The ABCs of nursing refers to a systematic assessment framework: Airway, Breathing, and Circulation. These three checks, performed in that exact order, help nurses quickly identify and address the most immediate threats to a patient’s life. The logic is simple: if the airway is blocked, breathing doesn’t matter yet, and if the patient isn’t breathing, circulation problems come second. Many clinical settings use an expanded version, ABCDE, which adds Disability (neurological status) and Exposure (a full physical inspection).
A: Airway
The airway is always assessed first because nothing else matters if air can’t reach the lungs. A nurse looks, listens, and feels for signs that the airway is open. A conscious patient who is speaking clearly has a patent airway. In an unconscious or deteriorating patient, the tongue can fall backward and block the throat, especially in infants, whose larger head size naturally flexes the neck into a position that narrows the airway.
Signs of a blocked or partially blocked airway include gurgling, snoring sounds, stridor (a high-pitched noise heard on inhaling), or complete silence where breath sounds should be. If the patient is choking or unresponsive, first-line interventions include a head tilt with chin lift, or a jaw thrust if a spinal injury is suspected. Suctioning with a bulb syringe or mechanical device can clear mucus or debris. In infants, suctioning should last no longer than 10 seconds because the stimulation can slow the heart rate. Devices like oral or nasal airways can also be inserted to keep the passage open in patients who are breathing on their own but struggling to maintain airway patency.
B: Breathing
Once the airway is confirmed open, the next step is evaluating whether the patient is actually moving air effectively. A normal adult breathes 12 to 20 times per minute at rest. Fewer than 12 breaths per minute is considered abnormally slow, while more than 20 is abnormally fast. Infants breathe much faster: 30 to 60 breaths per minute is normal depending on whether the baby is sleeping or active.
Rate alone doesn’t tell the full story. Nurses also assess the depth, rhythm, and effort of breathing. Normal breathing looks effortless and rhythmic. Warning signs of respiratory distress include nasal flaring, visible pulling in of the skin between the ribs (called retractions), pursed lips, use of neck and shoulder muscles to breathe, audible breathing, and visible anxiety.
Listening to the chest with a stethoscope adds another layer. Normal breath sounds vary by location: louder and higher-pitched near the throat, softer and rustling over the outer lung surfaces. Abnormal sounds each point to different problems. Crackles (small popping sounds on inhaling) suggest fluid in the air sacs, common in pneumonia or heart failure. Wheezes (whistling sounds, usually on exhaling) indicate narrowed airways, as in asthma. Stridor, heard only on inhaling, signals an obstruction high in the airway. A rubbing, leathery sound suggests inflammation of the lining around the lungs.
C: Circulation
With airway and breathing addressed, circulation comes next. The goal is to determine whether the heart is pumping blood effectively to the organs and tissues. Nurses check heart rate, blood pressure, skin color, temperature, and moisture. Pale, cool, clammy skin can indicate poor blood flow, while warm and dry skin is generally reassuring.
One quick bedside test is capillary refill time. Pressing firmly on a fingertip or toenail for about 10 seconds blanches the color out. After releasing, the normal pink color should return in under 3 seconds. A slower return suggests reduced circulation. Other markers of poor perfusion include a fast heart rate, low blood pressure, dry mucous membranes, poor skin elasticity, decreased urine output, and altered mental status.
CAB vs. ABC: When the Order Flips
There is one important exception to the ABC sequence. During cardiac arrest, the American Heart Association recommends a CAB approach: Circulation (chest compressions) first, then Airway and Breathing. This change was introduced in 2010 and reaffirmed in the 2025 guidelines, supported by a 2024 international review of the evidence. The reasoning is practical: in cardiac arrest, the heart has stopped, and getting blood moving with compressions takes priority. Studies on training manikins show that starting with compressions shortens the time to the first breath and the completion of the first full CPR cycle.
For every other clinical scenario, including patients who are breathing but deteriorating, the traditional ABC order applies. The distinction matters: ABC is an assessment framework for identifying and prioritizing problems, while CAB is a resuscitation sequence for someone whose heart has stopped.
D: Disability (Neurological Status)
In the expanded ABCDE model, the fourth step evaluates the patient’s brain function. The fastest method is the AVPU scale, which categorizes a patient as Alert, responsive to Voice, responsive to Pain, or Unresponsive. A more detailed option is the Glasgow Coma Scale, which scores eye opening, verbal responses, and motor responses.
Nurses also check whether the pupils react normally to light, whether limb movements are equal on both sides of the body, and whether blood sugar is within range. Low blood sugar is a common and rapidly reversible cause of altered consciousness, correctable with oral or intravenous glucose. When a patient responds only to pain or is completely unresponsive, securing the airway becomes urgent, often by placing them in the recovery position while calling for advanced help.
E: Exposure
The final step is a thorough visual inspection of the entire body. This means carefully removing clothing to look for injuries, bleeding, rashes, needle marks, swelling, or anything else that might explain the patient’s condition or reveal a problem that wasn’t obvious with clothes on. Body temperature is checked, either by feeling the skin or using a thermometer. Throughout this step, patient dignity is a priority: the exam is systematic but respectful, with areas re-covered as soon as they have been assessed.
Why the Sequence Matters
The ABCDE approach works because it forces a structured, repeatable process during high-stress moments when it’s easy to get distracted by the most visually dramatic problem rather than the most lethal one. A patient with a badly broken leg will draw your attention immediately, but an unnoticed airway obstruction will kill them faster. The sequence ensures the most time-sensitive threats are caught and treated first, with each step building on the stability established by the one before it. If at any point during the assessment a patient deteriorates, the nurse returns to A and starts the sequence over.