When an adult collapses from sudden cardiac arrest, the root cause is most often an electrical malfunction of the heart, such as ventricular fibrillation. This primary heart problem means the organ suddenly stops pumping effectively, which is why immediate chest compressions are the priority for bystander rescue. In sharp contrast, cardiac arrest in infants and children is rarely a primary heart issue. Instead, it is overwhelmingly the final step in a progression of respiratory failure and a profound lack of oxygen, known as asphyxial arrest. This fundamental difference in cause is why providing breaths is a uniquely important and immediate action when resuscitating a child.
Respiratory Failure as the Precursor to Cardiac Arrest
In the pediatric population, the heart is typically healthy. The sequence of events leading to cardiac arrest usually begins with a respiratory insult, such as severe asthma, choking, drowning, or an overwhelming infection like pneumonia. These conditions prevent the child from taking in enough oxygen, leading to low oxygen in the blood (hypoxemia). This oxygen deprivation then causes the body’s tissues to become starved, resulting in profound tissue hypoxia.
The heart initially attempts to compensate for the lack of oxygen by beating faster, a state called tachycardia, but this compensation is quickly overcome. As the oxygen levels continue to drop, the heart muscle itself begins to suffer from the lack of fuel. The heart rate then dramatically slows down, a condition known as bradycardia, which serves as a major warning sign of impending cardiac collapse in children.
If the respiratory problem is not corrected and oxygen is not restored, the heart muscle weakens under hypoxic stress and eventually becomes too weak to sustain an effective rhythm. The heart’s electrical activity may continue for a short period, but without the mechanical strength to pump, the child enters cardiac arrest, typically presenting with asystole or pulseless electrical activity. Since the cardiac arrest is a consequence of the breathing problem, reversing the respiratory failure is the only way to effectively reverse the cardiac arrest.
Physiological Differences in Oxygen Reserve and Metabolism
Children are less tolerant of oxygen deprivation compared to adults, explaining the urgency of providing breaths during a rescue. One reason for this rapid decline is the infant and young child’s significantly higher metabolic rate. They consume oxygen at roughly double the adult rate relative to their body weight, meaning their limited oxygen stores are depleted much faster. This increased consumption rate shortens the time available before organ damage begins.
Young children possess a much smaller functional residual capacity (FRC), the volume of air remaining in the lungs after a normal breath. This FRC acts as the body’s oxygen reserve tank. In an infant, this reserve is proportionally much smaller, holding an estimated 18 milliliters per kilogram of body weight compared to about 70 milliliters per kilogram in an adult. With a smaller reserve and a higher metabolic rate, a child can progress from adequate oxygenation to severe hypoxia in mere minutes.
The brain is particularly vulnerable to this rapid oxygen depletion. It is proportionally larger and demands a disproportionately high amount of the body’s total oxygen supply at rest. Even a brief period of oxygen starvation can cause irreversible damage. The combination of high oxygen demand and low oxygen reserve means the window for intervention is extremely narrow before neurological injury occurs.
The Immediate Goal of Ventilation During Pediatric Resuscitation
In a cardiac arrest caused by a lack of oxygen, chest compressions alone are significantly less effective because the blood being circulated is already severely deoxygenated. Compressing the chest only moves this “stale” blood around the body without adding the necessary oxygen to sustain life. Therefore, the immediate goal of rescue breathing is to re-oxygenate the blood within the lungs.
By providing effective ventilation, the rescuer is essentially reloading the circulatory system with fresh, oxygen-rich blood. This oxygenated blood is then distributed by the chest compressions to the body’s most sensitive organs, particularly the brain and the heart muscle. The heart muscle requires this oxygenated blood to regain the strength and electrical stability needed to restart its own pumping action.
This physiological necessity is reflected in resuscitation guidelines, which emphasize ventilation from the very beginning. For a lone rescuer performing cardiopulmonary resuscitation (CPR) on a child, the protocol involves a 30 compressions to 2 breaths ratio. A two-rescuer team uses a 15 compressions to 2 breaths ratio. The initial breaths are designed to quickly reverse the underlying hypoxia, giving the heart the fuel it needs to respond to chest compressions and potentially restoring a perfusing rhythm.