ACLS Algorithms

Advanced Cardiac Life Support — four algorithms with medication protocols per AHA 2020 guidelines.

AHA 2020 Guidelines

⚡ SHOCKABLE RHYTHM — Defibrillation is the priority

Initial Assessment

Patient unresponsive, pulseless. VFib or pulseless VTach confirmed on monitor.

Start high-quality CPR immediately
Give supplemental oxygen
Attach monitor/defibrillator

⚡ Defibrillation (Shock First)

Charge while CPR continues — do not pause compressions until device is ready.

Biphasic: 120–200 J (device-specific)
Monophasic: 360 J
Clear patient, deliver shock
Resume CPR immediately — do not pause to check rhythm

IV/IO Access & Medications

Establish access during CPR. Do not interrupt compressions for drug administration.

Epinephrine 1 mg IV/IO — give after 2nd shock, then every 3–5 min
After 3rd shock: Amiodarone 300 mg IV/IO bolus
Consider 2nd dose Amiodarone 150 mg
Lidocaine if amiodarone unavailable: 1–1.5 mg/kg IV/IO

Cycle: CPR → Rhythm Check → Shock

Every 2 minutes: pause briefly to check rhythm. Minimize interruptions — compressions should resume within 10 seconds.

Still VFib/VTach: shock again, resume CPR
Organized rhythm: check pulse
ROSC: post-cardiac arrest care

Advanced Airway

Consider endotracheal intubation or supraglottic airway. Waveform capnography to confirm placement.

Once advanced airway placed: continuous compressions at 100–120/min
Ventilate at 10 breaths/min (1 breath every 6 sec)
ETCO₂ <10 mmHg after 20 min suggests poor prognosis

Medications

Drug	Dose	Route	Notes
Epinephrine	1 mg	IV/IO q3–5 min	Vasoconstrictor; give ASAP for non-shockable, after 2nd shock for VFib
Amiodarone	300 mg, then 150 mg	IV/IO bolus	First-line antiarrhythmic; after 3rd unsuccessful shock
Lidocaine	1–1.5 mg/kg	IV/IO	Alternative if amiodarone unavailable; max 3 mg/kg
Magnesium	1–2 g	IV/IO over 5–20 min	For torsades de pointes

H's (Reversible Causes)

Hypovolemia
Hypoxia
Hydrogen ion (acidosis)
Hypo/Hyperkalemia
Hypothermia

T's (Reversible Causes)

Tension pneumothorax
Tamponade (cardiac)
Toxins
Thrombosis (pulmonary)
Thrombosis (coronary)

⚠ NON-SHOCKABLE — DO NOT DEFIBRILLATE

Initial Assessment

PEA: organised rhythm on monitor but no palpable pulse. Asystole: flatline (confirm in 2 leads).

Start high-quality CPR immediately
Supplemental oxygen

CPR & NO Shock

These are non-shockable rhythms. Defibrillation will not help — focus on CPR quality and reversible causes.

Continuous CPR: 100–120/min, at least 2 inches depth
Establish IV/IO access
Do not interrupt compressions

Medications

Epinephrine 1 mg IV/IO — as soon as access established, then q3–5 min
Consider advanced airway (ETT or supraglottic)
Waveform capnography to confirm airway and gauge CPR quality

Aggressively Treat Reversible Causes

PEA is almost always caused by something treatable. Simultaneously search and treat.

Hypovolemia → IV fluid bolus
Hypoxia → optimize airway/ventilation
Tension pneumothorax → needle decompression
Cardiac tamponade → pericardiocentesis
Toxins → antidote where available
Pulmonary embolism → thrombolytics

Every 2 Minutes: Rhythm Check

Organised rhythm: check pulse immediately
ROSC: begin post-cardiac arrest care
Shockable rhythm appears: switch to VFib algorithm
Still PEA/asystole: continue CPR

Medications

Drug	Dose	Route	Notes
Epinephrine	1 mg	IV/IO q3–5 min	Give ASAP; first-line for PEA and asystole
Sodium Bicarb	1 mEq/kg	IV/IO	Only if known hyperkalemia, TCA overdose, or severe acidosis
Calcium Chloride	500–1000 mg	IV slow push	Hyperkalemia, hypocalcemia, Ca²⁺-channel blocker OD

H's

Hypovolemia
Hypoxia
Hydrogen ion
Hypo/Hyperkalemia
Hypothermia

T's

Tension pneumothorax
Tamponade
Toxins
Thrombosis (PE)
Thrombosis (MI)

Identify & Assess

Bradycardia: HR <60 bpm. Determine if haemodynamically unstable (hypotension, altered mental status, ischaemia, acute heart failure).

12-lead ECG to identify rhythm
IV access, continuous monitoring
Supplemental O₂ if SpO₂ <94%

Identify & Treat Reversible Causes

Medications (beta-blockers, Ca²⁺-channel blockers, digoxin)
Hypoxia, hypothermia, hyperkalaemia
Acute MI (especially inferior MI → AV block)
Increased vagal tone

If Haemodynamically Unstable

Atropine 0.5 mg IV — repeat q3–5 min, max 3 mg total
If ineffective: transcutaneous pacing (TCP) — ensure capture, analgesia/sedation
Dopamine infusion: 2–20 mcg/kg/min IV
Epinephrine infusion: 2–10 mcg/min IV

Consider Expert Consultation

Transvenous pacing if TCP fails
Cardiology consult for complete heart block, new LBBB/RBBB
Prepare for invasive pacing

Medications

Drug	Dose	Route	Notes
Atropine	0.5 mg q3–5 min, max 3 mg	IV	First-line; ineffective in 2nd/3rd degree AV block below AV node
Dopamine	2–20 mcg/kg/min	IV infusion	Titrate to response; 2nd-line or concurrent with pacing
Epinephrine	2–10 mcg/min	IV infusion	If atropine & dopamine ineffective
Isoproterenol	2–10 mcg/min	IV infusion	For beta-blocker overdose; specialist use

Transcutaneous Pacing (TCP)

Rate: 60–80 bpm. Start at lowest current, increase until capture (electrical + mechanical). Provide analgesia/sedation (morphine or midazolam). Confirm mechanical capture by palpating a pulse.

Assess Stability

HR >150 bpm. Assess for haemodynamic instability: hypotension, altered consciousness, ischaemia, pulmonary oedema.

12-lead ECG — is QRS narrow or wide?
IV access, continuous monitoring, O₂ if needed

Unstable: Synchronised Cardioversion

If haemodynamically unstable and tachycardia is causing the instability — proceed immediately.

Sedate if conscious (do not delay if critical)
Synchronise (sync) mode — confirm sync markers on each QRS
Narrow regular: 50–100 J | AF: 120–200 J | Wide regular: 100 J
Increase energy if no conversion

Stable Narrow-Complex (SVT)

Vagal manoeuvres first: Valsalva, carotid sinus massage
Adenosine 6 mg rapid IV push — flush immediately with 20 mL saline
If no conversion: Adenosine 12 mg IV
If AF/flutter: rate control (diltiazem, metoprolol, verapamil)

Stable Wide-Complex (VTach)

Regular and monomorphic: Amiodarone 150 mg IV over 10 min
Alternative: Procainamide 20–50 mg/min until conversion or max 17 mg/kg
Irregular wide-complex (AF+WPW): avoid AV nodal blockers → cardioversion
Torsades: Magnesium 1–2 g IV over 5–60 min

Medications

Drug	Dose	Route	Notes
Adenosine	6 mg then 12 mg	Rapid IV + flush	SVT; very short half-life; warn patient of brief chest tightness
Amiodarone	150 mg over 10 min	IV	Stable wide-complex VTach; then 1 mg/min infusion
Diltiazem	15–20 mg IV over 2 min	IV	AF/flutter rate control; avoid in WPW, hypotension
Metoprolol	2.5–5 mg q5 min (max 15 mg)	IV	AF/flutter rate control; avoid in bronchospasm, decompensated HF
Magnesium	1–2 g over 5–60 min	IV	Torsades de pointes; hypomagnesaemia
Procainamide	20–50 mg/min, max 17 mg/kg	IV infusion	Stable VTach; stop if QRS widens >50%, hypotension

Source: AHA 2020 ACLS Guidelines. Reviewed Sep 2026. Obtain ACLS certification for clinical practice.

Training reference only. Not a substitute for ACLS certification or clinical judgement. Follow your institution's current protocols. Activate emergency services in a real emergency.