Cardiac Arrest

This chapter presents the essential elements of cardiopulmonary resuscitation (CPR) and post-CPR care, including criteria for predicting a poor neurologic outcome after cardiac arrest. The material in this chapter is based on the most recent clinical practice guidelines on CPR from the American Heart Association (1,2,3).

I. Basic Life Support

The essential components of basic life support (BLS) are: (a) chest compressions, (b) airway opening (i.e., establishing a patent oropharynx), and (c) periodic lung inflations.

A. Chest Compressions

The original mnemonic ABC (Airway, Breathing, Circulation) for the components of BLS has been rearranged to CAB (Circulation, Airway, Breathing), reflecting the shift in emphasis to chest compressions in the resuscitation effort. The rationale for this shift was the realization that cardiac arrest is primarily a circulatory (not ventilatory) disorder.
The recommendations for chest compressions in the BLS guidelines are shown in Table 15.1. Early and uninterrupted chest compressions are a major emphasis of the guidelines.

B. Airway Opening

Airway opening refers to the act of establishing a patent
oropharynx, which can become obstructed by a flaccid tongue in comatose patients who are supine. The “head tilt/chin up” maneuver (which hyperextends the neck and moves the lower jaw forward) is designed to pull the tongue away from the posterior oropharynx and relieve any obstruction from a floppy tongue.

Table 15.1 Chest Compressions

From the BLS Guidelines:

1. Chest compressions should be delivered to the lower half of the sternum at a rate of 100–120/min.
2. Each chest compression should achieve a depth of at least 2 inches (5 cm) but no greater than 2.4 inches (6 cm), and the chest should be allowed to recoil completely, to allow the heart to fill before the next compression.
3. First responders should begin CPR with a series of 30 chest compressions, followed by a brief pause for 2 rescue breaths. This compression-ventilation ratio (30:2) should be continued until an advanced airway is placed.
4. Once an advanced airway is in place, chest compressions should continue uninterrupted, with no pause for lung inflations.
5. Chest compressions should only be interrupted when absolutely necessary (e.g., to deliver electric countershocks).

From Reference 1.

C. Ventilation

Prior to endotracheal intubation, ventilation can be delivered with a face mask that is connected to a self-inflating ventilation bag (e.g., Ambu Respirator) that fills with oxygen. The bag is compressed by hand to deliver the breath, and 2 breaths are provided for every 30 chest compressions (as in Table 15.1).
After an endotracheal tube is in place, lung inflations should be delivered at 6-second intervals (10 breaths/min)
while chest compressions continue uninterrupted.

3. Inflation Volumes

Large inflation volumes are common during CPR, resulting in hyperinflation of the lungs (4), which can impede cardiac filling and diminish the effectiveness of chest compressions.
The recommended inflation volume during “bagged breathing” is 6–7 mL/kg (5), or about 500 mL for an average-sized adult. However, the volume of lung inflations is not monitored during CPR, so adhering to this recommendation does not seem possible.
One method of avoiding large inflation volumes is based on the volume capacity of the inflation bag (which is 1–2 liters in most bags). For example, if the inflation bag has a capacity of 1 liter, then compressing the bag until it is about half full will deliver about 500 mL to the lungs. Another approach is “one-handed bagging”; i.e., squeezing the bag with one hand expels a volume of 600–800 mL (personal observation), which is unlikely to produce serious hyperinflation.

4. Rapid Inflations

Rapid lung inflation rates are common during CPR (4,6), with average rates of 30 inflations/min in one report (6). Rapid breathing is problematic because there is insufficient time for the lungs to empty, and the extra volume in the lungs at the end of expiration creates a positive pressure; i.e., positive end-expiratory pressure, or PEEP. This self-generated or “intrinsic PEEP” increases intrathoracic pressure, which reduces venous return to the heart, and can restrict expansion of the ventricles during diastole; both of these effects diminish the ability of chest compressions to augment cardiac output. Intrinsic PEEP is described in more detail in Chapter 21.

II. Advanced Life Support

Advanced cardiovascular life support, or ACLS, includes a variety of interventions, such as airway intubation, mechanical ventilation, defibrillation, and the administration of circulatory-support drugs (2). This section will focus on defibrillation and circulatory-support drugs, and how these interventions are used in cardiac arrests associated with ventricular fibrillation (VF) or pulseless ventricular tachycardia (VT), and cardiac arrests associated with asystole or pulseless electrical activity (PEA).

A. VF or Pulseless VT

The outcomes in cardiac arrest are most favorable when the initial rhythm is VF or pulseless VT, which are “shockable” arrhythmias.

1. Defibrillation

Electrical cardioversion using asynchronous shocks (i.e., not timed to the QRS complex), which is called defibrillation, is the most effective resuscitation measure for cardiac arrest associated with VF or pulseless VT. However, the survival benefit from defibrillation is time-dependent, as shown in Figure 15.1 (7).

IMPULSE ENERGY: Modern defibrillators use biphasic waveforms to deliver the shocks (because they are effective at lower energy levels than monophasic waveforms), but there are 3 different biphasic waveforms, and each delivers a different current at the same energy setting. This creates difficulty in recommending a single energy level for defibrillation, and the current ACLS guidelines recommend using the manufacturer’s suggested energy level for the initial shock (2). If this is not available, the maximum effective energy level (about 200 J for biphasic and 360 J for monophasic shocks) should be selected for the
initial shock (2). (Automated external defibrillators, or AEDs, use a preselected energy level.)

FIGURE 15.1 Relationship between survival and elapsed time from cardiac arrest to initial defibrillation attempt in out-of-hospital cardiac arrest with VF or pulseless VT. N = number of cases studied. Data from Reference 7.

2. Protocol

The flow diagram in Figure 15.2 is the ACLS algorithm for cardiac arrest in adults, and the defibrillation protocol for pulseless VT and VF is shown in the left half of the diagram.

Three defibrillation attempts are allowed, if needed, using the same impulse energy.
After each shock is delivered, 2 minutes of uninterrupted chest compressions are advised before checking the post-shock rhythm (to prevent repeat shocks in rapid succession, which prolongs the interruption of chest compressions) (2).

FIGURE 15.2 The ACLS algorithm for adult cardiac arrest. IO = intra-osseous. From Reference 2.
If a second defibrillation attempt is required, bolus injections of epinephrine are started (1 mg IV, or intraosseous, every 3–5 min, for the duration of the resuscitation effort).
If a third defibrillation attempt is required, amiodarone is administered IV or IO using a dose of 300 mg, which can be followed by a second dose of 150 mg, if needed.
Failure to terminate VF/VT with two defibrillation attempts carries a poor prognosis.

B. Asystole or PEA

The resuscitation of cardiac arrests associated with asystole or PEA (“nonshockable” arrhythmias) is notoriously unsuccessful. The resuscitation scheme is shown on the right half of the flow diagram in Figure 15.2. The major intervention is epinephrine injections (same regimen as used for VF and pulseless VT), and there are no defibrillation attempts unless the rhythm changes to VF or VT.

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