Automatic External Defibrillation.
Charles Robinson was admitted to the ambulatory surgical center this morning. He is 66 years old and is scheduled to have a hernia repair today. As the nurse enters his room to start an IV, she/he notices that Mr. Robinson is diaphoretic and slightly short of breath. With a fearful look on his face, he states that it feels like someone is standing on his chest. Suddenly, he collapses back onto the stretcher. The nurse determines that Mr. Robinson is unresponsive, is not breathing, and has no pulse. The nurse shouts for help, and with the use of a barrier device, she/he begins cardiopulmonary resuscitation (CPR). A co-worker brings the automatic external defibrillator (AED) that is kept at the nurses' station. The AED electrode pads are attached to the patient's chest. The AED detects a shockable rhythm, and delivers a 200 joule shock. Following a second shock, the AED analyzes the rhythm and a voice prompt states "No Shock Advised." The carotid artery is checked and a pulse is present. Other vital signs are assessed, and the nurse supports the airway and breathing. The patient is monitored closely until an ambulance arrives to transport Mr. Robinson to the hospital.
Unfortunately, Mr. Robinson's story is not unique. More than 1 million myocardial infarctions occur each year. More than 480,000 adults die in the United States each year as a result of heart disease. More than half of these deaths are caused by sudden myocardial infarction with ventricular fibrillation (American Heart Association [AHA], 2001). Automatic external defibrillation is the most significant intervention used to revive adult heart attack victims. This update on AED describes how nurses can use this technology to save lives. The rationale, procedures, and nursing responsibilities associated with its use are described.
Lethal Rhythms: VT and VF
The most common cardiac disturbance in adult cardiopulmonary arrest is ventricular fibrillation (VF). Ventricular fibrillation is uncoordinated electrical activity of the ventricles, which results in no directional blood flow. Ventricular tachycardia (VT) is electrical activity that originates in the ventricles. A person in VT may or may not have a pulse. VT may rapidly turn into VF. If VF is not corrected in a timely manner, the rhythm will deteriorate to asystole. Once a patient enters an asystolic state, where there is no electrical activity in the heart, recovery is rare.
Chain of Survival
The AHA identifies the critical steps of response to a cardiac arrest as the "chain of survival." The four links in this chain are: (a) early access, (b) early CPR, (c) early defibrillation, and (d) early advanced cardiac life support (ACLS). It is essential that early CPR and defibrillation are started immediately in an adult with cardiac arrest. CPR may prolong the time in which a patient may recover from VF. Defibrillation is the treatment used to convert the patient back into a normal cardiac rhythm.
When a person is in ventricular fibrillation, the sooner defibrillation occurs, the greater the chance of survival. Figure 1 demonstrates the relationship between the time in which defibrillation occurs and the chance of a successful resuscitation. If defibrillation occurs within 5 minutes, the chance of successful recovery is about 50%. With each additional minute, the chance of recovery is decreased by 7% to 19%. After 10 minutes there is very little chance of recovery. In addition to the time that elapses before defibrillation occurs, other factors that affect the success of defibrillation include the patient's age, underlying medical condition, and presence and extent of hypoxia and acidosis.
Defibrillation is the intervention effective for treating VF and pulseless VT. It is the intervention most likely to improve survival in adults in emergency cardiac situations. With defibrillation, a large amount of unsynchronized electricity is delivered into the myocardium. The goal of the defibrillatory shock is to depolarize the myocardium and allow for organized electrical activity to resume.
A defibrillator is a medical equipment device that delivers electrical energy with the goal of terminating a cardiac dysrhythmia. There are three basic types of external defibrillators: (a) manual, (b) semi-automatic, and (c) automatic. The use of a manual defibrillator requires skill in cardiac rhythm interpretation. Automatic and semi-automatic defibrillators analyze the rhythm, and an electrical charge is generated and delivered when appropriate. The operator is not required to interpret the cardiac rhythm when using an AED. Components of all AEDs include two adhesive electrode pads that are attached to the defibrillator by connecting cables. The electrode pads have two functions. First, the pads transmit the rhythm to the microprocessor, which is inside the AED, for analysis. If a shock is indicated, it is delivered through the electrode pads.
There are four universal steps to the operation of AEDs (see Table 1). Fully automatic AEDs immediately defibrillate any shockable rhythm that is detected. Semi-automatic AEDs require additional steps for operation but also provide greater control of the response situation. With semi-automated AEDs, the operator must press a button to initiate rhythm analysis. If VF (or VT at a pre-set rate) is present, the AED will indicate that a shock is advised. The "shock advised" announcement may occur by a written message, a visual alarm, and/or an audible computerized statement. The operator must then press the "shock" button before the shock is delivered.
Table 1 Automatic External Defibrillator Operation 1. Turn the power on. 2. Attach the electrode pads. 3. Analyze the rhythm. 4. Deliver the shock if indicated.
AEDs are preset to deliver 200 joules of energy for the initial shock. Some models maintain a constant energy level for all defibrillation attempts, and some automatically increase the energy level to 300 and then 360 joules for subsequent shocks. Some models allow the operator to adjust the energy setting. The equipment operating manual provides specific information about energy settings for each model.
There are several possible advantages of AEDs as compared to manual defibrillators. More rapid delivery of defibrillation may occur as AEDs are increasingly available. Less training time and skill are required with AEDs. Also, they are easier to operate and allow a "hands-free" defibrillation procedure.
Patient Preparation and Precautions
AEDs are approved for use in individuals over the age of 8. The accuracy of rhythm analysis in the pediatric age group has not been extensively researched. The amount of current that is delivered by standard AEDs is intended for adults and is too large for small children. Most cardiac arrest in children is a result of respiratory arrest, and VF is not a common event in children.
Some preparation may be required prior to attaching the electrode pads to an adult. These steps must be completed very quickly. If the chest is wet, quickly dry it with a towel. Do not use alcohol. If chest hair is excessive, shave the area where the pads must be attached. Remove transdermal patches and quickly wipe the area dry. Remove metal, such as glasses, prior to defibrillation. Avoid placing electrode pads directly over pacemakers, implanted defibrillators, or implanted ports. The person should be positioned supine, away from water sources and metal surfaces. If the person is lying on a metal-framed bed, a small amount of electrical current may be transferred to anyone touching the metal. Always shout "clear" and visually check to be sure that everyone is clear before a shock is delivered.
The AED cannot analyze the cardiac rhythm when the person is being moved, when CPR is being performed, or when the cables are being handled. Stop CPR and stand back when the AED is in the process of rhythm analysis and defibrillation.
Electrode Pad Placement
The electrode pads should be attached in a sternal/apex placement. The right electrode pad should be placed to the right of the sternum, just beneath the clavicle and above the right nipple. Proper placement for the left electrode pad is lateral to the left nipple, approximately three inches below the axillary. A diagram of the AED components and electrode pad placement is pictured in Figure 2. Electrode pads should be applied with pressure on all sides to ensure good adhesion.
Using the AED
Assess the patient. Determine unresponsiveness. Check to see if the person is breathing. If breathing is absent, give two breaths with the use of a barrier device. Check the carotid pulse. If no pulse is present, start CPR. When the AED is attached, stop CPR, shout "all clear," and defibrillate up to three times if necessary. Check the pulse. If no pulse is detected at this time, perform CPR for 1 minute. Check the pulse. Repeat three-shock sets until the AED gives a "no shock indicated" message.
When a person has been successfully resuscitated following defibrillation with an AED, continue to monitor the patient closely. Provide supportive care. Leave the electrode pads attached, in case the person arrests again. And remember the ABCDs: Airway, Breathing, Circulation, and Defibrillation.
Increasing Use of AEDs
AEDs may be appropriate for use in the home for patients at increased risk for cardiac arrest and by the pre-hospital response and transport. They should be considered for use in physician offices, health clinics, urgent care facilities, and clinical sites such as non-monitored inpatient units. AEDs are increasingly available in public places such as hotels, shopping malls, and sports stadiums. AEDs may be available in airport terminals and are routinely carried on airplanes by some commercial airliner.
Availability of early defibrillation is the standard of care for adult patients in cardiac arrest (AHA, 1992). Regardless of the setting, successful adult resuscitation depends most often on early defibrillation. Adult-health nurses must understand why and when early defibrillation is indicated and should be thoroughly familiar with standard resuscitation procedures.
American Heart Association. (2001). Fundamentals of BLS for healthcare providers. Dallas, TX: AHA.
American Heart Association. (1997). R.O. Cummins (Ed.), Basic life support for healthcare providers. South Deerfield, MA: Channing L. Bete Co., Inc.
American Heart Association. (1992). Guidelines for cardiopulmonary resuscitation and emergency cardiac care. Emergency Cardiac Care Committees and Subcommittees. JAMA, 268, 2171-2302.
Deborah Goodman, MSN, RN, CS, is Executive Director, Mountain Hospice, Belington, WV. She is a Basic Life Support Instructor Trainer and an Advanced Cardiac Life Support Instructor.