BLS Chain of Survival

🟢 Lite — Quick Review (1h–1d)

Cardiac Arrest is the sudden loss of effective heart pumping due to uncontrolled electrical activity, causing unconsciousness with absent pulse and breathing. The BLS sequence: check safety → check responsiveness → call for help → start CPR → apply AED. For adults, deliver 30 compressions at 5 cm depth, rate 100–120/min, then 2 breaths (30:2 ratio). Shockable rhythms (VF/pVT) need immediate defibrillation; non-shockable rhythms (asystole/PEA) need CPR first. Give adrenaline 1 mg IV every 3–5 min and amiodarone 300 mg IV for VF/pVT. Memorise the H’s and T’s (Hypovolemia, Hypoxia, Hyper/hypokalemia, Hypothermia, Tension pneumothorax, Tamponade, Toxic, Thrombosis). ROSC (return of spontaneous circulation) requires post-resuscitation care including targeted temperature management.

🟡 Standard — Regular Study (2d–2mo)

Definition and Recognition

Cardiac arrest occurs when the heart stops pumping effectively due to chaotic electrical activity. Clinical recognition requires three findings simultaneously: unresponsiveness, absent normal breathing (or gasping), and no palpable pulse (carotid in adults). Any delay in recognition worsens outcomes — seconds matter.

BLS Chain of Survival

The Saudi GP Board exam tests the correct sequence: Safety → Responsiveness → Activate emergency response → CPR → Defibrillation. For a single rescuer, call for help before starting compressions only if the collapse is unwitnessed. Chest compressions generate forward flow by increasing intrathoracic pressure; depth must be ≥5 cm (2 inches) with complete recoil to allow ventricular filling.

Rhythm Classification and Management

Rhythm	Recognition	Initial Action
VF / pulseless VT	Chaotic, wide-complex tachycardia	Immediate defibrillation (biphasic 150–200 J or monophasic 360 J)
Asystole	Flat line or near-flat line	CPR 30:2, confirm in multiple leads, give adrenaline
PEA	Organized ECG with no pulse	CPR 30:2, identify and treat reversible cause

After any shock, resume compressions immediately for 2 minutes before reassessing rhythm — this avoids “hands-off” time that reduces coronary perfusion pressure.

ACLS Medications

Adrenaline 1 mg IV/IO every 3–5 minutes (first dose given after the third cycle of CPR)
Amiodarone 300 mg IV first dose for VF/pVT refractory to defibrillation; 150 mg second dose
Vasopressin is no longer recommended as a routine first-line agent

Reversible Causes (H’s and T’s)

examiners frequently embed one of these in scenario questions. The list: Hypovolemia, Hypoxia, Hydrogen ion (acidosis), Hyper/Hypokalemia, Hypothermia, Tension pneumothorax, Tamponade (cardiac), Toxic (drug overdose), Thrombosis — Pulmonary embolism or Acute coronary syndrome. Identifying and correcting these reversible causes during CPR is the single most impactful intervention for non-shockable rhythms.

🔴 Extended — Deep Study (3mo+)

Mechanisms of Circulatory Generation During CPR

Chest compressions produce blood flow through two mechanisms: direct cardiac compression (sternum pushes the ventricles between the spine and sternum) and the thoracic pump mechanism (increased intrathoracic pressure opens the mitral valve in diastole and forces blood forward). Complete chest recoil is essential because residual pressure prevents ventricular filling — a common error is leaning forward between compressions, which reduces coronary perfusion pressure below the critical threshold of 15–20 mmHg needed for ROSC.

Defibrillation Physics and Timing

For biphasic defibrillators, deliver 150–200 J (or the manufacturer’s recommended dose); for monophasic, 360 J. The critical concept is “hands-off time” — each second without compressions during charging or after shock delivery reduces survival by approximately 1%. Newer feedback devices demonstrate that hands-off time frequently exceeds guidelines. Early defibrillation for VF within 3 minutes of collapse improves survival rates to >50% in monitored settings.

Post-Cardiac Arrest Care (Targeted Temperature Management)

After ROSC, targeted temperature management (TTM) between 32–36°C for 24 hours reduces neurological injury by suppressing the cascade of cellular apoptosis triggered by global ischaemia. Key considerations: maintain normothermia for at least 72 hours post-rewarming, avoid fever (increases cerebral metabolic demand), and perform neurological prognostication no earlier than 72 hours after return of normothermia. Airway protection with endotracheal intubation and haemodynamic optimisation (MAP ≥65 mmHg, SBP ≥90 mmHg) complete the bundle.

Common Exam Mistakes

Delaying compressions to palpate a pulse — current guidelines permit only 10 seconds for pulse check
Inadequate compression depth — many candidates underestimate; use a metronome at 100–120/min
Failing to call for help before starting CPR on a witnessed collapse — a lone rescuer must get the AED before CPR for a witnessed arrest
Pad placement near a pacemaker — place pads at least 2.5 cm away; do not place over the device
Administering amiodarone before defibrillation — medications come after the first shock for VF/pVT

Practice Prompts

A 60-year-old man collapses in your clinic; you find him unresponsive with no pulse. Describe your step-by-step management in the first 10 minutes, including rhythm identification and medication timing.
A patient in PEA is being resuscitated. She has a history of recent orthopaedic surgery and is on a plaster cast. What reversible cause should you suspect first, and how would you confirm and treat it?

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BLS Chain of Survival