By Eileen S. Robinson, RN, MSN
Every year, sudden cardiac arrest (SCA) causes more than one-third of all deaths that occur from cardiovascular disease. Ventricular fibrillation is responsible for most of these SCA events.
Unfortunately, the outcomes for in-hospital SCA resuscitation remain bleak, even though defibrillation has been available for more than 30 years. Only about 15% of in-hospital victims of cardiac arrest survive. What’s more, for every minute of delay in instituting appropriate external defibrillation, there is an estimated 7%-10% reduction in survival of victims who suffer SCA due to VF. These figures are the impetus behind the American Heart Association (AHA) Guidelines 2000 recommendation that external defibrillation be initiated within 3 minutes of SCA induced by pulseless ventricular tachycardia (VT) or ventricular fibrillation (VF) in the hospital setting. In addition to AHA's new guidelines, the Joint Commission on Accreditation of Healthcare Organizations now requires organizations to collect resuscitation data, which is to be used to evaluate the impact of resuscitation processes and performance on patient outcome.
Whether you’re performing defibrillation or assisting with the procedure, you need to understand the details of this life-saving measure, including the devices available and your specific nursing responsibilities. I’ll discuss that and more, but first let’s review some basics.
When VF occurs, the normal atrioventricular (AV) synchrony of cardiac electrical conduction, depolarization and contraction is lost. Instead there is abnormal electrical activity, which causes a quivering ventricular muscle that can’t sustain cardiac output. Perfusion to the brain and the rest of the body is disrupted, hemodynamic instability ensues, and rapid deterioration to complete cardiac arrest and death will occur with uncorrected VF.
Defibrillation depolarizes all cardiac cells at once, breaking the cycle of ventricular fibrillation’s chaotic electrical discharge. This action interrupts the abnormal electrical activity and restores the heart’s natural pacemaker for AV synchronous functions – conduction, depolarization and contraction.
To be effective, the defibrillator’s electrical current (energy) must pass through a critical mass of myocardium. Creating the conditions to achieve this outcome include delivering the appropriate level of current, overcoming transthoracic impedance and ensuring proper paddle/pad positioning.
Monophasic versus biphasic
Contemporary defibrillators deliver the current in a waveform pattern, either monophasic or biphasic. The basic differences between these waveforms are the direction in which the current flows through the heart, the speed of delivery, and the amount of energy delivered.
Monophasic waveform defibrillators, the more common type, deliver the current in one direction, over a shorter time period, and require higher energy levels. The higher energy requirement exists because the stored energy in a monophasic defibrillator isn’t necessarily the energy that is delivered to the heart.
That’s because transthoracic impedance is a major factor in reducing the current delivered. This refers to the resistance to the electrical current’s flow created by chest wall structures such as skin and muscle. Essentially these structures absorb some of the energy intended for the myocardium.
Various factors reduce impedance: a conduction medium on the paddles such as gel; the correct amount of pressure exerted on the paddles against the chest wall; and the delivery of 3 stacked defibrillator shocks. The AHA guidelines recommend 200 joules initially, followed by 200-300 joules, and then 360 joules when using a monophasic defibrillator to treat VF.
Most of the energy from a biphasic waveform defibrillator is delivered in a forward (positive) direction, but then the current flow reverses itself and travels in a backward (negative) direction. In addition, biphasic defibrillators are capable of adjusting for transthoracic impedance and therefore use lower energy levels.
Research shows that biphasic defibrillators are more successful in converting VF on the first shock and can do so at energy levels as low as 150 joules. Lower energy levels and fewer defibrillation attempts mean less myocardial damage, a consequence of defibrillation. The AHA guidelines indicate that energy levels equal to or less than 200 joules when using a biphasic defibrillator are safe and effective in treating VF.
Paddles and electrodes
Defibrillator paddles or disposable defibrillator electrodes (DDE) are positioned on the chest wall so that the axis of the heart lies between them. The objective is to deliver the energy along the normal cardiac axis or conduction pathway. One paddle or DDE is positioned under the patient’s right clavicle along the sternal border and the other paddle or DDE is positioned over the heart’s apex located at the left 5th intercostal space left of the nipple and between the anterior and mid-axillary line. In some circumstance, you’ll need to modify the positioning. A conductive gel applied to the paddles serves to facilitate the current delivery, prevent arcing of the current, and protect the skin from burns. The person using the paddles must exert 25 pounds per square inch of pressure against the chest wall with the paddles to ensure optimum energy delivery to the heart and avoid complications such as current arcing.
For DDE, the conductive medium, either gel or saline, is embedded in the DDE. If the DDE package is breached, the medium can dry and lose effectiveness.
Initial defibrillation for VF continues until a pulse is established, the rhythm converts to a normal rhythm or one in which defibrillation isn’t indicated, or the three AHA recommended shocks have been delivered. The team will start CPR if the patient remains pulseless after the first three shocks and will institute advanced cardiac life support measures including subsequent defibrillation if indicated.
Conventional and automatic
There are two major types of external defibrillators, the conventional or manual type and the automatic external defibrillator. The conventional defibrillator is designed for use by or in the presence of an individual who has ECG rhythm recognition skills. In this case, rhythm recognition, the decision to defibrillate, and charging and discharging the defibrillator are dependent on human judgment.
All of this impacts response time in a hospital unit without staff trained in ECG recognition. Currently the average response time to initiation of defibrillation is 5 to 7 minutes and survival rate is 15% for in-hospital SCA.
The automatic external defibrillator (AED), initially developed for use by first responders in the prehospital setting, doesn’t require the user to have ECG rhythm recognition skills. The AED device is a computer that is capable of analyzing the ECG rhythm, charging the defibrillator and discharging the energy.
There are two types of AEDs: semiautomatic and fully automatic. The semiautomatic model requires the user to initiate some or all of the AED functions by pressing buttons on the equipment following the AED visual, audio or visual/audio prompts. The fully automatic model functions independently of the user, once the DDE are applied and the system is turned on.
Some AEDs have ECG display screens and manual override features, which are used when ACLS-trained personnel arrive. In the hospital setting, a comparative study between conventional defibrillator and AED response times indicated that defibrillation with an AED occurred an average of one minute sooner than conventional defibrillation.
The newest advance in defibrillation technology narrows the gap between recognition and initiation of treatment to an average of 21 seconds. This latest technology is comparable to the automatic internal cardioverter defibrillator (AICD)--only it’s external.
Patients at risk for SCA are monitored with systems that integrate this new technology. If the patient has an episode of VF, the device recognizes the rhythm and starts defibrillation without human intervention. Clinical studies demonstrate that the technology’s sensitivity for rapid rate arrhythmia detection is 100% and that VF was converted with the first shock in more than 96% of the cases. Currently only one defibrillator, Powerheart (from Cardiac Science, Irvine, CA) has this new technology, but LifePak defibrillators (from Medtronic Physio-Control, Redmond, WA) will soon include this technology.
Both the patient and the personnel using the defibrillator are at risk for injuries such as burns from arcing current or fire. Keeping defibrillation safe requires attention to various details:
- Make sure no one is in contact with the bed before defibrillator discharges.
- Use only enough gel to cover the surface of the paddle in contact with the chest.
- Remove all excess gel from paddles and the patient’s chest.
- Keep gel off your hands.
- Refrain from the use of alcohol to clean the patient’s chest wall.
- Keep the floor dry underneath the person operating the defibrillator.
- Turn off a temporary pacemaker, disconnect the electrodes and insulate them with a rubber glove.
- Remove metal objects such as jewelry from the patient’s chest.
Your responsibility starts with knowing your facility’s policy and procedure for defibrillation and how the unit’s defibrillator operates. You’re responsible for many of the following activities related to defibrillation:
- Confirming the rhythm.
- Setting up equipment.
- Checking pulse and rhythm.
- Time of SCA.
- Cardiac rhythms.
- Times of defibrillation and energy discharged.
- Presence or absence of pulse.
Although the size, portability, accessibility and capability of defibrillators has evolved with technology, the survival rate remains low. As advances continue, clinicians will strive to further narrow the gap between rhythm recognition and initiation of defibrillation, because a few moments can make a big difference.
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Eileen S. Robinson, RN, MSN, has more than 20 years of experience encompassing clinical, education, publishing and business aspects of nursing. She has been a staff nurse in a medical/surgical unit, a staff, charge and pool nurse in ICU and CCU, and an OR nurse for a plastic and reconstructive surgeon.
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Article provided by Nurses.com