2.2 Compressions: Rate, Depth, Recoil, and Interruptions

2.2 Compressions: Rate, Depth, Recoil, and Interruptions

Chest compressions are the single most tested BLS skill because they generate the artificial circulation that keeps the brain and heart viable until a perfusing rhythm returns. The current AHA Guidelines define high-quality CPR by five measurable components. Memorize the exact numbers; exam items frequently swap one digit to create a wrong answer.

The five components of high-quality adult CPR

Rate: 100-120, not faster

The goal is 100 to 120 compressions per minute. A common misconception is that faster is always better. In fact, rates above 120 are linked to incomplete recoil and shallower depth because the rescuer cannot fully release and re-load the chest. Familiar cadence anchors include the songs "Stayin' Alive" (~103 bpm) and "Baby Shark." Hand placement is the heel of one hand on the lower half of the sternum (center of the chest) with the second hand on top, fingers interlaced, elbows locked, and shoulders directly over the hands so the rescuer pushes with body weight rather than arm strength.

Depth: a precise window of 5-6 cm

Adult depth is at least 2 inches (5 cm) and should not exceed 2.4 inches (6 cm). This is one of the most frequently mis-remembered facts: the answer is a window, not just a floor. Compressions shallower than 5 cm fail to squeeze enough blood from the heart; compressions deeper than 6 cm increase the risk of injury (rib fractures, organ trauma) without improving outcomes. On a firm surface (backboard or floor) the rescuer can judge depth more reliably; a soft mattress absorbs force and produces false shallow compressions.

Recoil: do not lean

Complete chest recoil means letting the chest return fully to its resting position after each compression without lifting the hands off the sternum. The chest acts like a bellows: during recoil, negative intrathoracic pressure draws blood back into the heart (venous return), which refills the ventricles for the next compression. Leaning on the chest between compressions is a classic quality killer because it traps the heart in a partially compressed state and cuts cardiac output. Coaching cue: "hands stay on, weight comes off."

Interruptions and chest compression fraction

Every pause in compressions drops the coronary perfusion pressure toward zero, and it takes many compressions to rebuild it. Therefore the team minimizes interruptions and keeps any necessary pause (rhythm check, shock, pulse check, airway placement) under 10 seconds. The summary metric is the chest compression fraction (CCF): the proportion of the resuscitation time that hands are actually on the chest. Target at least 60%, and high-performing teams exceed 80%.

To protect CCF, the team plans the next task before the pause begins, charges the defibrillator while compressions continue, and resumes compressions immediately after a shock.

Compressor rotation

Switch compressors every 2 minutes (about every 5 cycles of 30:2) to prevent fatigue, which silently degrades rate, depth, and recoil within 1-2 minutes even when the rescuer feels fine. Time the switch to coincide with a rhythm check so the swap costs no extra pause (target under 5 seconds).

Common traps

• Counting fast compressions as good CPR even when depth is poor.
• Forgetting the upper depth limit (6 cm) and only recalling "at least 2 inches."
• Leaning between compressions, killing recoil.
• Letting rhythm and pulse checks stretch past 10 seconds.

Putting it together: the quality coach role

In a team resuscitation, one member often serves as a CPR quality coach who watches only the compressions and gives real-time corrections: push faster, push deeper, let it recoil, switch in 10 seconds. Modern manikins and many real defibrillators provide audiovisual feedback (a metronome, depth bar, and recoil indicator), and AHA guidance endorses using such feedback devices to keep rate and depth in range, because rescuers reliably overestimate their own depth and drift on rate.

End-tidal carbon dioxide (ETCO2) monitoring through an advanced airway is another quality signal: a sudden rise in ETCO2 can indicate return of spontaneous circulation, while a persistently low ETCO2 (under about 10 mm Hg) suggests compressions are not generating adequate output and should prompt a check of technique. ** Every other compression fact on the exam is a variation or distractor built around those five numbers, so anchoring them precisely is the highest-yield study action for this chapter.

The High-Quality CPR Metrics, Stated Exactly

The exam treats high-quality chest compressions as a set of precise, memorizable numbers, and nearly every compression question is a variation on these five metrics. Memorize them as numbers, not as ranges you can fudge.

The rate window of 100–120/min is the single most-tested figure. A rate faster than 120 is a classic distractor — it sounds aggressive and helpful, but pushing too fast prevents the chest from re-expanding and the rescuer rarely reaches full depth. The depth window is the second anchor: ≥ 2 inches (5 cm) and ≤ 2.4 inches (6 cm) for an adult. Questions love to offer "as deep as possible" as a wrong answer — depth has a defined ceiling.

Full Recoil and the Leaning Trap

After each compression the rescuer must allow the chest to fully re-expand (complete recoil) before the next downstroke. Failing to do so — typically by leaning on the chest between compressions — is a graded skills-test fault. The physiology is the point: the heart refills during the recoil phase, so incomplete recoil keeps intrathoracic pressure elevated, impedes venous return, and reduces the volume available for the next compression. A common exam stem describes a rescuer who is fast and deep but leaning, and the correct critique is "allow full chest recoil," not "compress harder."

Chest Compression Fraction and Minimizing Interruptions

Chest compression fraction (CCF) is the fraction of total resuscitation time during which compressions are actually being delivered. AHA sets a floor of ≥ 60% and an ideal of > 80%. Every interruption — for rhythm checks, intubation, pulse checks, or charging the defibrillator — lowers CCF and is therefore minimized.

The hard rule is that interruptions should be kept to under 10 seconds, and the pre-shock pause (the gap between stopping compressions and delivering the shock) should be as short as possible because perfusion pressure decays quickly when hands come off the chest and must be rebuilt over many subsequent compressions.

The Underlying Physiology

These numbers exist to maximize coronary perfusion pressure (which determines myocardial blood flow and the chance of return of spontaneous circulation) and cerebral perfusion pressure (which protects the brain). Compressions generate forward flow; pauses and incomplete recoil let that pressure collapse.

End-tidal CO2 (ETCO2) is the bedside proxy — a persistently low ETCO2 (roughly under 10 mm Hg) suggests compressions are not generating adequate output and should prompt a check of technique, while a sudden rise often signals return of spontaneous circulation. Every other compression fact on the exam is a variation or distractor built around the five core numbers, so anchoring them precisely — rate 100–120, depth 5–6 cm, full recoil, CCF ≥ 60% (ideal > 80%), interruptions < 10 sec — is the highest-yield study action for this chapter.