CPR and Basic Life Support — High-Quality Compressions, AED, ACLS Drugs and Paediatric Differences

Basic life support (BLS) is the set of actions that keeps oxygenated blood moving to the brain and heart until the circulation can be restored: recognising cardiac arrest, calling for help, high-quality chest compressions, rescue breaths and early defibrillation with an automated external defibrillator (AED). Advanced life support (ACLS/ALS) adds manual defibrillation, drugs, advanced airways and treatment of the cause.

Recognition is deliberately simple. The Resuscitation Council UK 2025 guideline says that if a person is unresponsive with abnormal breathing, cardiac arrest should be assumed. Slow, laboured breathing, agonal gasping or panting are signs of arrest, not reassurance — and a short seizure-like episode can occur at the onset of arrest. The 2025 UK change: call the emergency number for any unresponsive person first, then assess breathing while the call connects.

Healthcare professionals check for a pulse and breathing together, within 10 seconds (StatPearls; AHA: pulse check of no more than 10 s). If no definite pulse is felt in that time, start compressions — the risk of CPR to someone who is not in arrest is low, while delay is lethal.

The chain of survival is the sequence of time-critical actions that determines whether a cardiac arrest victim survives. Each link depends on the one before it, and survival is only as good as the weakest link.

In 2020 the AHA introduced a sixth link (recovery) and published four separate chains (adult/paediatric, in-hospital/out-of-hospital). The 2025 AHA guidelines consolidated these into a single six-link chain of survival. AHA Part 4 walks through it in order: prevention and preparedness, early identification of cardiac arrest and activation of help, effective resuscitation (high-quality CPR and rapid defibrillation, then advanced care), post-cardiac arrest care, and survivorship and recovery.

Both the 2025 AHA and the 2025 UK/European guidelines use the same core numbers for adults. Learn them as a set — they are asked individually and as 'all of the following except'.

CPR works best on a firm surface, but the UK guideline advises not moving a patient from a bed to the floor — start CPR on the bed and compress deeper if needed to compensate for the mattress. Lay rescuers who are not trained or not willing to give breaths should give continuous compression-only CPR; dispatchers coach compression-only CPR by default.

StatPearls (Cardiopulmonary Resuscitation) states that if an individual is not breathing and has no pulse, CPR should begin with the C-A-B sequence — chest compressions, then airway, then breathing. The older A-B-C order delayed the first compression while the rescuer positioned the head, looked for a mask and gave breaths.

• In a sudden adult arrest — usually VF from a cardiac cause — the blood is still oxygenated for the first minutes; what is missing is flow, so compressions come first.
• Starting with compressions shortens the time to first compression and reduces rescuer hesitation.
• After 30 compressions the airway is opened (head tilt–chin lift, or jaw thrust if spinal injury is suspected) and 2 breaths are given.
• Exception in children: paediatric arrests are mostly secondary to respiratory or circulatory failure, which is why the UK paediatric guideline starts with five initial rescue breaths before compressions.

Attach an AED as soon as it is available and follow its prompts. With more than one rescuer, compressions continue while the pads are being applied. Nobody touches the patient during rhythm analysis or the shock, and compressions restart immediately after the shock (or immediately if no shock is advised) — do not stop for a pulse check. The AED then prompts a pause for rhythm analysis after a set interval of CPR.

• Energy: biphasic defibrillators have largely replaced monophasic ones. The UK guideline advises a first biphasic shock of at least 150 J (130–150 J for pulsed biphasic); AHA advises using the manufacturer's recommended setting. If the setting is unknown, use the highest available energy.
• Single shocks followed by 2 minutes of CPR. Up to three stacked shocks may be given only for a witnessed, monitored VF/pVT arrest with a defibrillator immediately at hand.
• Refractory VF (continuous VF after three shocks): consider changing pad position to antero-posterior (vector change).
• Children < 25 kg: use the AED's paediatric mode if available and an antero-posterior pad position.

AHA notes that giving adrenaline every second 2-minute cycle after the first dose meets the 3–5 minute recommendation. In shockable rhythms, defibrillation takes priority over drugs — the evidence supports early shocks and adding adrenaline only once the first shocks and CPR have not worked.

Capnography guides the resuscitation: in an intubated patient an end-tidal CO₂ below 10 mmHg indicates little or no blood flow and should prompt better compressions; a sudden, sustained rise above 10 mmHg may signal return of spontaneous circulation (ROSC). StatPearls notes that an EtCO₂ below 10 mmHg after 20 minutes of ALS strongly — though not perfectly — predicts futility.

Before an advanced airway (supraglottic airway or endotracheal tube), CPR is given in cycles of 30 compressions to 2 breaths, pausing compressions only for the breaths. Once an advanced airway is in place, AHA 2025 advises 1 breath every 6 seconds (10 breaths/min) with continuous chest compressions — no more pauses for ventilation.

• Tube position: a sustained waveform on continuous capnography confirms tracheal (not oesophageal) placement; intubation should be attempted only by rescuers with a high success rate.
• Respiratory arrest with a pulse: give rescue breaths at 1 breath every 6 seconds (10/min) and recheck the pulse regularly.

The Hs and Ts are especially important in PEA and asystole, where no shock will help and survival depends on finding the cause. Point-of-care ultrasound may identify tamponade and tension pneumothorax, but must not add interruptions to compressions. If pulmonary embolism is the suspected cause, the UK guideline advises considering immediate thrombolysis and continuing CPR for 60–90 minutes afterwards in selected patients.

Child guidelines apply from about 1 year of age until puberty (AHA defines puberty for teaching as breast development in girls and axillary hair in boys); after that, use adult BLS. Most paediatric arrests are secondary to respiratory or circulatory failure, so oxygenation and ventilation matter more than in adults.

Newborns at birth follow a separate neonatal resuscitation algorithm, assessed alongside the APGAR score — do not mix it with infant BLS.

• Rib fractures occur in up to 70% of resuscitations and sternal fractures in about 30% (StatPearls); haemothorax and pneumothorax can follow. These are not a reason to compress less deeply.
• Mechanical CPR devices (load-distributing bands, pistons) give consistent compressions during prolonged resuscitation or transport; a manual shock can be delivered without stopping mechanical compressions.
• Opioid overdose: naloxone is incorporated into the AHA BLS algorithms, but high-quality CPR comes first in a patient without a pulse.
• Post-ROSC: look for signs such as purposeful movement, an arterial waveform or a sharp rise in EtCO₂ before pausing compressions for a rhythm and pulse check.