The primary ACLS assessment should be conducted immediately after completing the Basic Life Support (BLS) assessment on an unconscious patient, or as the initial evaluation step when encountering a conscious patient in a cardiac or respiratory emergency. It serves as the bridge between basic interventions (CPR, defibrillation) and the advanced treatments that follow. In practice, this means the primary assessment begins the moment an advanced care provider is on scene and ready to take over.
BLS First, Then the Primary Assessment
The sequence matters. For an unconscious, pulseless patient, BLS actions come first: checking for responsiveness, activating emergency response, starting chest compressions, and using an AED. The primary ACLS assessment picks up where BLS leaves off, layering in more advanced evaluation and interventions. You don’t skip ahead to ACLS steps while basic resuscitation is still being established.
For a conscious patient experiencing a cardiac or respiratory emergency, the BLS assessment typically isn’t required because the person is breathing and has a pulse. In that scenario, the primary ACLS assessment is your starting point.
What the Primary Assessment Covers
The primary assessment follows the ABCDE framework, a systematic check that ensures nothing critical gets missed under pressure. Each letter represents a step, and you move through them in order.
- Airway: Ensure the airway is open. In unconscious patients, this may involve a head tilt/chin lift or inserting a basic airway device. If those aren’t enough, an advanced airway can be placed, though guidelines note this can be delayed until after two rounds of chest compressions if bag-mask ventilation is working adequately.
- Breathing: Provide supplemental oxygen and ventilation as needed. In cardiac arrest, deliver 100% oxygen. In a patient who isn’t in cardiac arrest, titrate oxygen to keep saturation at 94% or above. Avoid excessive ventilation, which can reduce blood return to the heart and worsen outcomes.
- Circulation: Check for a pulse, taking no more than 10 seconds. If you don’t feel a definite pulse within that window, assume cardiac arrest and start compressions immediately. If a pulse is present, assess whether the patient is hemodynamically stable. After return of spontaneous circulation, the target is a systolic blood pressure above 90 mmHg.
- Disability: Perform a rapid neurological check. The AVPU scale is the standard quick tool: is the patient Alert, responding to Voice, responding only to Pain, or Unresponsive? Check pupil reactions and measure blood glucose, since low blood sugar can mimic or worsen a decreased level of consciousness and is rapidly correctable.
- Exposure: Remove clothing to visually inspect the body for clues: trauma, bleeding, burns, rashes, needle marks, or a medical alert bracelet. Also assess body temperature, since both hypothermia and hyperthermia can contribute to cardiac emergencies.
Timing During Active Resuscitation
During cardiac arrest, CPR runs in 2-minute cycles. At the end of each cycle, you pause for no more than 10 seconds to check the heart rhythm and feel for a pulse. These brief pauses are the windows where you reassess and decide what comes next: another shock, continued compressions, or a medication. The primary assessment isn’t a one-time event in this context. Its components get revisited with every cycle as the situation evolves.
Minimizing interruptions to chest compressions is a core principle. Advanced airway placement, IV access, and other interventions should be worked in without stopping compressions for extended periods. If bag-mask ventilation is adequate, placing a more advanced airway device can wait until the initial rounds of CPR are underway.
How It Differs From the Secondary Assessment
The primary assessment focuses on identifying and treating immediate life threats. It answers one question: what is killing this patient right now, and what do I do about it?
The secondary assessment comes afterward, once the patient is somewhat stabilized. It digs into the underlying cause of the emergency by reviewing the H’s and T’s of ACLS, which are the most common reversible causes of cardiac arrest (things like low oxygen, blood loss, blood clots, drug overdose, and electrolyte imbalances). It also includes gathering a focused medical history using the SAMPLE framework: Signs and symptoms, Allergies, Medications, Past medical history, Last oral intake, and Events leading up to the emergency.
Think of the primary assessment as stopping the immediate crisis and the secondary assessment as figuring out why it happened in the first place.
The Primary Assessment Across ACLS Algorithms
The ABCDE primary assessment appears in every ACLS algorithm, whether you’re managing a cardiac arrest, a symptomatic slow heart rate, a dangerously fast rhythm, or a stroke. The specific interventions change depending on the scenario, but the systematic approach stays the same. This consistency is deliberate. In high-stress emergencies, having a repeatable framework reduces the chance of missing something critical. Regardless of the presenting problem, you always start by securing the airway, ensuring adequate breathing, evaluating circulation, checking neurological status, and exposing the patient for a full visual assessment.