Basic life support (BLS) is the level of medical care which is used for victims of life-threatening illnesses or injuries until they can be given full medical care at a hospital. It can be provided by trained medical personnel, including emergency medical technicians, paramedics, and by laypersons who have received BLS training. BLS is generally used in the pre-hospital setting, and can be provided without medical equipment. Many countries have guidelines on how to provide basic life support (BLS) which are formulated by professional medical bodies in those countries. The guidelines outline algorithms for the management of a number of conditions, such as cardiac arrest, choking and drowning. BLS generally does not include the use of drugs or invasive skills, and can be contrasted with the provision of Advanced Life Support (ALS). Most laypersons can master BLS skills after attending a short course. Firefighter, lifeguards, and police officers are often required to be BLS certified. BLS is also immensely useful for many other professions, such as daycare providers, teachers and security personnel and social workers especially working in the hospitals and ambulance drivers. CPR provided in the field increases the time available for higher medical responders to arrive and provide ALS care. An important advance in providing BLS is the availability of the automated external defibrillator or AED. This improves survival outcomes in cardiac arrest cases. Basic life support promotes adequate blood circulation in addition to breathing through a clear airway: Circulation: providing an adequate blood supply to tissue, especially critical organs, so as to deliver oxygen to all cells and remove metabolic waste, via the perfusion of blood throughout the body. Airway: the protection and maintenance of a clear passageway for gases (principally oxygen and carbon dioxide) to pass between the lungs and the atmosphere. Breathing: inflation and deflation of the lungs (respiration) via the airway These goals are codified in mnemonics such as ABC and CAB. The American Heart Association (AHA) endorses CAB in order to emphasize the primary importance of chest compressions in cardiopulmonary resuscitation. Healthy people maintain the CABs by themselves. In an emergency situation, due to illness (medical emergency) or trauma, BLS helps the patient ensure his or her own CABs, or assists in maintaining for the patient who is unable to do so. For airways, this will include manually opening the patients airway (Head tilt/Chin lift or jaw thrust) or possible insertion of oral (Oropharyngeal airway) or nasal (Nasopharyngeal airway) adjuncts, to keep the airway unblocked (patent). For breathing, this may include artificial respiration, often assisted by emergency oxygen. For circulation, this may include bleeding control or cardiopulmonary resuscitation (CPR) techniques to manually stimulate the heart and assist its pumping action.