BLS — Basic Life Support — All Questions

An AED arrives while you are performing CPR on an adult in cardiac arrest. What should you do?

• a.Turn it on and follow its prompts✓
• b.Wait for a physician to authorize it
• c.Finish 5 more minutes of CPR first
• d.Check a pulse for a full minute first

The AED is used as soon as it arrives, with compressions continuing until the pads are on and pausing only for analysis and the shock.

You are using an AED on a 5-year-old child. Which is correct?

• a.Use pediatric pads or a pediatric dose attenuator if available✓
• b.Never use an AED on a child under 8 years old
• c.Delay defibrillation until EMS brings a pediatric AED
• d.Always use adult pads at full energy regardless of availability

For a child under 8 years, use pediatric pads or a dose attenuator if they are available to reduce the delivered energy. However, if only adult pads are available, use them rather than withhold a needed shock — just ensure the pads do not touch each other. Defibrillation should never be delayed for a shockable rhythm.

Immediately after the AED delivers a shock to an adult, the rescuer should:

• a.Give 2 breaths and reassess the airway
• b.Wait for the AED to re-analyze
• c.Check for a pulse for 10 seconds
• d.Resume compressions immediately✓

Immediate resumption of compressions after a shock shortens the perishock pause; the AED reanalyzes after about 2 minutes.

Before the AED analyzes the rhythm and before delivering a shock, the rescuer must:

• a.Remove the victim's clothing but leave medication patches in place
• b.Ensure no one is touching the victim and clearly state 'Clear'✓
• c.Place both pads on the same side of the chest
• d.Pour water on the chest to improve pad conduction

Everyone must be clear of the victim during analysis and shock so the reading is accurate and no rescuer is shocked; announce 'Clear' and visually confirm no contact. The chest should be dry (not wet), pads are placed in the diagonal positions shown, and any transdermal medication patch is removed and the area wiped so it does not block energy or cause a burn.

An AED arrives while CPR is in progress on an adult. When should compressions stop?

• a.As soon as the AED case is opened
• b.After 5 more cycles of CPR
• c.While the pads are being applied
• d.Only for analysis and the shock✓

CPR continues until the defibrillator is applied, and minimizing interruptions around the shock is associated with better defibrillation success and outcomes.

A witnessed adult collapses right next to an AED that is immediately available. What is appropriate?

• a.Use the AED and shock right away✓
• b.Give 5 minutes of CPR before using the AED
• c.Check the pulse for a minute first
• d.Wait for EMS to operate the AED

When the collapse is witnessed and a defibrillator is immediately available, defibrillation can be performed right away; long periods of CPR before the first shock are not required.

After an AED shock, the patient does not move. What should rescuers do?

• a.Resume compressions immediately✓
• b.Give two breaths before anything else
• c.Check for a pulse first
• d.Wait for the AED to reanalyze

Immediate resumption of compressions after a shock shortens the perishock pause and improves the compression fraction; the AED reanalyzes after about 2 minutes.

What is the approximate pad size range that lowers transthoracic impedance for adults?

• a.2 to 3 cm in diameter
• b.20 to 25 cm in diameter
• c.8 to 12 cm in diameter✓
• d.Size has no effect

The Guidelines state that a larger pad or paddle size, within the limits of 8 to 12 cm in diameter, lowers transthoracic impedance; adults get adult pads.

Which adult pad placements do the Guidelines describe as comparably effective?

• a.Anterolateral and anteroposterior✓
• b.Only anteroposterior
• c.Only anterolateral
• d.Both pads on the back

Anterolateral, anteroposterior, anterior-left infrascapular and anterior-right infrascapular placements are comparably effective for treating arrhythmias.

In anterolateral pad placement, where does the lateral pad belong?

• a.On the abdomen below the ribs
• b.On the upper back
• c.In the midaxillary line✓
• d.Directly over the breastbone

With anterolateral placement, the lateral pad should be placed in the midaxilla and not too anteriorly so that current flows through the heart.

Registry data show first-shock success in witnessed VF was 93% within 6 minutes. What was it when the first shock was delayed beyond 16 minutes?

• a.75%✓
• b.25%
• c.93%
• d.99%

The ARREST registry data cited by the Guidelines show first-shock success falling from 93% within 6 minutes to 75% after 16 minutes, with about a 6% drop in survival probability per minute of delay.

A lone rescuer knows an AED is mounted in the hallway 20 meters away from an adult who has collapsed. What does lay teaching advise?

• a.Get it, even if you must leave briefly✓
• b.Use the AED only after 10 minutes of CPR
• c.Wait for someone else to find the AED
• d.Never leave the patient for any reason

MedlinePlus advises retrieving a known nearby AED even if the rescuer has to leave the person, because early defibrillation is critical for shockable rhythms.

What share of public cardiac arrests had an AED applied by a lay rescuer in the U.S. registry data cited in 2025?

• a.12.6%✓
• b.85%
• c.50%
• d.2%

The 2025 executive summary reports that only 12.6% of patients who arrested in public had an AED applied by a lay rescuer, showing how underused public AEDs are.

An infant is in cardiac arrest, and the AED has an attenuator and pediatric pads. What should rescuers do?

• a.Wait until 10 minutes of CPR are done
• b.Attach it now with pediatric pads✓
• c.Use adult pads without the attenuator
• d.Never use an AED on an infant

For infants and children in cardiac arrest, an AED should be attached as soon as possible, using a pediatric attenuator and pediatric pads if available.

Pediatric pads on a toddler would touch if both were placed on the front of the chest. What separation do the Guidelines call for?

• a.At least 15 cm between pads
• b.Pads may overlap
• c.Separation does not matter
• d.At least 1–2 cm apart✓

Pads of the largest size that can still be separated by at least 1 to 2 cm allow appropriate current flow; front-and-back placement keeps them apart on a small chest.

Why is a single shock followed by CPR preferred over three stacked shocks?

• a.Shorter pauses and better survival✓
• b.Stacked shocks deliver too little energy
• c.Stacked shocks are impossible with AEDs
• d.Single shocks allow pulse checks

The single-shock strategy shortens CPR interruptions and was associated with improved survival to hospital admission and discharge compared with stacked shocks.

A woman in cardiac arrest is wearing a bra. What approach did a 2024 review support?

• a.Avoiding the AED in women
• b.Always removing all clothing first
• c.Placing pads over the bra
• d.Adjust the bra; pads on skin✓

The review found insufficient evidence to require routine bra removal and noted pads can be placed directly on skin by adjusting the bra; bare-chest concerns have been linked to lower AED use in women.

Why are shockable rhythms less common in children than in adults?

• a.Children's hearts cannot fibrillate
• b.Children rarely need CPR
• c.Most start with breathing failure✓
• d.AEDs cannot detect pediatric rhythms

Pediatric arrest usually follows respiratory failure or shock and often presents as asystole or PEA; shockable rhythms are rare but occur, so the AED is still applied.

In adults, what did a study of AED use inside hospitals find?

• a.It doubled survival compared with manual defibrillators
• b.It shortened every pause in CPR
• c.It did not improve survival and lengthened pauses✓
• d.It is required for all hospital arrests

The Pediatric chapter notes that in adults, AED use in hospitals did not improve survival and prolonged the peri-shock pauses needed for rhythm analysis.

A rescuer asks why CPR should continue while the AED charges. What is the reason?

• a.Pauses before shocks lower survival✓
• b.It prevents the pads from slipping
• c.Charging requires chest movement
• d.The AED needs compressions to analyze

Prolonged pauses before and after shock delivery decrease blood flow to the brain and heart and are associated with decreased survival.

What does current evidence say about drying the chest of a drowned person before using an AED?

• a.It is proven to double shock success
• b.It must always take at least 2 minutes
• c.It remains an open research question✓
• d.The AED cannot be used on a wet person

The 2025 executive summary lists whether drying the chest before AED use after drowning is necessary as a knowledge gap, so no drying rule is established.

A lay rescuer arrives with an AED to find an adult who collapsed about 8 minutes ago and has had no CPR. What should happen?

• a.Shock at once without any compressions ever
• b.Wait for EMS because too much time has passed
• c.Start CPR and apply the AED when it is ready✓
• d.Give 5 minutes of CPR before turning on the AED

For unmonitored arrest, a brief period of CPR while the defibrillator is readied may be sufficient; longer mandatory CPR periods before analysis showed no benefit, and the AED should be used as soon as possible.