Cardiac arrest in infants and children is a devastating event that requires immediate and specific intervention to ensure the best chance of survival and neurological recovery. Unlike in adults, where the heart often stops due to a sudden electrical problem, a child’s heart typically fails as a secondary consequence of a lack of oxygen. For this reason, the administration of rescue breaths, or ventilation, is paramount in pediatric resuscitation, serving as the foundational step to reverse the underlying physiological crisis.
The Primary Role of Respiratory Failure
In most adult cases, the heart stops due to a primary electrical malfunction, such as ventricular fibrillation. A child, however, usually experiences an asphyxial arrest, meaning the heart stops only after a prolonged period of respiratory distress or failure.
This respiratory failure can result from a variety of common pediatric emergencies, including severe infections like pneumonia or bronchiolitis, airway obstruction from choking, or traumatic injuries. These conditions initially lead to a drop in blood oxygen levels, a state known as hypoxia, and a buildup of carbon dioxide. The heart muscle, which is generally healthy in a child, is simply starved of the oxygen it needs to function.
Oxygen deprivation causes a progressive slowing of the heart rate, termed bradycardia, which leads to a critical drop in blood pressure. Cardiac arrest, where the heart loses its ability to pump blood effectively, is the final stage of this sequence that began with a breathing problem. Respiratory etiologies account for a large majority of pediatric cardiac arrests, making the immediate delivery of oxygen through rescue breaths the most direct way to treat the root cause.
While chest compressions are necessary to circulate blood, they are ineffective if the blood contains almost no oxygen. The resuscitation effort must first address the oxygen deficit before circulation can be meaningful. This focus on ventilation contrasts sharply with the strategy for adult cardiac arrest, which emphasizes immediate chest compressions to circulate existing oxygenated blood.
The Speed of Hypoxic Damage in Children
Children’s bodies are physiologically less tolerant of oxygen deprivation than adult bodies, which means the window for successful intervention is significantly shorter. This vulnerability is partly due to their higher metabolic rate, meaning the rate at which the body consumes oxygen. A higher metabolic rate means oxygen stores are depleted much more quickly when breathing stops, shortening the window for successful intervention.
Another contributing factor is their smaller functional residual capacity (FRC), the volume of air remaining in the lungs after a normal exhale. This smaller reservoir of oxygen-rich air, combined with a more pliable rib cage, causes a child to desaturate and become critically hypoxic much faster than an adult. When breathing stops, this small oxygen reserve is rapidly consumed, accelerating the progression toward cardiac arrest and irreversible organ damage.
Once oxygen levels drop, the body switches to anaerobic metabolism, which produces a rapid buildup of waste products, primarily lactic acid. This severe increase in acidity in the blood and tissues is called metabolic acidosis. Acidosis is particularly damaging because it directly impairs the function of the heart muscle (myocardium) and the brain.
The acidic environment weakens the heart’s ability to contract effectively and significantly reduces its responsiveness to catecholamines, the stimulating hormones used during resuscitation. This creates a vicious cycle where acidosis further cripples the heart, making it harder to restart. Because of this rapid physiological decline, irreversible brain damage can begin within just five to ten minutes following a complete lack of oxygen.
Oxygenating the Blood to Support the Heart
Rescue breaths reintroduce oxygen into the bloodstream, reversing the physiological cascade that led to the heart stopping. Chest compressions alone circulate unoxygenated blood, which cannot sustain the brain or heart muscle. Ventilation is required to “prime” the blood with oxygen so that subsequent compressions deliver life-sustaining components to vital organs.
The oxygen delivered through rescue breaths addresses the critical state of hypoxia, which is the primary insult to the child’s system. By replenishing oxygen, the body can shift away from damaging anaerobic metabolism. This allows the heart muscle to regain the necessary resources to contract forcefully and respond to resuscitation efforts.
Ventilation plays a role in managing the severe acidosis that develops during arrest. The buildup of carbon dioxide ($CO_2$) is a major component of this acid load. Effective rescue breaths eliminate excess $CO_2$ from the lungs and the blood. This process creates a hypocarbic (low $CO_2$) state in the arteries, which helps to neutralize the overall acidemia.
The reversal of acidosis is necessary for medications and the heart’s electrical system to function properly. The improved acid-base balance enhances the heart’s contractility and its sensitivity to adrenaline. Rescue breaths are a direct therapeutic intervention that counteracts the two most dangerous physiological consequences of pediatric cardiac arrest: hypoxia and profound acidosis.