Causes Of Cardiac Arrest

Cardiorespiratory arrest may occur because of a primary airway, breathing or circulation problem (Resuscitation Council UK 2000a). However, it is important to remember that many life-threatening diseases can cause secondary respiratory or cardiac problems, which may ultimately result in the patient suffering a respiratory and/or cardiopulmonary arrest (see Table 11.1).

Respiratory inadequacy may be due to disorders of the respiratory system such as asthma or pulmonary oedema. A decrease in the patient's respiratory drive may be due to central nervous system depression or decreased respiratory effort because of exhaustion or drugs depressing the patient's respiratory drive. In turn, the resulting hypoxia may have a direct effect on the heart by causing a bradycardia, which causes inadequate perfusion of the brain or heart and leads to cardiac arrest (Resuscitation Council UK 2000a). Cardiac abnormalities may be a primary or contributory cause of the cardiac arrest (see Table 11.2).

Table 11.1 Causes of airway obstruction.

Blood Vomit

Foreign body, e.g. food or a broken tooth Direct trauma to the face Decreased level of consciousness Epiglottitis

Swelling to the pharynx, e.g. caused by infection

Laryngospasm

Bronchospasm

Cardiomyopathy

Table 11.2 Causes of primary cardiac arrest.

Ischaemia

Myocardial infarction Hypertensive heart disease Valve disease

Drugs (e.g. antiarrhythmic drugs, tricyclic antidepressants, digoxin) Acidosis

Abnormal electrolyte concentration Hypothermia

Electrocution (which can cause paralysis of the respiratory muscles or send the patient into VF or asystole) Cardiac failure Cardiac tamponade Cardiac rupture Myocarditis

A secondary cardiac abnormality is one where the heart is affected by a problem originating elsewhere (Resuscitation Council UK 2000a). Thus cardiac arrest may occur following:

• asphyxia from airway obstruction or apnoea

• tension pneumothorax

• hypovolaemia

• hypothermia

• severe septic shock.

The treatment of any potentially reversible cause of a cardiac arrest is of paramount importance irrespective of the underlying rhythm. The most recent resuscitation guidelines (Resuscitation Council UK 2000b) highlight the importance of considering reversible causes in all cardiac arrest rhythms.

The reversible causes of cardiac arrest can be most easily remembered as 'the four Hs and four Ts', as shown in Table 11.3.

An important part of the process of resuscitation is the gathering of clues to piece together as much history as possible in order to elicit the cause or causes of the cardiac arrest. Thus the team leader directing the resuscitation process may try to elicit further information about the events leading up to the point of cardiac arrest in the patient.

Table 11.3 Reversible causes of cardiac arrest, the four Hs and four Ts.

Hypoxia Hypovolaemia

Hyperkalaemia/hypokalaemia (and other metabolic disorders)

Hypothermia

Tension pneumothorax

Tamponade

Thromboembolic

Toxic/therapeutic disturbances

• Was there a history of trauma prior to the event?

• Does the patient suffer from any underlying disease processes, which may have been a contributory factor to their collapsed state?

• Does the patient take any prescribed (or non-prescribed) medication?

• Have environmental factors been a contributory factor to the collapse? Where was the patient found? When had they last been seen conscious by a witness?

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