation energy
occurs for pulse durations of 3 - 10 ms (for most pulse shapes).
pulse amplitude in tens of amperes (few thousand volts). 12.
operator selects energy delivered: 50-360 joules, depends on:
intrinsic characteristics of patient patients disease duration of
arrhythmia patients age type of arrhythmia (more energy required
for v. fib.) 13. 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.
14. Higher voltages are required for external defibrillationthan
for internal defibrillation. A corrective shock of 750-800 volts is
applied within atenth of a second. That is the same voltage as
500-533 no of AA batteries! 15. Electrical patternECG tracing 16.
Occulsion of thecoronary artery leads to ischemia Ischemia leads to
infarct which causes interruption of normal cardiac conduction
Infarct = VF/VT 17. Ventricular FibrillationVentricular Tachycardia
18. Types of Defibrillator electrodes:a) Spoon shaped electrode
Applied directly to the heart. b) Paddle type electrode Applied
against the chest wall c) Pad type electrode Applied directly on
chest wall 19. 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. 20. Fig.- Pad electrode 21. Anterior electrode padApex
electrode padFig: anterior apex scheme of electrode placement 22.
Monophasic pulse or waveformBi-phasic pulse or waveform 23. There
are two general classes of waveforms: a) mono-phasic waveformEnergy
delivered in one direction through the patients hearta) Biphasic
waveform Energy delivered in both direction through the patients
heart 24. Fig:- Generation of bi-phasic waveform 25. 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 lowerenergy shocks of 120 - 200 joules, with each shock
moving in an opposite polarity between the pads. 26.
InternalExternal28 27. Internal defibrillatora) Electrodes placed
directly to the hearte.g..-Pacemakerb) External defibrillator
Electrodes placed directly on the hearte.g..-AED 28. 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:WC1 CVC2 2Vc = capacitor voltage 29. standby power
supplychargedischargegatepatientswitch is under operator
controlenergy storagetiming circuitryapplies shock about 20 ms
after QRS complex, avoids T-waveECG monitor 30. AED is a portable
electronic device that automatically diagnoses the ventricular
fibrillation in a patient. Automatic refers to the ability to
autonomously analyse the patient's condition. AED is a type of
external defibrillation process. 31. AEDs require self-adhesive
electrodes instead of hand held paddles. The AED uses voice
prompts, lights and text tell the rescuer what steps have to take
next.messages to 32. 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 33. 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. 34. 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 35. 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. 36. 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. 37. 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. 38. 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
