Irrespective of the cause of cardiac arrest, early recognition and calling for help, including appropriate management of the deteriorating patient, early defibrillation, high-quality cardiopulmonary resuscitation (CPR) with minimal interruption of chest compressions and treatment of reversible causes, are the most important interventions. In certain conditions, however, advanced life support (ALS) guidelines require modification.
The following guidelines for resuscitation in special circumstances are divided into three parts: special causes, special environments and special patients. The first part covers treatment of potentially reversible causes of cardiac arrest, for which specific treatment exists, and which must be identified or excluded during any resuscitation.
For improving recall during ALS, these are divided into two groups of four, based upon their initial letter - either H or T - and are called the '4Hs and 4Ts': Hypoxia; Hypo-/hyperkalaemia and other electrolyte disorders; Hypo-/hyperthermia; Hypovolaemia; Tension pneumothorax; Tamponade (cardiac); Thrombosis (coronary and pulmonary); Toxins (poisoning). The second part covers cardiac arrest in special environments, where universal guidelines have to be modified due to specific locations or location-specific causes of cardiac arrest.
The third part is focused on patients with specific conditions, and those with certain long-term comorbidities where a modified approach and different treatment decisions may be necessary.