A nurse discovers an unresponsive 3-month-old infant in the nursery who is not breathing and has no pulse. Which action should the nurse take first when initiating CPR for this infant?

For an unresponsive infant without breathing or pulse, immediate chest compressions are prioritized first. Other options delay compressions: airway opening, rescue breaths, or pulse checks should follow after starting compressions.

Understanding the Scenario and the Core Question

This question presents a high-acuity, low-frequency event: an unresponsive, pulseless, and apneic 3-month-old infant. The question asks for the first action when initiating CPR. This is a critical distinction because pediatric basic life support (PBLS) has a specific sequence of actions that differs from the adult approach, primarily due to the etiology of cardiac arrest in this population.

Why the Sequence Matters: Asphyxial vs. Cardiac Etiology

In adults, cardiac arrest is most often a primary cardiac event, making early defibrillation and chest compressions the immediate priority (C-A-B sequence). However, in infants and children, cardiac arrest is rarely a sudden primary cardiac event. According to the 2025 Korean Guidelines for CPR, pediatric cardiac arrest primarily arises from asphyxia in infants ^[1]. This means the heart stops because the body has been progressively deprived of oxygen, not because the heart itself failed first. The underlying cause is often respiratory failure or shock leading to profound hypoxemia and acidosis, which then causes bradycardia and eventual asystole.

Because the root problem is a lack of oxygen, the priority sequence for a single rescuer witnessing a pediatric collapse is modified. The guidelines emphasize that prevention is the cornerstone, but once arrest occurs, the rescuer must quickly deliver oxygen to the deprived tissues. Therefore, the sequence for a lone rescuer is to start with 2 minutes of CPR before leaving to activate the emergency response system, and critically, to begin with chest compressions, not rescue breaths, if the rescuer is alone. However, the question is about the very first physical action of the CPR sequence itself after unresponsiveness, apnea, and pulselessness are confirmed.

Analysis of the Correct Answer: Option 1

The correct action is to position two fingers on the lower half of the breastbone and compress at least one-third the depth of the chest. This is the first step in the "C-A-B" (Compressions-Airway-Breathing) sequence for a single rescuer. The 2025 guidelines maintain this sequence, recognizing that starting with compressions immediately circulates the remaining oxygenated blood and is less intimidating for bystanders, promoting earlier action [1,2]. For an infant, the correct technique is a two-finger technique on the sternum, just below the intermammary line. The compression depth must be at least one-third of the anterior-posterior diameter of the chest, which is approximately 1.5 inches (4 cm). The rate should be 100-120 compressions per minute.

Why the Other Options Are Incorrect

- Option 2: Tilt the head back and lift the chin to open the airway before beginning chest compressions. This describes the "A" in the old A-B-C sequence. In the current C-A-B sequence for a single rescuer, chest compressions are initiated before opening the airway. The head tilt-chin lift maneuver is performed after the first cycle of 30 compressions, just before delivering rescue breaths.

- Option 3: Provide 2 rescue breaths using a bag-mask device before starting chest compressions. This also follows the old A-B-C sequence. While ventilation is crucial in asphyxial arrest, the guidelines now recommend starting with compressions to immediately generate blood flow. Rescue breaths are delivered after the first set of compressions. Furthermore, in a witnessed sudden collapse, a lone rescuer would start with compressions. The 2025 PALS guidelines do suggest that for in-hospital arrest, bag-mask ventilation is a reasonable initial approach over advanced airways , but this refers to airway management strategy, not the initial step of the CPR sequence itself.

- Option 4: Check for a pulse at the brachial artery for 10 seconds before beginning compressions. This is a critical step in the assessment phase, which must be completed before initiating CPR. The question states the nurse has already discovered the infant is unresponsive, not breathing, and has no pulse. This means the assessment phase is complete. The question asks for the first action when initiating CPR. Performing another pulse check would delay the initiation of life-saving compressions and is not part of the CPR sequence once pulselessness has been confirmed. The brachial artery is the correct site for an infant pulse check, but the timing in this scenario is incorrect.

Clinical Application and Evidence Synthesis

The rationale is firmly grounded in the 2025 Korean PBLS guidelines, which align with international consensus. The shift to C-A-B for a single rescuer was designed to simplify the process, reduce the time to first compression, and acknowledge that even in asphyxial arrest, circulating blood via compressions is the immediate priority ^[1]. The study on bystander CPR timing reinforces that any delay in initiating CPR, particularly chest compressions, is associated with worse survival outcomes . The nurse in this in-hospital scenario must act as the immediate responder, transitioning seamlessly from a quick assessment to the first compression. The PALS guideline update further supports a focus on high-quality basic life support as the foundation, with advanced interventions like airway placement being secondary and not delaying the initiation of compressions .