This article contains instructions, advice, or how-to content. (January 2011)
Basic life support (BLS) is a 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 qualified bystanders.
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 does not include the use of drugs or invasive skills, and can be contrasted with the provision of Advanced Life Support (ALS). Firefighters, lifeguards, and police officers are often required to be BLS certified. BLS skills are also appropriate 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. 
- 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.
Basic Life Support Emergency Medical Services in the United States is generally identified with Emergency Medical Technicians-Basic ( EMT-B). However, the American Heart Association's BLS protocol is designed for use by laypeople, as well as students and others certified first responder, and to some extent, higher medical function personnel. It includes cardiac arrest, respiratory arrest, drowning, and foreign body airway obstruction (FBAO, or choking). EMT-B is the highest level of healthcare provider that is limited to the BLS protocol; higher medical functions use some or all of the Advanced Cardiac Life Support (ACLS) protocols, in addition to BLS protocols.
The AHA uses a four-link " chain of survival" to illustrate the steps needed to resuscitate a collapsed victim:
- Early recognition of the emergency and activation of emergency medical services
- Early bystander CPR, so as not to delay treatment until arrival of EMS
- Early use of a defibrillator
- Early advanced life support and post-resuscitation care
Bystanders with training in BLS can perform the first three of the four steps. 
The AHA-recommended steps for resuscitation are known as DRS CABCDE:
- Check for Danger
- Check for a Response
- Send or shout for help
- C directs rescuers to first attend to Catastrophic haemorrhage (life-threatening bleeding) and to stop the bleeding if possible.
- A directs rescuers to open the Airway and look into the mouth for obvious obstruction. Also to apply a 'head tilt chin lift' or 'jaw thrust' to open the airway.
- B directs rescuers to check Breathing for 10 seconds by listening for breath at the patients nose and mouth and observe the chest for regular rising and falling breathing movements.
- C directs rescuers to maintain Circulation which may be through administration of chest compressions for Cardio Pulmonary Resuscitation (CPR).
- D directs rescuers to identify Disabilities (e.g. diabetic or any allergies), Damage (identify broken bones or any minor bleeding), Devices (including use of AED devices available and follow prompts) and Dry (if casualty is very wet, an AED device will pass current through body surface water and will harm the casualty).
- E directs rescuers to take the environment into consideration for weather, location and crowds.
If the patient is unresponsive and not breathing, the responder begins CPR with chest compressions at a rate of 120 beats per minute in cycles of 30 chest compressions to 2 breaths. If responders are unwilling or unable to perform rescue breathing, they are to perform compression-only CPR, because any attempt at resuscitation is better than no attempt. For children, for whom the main cause of cardiac arrest is from breathing related issues, 5 initial rescue breaths is highly advised followed by the same 30-2 cycles.
According to the American Heart Association, in order to be certified in BLS, a student must take an online or in-person course. However, an online BLS course must be followed with an in-person skills session in order to obtain a certification issued by The American Heart Association. 
- C-A-B is recommended in the new AHA EU guidelines so as to ensure the blood supply to the vital organs and to prevent degeneration of the brain cells . Keeping these facts as such follow the sequence introduced by AHA guidelines 2010 recommendations C-A-B should be followed in learning and teaching BLS.
- Ensure that the scene is safe.
- Assess the victim's level of consciousness by asking loudly and shaking at the shoulders "Are you okay?" and scan chest for breathing movement visually. If no response call for help by shouting for an ambulance and ask for an AED.
Assess:* If the patient is breathing normally, and pulse is present then the patient should be placed in the recovery position and monitored. Transport if required, or wait for the EMS to arrive and take over.
- If patient is not breathing assess pulse at the carotid on your side for an adult, at the brachial for a child and infant for 6 seconds and not more than 10 seconds; begin immediately with chest compressions at a rate of 30 chest compressions in 18 seconds followed by two rescue breaths in 4 seconds each lasting for 2 second.
If the victim has no suspected cervical spine trauma, open the airway using the head-tilt/chin-lift maneuver; if the victim has suspected neck trauma, the airway should be opened with the jaw-thrust technique. If the jaw-thrust is ineffective at opening/maintaining the airway, a very careful head-tilt/chin-lift should be performed.
- Blind finger-sweeps are strongly discouraged and should never be performed, as they may push foreign objects further into the airway. This procedure has been discarded from current practice as this may push the foreign body down the airway and increase chances of an obstruction.
Continue chest compression at a rate of 100 compressions per minute for all age groups, allowing chest to recoil in between. For adults push up to 2-2.4 inches (6 cm) and for child up to 2 inches (5 cm). For infants 1-1.5 inches (4 cm) or 1/3 of the chest diameter antero-posteriorly.
- Keep counting aloud. Press hard and fast maintaining the rate of at about 100/minute. Allow recoil of chest fully between each compression. In adults,irrespective of the number or rescuers, for every 30 chest compressions give two rescue breaths and in child victim, give 2 breaths per 30 compression if only 1 rescuer is present,but 2 breaths per 15 compressions in case where there are 2 rescuers.
- Continue for five cycles or two minutes before re-assessing pulse.
- Attempt to administer two artificial ventilations using the mouth-to-mouth technique, or a bag-valve-mask (BVM). The mouth-to-mouth technique is no longer recommended, unless a face shield is present. Verify that the chest rises and falls; if it does not, reposition (i.e. re-open) the airway using the appropriate technique and try again. If ventilation is still unsuccessful, and the victim is unconscious, it is possible that they have a foreign body in their airway. Begin chest compressions, stopping every 30 compressions, re-checking the airway for obstructions, removing any found, and re-attempting ventilation.
- If the ventilations are successful, assess for the presence of a pulse at the carotid artery. If a pulse is detected, then the patient should continue to receive artificial ventilations at an appropriate rate and transported immediately. Otherwise, begin CPR at a ratio of 30:2 compressions to ventilation's at 100 compressions/minute for 5 cycles.
- After 5 cycles of CPR, the BLS protocol should be repeated from the beginning, assessing the patient's airway, checking for spontaneous breathing, and checking for a spontaneous pulse as per new protocol sequence C-A-B. Laypersons are commonly instructed not to perform re-assessment, but this step is always performed by healthcare professionals (HCPs).
If an AED is available it should be activated immediately and its directives followed and (if indicated), call for clearance before defibrillation/shock should be performed. If defibrillation is performed, begin chest compression immediately after shock.
- BLS protocols continue until (1) the patient regains a pulse, (2) the rescuer is relieved by another rescuer of equivalent or higher training (see patient abandonment), (3) the rescuer is too physically tired to continue CPR, or (4) the patient is pronounced dead by a medical doctor or other approved healthcare provider. 
- At the end of five cycles of CPR, always perform assessment via the AED for a shockable rhythm, and if indicated, defibrillate, and repeat assessment before doing another five cycles.
Rescuers should provide CPR as soon as an unresponsive victim is removed from the water. In particular, rescue breathing is important in this situation.
A lone rescuer is typically advised to give CPR for a short time before leaving the victim to call emergency medical services.
Since the primary cause of cardiac arrest and death in drowning and choking victims is hypoxia, it is more important to provide rescue breathing as quickly as possible in these situations, whereas for victims of VF cardiac arrest chest compressions and defibrillation are more important.
- In unresponsive victims with hypothermia, the breathing and pulse should be checked for 30 to 45 seconds as both breathing and heart rate can be very slow in this condition.
- If cardiac arrest is confirmed, CPR should be started immediately. Wet clothes should be removed, and the victim should be insulated from wind. CPR should be continued until the victim is assessed by advanced care providers.
Choking can occur from foreign body airway obstruction.
- Rescuers should intervene in victims who show signs of severe airway obstruction, such as a silent cough, cyanosis, or inability to speak or breathe.
- If a victim is coughing forcefully, rescuers should not interfere with this process.
- If a victim shows signs of severe airway obstruction, abdominal thrusts should be applied in rapid sequence until the obstruction is relieved. If this is not effective, chest thrusts can also be used. Chest thrusts can also be used in obese victims or victims in late pregnancy. Abdominal thrusts should not be used in infants under 1 year of age due to risk of causing injury.
- If a victim becomes unresponsive he should be lowered to the ground, and the rescuer should call emergency medical services and initiate CPR. When the airway is opened during CPR, the rescuer should look into the mouth for an object causing obstruction, and remove it if it is evident.
This article needs to be updated.November 2011)(
Adult BLS guidelines in the United Kingdom were also published in 2005 by the Resuscitation Council (UK),  based on the 2005 International Consensus on Cardiopulmonary Resuscitation and Emergency Cardiovascular Care Science with Treatment Recommendations (CoSTR) published in November 2005. 
- Ensure the safety of the victim, the rescuer, and any bystanders.
- Check the victim for a response by gently shaking the victim's shoulders and asking loudly "Are you all right?"
- If the victim responds, leave him in the position in which he was found provided there is no further danger, try to find out what is wrong with him and get help if needed, and reassess him regularly.
- If the victim does not respond, turn him on to his back and open the airway using the head-tilt/chin-lift. Shout for help.
- Look, listen and feel for normal breathing for no more than 10 seconds. If the victim is breathing normally, turn him into the recovery position and get help. Continue to check for breathing.
- If the victim is not breathing normally, call for an ambulance.
These guidelines differ from previous versions in a number of ways:
- They allow the rescuer to diagnose cardiac arrest if the victim is unresponsive and not breathing normally.
- Rescuers are taught to give chest compressions in the center of the chest, rather than measuring from the lower border of the sternum.
- Rescue breaths should be given over 1 second rather than 2 seconds.
- For an adult victim, the initial 2 rescue breaths should be omitted, so that 30 chest compressions are given immediately after a cardiac arrest has been diagnosed.
These changes were introduced to simplify the algorithm, to allow for faster decision making and to maximize the time spent giving chest compressions; this is because interruptions in chest compressions have been shown to reduce the chance of survival.  It is also acknowledged that rescuers may either be unable, or unwilling, to give effective rescue breaths; in this situation, continuing chest compressions alone is advised, although this is only effective for about 5 minutes. 
- Assess the severity of airway obstruction. If the victim is able to speak and cough effectively, the obstruction is mild. If the victim is unable to speak or cough effectively, or is unable to breathe or is breathing with a wheezy sound, the airway obstruction is severe.
- If the victim has signs of mild airway obstruction, encourage him to continue coughing; do nothing else.
- If the victim has signs of severe airway obstruction, and is conscious, give up to 5 back blows (sharp blows between the shoulder blades with the victim leaning well forwards). Check to see if the obstruction has cleared after each blow. If 5 back blows fail to relieve the obstruction, give up to 5 abdominal thrusts, again checking if each attempt has relieved the obstruction.
- If the obstruction is still present, and the victim still conscious, continue alternating 5 back blows and 5 abdominal thrusts.
- If the victim becomes unconscious, lower him to the ground, call an ambulance, and begin CPR.
- Spain: SVB (soporte vital básico)
- Belgium: aide médicale urgente ("emergency medical assistance")/ EHBO (eerste hulp bij ongelukken, "first aid")
- Brazil: SBV (Suporte básico de vida)
- France: PSE 1 & PSE 2 (Premiers Secours en Equipe niveaux 1 & 2), "First Aid as part of a team," level 2 includes stretchering and teamwork, (former CFAPSE before 2007 Certificat de Formation aux Activités des Premiers Secours en Equipe, "Training certificate for first aid teamwork")
- Poland: Podstawowe zabiegi resuscytacyjne/ KPP (Kwalifikowana pierwsza pomoc)
- Portugal: SBV (Suporte Básico de Vida)
- Germany: Lebensrettende Sofortmaßnahmen (basic life support)
- Romania: SVB (support vital de bază)
- Netherlands: BLS ("first aid" is referred to as EHBO (Eerste hulp bij ongelukken))
- Turkey: TYD (temel yaşam desteği, "basic life support")
- Hallstrom, A. P.; Ornato, J. P.; Weisfeldt, M.; Travers, A.; Christenson, J.; McBurnie, M. A.; Zalenski, R.; Becker, L. B.; Schron, E. B.; Proschan, M.; Public Access Defibrillation Trial Investigators (2004). "Public-access defibrillation and survival after out-of-hospital cardiac arrest". The New England Journal of Medicine. 351 (7): 637–46. doi: 10.1056/NEJMoa040566. PMID 15306665.
- Khalid, U.; Juma, A A. (2010). "Paradigm shift: 'ABC' to 'CAB' for cardiac arrests". Scandinavian Journal of Trauma, Resuscitation and Emergency Medicine. 18: 59. doi: 10.1186/1757-7241-18-59. PMC 2992496. PMID 21078163.
- Ecc Committee, Subcommittees Task Forces of the American Heart Association (December 2005). "2005 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care". Circulation. 112 (24 Suppl): IV–19–34. doi: 10.1161/CIRCULATIONAHA.105.166553. PMID 16314375.
- American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care Science, Part 5: Adult Basic Life Support
- "HUT RI 73th". savingchicagocpr.com. Retrieved 2018-10-28.
- Resuscitation Council (UK) Adult Basic Life Support (2005) Archived 2005-12-02 at the Wayback Machine
- "European Resuscitation Council guidelines and CoSTR documents". erc.edu. Archived from the original on 2009-01-24. Retrieved 23 March 2018.
- Eftestøl T, Sunde K, Steen PA (May 2002). "Effects of interrupting precordial compressions on the calculated probability of defibrillation success during out-of-hospital cardiac arrest". Circulation. 105 (19): 2270–3. doi: 10.1161/01.cir.0000016362.42586.fe. PMID 12010909.
- Hallstrom A, Cobb L, Johnson E, Copass M (May 2000). "Cardiopulmonary resuscitation by chest compression alone or with mouth-to-mouth ventilation". N. Engl. J. Med. 342 (21): 1546–53. CiteSeerX 10.1.1.456.8789. doi: 10.1056/NEJM200005253422101. PMID 10824072.
- Nozioni primo soccorso BLS Archived October 28, 2005, at the Wayback Machine ( Italian), PDF document (12p, 912 Kb)