205 Defibrillation Flashcards
The application of an asynchronous electrical current through the heart in order to terminate a rhythm of ventricular fibrillation or pulseless ventricular tachycaradia
Debrillation
A ___________ and __________ myocardium improves the chances of defibrillation success.
Well-oxygenated
Perfused
_______ ________ of shockable rhythms with an electrical defibrillator carries the best chance of success
Early treatment
__________ occur when cardiac myocytes depolarize in an uncoordinated fashion
Ventricular fibrillation
Typically, depolarization starts at the __________ _____ and spreads in an organized fashion throughout the conducting apparatus of the heart, causing sequential contraction of the cardiac chambers.
Pacemaker node
In the context of cardiopulmonary resuscitation, defibrillation is indicated to:
Treat patients in ventricular fibrillation or less commonly, pulseless ventricular tachycardia
The application of an electrical current causes simultaneous depolarization of the cardiac myocytes to force them into:
their refractory period, which breaks the cycle of uncontrolled firing of cells, which is the cause of a fibrillating rhythm
If enough of the myocardium enters the refractory period at the same time:
The malignant rhythm is terminated and the underlying pacemaker rhythm can take over
What are the two main types of defibrillator units:
Monophasic
Biphasic
In a monophasic defibrillator, the machine generates
A positive current only
A biphasic device generates
A positive followed by a negative current
While both types of defibrillators can be effective in terminating ventricular fibrillation or pulseless vtach, studies have demonstrated which to be better?
Lower energy requirements for successful arrhythmia termination using a biphasic device
By switching out the type of defibrillator paddle attachment, many defibrillators can be used for either
External or internal defibrillation
Alcohol should not be used during defibrillation due to
risk of fire when the electrical charge is applied
List the three arrangements of contact paddles available
- Most common: system of two handheld paddles. The animal is placed into dorsal recumbency, and the person performing defibrillation uses the paddles to stabilize the animal and prevent it from falling to either side. During the technique, operator has to take great care to avoid coming into contact with any part of the patient while discharging the defibrillator current.
- In lateral recumbency- a long paddle (posterior paddle) that can be slide underneath the patient is placed first and a conventional paddle is then applied to the opposite side of the chest, and then defibrillation performed.
- Preplaced adhesive patches that connect directly to the defibrillator. This requires clipping of the fur and preparation of the skin and so is typically only used in scenarios where the need for defibrillation is expected and planned for, such as interventional cardiology procedures, rather than in an emergency room setting.
Internal defibrillator paddles are described as:
Sterile, wand-like with a smaller contact area
How do you apply internal defibrillator paddles?
A thin layer of saline soaked gauze is placed between the metal surface of the paddle and the heart to reduce the risk of causing burn injury to the epicardium.
It is ideally performed after removal of the pericardium.
If the arrest is of four minute duration or less, usually meaning it was a witnessed event and a shockable rhythm was/is present, when should defibrillation be utilized?
Immediately. The only delay should be the time it takes to prepare for defibrillation. If there is a delay, begin/continue with chest compressions. The more prompt the defib, the higher the chance of success.
If the cardiac arrest is of a longer duration than four minutes, then it is likely that what will be present? What does that change?
Significant myocardial ischemia, defibrillation success will be less likely. A cycle of CPR prior to defib is recommended.
Most published recommended defibrillation energies are for what kind of defibrillator?
Monophasic
biphasic may require slightly lower initial energy settings
What is the first step for patients who are refractory to defibrillation?
Optimize basic life support
A single shock approach is usually performed because?
Minimizing interruptions to chest compressions.
A shock is applied, then chest compressions immediately resumed for one cycle prior to another attempt at defibrillation
Typically, after an unsuccessful defibrillation, the next shock is delivered with a:
~50% increased in energy
Increasing the energy of the next shock is called an ______ _____ _____
Escalating energy protocol
What two drugs are examples of what have been recommended as adjunctive treatments in patients with refractory ventricular fibrillation, along with chest compressions and electrical defibrillation.
Lidocaine (may increase defibrillation threshold- defib energy required with monophasic defibrillators)
Amiodarone (drug of choice)
Usually reserved for use until two to three attempts at defibrillation have been unsuccessful
Recent studies suggest ibutilide may be promising, which may have fewer negative cardiovascular effects than amiodarone. This drug has not been used clinically for this indication in veterinary medicine.
Describe at least 3 precautions when performing defibrillation.
- Performed on an insulated surface (ie rubber mat)
- Inform about impending discharge by announcing CLEAR prior to delivering shock.
- Visually ensure no one is touching the patient or table prior to shock delivery
- Avoid excessive contact gel getting on their hands or arms that could conduct a shock back towards them
- Good contact between paddles and patient reduces the risk of arcing of the current.
- Strictly avoid the use of alcohol as a contact agent
- Extra care when using conventional paddles in dorsal recumbency as the animal may slip or the limbs can move during current application, potentially bringing animal in contact with the operator or other staff members
While rare, what is a potentially delayed consequence or complication to defibrillator use in the patient?
Burns
Monitor the skin where the pads or paddles were applied over the next several days
What monitoring is indicated following post-ROSC care following defibrillation?
Extra attention paid to monitoring ECG rhythm and the potential need for antiarrhythmic therapy
Recurrence of fibrillation can occur, and the risk can be reduced by appropriate antiarrhythmic therapy and hemodynamic optimization
