Which of these best describes the purpose for hands-only CPR? The purpose is to keep oxygenated blood circulating to the brain and heart after sudden cardiac arrest by delivering continuous chest compressions without rescue breaths, buying time until an AED or EMS arrives. Hands-only CPR (also called compression-only CPR) exists to remove barriers to bystander action: it is simpler to learn, safer to perform on strangers, and shown in randomized trials to produce survival outcomes comparable to conventional CPR for adult out-of-hospital cardiac arrest of cardiac origin (Svensson et al., NEJM 2010; Rea et al., NEJM 2010).
That single purpose statement answers the test question, but the mechanism, the numbers, and the boundaries of that claim are where most short explainers fall apart. This article works through why compressions alone can sustain a brain, what the trial data actually show, when hands-only is the wrong choice, and how bystanders should act in the first 60 seconds.
The circulatory mechanism behind compression-only CPR
During sudden cardiac arrest, the heart stops pumping, but the blood in the chest and lungs remains oxygenated for a short window. Chest compressions work as a manual pump. Pushing the sternum down about 2 inches (5 cm) compresses the heart between the sternum and spine and squeezes blood out into the aorta and pulmonary artery. Releasing the chest lets it recoil and refill. At 100 to 120 compressions per minute, that cycle generates a fraction of normal cardiac output, typically cited as roughly 20 to 30 percent, but that fraction is enough to keep brain tissue perfused.
The key physiologic detail is the "no-flow" time. Brain tissue begins to suffer irreversible injury after roughly 4 to 6 minutes without circulation at normal body temperature. Every minute of delay before compressions begin reduces survival by an estimated 7 to 10 percent in out-of-hospital cardiac arrest. Hands-only CPR does not restart the heart; defibrillation does that. Its job is to slow the decay of the brain and heart muscle until a shock can be delivered.
Rescue breaths matter most when the blood is already deoxygenated, as in drowning, suffocation, or pediatric arrest, where the arrest is caused by hypoxia rather than a primary electrical failure. In a primary cardiac arrest, the blood is still oxygenated at the moment of collapse, so circulating it takes priority over adding more oxygen. That is the physiologic logic behind the compression-only recommendation for witnessed adult collapse.
Put plainly: hands-only CPR is a bridge, not a cure. It keeps the brain alive long enough for a defibrillator to do the real work.
What the trial evidence shows, and what it does not
The strongest evidence for hands-only CPR comes from two randomized trials published in the New England Journal of Medicine in 2010. In the Swedish trial (Svensson et al.), dispatcher-assisted compression-only CPR produced a 30-day survival of 8.7 percent versus 7.0 percent for standard CPR, a difference that did not reach statistical significance but met the criteria for non-inferiority. In the Washington-state trial (Rea et al.), survival to hospital discharge was 12.5 percent with compression-only versus 11.0 percent with conventional CPR, again statistically comparable.
| CPR approach | Typical survival (adult OHCA, cardiac cause) | When it is preferred |
|---|---|---|
| Hands-only (compression-only) | Roughly 8–13 percent in the major trials | Witnessed adult collapse, untrained or reluctant bystander |
| Conventional (30:2 compressions:breaths) | Roughly 7–11 percent in the same trials | Hypoxic arrest, pediatric arrest, trained provider |
| High-performance CPR with team + AED | Higher in systems with strong response chains | In-hospital and optimized EMS systems |
| Compression-only with dispatcher coaching | Comparable to conventional in trials | Phone-guided bystander response |
The caveats matter. These trials enrolled adults with out-of-hospital cardiac arrest, most of cardiac origin, and they compared dispatcher-coached bystanders, not trained professionals. The evidence does not establish that hands-only CPR is superior; it establishes that it is not meaningfully worse for that population and is far more likely to be attempted. A 2010 meta-analysis in the Journal of the American Medical Association reached a similar conclusion: compression-only CPR was associated with outcomes comparable to conventional CPR for adult cardiac arrest, with a possible advantage for compression-only in the subgroup of arrests of cardiac origin.
The counterintuitive detail: hands-only CPR may actually be better than conventional CPR in one specific way: it eliminates interruptions. Every pause to deliver breaths drops the perfusion pressure that compressions built up, and it takes several compressions to rebuild it. Continuous compressions keep the coronary perfusion pressure higher, which is one reason some systems now coach bystanders to skip breaths entirely.
Time course: what happens minute by minute
The timeline below reflects the general physiology of untreated sudden cardiac arrest; individual outcomes vary widely and depend on the cause, the patient, and the response chain.
| Time after collapse | Physiologic state | Best action |
|---|---|---|
| 0–30 seconds | Blood still oxygenated; brain conscious briefly | Recognize arrest, call 911, start compressions |
| 1–4 minutes | Oxygen reserves depleting; brain at risk | Continuous compressions; retrieve AED |
| 4–6 minutes | Brain injury threshold approaching | Compressions plus AED if available |
| 6–10 minutes | Brain injury increasingly likely without flow | Sustained CPR; EMS arrival critical |
| 10+ minutes | Survival without circulation becomes rare | Continue CPR until defibrillation or termination |
| Post-ROSC | Return of spontaneous circulation | Advanced care, targeted temperature management |
The practical takeaway from the timeline is that the first 4 minutes are the highest-leverage window, and that window belongs to bystanders, not EMS. Median EMS response time in urban areas is often 6 to 8 minutes; in rural areas it can exceed 15. Hands-only CPR is designed to fill that gap.
Red flags and edge cases where hands-only is wrong
Drowning, suffocation, or smoke inhalation: the arrest is hypoxic, so rescue breaths are needed in addition to compressions. Pediatric arrest: children and infants usually arrest from respiratory causes, so conventional CPR with breaths is recommended. Opioid overdose: the arrest is respiratory first; naloxone and rescue breaths take priority. Unresponsive but breathing normally: do not start compressions; this may be a seizure, syncope, or another non-arrest event, and compressions on a beating heart can cause harm. Do not delay compressions to search for a pulse if you are untrained; agonal gasps are not normal breathing and should be treated as arrest.
The professional caveat: hands-only CPR is a bystander strategy, not a universal standard. Professional rescuers and trained teams still deliver ventilations, and modern EMS protocols emphasize high-quality compressions with minimal interruptions plus early defibrillation. The purpose of hands-only CPR is to widen the pool of people willing and able to act, not to replace the full resuscitation bundle.
Practical actions: the first 60 seconds
Check responsiveness and breathing. Tap the person and shout. If there is no normal breathing (gasping does not count), assume cardiac arrest. Call 911 immediately and put the phone on speaker. The dispatcher can coach compressions in real time. Start compressions. Place the heel of one hand on the center of the chest, the other hand on top, and push hard and fast: at least 2 inches deep at 100 to 120 per minute. Allow full recoil between compressions and minimize interruptions. Switch rescuers every 2 minutes if another person is available. Use an AED as soon as one is retrieved. Turn it on and follow the voice prompts; do not stop compressions until the AED instructs you to. Continue until EMS arrives, the person shows signs of life, or you are physically unable to continue.
The reconciliation of thresholds: the compression rate of 100 to 120 per minute and depth of at least 2 inches are the American Heart Association bystander standards; depth beyond about 2.4 inches increases injury risk without clear benefit. The 30:2 ratio applies to conventional CPR, not hands-only. If you are untrained and alone, compressions only are the correct choice.
Limitations and what the evidence cannot settle
Hands-only CPR has real limits. It does not address hypoxia, so it is the wrong tool for drowning, pediatric, and overdose arrests. It cannot restart a heart; only defibrillation and advanced care can. Survival rates even with perfect bystander CPR remain low, typically in the single digits to low teens for out-of-hospital cardiac arrest, because outcome depends on the entire chain of survival: recognition, early CPR, early defibrillation, advanced care, and post-arrest treatment. The trials that support hands-only CPR were conducted in specific EMS systems and may not generalize to every setting. And no trial has shown hands-only CPR to be clearly superior to conventional CPR in trained hands; the case for it rests on comparable outcomes plus dramatically higher bystander uptake.
The honest summary: hands-only CPR is best described as a barrier-reducing, perfusion-preserving bridge for adult cardiac arrest, and the correct answer to the test question is that it circulates oxygenated blood without breaths until help arrives.
This article is general educational information, not a diagnosis, treatment plan, or substitute for certified CPR training. For a real emergency, call your local emergency number immediately and follow dispatcher instructions; take a hands-on CPR and AED course from a qualified local provider to prepare.