Out of hospital arrest
Most out-of-hospital cardiac arrests occur following a myocardial infarction (heart attack), and present initially with a heart rhythm of ventricular fibrillation. The patient is therefore likely to be responsive to defibrillation, and this has become the focus of pre-hospital interventions. Several organisations promote the idea of a "chain of survival", of which defibrillation is a key step. The links are:
- Early recognition - If possible, recognition of illness before the patient develops a cardiac arrest will allow the rescuer to prevent its occurrence. Early recognition that a cardiac arrest has occurred is key to survival - for every minute a patient is in cardiac arrest, their chances of survival drop by roughly 10% : these areas often have first responder schemes, whereby members of the community receive training in resuscitation and are given a defibrillator, and called by the emergency medical services in the case of a collapse in their local area.
Hospital treatment
Treatment within a hospital usually follows advanced life support protocols. In the US, non-traumatic adult resuscitation is described by ACLS (Advanced Cardiac Life Support), pediatric resuscitation is described by PALS (Pediatric Advanced Life Support), and neonatal resuscitation is described by NALS (Neonatal Advanced Life Support). Depending on the diagnosis, various treatments are offered, ranging from defibrillation (for ventricular fibrillation or ventricular tachycardia) to surgery (for cardiac arrest which can be reversed by surgery - see causes of arrest, above) to medication (for asystole and PEA). All will include CPR.
While specific details may vary, all hospitals have protocols as to how resuscitations should be performed in patients, visitors, or employees who have arrested unexpectedly in the hospital. These protocols are often initiated by a Code Blue, which usually denotes impending or acute onset of cardiac arrest or respiratory failure, although in practice, Code Blue is often called in less life-threatening situations that require immediate attention from a physician.
If not already done, a definitive airway will be establish by the placement of an endotracheal tube which is then attached to a mechanical ventilator.
Cardiac arrest is generally divided into two cases: presence of disorganized mechanical cardiac activity, or complete absence of mechanical cardiac activity.
Disorganized mechanical cardiac activity includes ventricular fibrillation and hemodynamically unstable or pulseless ventricular tachycardia. This also includes torsade de pointes. These must all be treated primarily with defibrillation. Advanced cardiac life support algorithms also detail the stepwise administration of epinephrine, vasopressin, the antiarrhythmic agent amiodarone, as well as attempts to correct possible underlying causes.
Complete absence of mechanical cardiac activity includes asystole and pulseless electrical activity. This is treated entirely with pharmacologic agents, specifically epinephrine and atropine. However, resuscitation is rarely successful without effective treatment of the underlying cause.
Therapeutic hypothermia
In some cases, doctors may choose to induce hypothermia after return of spontaneous Circulatory system|circulation (ROSC). This procedure is called therapeutic hypothermia. The first study conducted in Europe focused on people who were resuscitated 5–15 minutes after collapse. Patients participating in this study experienced spontaneous return of Circulatory system|circulation (ROSC) after an average of 105 minutes. Subjects were then cooled over a 24 hour period, with a target temperature of 32-34°C (89.6-93.2°F). 55% of the 137 patients in the hypothermia group experienced favorable outcomes, compared with only 39% in the group that received standard care following resuscitation. Death rates in the hypothermia group were 14% lower, meaning that for every 7 patients treated one life was saved.
Peri-arrest period
The period (either before or after) surrounding a cardiac arrest is known as the peri-arrest period. During this period the patient is in a highly unstable condition and must be constantly monitored in order to halt the progression or repeat of a full cardiac arrest. The preventative treatment used during the peri-arrest period depends on the causes of the impending arrest and the likelihood such an event occurring.
Further Reading
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