What is the adult ALS algorithm?
The ALS algorithm is the structured approach UK hospital teams use to manage adult cardiac arrest. It is published by RCUK and aligned with European Resuscitation Council guidance. RCUK published updated Resuscitation Guidelines in October 2025, replacing the 2021 edition, with updated RCUK courses from January 2026.
For adult ALS, RCUK describes no major changes from 2021. The core sequence and drug timings are the same. The 2025 guidance puts more emphasis on oxygenation and ventilation during CPR and on getting defibrillator pad placement right first time.
The algorithm rests on a few priorities that do not change: recognise deterioration early, start high-quality CPR quickly, defibrillate shockable rhythms early, minimise pauses in compressions, and find and treat the cause.
What happens before the algorithm starts?
Many in-hospital arrests follow hours of warning signs, such as a rising respiratory rate, falling saturations, low blood pressure or new confusion. Recognising this with NEWS2, assessing with ABCDE and escalating using SBAR can prevent the arrest altogether.
- Make it safe and check for a response: Use appropriate PPE. Shake the shoulders gently and ask loudly whether the patient is all right.
- Shout for help, open the airway: Turn the patient onto their back and open the airway with head tilt and chin lift, or jaw thrust if trained.
- Check breathing and pulse: Take no more than 10 seconds. Agonal gasps are not normal breathing and should be treated as cardiac arrest.
- Call the team: Ask a colleague to call the resuscitation team on your hospital's emergency number and bring the defibrillator and equipment.
- Start CPR 30:2: Give 30 compressions then 2 ventilations with a pocket mask or bag-mask and oxygen, until the defibrillator arrives.
- Attach pads and assess the rhythm: Apply pads while compressions continue, then pause briefly to read the rhythm and follow the ALS algorithm.
What does high-quality CPR look like?
- Hands on the lower half of the sternum, centre of the chest.
- Depth 5 to 6 cm, rate 100 to 120 per minute, with full recoil after each compression.
- 30 compressions to 2 ventilations until an advanced airway is in place, then continuous compressions with about 10 ventilations a minute.
- Give the highest feasible inspired oxygen during CPR.
- Change the person compressing about every 2 minutes, usually at a rhythm check.
- Keep every pause as short as possible. Cannulation, airway work and charging the defibrillator should happen while compressions continue.
Shockable and non-shockable rhythms: what is the difference?
At each rhythm check the team decides which side of the algorithm to follow. Getting this right drives everything that follows.
| Shockable | Non-shockable | |
|---|---|---|
| Rhythms | Ventricular fibrillation (VF), pulseless ventricular tachycardia (pVT) | Pulseless electrical activity (PEA), asystole |
| Main treatment | Defibrillation, then 2 minutes of CPR | CPR and treating the cause |
| Adrenaline 1 mg IV or IO | After the third shock, then every 3 to 5 minutes | As soon as access is obtained, then every 3 to 5 minutes |
| Antiarrhythmic | Amiodarone 300 mg after the third shock; a further 150 mg may be considered after the fifth | Not indicated |
| Key question | Is the pad position and shock delivery right? | What is causing this arrest? |
RCUK 2025 guidance also lists lidocaine (100 mg, with a further 50 mg after five shocks) as an alternative where amiodarone is unavailable or locally preferred. Use the doses in the current RCUK algorithm and your local policy, and flush each drug.
Before calling asystole, check the leads are attached, the gain is appropriate and the rhythm is not fine VF. If P waves are present without QRS complexes, consider pacing.
How should a shock be delivered safely?
- Plan the pause: Towards the end of the two-minute cycle the leader warns the team and allocates who will check the rhythm and who will shock.
- Pause and identify: Stop compressions briefly and read the rhythm.
- Restart and charge: If shockable, compressions resume while the operator charges. Everyone else stands clear and oxygen is moved at least a metre away.
- Clear and shock: The compressor stands back, the operator checks visually that nobody is touching the patient, announces the shock and delivers it.
- Resume CPR at once: Restart compressions immediately for two minutes. Do not pause to check the pulse straight after a shock.
Standard pad position is antero-lateral: one pad below the right clavicle and the other on the left mid-axillary line, directly below the armpit. For VF that persists after three shocks, RCUK 2025 guidance suggests considering a change of vector to an antero-posterior position. Energy levels follow the manufacturer's advice; for most biphasic devices the first shock is at least 150 J.
Airway, access and capnography during the arrest
Start with basic airway manoeuvres and bag-mask ventilation with oxygen, and step up only to what you are trained to do. A supraglottic airway is an option for trained staff. Tracheal intubation should be left to people with a high success rate and done with minimal interruption to compressions.
Try intravenous access first. RCUK 2025 guidance suggests considering intraosseous access if IV access cannot be achieved within two attempts.
Use continuous waveform capnography whenever an advanced airway is in place. It helps confirm the tube is in the trachea, shows the quality of compressions and can signal return of spontaneous circulation (ROSC) with a sudden rise. A flat trace suggests oesophageal placement. Do not stop resuscitation on a low end-tidal carbon dioxide value alone.
What are the 4 Hs and 4 Ts?
Every arrest has a cause, and some can be reversed during the arrest. This matters most in PEA. Work through the list during each cycle, using the history, notes, recent results, examination and a blood gas. Point-of-care ultrasound can help in skilled hands if it does not lengthen pauses.
| Cause | Clues | Examples of treatment |
|---|---|---|
| Hypoxia | Respiratory illness, airway obstruction, low saturations before arrest | Effective ventilation with high-flow oxygen, check the airway |
| Hypovolaemia | Bleeding, recent surgery, severe fluid loss | Control bleeding, fluids or blood, major haemorrhage protocol |
| Hypo- or hyperkalaemia and metabolic causes | Kidney disease, blood gas, medicines | Correct according to RCUK guidance and local protocol |
| Hypothermia | Immersion, exposure, low temperature reading | Rewarm; check with a low-reading thermometer |
| Thrombosis | Chest pain before arrest, risk factors for pulmonary embolism | Consider thrombolysis for suspected PE; coronary intervention after ROSC |
| Tension pneumothorax | Trauma, recent central line, ventilated patient | Immediate decompression by a trained clinician |
| Tamponade | Penetrating chest trauma, after cardiac surgery | Pericardial decompression by a skilled clinician |
| Toxins | Overdose, prescribed drugs, history from relatives | Specific antidotes; advice from TOXBASE or the National Poisons Information Service |
Worked example: VF arrest on a ward
At 02:40 a healthcare assistant finds Mohammed unresponsive. Ellie, the staff nurse, finds no normal breathing and no pulse within 10 seconds, shouts for help and starts 30:2 CPR while a colleague calls the team and brings the defibrillator. Pads go on during compressions. The first rhythm check shows VF and a shock is given, then CPR resumes. The medical registrar arrives, introduces herself as leader and allocates compressions, airway, drugs and a scribe. VF persists at the second and third checks and shocks are given. After the third shock the leader asks for adrenaline 1 mg and amiodarone 300 mg IV, using closed-loop communication. The scribe records the times. At the next check the rhythm is organised, there is a pulse, and ROSC is declared. A 12-lead ECG shows ST elevation and cardiology is called.
Leader: 'Can someone give adrenaline?' Two nurses start drawing it up, and nobody notes the time.
Leader: 'Aisha, please give 1 mg adrenaline IV now.' Aisha: '1 mg adrenaline IV, giving now.' After flushing: 'Adrenaline 1 mg given at 02:47.' Scribe: 'Recorded at 02:47, next dose due about 02:51.'
Closed-loop communication like this prevents doses being missed or doubled. Any team member, whatever their grade, should feel able to say 'Stop, safety concern' if they see someone touching the patient during a shock or poor compressions.
What happens after ROSC, and when do you not start CPR?
ROSC begins a new phase of care. Reassess with ABCDE, secure the airway if needed, titrate oxygen to saturations of 94 to 98% once they can be measured reliably, get a 12-lead ECG, support blood pressure, check glucose, prevent fever in patients who remain comatose, treat the cause and involve critical care. Follow the current RCUK post-resuscitation guidance for targets.
CPR is not right for every patient. Decisions are best made in advance as part of a wider conversation about goals of care, often recorded using ReSPECT or a local form. Joint guidance from the BMA, RCUK and RCN explains that a decision not to attempt CPR applies only to CPR, not to other treatment. If there is no recorded decision, you should usually start CPR. Afterwards, document times, rhythms, shocks, drugs, causes found and the outcome, and debrief the team.
Keeping your resuscitation knowledge current
Resuscitation skills fade without practice. Attend your organisation's mandatory training, take part in simulation, and consider an accredited RCUK ALS course if your role needs it.
Our Adult Advanced Life Support course is a knowledge update on the current RCUK algorithm, covering CPR quality, defibrillation, drugs, reversible causes, team leadership and post-resuscitation care, with a worked scenario and reflection. Paediatric Life Support and Trauma Primary Survey and Initial Management cover related emergencies. None of these replace hands-on accredited training.
Frequently asked questions
When do you give adrenaline in cardiac arrest?
In adults, RCUK guidance is adrenaline 1 mg IV or IO as soon as possible for non-shockable rhythms (PEA and asystole), then every 3 to 5 minutes. For shockable rhythms (VF and pulseless VT), give the first 1 mg after the third shock, then every 3 to 5 minutes, which in practice is after alternate shocks. Always check the current RCUK algorithm and local policy.
When do you give amiodarone in the ALS algorithm?
For adults in VF or pulseless VT, amiodarone 300 mg IV or IO is given after the third shock. A further 150 mg may be considered after the fifth shock. RCUK 2025 guidance lists lidocaine as an alternative where amiodarone is unavailable or locally chosen. Amiodarone is not used for PEA or asystole.
Did the ALS algorithm change in 2025?
RCUK published updated Resuscitation Guidelines in October 2025. For adult ALS it describes no major changes from 2021: the sequence, CPR targets and drug timings are the same. There is more emphasis on oxygenation and ventilation and on correct initial pad placement, with advice to consider an antero-posterior vector change for refractory VF.
What are the shockable rhythms?
The shockable rhythms are ventricular fibrillation (VF) and pulseless ventricular tachycardia (pVT). They are treated with defibrillation followed immediately by two minutes of CPR. The non-shockable rhythms are pulseless electrical activity (PEA) and asystole, which are treated with CPR, early adrenaline and a focused search for reversible causes.
What are the 4 Hs and 4 Ts?
They are the reversible causes of cardiac arrest. The 4 Hs are hypoxia, hypovolaemia, hypo- or hyperkalaemia and other metabolic disorders, and hypothermia. The 4 Ts are thrombosis (coronary or pulmonary), tension pneumothorax, tamponade and toxins. Teams should consider each one during every cycle, especially in PEA.
How long is each CPR cycle in ALS?
Each cycle is about two minutes of CPR, followed by a brief pause to check the rhythm. If a shock is given, compressions restart immediately for another two minutes without a pulse check. A pulse is only checked if the rhythm looks organised and could produce a cardiac output.
Does an online course count as ALS certification?
No. Online learning can refresh your knowledge, but recognised ALS certification requires an accredited course with hands-on assessment, such as the RCUK Advanced Life Support course. Check what your employer requires for your role and attend your organisation's mandatory resuscitation training.
Related courses
Adult Advanced Life Support (UK Guidelines)
This course explains the recognition and management of adult in-hospital cardiac arrest, based on the current Resuscitation Council UK adult advanced…
Paediatric Life Support (UK Guidelines)
This course teaches the recognition of the seriously ill or injured child and the management of paediatric cardiorespiratory arrest, based on current…
Trauma: Primary Survey and Initial Management
This course teaches a structured approach to the first hour of care for a seriously injured adult, based on UK practice and NICE major trauma…
Sources and further reading
- Adult advanced life support guidelines (2025). Resuscitation Council UK.
- In-hospital resuscitation guidelines. Resuscitation Council UK.
- Post-resuscitation care guidelines. Resuscitation Council UK.
- Decisions relating to cardiopulmonary resuscitation. British Medical Association, Resuscitation Council UK and Royal College of Nursing.
- ReSPECT: Recommended Summary Plan for Emergency Care and Treatment. Resuscitation Council UK.
- National Early Warning Score (NEWS) 2. Royal College of Physicians.
Practitioner Insight is an independent education provider. It is not affiliated with or endorsed by the GMC, MPTS, NMC, HCPC, GPhC or any NHS organisation, and this information is not legal advice. If you have been referred to a regulator, speak to your defence organisation, trade union or legal representative.
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