Mouth-to-mouth (MTM) rescue breaths are a fundamental part of conventional Cardiopulmonary Resuscitation (CPR), used to maintain oxygenation and circulation when a person’s heart or breathing has stopped. Modern resuscitation guidelines, primarily from organizations like the American Heart Association (AHA), distinguish recommendations based on the cause of the emergency. This clarifies when MTM is an optional component of CPR and when it becomes a necessary intervention. Understanding the specific clinical context—whether the emergency stems from a heart problem or a breathing problem—is the key to knowing the correct time to provide rescue breaths.
Context: When Compressions Alone Are Recommended
For an adult experiencing a sudden, unwitnessed collapse outside of a hospital, the standard protocol for an untrained bystander is to perform hands-only CPR, which involves continuous chest compressions without rescue breaths. This approach is recommended because the immediate cause of collapse is most often a primary cardiac event, such as a heart attack or ventricular fibrillation. In these cases, the person’s blood typically retains enough residual oxygen to sustain the brain and vital organs for the first few minutes after the heart stops pumping.
The priority action is to circulate this remaining oxygenated blood by pushing hard and fast in the center of the chest at a rate of 100 to 120 compressions per minute. Minimizing interruptions to chest compressions is paramount, as pausing to give breaths can decrease the effectiveness of blood flow. Hands-only CPR is simpler for lay rescuers to perform, which encourages more people to intervene quickly. Studies have shown that compression-only CPR can be effective in the initial minutes of a sudden cardiac arrest until professional help arrives.
Mandatory Indications for Respiratory Emergencies
The indication for MTM rescue breaths shifts to mandatory when the underlying cause of the collapse is a failure of the respiratory system, leading to an acute lack of oxygen. In these asphyxial arrests, the blood is rapidly depleted of oxygen before the heart stops, meaning chest compressions alone would only circulate deoxygenated blood. Therefore, providing oxygen via rescue breaths is the immediate priority to prevent irreversible damage.
One scenario is near-drowning, where the victim’s lungs are filled with water, causing rapid and severe oxygen deprivation. For a drowning victim, the rescuer should begin with two rescue breaths immediately, even before starting chest compressions, if the person is unresponsive and not breathing normally.
In cases of opioid overdose, the drug suppresses the central nervous system, causing breathing to slow down and eventually stop entirely. The victim is dying from a lack of oxygen before cardiac arrest occurs, and rescue breathing—one breath every five to six seconds—is the most effective way to prevent the heart from stopping.
Other situations demanding immediate ventilation include suffocation or choking, once the airway obstruction has been successfully cleared, and exposure to toxic gas, such as carbon monoxide. In these instances, the primary problem is a lack of oxygen transfer into the bloodstream, not a sudden electrical failure of the heart. For trained rescuers, the standard conventional CPR ratio of 30 compressions alternating with two rescue breaths is recommended for these respiratory-driven arrests to simultaneously restore oxygenation and circulation.
Age-Based Indications: Infants and Children
The indication for mouth-to-mouth (or mouth-to-mouth-and-nose for infants) rescue breaths is mandatory for infants and children experiencing cardiac arrest, regardless of the bystander’s training level. This is because pediatric cardiac arrests are overwhelmingly secondary to respiratory failure, not primary heart problems like those seen in adults. Common causes include respiratory illnesses, choking, severe trauma, or Sudden Infant Death Syndrome (SIDS).
Because the issue is nearly always a lack of oxygen, the resuscitation protocol for this age group mandates the inclusion of rescue breaths from the very beginning. For a lone rescuer, the recommended ratio is 30 chest compressions followed by two rescue breaths, while a two-rescuer team typically uses a ratio of 15 compressions to two breaths to deliver more frequent ventilation. An infant is defined as a child under the age of one, and a child is typically defined as one to the onset of puberty.
Rescuers should ensure a proper seal and deliver only a small puff of air for infants or a gentle breath for children, watching for the chest to rise, to prevent injury to the smaller lungs. The emphasis on early and effective ventilation for these younger patients reflects the physiological reality that their hearts are generally healthy but stop beating because of severe and prolonged oxygen starvation. This age-based distinction ensures that the most effective intervention for the most likely cause of their collapse is performed immediately.