What is the difference between BLS and ACLS?
Basic life support (BLS) is the set of skills that can keep a person with cardiac arrest alive until a defibrillator and a team arrive: recognising arrest, activating the emergency response system, high-quality CPR and early defibrillation with an automated external defibrillator (AED). Advanced cardiac life support (ACLS) sits on top of BLS. It adds cardiac monitoring, rhythm interpretation, manual defibrillation, IV or intraosseous drugs, advanced airway, treatment of reversible causes and post-arrest care.
StatPearls states the current consensus plainly: early recognition, high-quality CPR and defibrillation of shockable rhythms. High-quality chest compressions are the cornerstone of neurologically intact survival, and ACLS relies heavily on BLS principles. Much of the ACLS evidence is expert opinion, observational data and animal studies, which is why the algorithms are periodically revised — the American Heart Association (AHA) published its 2025 guidelines in October 2025.
What are the CPR numbers: rate, depth, ratio and recoil?
| Parameter | Adult | Child (1 year to puberty) | Infant (< 1 year) |
|---|---|---|---|
| Compression site | Lower half of the sternum, heel of both hands | Lower half of sternum, heel of 1 or both hands | Sternum just below the nipple line, 2 fingers |
| Rate | 100 to 120 per minute | 100 to 120 per minute | 100 to 120 per minute |
| Depth | At least 5 cm (2 inches) | About 2 inches | About 1.5 inches |
| Ratio before advanced airway | 30 compressions : 2 breaths | 30 : 2 (one rescuer); 15 : 2 (two rescuers) | 30 : 2 (one rescuer); 15 : 2 (two rescuers) |
| Recoil | Complete recoil between compressions | Complete recoil | Complete recoil |
- Minimise interruptions. Chest compression fraction should stay above 80%; pauses before a shock must be as short as possible.
- Rotate compressors every 2 minutes or sooner if fatigued — quality falls with fatigue.
- Avoid excessive ventilation. Over-ventilation raises intrathoracic pressure, impedes venous return and reduces coronary and cerebral perfusion.
- Firm surface, supine patient, scene safe. Do not delay CPR to move the patient unless the scene is unsafe.
- Airway: head tilt-chin lift; use jaw thrust without head tilt if cervical spine injury is suspected. Each breath is given over about 1 second, just enough to see the chest rise.
- Child or infant, two healthcare providers, no advanced airway: 15:2 (30:2 with a single rescuer). Adults stay at 30:2 whether one or two rescuers.
How is an AED used and what energy does a defibrillator deliver?
The definitive treatment of ventricular fibrillation and pulseless ventricular tachycardia is electrical defibrillation; CPR only buys time until it is available. StatPearls notes that if defibrillation is not performed promptly, brain death can occur in under 10 minutes. In the VF literature, prompt defibrillation was associated with survival of 39.3% compared with 22.2% when defibrillation was delayed by 2 minutes or more.
- Continue 30:2 CPR until the AED arrives; switch it on and follow the voice prompts.
- Apply pads on the front and back of the chest (as described for adults in StatPearls), keeping delay in resuming compressions to a minimum.
- Let the AED analyse the rhythm — everyone clear. If a shock is advised, pause compressions, ensure no one is touching the patient and deliver it.
- Resume CPR immediately after the shock, starting with compressions; do not stop to check the pulse first. The cycle is repeated after 2 minutes.
| Device | Energy for VF / pulseless VT | Note |
|---|---|---|
| Biphasic (standard today) | 120 to 200 J; follow the manufacturer's recommendation | If unknown, the maximum dose may be used; subsequent shocks the same or higher |
| Escalating biphasic | 200 – 300 – 360 J | Better conversion rates when several shocks are needed; overall survival similar to fixed energy |
| Monophasic | 360 J | Largely replaced by biphasic devices |
Which cardiac arrest rhythms are shockable?
Pulseless rhythms split into two groups on the monitor. Shockable: ventricular fibrillation (VF) and pulseless ventricular tachycardia (pVT). Non-shockable: pulseless electrical activity (PEA) and asystole. A shock only helps when there is chaotic or rapid ventricular activity that can be reset — shocking asystole or PEA does nothing.
| Rhythm | What it is | Shock? | Core treatment |
|---|---|---|---|
| VF | Chaotic ventricular activity, inherently non-perfusing | Yes | Defibrillate, CPR, epinephrine, amiodarone or lidocaine |
| Pulseless VT | Rapid organised ventricular rhythm without a pulse | Yes | Same as VF |
| PEA | Any organised or semi-organised rhythm that fails to produce a detectable pulse | No | CPR, epinephrine, treat Hs and Ts |
| Asystole | Complete absence of electrical and mechanical activity | No | CPR, epinephrine, treat Hs and Ts |
What is the ACLS cardiac arrest algorithm and which drugs are given?
After starting BLS, attach the monitor or defibrillator and identify the rhythm. The loop below repeats in 2-minute cycles of CPR, with the rhythm check at the end of each cycle (compressors swap at the same time).
| Step | VF / pulseless VT | PEA / asystole |
|---|---|---|
| 1. Start | CPR 30:2 until the defibrillator is attached; give oxygen | CPR 30:2; attach monitor |
| 2. Rhythm check | Shockable: defibrillate immediately, then resume CPR at once | Non-shockable: continue CPR, no shock |
| 3. Epinephrine | 1 mg IV or IO every 3 to 5 minutes — after defibrillation and 1 cycle of CPR if VF/pVT persists | 1 mg IV or IO every 3 to 5 minutes (about every 2 cycles); give as early as possible |
| 4. Antiarrhythmic | If VF/pVT persists despite defibrillation, epinephrine and good CPR: amiodarone 300 mg IV or lidocaine 1 to 1.5 mg/kg IV | Not used |
| 5. Advanced airway | Consider ETT or supraglottic airway; then 10 breaths per minute with continuous compressions; confirm with waveform capnography | Same |
| 6. Cause | Hs and Ts | Hs and Ts — the main focus |
| 7. Outcome | ROSC: post-arrest care | ROSC: post-arrest care |
- Waveform capnography: EtCO2 persistently below 10 mm Hg indicates inadequate cardiac output and a need to improve CPR quality. A sudden sustained rise above 10 mm Hg during CPR may indicate ROSC. Data are most reliable in intubated patients.
- Prognosis: outcomes in PEA are poor compared with VF or pVT presentations.
- Magnesium: 2 g IV for torsades de pointes (long QT polymorphic VT); it shortens the QT interval and prevents recurrence.
What are the reversible causes (Hs and Ts)?
| Category | Cause | Typical fix |
|---|---|---|
| H | Hypovolaemia | Fluid or blood |
| H | Hypoxia | Oxygenation, airway |
| H | Hydrogen ion (acidosis) | Ventilation; treat cause |
| H | Hypo- or hyperkalaemia (other electrolytes) | Calcium or bicarbonate for hyperkalaemia |
| H | Hypothermia | Active rewarming |
| T | Tension pneumothorax | Needle or finger decompression |
| T | Tamponade (cardiac) | Pericardiocentesis |
| T | Toxins (beta-blockers, calcium channel blockers, sodium-channel blockers) | Antidote and supportive care |
| T | Thrombosis — pulmonary or coronary | Thrombolysis, PCI as appropriate |
How are bradycardia and tachycardia managed in ACLS?
ACLS also covers patients with a pulse who are deteriorating. StatPearls lists signs of clinical deterioration such as bradycardia below 40 per minute, tachycardia above 140 per minute, systolic BP below 90 mm Hg, altered consciousness and respiratory distress. Start with ABCDE, monitor, 12-lead ECG, and look at rate, width and regularity.
| Step | Intervention |
|---|---|
| First line | Atropine 1 mg IV, repeated every 3 to 5 minutes up to a maximum of 3 mg. Smaller doses are not recommended and may paradoxically worsen bradycardia |
| Second line | Epinephrine infusion 2 to 10 mcg/min or dopamine 5 to 20 mcg/kg/min; transcutaneous pacing — consider early in high-degree block |
| Note | Wide-QRS heart blocks are usually infranodal and unlikely to respond to atropine — go straight to pacing |
| Situation | Management |
|---|---|
| Unstable (hypotension, shock, ischaemic chest pain, acute heart failure, altered mental state) | Synchronised cardioversion (wide or narrow complex) |
| Unstable polymorphic VT | Unsynchronised shock (defibrillation) |
| Stable regular narrow-complex (SVT) | Vagal manoeuvres, then adenosine 6 mg rapid IV; if no conversion 12 mg |
| Stable narrow irregular (probably AF) | Rate control: diltiazem, verapamil, beta-blockers, amiodarone or digoxin |
| Torsades / long-QT polymorphic VT (stable) | Magnesium sulphate 2 g IV |
What is post-cardiac-arrest care after ROSC?
ROSC is the start of the next phase, not the end. Ischaemia-reperfusion injury affects multiple organs, so the priorities are airway and oxygenation, haemodynamics, a 12-lead ECG for coronary intervention decisions, temperature control and treatment of the cause and seizures.
| Parameter | Target |
|---|---|
| SpO2 | 92% to 98% |
| PaCO2 | 35 to 45 mm Hg |
| Blood pressure | MAP above 65 mm Hg or systolic above 90 mm Hg (fluids, vasopressors, inotropes) |
| Temperature | Targeted temperature management for patients who do not follow commands — controlled cooling between 32 and 36 degrees C. StatPearls adds that newer evidence supports maintaining normothermia |
| Other | Normoxia, normocapnia, normoglycaemia; lung-protective ventilation; EEG monitoring where available |
What do exams ask about BLS and ACLS?
- Compression rate and depth — 100 to 120 per minute; at least 5 cm in adults.
- Ratio — 30:2 for one or two lay rescuers; with an advanced airway, continuous compressions plus 10 breaths per minute.
- Pulse check — not more than 10 seconds.
- Shockable rhythm — VF and pulseless VT; PEA and asystole are not.
- First drug in arrest — epinephrine 1 mg every 3 to 5 minutes; amiodarone 300 mg for refractory VF/pVT.
- Atropine — 1 mg for bradycardia (max 3 mg); not recommended in PEA or asystole.
- Adenosine — 6 mg then 12 mg for regular narrow-complex tachycardia.
- Biphasic vs monophasic energy — 120 to 200 J vs 360 J.