Cardiac arrest, CPR and AEDs

Do not wait for diagnostic certainty

After approaching safely, call emergency services on speakerphone for an unresponsive adult and quickly assess breathing. If breathing is absent or not normal, including gasping, begin compressions and send someone for an AED. Lay rescuers do not wait for a pulse check or blue skin. The AHA 2025 adult lay-rescuer algorithm connects calling, CPR, and AED use. If alone without a usable phone, obtain emergency help as quickly as possible and immediately begin or resume CPR on return.

Loss of effective pumping deprives the brain and heart muscle of oxygen. Compressions buy time rather than fully replacing cardiac function. An AED does not recharge every stopped heart: shocks treat selected abnormal rhythms. No shock advised means neither recovery nor futility. This lesson covers community basic response, not resuscitation at birth or professional pulse-assessment pathways.

Adult compressions need position, depth, and recoil

Place the person on their back where safe, effective CPR can begin, with firm support where feasible; do not create a long delay by moving them to an ideal location. Kneel beside the chest. Put the heel of one hand on the lower half of the sternum in the center of the chest, place the other hand above it, interlock fingers, and keep straight arms with shoulders over the hands. Compress at 100–120 per minute, at least 5 cm deep in an average adult while avoiding depths beyond 6 cm. Allow full recoil without leaning.

Faster is not automatically better: depth and recoil may suffer. Bent arms also increase fatigue. Interruptions reduce generated blood flow, so keep necessary pauses brief. With two rescuers, switch about every two minutes or when fatigued. AHA 2025 specifies these quality targets; feedback from manikin practice helps reveal errors that are difficult to notice by feel alone.

Breaths should produce visible chest rise

If trained and willing, alternate 30 compressions with two breaths. Without suspected neck injury, open the airway using head tilt and chin lift, pinch an adult’s nose, seal the mouth, and give each breath over about one second, just until the chest visibly rises. Allow exhalation. Large rapid breaths can inflate the stomach, promote regurgitation, and impair circulation. If the first breath does not raise the chest, reopen the airway and improve the seal before the second attempt; do not prolong the pause with repeated attempts.

Untrained, unable, or unwilling rescuers should give continuous compressions rather than do nothing. Breaths are particularly important for children, infants, and oxygen-deprivation events such as drowning. Adult compression-only messaging is not the optimal protocol for every situation. Red Cross CPR steps explain coordination. Bag-mask ventilation requires practice; unfamiliar equipment should not interrupt useful care already underway.

Suspected neck injury must not prevent airway opening or delay CPR. Rescuers trained in jaw thrust may first use it without head extension. If the airway remains closed, oxygenation and ventilation take priority and head tilt–chin lift may be necessary. Lay rescuers should use dispatcher guidance on speakerphone, without interrupting compressions to learn an unfamiliar technique or applying a rigid cervical collar themselves.

Age changes technique and depth

Using AHA categories, infants are younger than about one year, excluding resuscitation at birth; children extend from about one year to puberty, after which adult guidance applies. Compress the lower sternum in children with one or two hands. For infants, use the heel of one hand on the sternum or two thumbs with hands encircling the chest. AHA 2025 no longer recommends two-finger infant compressions. Rate is 100–120 per minute; pediatric depth is at least one-third of chest front-to-back diameter, approximately 4 cm in infants and 5 cm in children, with full recoil.

Use 30:2 alone; two rescuers trained in pediatric CPR may use 15:2. For infant breaths, cover mouth and nose, keep an appropriate near-neutral head position, and give only enough air for chest rise. Call immediately on speakerphone when possible. Alone without a phone after an unwitnessed pediatric arrest, provide about two minutes of CPR before briefly leaving to call and retrieve an AED; witnessed sudden collapse prioritizes emergency activation and AED retrieval. Do not interrupt CPR to duplicate an existing call.

Use the AED promptly and clear for analysis and shock

Turn the AED on immediately and follow its voice and pad diagrams. Expose the skin where pads belong and dry it if necessary. Adult placement is usually upper right chest and left lateral chest below the armpit. Connect the cable if required. Another rescuer can continue compressions during pad placement. Everyone must stop touching the person during analysis and again before a shock. Follow instructions to press the button or allow a fully automatic shock. After a shock, or no shock advised, immediately resume compressions and follow subsequent prompts.

For infants and children under eight, prefer pediatric mode or an attenuator and suitable pads. Their absence should not prevent use of an available AED with device and dispatcher guidance. Pads must not touch; use front-and-back placement as illustrated when the chest is too small, and never cut pads. See Red Cross AED steps and AHA pediatric guidance. Certification is not required before following an AED’s instructions.

Case: what does “no shock advised” mean?

During adult CPR, the AED announces no shock advised. A witness assumes the machine has established that emergency care is unnecessary. It has only assessed whether the current rhythm is suitable for a shock; it has not demonstrated restored blood flow. If the person remains unresponsive without normal breathing, resume CPR immediately rather than waiting for another announcement or trying to force a shock. If normal breathing and clear signs of life appear, stop compressions to reassess, protect the airway, monitor, and inform the dispatcher.

Continue until professionals take over, clear recovery requires reassessment, the scene becomes unsafe, or exhaustion makes continuation impossible. Do not declare death merely because a certain number of minutes has passed. The case separates device output from observation and shows the value of someone clearly coordinating the next action. Practice requires manikins and training AEDs, never real compressions on a healthy partner. Reading and quizzes do not certify practical competence.

Bilingual terms

心搏骤停 · Cardiac arrest

An emergency loss of effective cardiac circulation.

胸廓回弹 · Chest recoil

Return of the chest after each compression.

可电击心律 · Shockable rhythm

A rhythm suitable for defibrillation.

AED · Automated external defibrillator

A device analyzing rhythm and guiding or delivering an indicated shock.

儿科减能装置 · Pediatric attenuator

An attachment or function reducing AED energy for younger children.

Sources and further reading

• AHA 2025 Adult Basic Life Support
• AHA 2025 Adult Lay Rescuer Algorithm
• AHA/AAP 2025 Pediatric Basic Life Support
• AHA/AAP 2025 Pediatric Lay Rescuer Algorithm
• AHA/AAP 2025 Pediatric Single Rescuer Algorithm for Health Care Professionals (training reference)
• Red Cross: CPR Steps
• Red Cross: Child and Baby CPR
• Red Cross: AED Steps

Original course source-check record: 9 September 2026. Full Chinese and English sentence-by-sentence language review: 14 September 2026. AI editing and language review are not human clinical review. Linked institutions have not participated in or endorsed this course.