What Is Basic Life Support? UK BLS Guidance Explained

Clinical SKills

If a person is unresponsive, call 999 immediately and put your phone on speaker. Assess their breathing while waiting for the call to be answered. If they are not breathing normally, start CPR and use an automated external defibrillator (AED) as soon as one is available.

Do not delay the emergency call to complete a breathing assessment or look for a pulse. Follow the call handler’s instructions and send another person to fetch an AED if possible.

Basic life support (BLS) is the immediate care given when someone has a life-threatening problem involving responsiveness, breathing or circulation. It aims to maintain blood flow and oxygen delivery until emergency professionals take over. It cannot guarantee that the heart or normal breathing will restart.

This is an educational summary of current UK guidance from Resuscitation Council UK (RCUK). It is not personalised medical advice or a substitute for practical, assessed training. In an emergency, call 999 and follow the call handler’s directions.

Adult basic life support: what to do first

The order matters. The RCUK adult basic life support guidance says to call 999 as soon as you establish that the person is unresponsive. Assess breathing while waiting for the call to be answered.

Check for danger. Make sure it is reasonably safe to approach. Do not expose yourself or others to traffic, electricity, fire, violence or another serious hazard.
Check responsiveness. Speak loudly and gently shake the person’s shoulders. If they do not respond, shout for help.
Call 999 immediately. Use a mobile phone on speaker so you can continue helping. If someone else is present, ask them to call and send another person for an AED.
Assess breathing while waiting for the call to be answered. Open the airway by tilting the head and lifting the chin. Look, listen and feel for normal breathing for no more than 10 seconds.
Start CPR if breathing is absent or abnormal. Occasional gasps, snorts or slow, laboured breaths are not normal breathing. A member of the public should not delay CPR by trying to find a pulse.
Connect an AED as soon as it arrives. Switch it on, attach the pads and follow every spoken or visual instruction.

If you are uncertain whether breathing is normal, tell the 999 call handler exactly what you can see and hear. They can help you recognise cardiac arrest and coach you through CPR.

How to give adult CPR

Place the person on their back on a firm surface if you can do so safely. Kneel beside their chest, then:

Place the heel of one hand in the centre of the chest, on the lower half of the breastbone.
Put your other hand on top and interlock your fingers.
Keep your arms straight and position your shoulders above your hands.
Press down by 5–6 cm at a rate of 100–120 compressions each minute.
Allow the chest to return fully after each compression without lifting your hands away.
Keep pauses as short as possible.

If you are trained and willing to provide rescue breaths, give 30 compressions followed by two breaths. Open the airway, pinch the nose, make a seal over the person’s mouth and blow steadily for about one second—only enough to make the chest rise. Continue cycles of 30 compressions and two breaths.

If you cannot provide rescue breaths, give continuous chest compressions and follow the call handler’s instructions. Compression-only CPR is better than doing nothing. Rescue breaths are especially important for children and in emergencies primarily caused by oxygen deprivation, including drowning.

Continue CPR until the person begins breathing normally, emergency professionals tell you to stop, the scene becomes unsafe or you are physically unable to continue. If another capable helper is available, change the person performing compressions about every two minutes while keeping the interruption brief.

For an explanation of the terminology, see what CPR stands for.

How to use an AED

An AED analyses the heart’s electrical rhythm. It advises or administers a shock only when it detects a rhythm that may respond to defibrillation. It will not shock every person in cardiac arrest, so CPR remains essential.

Anyone can use an AED by following its instructions:

Switch on the AED and listen to its prompts.
Expose the chest and attach the adhesive pads in the positions shown on the device.
Make sure nobody is touching the person while the AED analyses the rhythm.
If a shock is advised, check that everyone is clear. Deliver the shock when prompted; some AEDs do this automatically.
Resume CPR immediately when instructed, whether or not a shock was delivered.

If the chest is wet, dry it quickly so the pads adhere properly. Do not position a pad directly over a visible implanted device or medicine patch. Follow the AED prompts and ask the 999 call handler if you are unsure. The RCUK guide to using a defibrillator provides further public guidance.

Adult, child and infant CPR: important differences

Children and infants require age-appropriate techniques. This table is a concise orientation based on the RCUK paediatric basic life support guidance, not a replacement for practical training.

Person	Starting sequence	Compression depth	Usual technique
Adult	Begin compressions after identifying abnormal breathing; use 30:2 if giving breaths	5–6 cm	Two hands in the centre of the chest
Child over one year	Give five initial rescue breaths, then start CPR	About 5 cm or one-third of the chest depth	One or two hands according to the child’s size
Infant under one year	Give five initial rescue breaths, then start CPR	About 4 cm or one-third of the chest depth	Two-thumb encircling technique when possible; a lone rescuer may use two fingertips if necessary

For a child or infant who is unresponsive and not breathing normally, give five initial rescue breaths and begin CPR. If you have a mobile phone, call 999 on speaker and follow the call handler’s instructions. If you are alone without a phone, give CPR for about one minute before leaving to call 999.

Use an AED as soon as possible. Use paediatric pads or a paediatric setting if available, but do not delay defibrillation while searching for them. Follow the device’s diagrams and prompts. If you are unsure about the precise technique, keep helping while the call handler guides you.

What to do when someone is choking

Your response depends on whether the person can cough effectively, whether they remain responsive and their age. These actions reflect the RCUK first-aid guidance.

Responsive adult or child over one year

If they can speak and cough effectively, encourage them to continue coughing. Do not leave them alone.
If the cough is ineffective, give up to five firm back blows between the shoulder blades. Check after each blow to see whether the object has cleared.
If the obstruction remains, give up to five abdominal thrusts.
Alternate up to five back blows with up to five abdominal thrusts until the blockage clears or the person becomes unresponsive.
Call 999 if the obstruction is not relieved.

Responsive infant under one year

Support the infant face down with their head lower than their chest and give up to five back blows. If these do not work, turn the infant face up while supporting the head and give up to five chest thrusts. Do not give abdominal thrusts to an infant. Call 999 if the blockage persists.

If the choking person becomes unresponsive

Lower them carefully to the ground, ensure that 999 has been called and begin CPR. Do not continue back blows or abdominal or chest thrusts after they become unresponsive.

Whenever you open the airway to provide rescue breaths, remove an object only if it is clearly visible and easily reachable. Never perform a blind finger sweep, as this can push the obstruction farther into the airway.

A person who has received abdominal thrusts or chest compressions should be assessed by a healthcare professional because internal injury can occur. Medical advice is also needed if coughing, difficulty swallowing or a feeling that something remains lodged continues after the incident.

Unresponsive but breathing normally

If the person is unresponsive but breathing normally, call 999 and place them in the recovery position if it is safe and appropriate to move them. This helps keep the airway open. Continue monitoring their breathing until help arrives.

If trauma is suspected, avoid unnecessary movement, but maintaining an open airway takes priority. Follow the call handler’s instructions. If breathing becomes absent or abnormal, roll the person onto their back and begin CPR.

Do not place someone in the recovery position if they require CPR. St John Ambulance provides a practical recovery-position guide.

Other emergencies in which BLS may be needed

BLS may be required following cardiac arrest, drowning, choking, poisoning or overdose, electrocution, a severe breathing emergency or major injury. The precise response depends on the circumstances, but early recognition, a prompt 999 call and following the call handler’s instructions remain central.

Suspected anaphylaxis

Anaphylaxis is a life-threatening allergic reaction. Signs can include sudden breathing difficulty, swelling of the tongue or throat, wheezing, collapse or dizziness. Skin changes such as hives or flushing may occur, but they are not always present.

Call 999 and say “anaphylaxis”. If the person has an adrenaline autoinjector, help them use it in the outer thigh according to its instructions. Do not delay adrenaline while waiting for an ambulance. If symptoms have not improved after five minutes and a second prescribed device is available, the MHRA autoinjector safety advice says to administer the second dose. If the person becomes unresponsive and is not breathing normally, begin CPR.

BLS does not treat the underlying allergic reaction. Adrenaline and urgent professional care are priorities.

Drowning

Do not enter water unless it is safe and you are trained to perform a rescue. Call for emergency help. Once the person is safely out of the water, follow the call handler’s instructions. Rescue breaths are especially important in drowning because lack of oxygen is usually central to the emergency.

Suspected overdose

Call 999, report what may have been taken and follow the call handler’s instructions. If opioid overdose is suspected and take-home naloxone is available, administer it according to its product instructions. Naloxone does not replace CPR or emergency medical care: if the person is unresponsive and not breathing normally, start CPR as directed.

A safe BLS memory aid

Use Check responsiveness, Call, Check breathing, CPR and Connect to remember the adult community sequence:

Check responsiveness: After checking for danger, speak to the person and gently shake their shoulders.
Call: If there is no response, call 999 immediately on speakerphone. Send someone for an AED if possible.
Check breathing: Open the airway and assess breathing for no more than 10 seconds while waiting for the call to be answered. Gasping is not normal breathing.
CPR: Begin chest compressions if breathing is absent or abnormal. Add rescue breaths if trained and willing.
Connect: Attach the AED as soon as it arrives and follow its instructions.

The critical distinction is that the emergency call comes immediately after establishing unresponsiveness—not after completing the breathing check. This memory aid supports, but does not replace, the full RCUK algorithm or instructions from a 999 call handler.

Why practical BLS training matters

Reading can help you understand the sequence, but practical training allows you to rehearse compression depth and rate, rescue breaths, AED pad placement, choking treatment and communication with emergency services. A trainer can also correct hand position and help you practise responding under pressure.

Skills can fade over time. Employers and certificate holders should consider workplace risk assessments, relevant first-aid requirements and the training provider’s renewal arrangements. These guides explain how long a first-aid certificate lasts and how much a first-aid course costs.

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Frequently asked questions

Is BLS the same as CPR?

No. CPR is a central component of BLS. BLS also covers recognising cardiac arrest, calling emergency services, using an AED, responding to choking and caring for an unresponsive person who is breathing normally.

When should I call 999 for an unresponsive adult?

Call 999 immediately after establishing that the person is unresponsive. Put the phone on speaker and assess breathing while waiting for the call to be answered. If breathing is absent or abnormal, begin CPR.

Should a member of the public check for a pulse?

No. Lay rescuers should not delay care by attempting a wrist or neck pulse check. If the person is unresponsive and not breathing normally, treat this as cardiac arrest, follow the 999 call handler and begin CPR.

What are agonal gasps?

Agonal breathing can sound like occasional gasps, snorts or slow, laboured breaths. It is not normal breathing and may occur during cardiac arrest. Start CPR if an unresponsive person is breathing abnormally.

Can an AED harm someone who does not need a shock?

An AED analyses the heart rhythm and advises or delivers a shock only when it identifies a shockable rhythm. Follow the device’s instructions and make sure nobody touches the person during rhythm analysis or shock delivery.

When should CPR stop?

Continue until the person begins breathing normally, emergency professionals take over, the scene becomes unsafe or you are physically unable to continue. Occasional gasps are not a reason to stop.

Who should learn basic life support?

Anyone can learn BLS. Practical training is particularly useful for parents, carers, teachers, sports staff, workplace first aiders and people responsible for public venues. Reading an article or completing knowledge-only learning cannot by itself demonstrate practical competence.

Guidance basis and editorial approach

This educational summary is published by Lead Academy and attributes clinical and first-aid instructions to current primary UK guidance. No named clinical reviewer is claimed. It does not diagnose individual cases or replace instructions from emergency services, practical training or advice from an appropriately qualified healthcare professional.

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