High-Quality CPR (Adult, Child, Infant)
High-quality chest compressions are the single most important intervention in cardiac arrest. Blood does not move to the brain and heart unless the compressions are fast enough, deep enough, allow full recoil, and are barely interrupted. The BLS exam expects you to know the exact numbers for adults, children, and infants and to defend why each number matters.
Rate, depth, and recoil
Compress the adult chest at a rate of 100 to 120 compressions per minute. Push at least 2 inches (5 cm) deep but no more than 2.4 inches (6 cm) — too shallow does not generate perfusion, too deep injures the chest. For a child, compress at least one-third the depth of the chest, about 2 inches (5 cm); for an infant, at least one-third the depth of the chest, about 1.5 inches (4 cm). After every compression, allow complete chest recoil — let the chest return fully to its resting position without leaning on it, because incomplete recoil raises intrathoracic pressure and reduces the blood that refills the heart between compressions.
Minimize interruptions and hand placement
Every pause in compressions drops coronary and cerebral perfusion, so keep interruptions to less than 10 seconds and aim for a chest compression fraction (the percentage of arrest time spent actually compressing) of at least 60%. For adults and children, place the heel of one hand (two hands for adults) on the lower half of the sternum. For a lone rescuer with an infant, use two fingers on the center of the chest just below the nipple line; with two rescuers, use the two-thumb encircling-hands technique, which produces better depth and blood pressure.
Compression-to-ventilation ratios
A single rescuer uses a 30:2 ratio (30 compressions to 2 breaths) for adults, children, and infants. When two rescuers care for a child or infant, switch to a 15:2 ratio so ventilation is delivered more often, reflecting that pediatric arrest is frequently respiratory in origin. Once an advanced airway is placed, rescuers no longer pause for breaths: they give continuous compressions and one breath every 6 seconds. Rotate the compressor about every 2 minutes (every 5 cycles of 30:2) to prevent fatigue-related shallowing, and make the switch in under 5 seconds.