4.1 BLS, Primary Assessment, and Secondary Assessment
Key Takeaways
- ACLS uses a three-layer survey: the BLS Assessment, the Primary Assessment (ABCDE), and the Secondary Assessment (SAMPLE history plus H's and T's).
- The BLS Assessment confirms responsiveness, breathing, and pulse, and triggers high-quality CPR and early defibrillation before any advanced step.
- The Primary Assessment uses Airway, Breathing, Circulation, Disability, and Exposure to find and treat immediate life threats, reassessing after every action.
- The Secondary Assessment gathers a focused history and hunts for the reversible H's and T's without interrupting CPR or shock timing.
- Assess, then act, then reassess — never let history-taking delay compressions, ventilation, or defibrillation.
4.1 BLS, Primary Assessment, and Secondary Assessment
The American Heart Association (AHA) ACLS course teaches a systematic approach so a team never skips fundamentals while still driving toward rhythm diagnosis, reversible causes, and definitive care. It is organized as three sequential surveys: the BLS Assessment, the Primary Assessment, and the Secondary Assessment. A single governing rule ties them together — assess first, perform the appropriate action, then reassess before moving on.
The BLS Assessment
The BLS Assessment is the foundation and always comes first. It is a rapid, hands-on sequence that confirms whether the patient needs CPR and a shock:
- Check responsiveness — tap and shout. If unresponsive, activate the emergency response system and get a defibrillator/AED.
- Check breathing and pulse simultaneously for no more than 10 seconds (carotid in adults).
- If no pulse, begin high-quality CPR: compressions at 100-120/min, depth at least 2 inches (5 cm) but not more than 2.4 inches (6 cm), full recoil, minimal interruptions, and a compression-to-ventilation ratio of 30:2 until an advanced airway is placed.
- Defibrillate as soon as a shockable rhythm is identified.
The BLS Assessment is not abandoned once ACLS begins; high-quality CPR and early defibrillation remain the interventions most strongly linked to survival.
The Primary Assessment — ABCDE
Once CPR and monitoring are underway, the Primary Assessment applies the ABCDE mental model to find and fix immediate threats. After each intervention you reassess before proceeding.
| Letter | Focus | Actions |
|---|---|---|
| A — Airway | Is the airway patent? | Open with head-tilt/chin-lift or jaw-thrust; suction; place an advanced airway only if it will not interrupt compressions or shocks. |
| B — Breathing | Is oxygenation/ventilation adequate? | Bag-mask with high-flow oxygen; confirm tube placement with waveform capnography; avoid excessive ventilation. With an advanced airway, give 1 breath every 6 seconds (10/min) with continuous compressions. |
| C — Circulation | Is there perfusion? | Monitor rhythm, obtain IV or IO access, give fluids/drugs, monitor CPR quality with ETCO2. |
| D — Disability | Neurologic status | Assess responsiveness (AVPU/GCS), pupils, and glucose. |
| E — Exposure | Hidden clues | Remove clothing to find trauma, rashes, patches, bleeding, or signs of toxidrome; control temperature. |
The ABCDE order is a priority order: a blocked airway is corrected before a breathing problem, and so on. In pulseless arrest, circulation tasks (CPR, defibrillation) dominate while airway and breathing are managed in parallel without interrupting compressions.
The Secondary Assessment — SAMPLE and H's & T's
The Secondary Assessment runs alongside ongoing resuscitation and answers "why did this happen?" It has two halves: a focused history and a structured search for reversible causes.
The history uses the SAMPLE mnemonic:
- S — Signs and symptoms
- A — Allergies
- M — Medications (including anticoagulants, insulin, antiarrhythmics)
- P — Past medical history (dialysis, MI, PE, diabetes)
- L — Last oral intake
- E — Events leading to the arrest
The reversible-cause search uses the H's and T's (detailed in 4.4): Hypovolemia, Hypoxia, Hydrogen ion (acidosis), Hypo-/Hyperkalemia, Hypothermia, Tension pneumothorax, Tamponade (cardiac), Toxins, Thrombosis (pulmonary), and Thrombosis (coronary).
How this is tested and common traps
BLS/ACLS items reward priority recognition. Read the patient state first — age, pulse, breathing, rhythm, stability, rescuer count — then pick the action that protects perfusion, oxygenation, or shock timing. A good code leader can call for glucose, potassium, dialysis status, and the medication list while CPR continues, because that history does not interrupt the algorithm.
Classic distractors: doing a long history before starting CPR; intubating during the first shock cycle; or having everyone investigate while no one owns compressions, airway, or the defibrillator. If an answer sounds advanced but delays CPR, defibrillation, or ventilation, it is almost always wrong.
Assess-act-reassess in practice
The systematic approach is not a checklist you complete once; it is a continuous loop. After each intervention, you reassess the same parameter before moving on. If you open the airway, you immediately recheck breathing. If you give fluids for hypovolemia, you recheck the blood pressure and rhythm. This loop is what lets a team catch a deteriorating airway, a dislodged tube, or a developing tension pneumothorax in real time rather than discovering it minutes later.
The three surveys also map cleanly onto team roles. While the compressor and ventilator execute the BLS Assessment, the team leader runs the Primary Assessment out loud ("airway is open, breathing supported, IV in, glucose normal") and assigns the Secondary Assessment — one person owns the SAMPLE history, another owns the H's and T's. Spoken, closed-loop communication keeps everyone synchronized.
Worked scenario
A 58-year-old collapses in the emergency department. BLS Assessment: unresponsive, no normal breathing, no pulse → CPR at 100-120/min, 30:2, defibrillator attached; the monitor shows VF → shock. Primary Assessment during the next cycle: airway managed with bag-mask, IV access obtained, glucose normal, no trauma on exposure. Secondary Assessment: the spouse reports the patient missed dialysis — a hyperkalemia (an 'H') clue, so the leader prepares calcium and insulin/glucose. Nothing in the history-taking interrupted compressions or the shock.
Comparing arrest vs peri-arrest states
A frequent exam discrimination is pulseless arrest versus a peri-arrest state with a pulse:
| State | Initial action |
|---|---|
| Pulseless arrest | CPR + defibrillation (if shockable) |
| Respiratory arrest with a pulse | Ventilate; do NOT do compressions |
| Unstable tachy/bradycardia with a pulse | Cardioversion or pacing/atropine |
Reading pulse and breathing first to recognize which state you are in is the core skill the systematic approach trains.
In the ACLS systematic approach, which survey comes FIRST and determines whether high-quality CPR and defibrillation are immediately needed?
What is the recommended energy for the FIRST biphasic defibrillation shock in adult cardiac arrest?
During a code, the leader asks the team for the patient's medication list, dialysis status, and the events before collapse while compressions continue. Which assessment component is this?