[Objectives 1, 3]

Defibrillation is the delivery of an electrical current across the heart muscle over a very brief period to terminate an abnormal heart rhythm. Defibrillation is also called unsynchronized countershock or asynchronous countershock, because the delivery of current has no relationship to the cardiac cycle. Indications for defibrillation include pulseless monomorphic VT, sustained polymorphic VT, and VF.

Manual defibrillation refers to the placement of paddles or pads on a patient’s chest, the interpretation of the patient’s cardiac rhythm by a trained healthcare professional, and the healthcare professional’s decision to deliver a shock, if indicated. Automated external defibrillation refers to the placement of paddles or pads on a patient’s chest and the interpretation of the patient’s cardiac rhythm by the defibrillator’s computerized analysis system. Depending on the type of automated external defibrillator (AED) used, the machine will deliver a shock (if a shockable rhythm is detected) or instruct the operator to deliver a shock. AEDs are discussed in more detail later in this chapter. Defibrillation does not “jump start” the heart. The shock attempts to deliver a uniform electrical current of sufficient intensity to depolarize myocardial cells (including fibrillating cells) at the same time, briefly “stunning” the heart. This provides an opportunity for the heart’s natural pacemakers to resume normal activity. When the cells repolarize, the pacemaker with the highest degree of automaticity should assume responsibility for pacing the heart.

[Objective 1]

There are three general types or classes of defibrillation waveforms: monophasic, biphasic, and triphasic.¹ Waveforms are classified by whether the current flow delivered is in one direction, two directions, or multiple directions.

When a monophasic waveform is used, current passes through the heart in one (i.e., mono) direction (Figure 4-3). Although few monophasic waveform defibrillators are manufactured today, many are still in use. With biphasic waveforms, energy is delivered in two (i.e., bi) phases. The current moves in one direction for a specified period, stops, and then passes through the heart a second time in the opposite direction during a very short period (i.e., milliseconds) (Figure 4-4).

Figure 4-3 When a monophasic waveform is used, current passes through the heart in one direction.

Figure 4-4 With biphasic waveforms, energy is delivered in two phases. The current moves in one direction for a specified period, stops, and then passes through the heart a second time in the opposite direction.

Most AEDs and manual defibrillators sold today make use of biphasic waveform technology. Biphasic defibrillators use either a biphasic truncated exponential (BTE) waveform or a rectilinear biphasic waveform (RBW) (Figure 4-5). The BTE waveform has been used in implantable defibrillator-cardioverters (ICDs) for many years; it was approved for use by the U.S. Food and Drug Administration in 1996 as part of the Heartstream AED, which is now a part of Philips Medical Systems (Seattle, WA). In 1999, Zoll Medical Corporation (Burlington, Mass) announced the development of RBW technology, which was subsequently approved for clinical use by the U.S. Food and Drug Administration.

Figure 4-5 Biphasic defibrillators use either a rectilinear biphasic waveform or a biphasic truncated exponential waveform.

Manufacturers of biphasic defibrillators recommend slightly different energy levels specific for their devices. Both escalating (i.e., increasing energy levels) and nonescalating (i.e., no increase in energy level) biphasic waveform defibrillators are available; however, there are insufficient data to recommend one type of device over another. When preparing to deliver electrical therapy to a patient, knowledge of the type of device you are using (i.e., monophasic versus biphasic) and the manufacturer’s recommended energy levels for the dysrhythmia you are treating is essential.

Triphasic and quadriphasic waveforms deliver multidirectional shocks. Future generations of defibrillators may implement this technology.

Body Tissue and Hair

The skin surface, fat, bone, and hair can cause significant increases in resistance. It may be difficult to ensure good electrode-to-skin contact in a patient who has a hairy chest. However, if good contact is not ensured, transthoracic impedance will be high and the effectiveness of defibrillation will be reduced.³ There is an increased risk of burns from arcing (i.e., sparks) from electrode to skin and from electrode to electrode; ECG identification and analysis may also be inhibited.

If excessive chest hair is present, quickly clip or shave the hair in the areas of intended electrode placement to ensure proper adhesion of the pads. If this is not feasible (or if a razor is not available), check to see if an extra set of electrodes is available. If so, apply one set to the patient’s chest and then quickly remove them. This should remove some hair and improve electrode-to-skin contact when you apply a second set of pads. However, do not delay defibrillation.

Paddle or Pad Size

Optimum pad sizes for defibrillation and pacing on the basis of patient age and weight vary by manufacturer. Carefully follow all manufacturer instructions.

Studies have shown that adult paddles or pads should be used for patients weighing more than 10 kg (22 lb) (i.e., generally older than 1 year).^4–7 For adults, the paddle or pad size ranges from 8 to 12 cm in diameter. Use pediatric paddles or pads for infants and children weighing less than 10 kg (22 lb) or for those whose chests are too small to accommodate standard paddles or pads.⁸ Generally, use the largest pads that will fit the patient’s chest with at least 1 inch (3 cm) separating the pads. Avoid using pediatric electrodes for adult defibrillation because myocardial injury can occur.⁹

When applying defibrillation paddles or pads, remove the patient’s clothing and expose his or her chest. Be sure to look for transdermal patches or disks, which may be used to deliver nitroglycerin, nicotine, analgesics, hormones, or antihypertensives. Do not apply paddles or pads directly over the medication patch or disk because the patch may prevent good electrode contact, hindering the delivery of energy from the defibrillation electrode to the heart. A lack of good contact can cause arcing and may cause skin burns.¹⁰ If a medication patch, disk, or ointment is located at or near the site of paddle or pad placement, remove it and wipe the area clean (do not use alcohol or alcohol-based cleansers) before applying defibrillation paddles or pads.¹¹

Because some patients wear jewelry in various body locations, take a moment to look for metal body piercings after the patient’s chest is exposed. Although the presence of these materials is not a contraindication to defibrillation, it is possible that their presence can divert the defibrillating current from the myocardium and decrease defibrillation effectiveness. If feasible and if time permits, the metal object should be removed to minimize the potential for burn injuries across the chest.

Paddle or Pad Position

[Objective 1]

When preparing the skin for paddle or pad placement, do not use alcohol, tincture of benzoin, or antiperspirant. Hand-held paddles or combination pads should be placed on the patient’s bare chest according to the manufacturer’s instructions. Paddles or pads may be labeled according to their intended position on the chest (e.g., sternum/apex, front/back) or according to their polarity (e.g., positive, negative). Studies have shown that the anterolateral, anteroposterior, anterior-left infrascapular, and anterior-right infrascapular paddle/pad positions are equally effective to treat atrial or ventricular dysrhythmias.¹³

The typical paddle or pad position used during resuscitation is the sternum-apex position, also called the anterolateral or apex-anterior position. This position is often used because the anterior chest is usually easy to get to and placement of the paddles or pads in this position approximates ECG electrode positioning in lead II. Place the sternum paddle or pad lateral to the right side of the patient’s sternum, just below the clavicle. Place the center of the left (apex) paddle or pad in the midaxillary line, lateral to the patient’s left nipple (Figure 4-6). If the patient is a woman, elevate the left breast and place the apex paddle or pad lateral to or underneath the breast. Placing defibrillation paddles or pads directly on breast tissue results in higher transthoracic impedance, reducing current flow.¹⁴

Figure 4-6 Combination pads and standard paddles in a sternum-apex position.

Another common position used for paddle or pad placement is the anterior-posterior position. In this position, one paddle or pad is placed over the patient’s left chest with the upper edge of the pad below the nipple. The other is placed on the back, just below the patient’s left scapula (Figure 4-7). Alternative positions may be considered based on individual patient characteristics.¹³

Figure 4-7 Combination pads in an anterior-posterior position.

Keeping It Simple

In resuscitation situations, precious seconds can be lost when rescuers try to make sure that the “sternum” pad is placed on the sternum and the “apex” pad is placed over the apex of the heart. Delays sometimes occur when rescuers realize that paddles or pads have been placed in reversed positions and then attempt to reposition them to their “proper” location. Reversal of the position of the electrodes is not important during defibrillation, provided the heart is located between them.¹⁵

Use of Conductive Material

When using hand-held paddles, the use of gels, pastes, or pregelled defibrillation pads aids the passage of current at the interface between the defibrillator paddles/electrodes and the body surface. Failure to use conductive material results in increased transthoracic impedance, a lack of penetration of current, and burns to the skin surface. Combination pads are pregelled and do not require the application of additional gel to the patient’s chest.

When applying adhesive pads to the patient’s chest, press from one edge of the pad across the entire surface to remove all air and avoid the development of air pockets (Figure 4-8). A hands-free defibrillation cable is used to attach the pads to the monitor/defibrillator.

Figure 4-8 When applying adhesive pads to the patient’s chest, press from one edge of the pad across the entire surface to remove all air and avoid the development of air pockets.

When using pregelled pads with hand-held paddles, make sure the pads cover the entire paddle surface to avoid arcing current and potential burns. Do not use saline-soaked gauze or alcohol-soaked pads for defibrillation. Excess saline on the chest may cause arcing and burns. Alcohol-soaked pads may ignite. Do not use gels or pastes (e.g., ultrasound gel) that are not specifically made for defibrillation. The use of improper pastes, creams, gels, or pads can cause burns or sparks and may pose a risk of fire in an oxygen-enriched environment.¹⁶ If too much gel is used, the material may spread across the chest wall during resuscitation. This can lead to arcing of the current from one paddle to another and away from the heart, and this can also produce a potentially dangerous spark or burns.

Paddle Pressure

When using hand-held paddles for adult defibrillation, apply firm pressure (i.e., about 25 pounds) to each paddle. This lowers transthoracic impedance by improving contact between the skin surface and the paddles and decreasing the amount of air in the lungs. No pressure is applied when combination pads are used.

Selected Energy

When electrical therapy is used to treat an abnormal heart rhythm, it is important to select the appropriate energy level (i.e., the right amount of joules). If the energy level selected and current delivered are too low, the shock will not eliminate the abnormal rhythm.

[Objective 1]

The procedure described below assumes that the patient is an adult and confirmed to be unresponsive, apneic, and pulseless. It also assumes that the patient’s cardiac rhythm is pulseless VT or VF and that a four-person team is available to assist with procedures during the resuscitation effort.

Be sure that the cardiopulmonary resuscitation (CPR) team member continues chest compressions as the defibrillator is readied for use (Figure 4-9). The airway team member should coordinate ventilations with the CPR team member until an advanced airway is placed and its position confirmed.

Figure 4-9 Continue chest compressions as the defibrillator is readied for use.

While high-quality CPR continues, instruct the defibrillation team member to expose the patient’s chest and remove any transdermal patches or ointment from the patient’s chest, if present. If hand-held paddles are used, apply conductive material (e.g., gel) to the defibrillator paddles or apply disposable pregelled defibrillator pads to the patient’s bare chest. If combination pads are used, remove the pads from their sealed package. Check the pads for the presence of adequate gel. Attach the pads to the hands-free defibrillation cable, and then attach the combination pads to the patient’s chest in the position recommended by the manufacturer.

Turn the power to the monitor/defibrillator on and verify the presence of a shockable rhythm on the monitor. Select an appropriate energy level. Use 360 J for all shocks if a monophasic defibrillator is used.^13,17 Use the energy levels recommended by the manufacturer for the initial and subsequent shocks if a biphasic defibrillator is used (i.e., 120 to 200 J). If you do not know what the recommended energy levels are, consider defibrillation at the maximal dose.^13,17

While the defibrillator is readied, instruct the IV/medication team member to prepare the initial drugs that will be used and start an IV after the first shock is delivered. If hand-held paddles are used, instruct the defibrillation team member to place the paddles in their proper positions on the patient’s chest. Be sure that firm downward pressure (about 25 lb) is applied to each paddle. Do not lean on the paddles because they may slip! Charge the defibrillator. If hand-held paddles are used, press the “Charge” button on the machine or the button located on the apex paddle. If combination pads are used, press the “Charge” button on the machine (Figure 4-10).

Figure 4-10 Select the appropriate energy level and charge the defibrillator.

All team members with the exception of the chest compressor should immediately clear the patient as the machine charges. As the airway team member clears the patient, he or she should be reminded to turn off the oxygen flow. Listen as the machine charges. The sound usually changes when it reaches its full charge. To help minimize interruptions in chest compressions, the person who is performing chest compressions should continue CPR while the machine is charging. When the defibrillator is charged, the chest compressor should immediately clear the patient.

If a shockable rhythm is still present, call “Clear!” Look around you (360 degrees) to be sure everyone—including you—is clear of the patient, the bed, and any equipment connected to the patient (Figure 4-11). Be sure oxygen is not flowing over the patient’s chest. Press the “SHOCK” control to discharge energy to the patient. Release the shock control after the shock has been delivered. Instruct the team to resume chest compressions immediately without pausing for a rhythm or pulse check. Instruct the airway team member to turn on the oxygen and coordinate ventilations with the chest compressor. Instruct the IV/medications team member to establish vascular access and give the patient a vasopressor during CPR. Remember that interruptions in chest compressions must be kept to a minimum throughout the resuscitation effort. Continue CPR for about 2 minutes. After five cycles of CPR (about 2 minutes), recheck the rhythm. If a shockable rhythm is present, charge the defibrillator to a higher dose and then call “Clear!” Check to be certain that everyone is clear and then defibrillate. Resume CPR immediately. While continuing CPR, instruct the IV/medications team member to give an antiarrhythmic (amiodarone or lidocaine if amiodarone is not available). Consider placement of an advanced airway. Use the memory aids PATCH-4-MD or the 5 H’s and 5 T’s to help identify possible reversible causes of the arrest or factors that may be complicating the resuscitation effort. After 2 minutes of CPR, repeat the sequence, beginning with a rhythm check.

Figure 4-11 Before delivering a shock, call “Clear!” and look around you. Make sure everyone is clear of the patient, bed, and any equipment connected to the patient.

If defibrillation restores an organized rhythm, check for a pulse. If a pulse is present, check the patient’s blood pressure and other vital signs and begin post–cardiac arrest care. If you are not sure if a pulse is present, resume CPR.¹⁷ If defibrillation successfully terminates pulseless VT/VF but the rhythm recurs, begin defibrillation at the last energy level used that resulted in successful defibrillation. If a rhythm check reveals a nonshockable rhythm, resume CPR, consider possible causes of the arrest, and give medications and other emergency care as indicated. Continue CPR for 2 minutes before performing another rhythm check.

What If …?

What if you charge the defibrillator and the patient spontaneously converts to a rhythm that is not shockable or an organized rhythm before the shock is delivered? Check the operating instructions that accompany the defibrillator you are using for a definitive answer to this question. In most cases, the machine will disarm (i.e., internally remove the stored energy) if the discharge buttons are not pressed within 60 seconds. The machine will also disarm if you change the selected energy or press the energy selector to remove the charge.

What energy should be used if you deliver a shock that eliminates pulseless VT/VF and then the rhythm recurs? If defibrillation terminates pulseless VT/VF that then recurs, defibrillate at the last successful energy setting.¹⁷

What if the rhythm on the monitor looks like a “flat line?” If the rhythm appears to be asystole, make sure the power to the monitor is turned on, check the lead and cable connections, make sure the correct lead is selected, and turn up the gain (i.e., the ECG size) on the monitor. If the patient is unresponsive, not breathing, or only gasping and has no pulse, begin CPR immediately.

What if the patient has a permanent pacemaker or an ICD? An ICD is typically placed subcutaneously in the left upper quadrant of the patient’s abdomen or the left pectoral area (Figure 4-12). It can deliver a range of therapies (also called tiered-therapy) including defibrillation, antitachycardia (i.e., “overdrive”) pacing, synchronized cardioversion, and bradycardia pacing, depending on the dysrhythmia detected and how the device is programmed (Figure 4-13). A physician determines the appropriate therapies for each patient. Depending on the manufacturer, the ICD may deliver a maximum of six shocks for VF. About 2 J are delivered at the body surface when the ICD discharges internally. Rescuers in contact with the patient may feel a tingling sensation when the ICD delivers a shock. Although the energy is enough to be felt by the rescuer, it is not enough to cause physiologic harm. If the ICD is delivering shocks, wait 30 to 60 seconds for the ICD to complete the treatment cycle before attaching an AED. When defibrillating or cardioverting a patient with a permanent (implanted) pacemaker or an ICD, be careful to not place the defibrillator paddles or combination pads directly over the device. The anterior-posterior and anterolateral paddle or pad positions are considered acceptable in these patients.¹³ Although placement of paddles or pads should not delay defibrillation, defibrillator paddles or combination pads should ideally be placed at least 3 inches (8 cm) from the pulse generator (there will be a bulge under the patient’s skin).¹³ Because some of the defibrillation current flows down the pacemaker leads, a patient who has a permanent pacemaker or ICD should have the device checked to ensure proper function after defibrillation.

Figure 4-12 Site of implantation of a permanent pacemaker or automatic implantable cardioverter-defibrillator (ICD). The device is usually implanted in the left pectoral region, but it may be placed elsewhere if necessary.