Pediatric thoracic trauma has unique features that differentiate it from adult thoracic trauma. Biomechanically, the smaller body mass of a child results in greater forces applied per unit of body area on traumatic impact. In addition, the force is applied to a body that has less fat, less elastic connective tissue, and closer proximity of vital organs, especially in the thorax. The blood volume of a pediatric patient is typically 7-8% of the total body weight. Thus, a relative small blood volume loss can lead to hypovolemia and shock.
Compliance of the pediatric thorax is much greater than that of the adult thorax, because of the pliability of the cartilage and bony structure. As such, the chest can absorb a large amount of kinetic energy from the impact, which is subsequently transferred to the intrathoracic structures. Often, the child has major intrathoracic injury with minimal or no injury to the structure of the chest. Rib fractures are rare and indicate a direct blow to the chest and extreme force.
Children often experience aerophagia and gastric distention, causing elevation of the diaphragm and severe compromise of vital capacity. In infants and young children, this can predispose to the sudden development of apnea when fatigued.
As a result of the proportionately smaller size of the chest compared with the abdomen or head in a young child, significant thoracic trauma is almost always accompanied by injury to other organ systems. Thus, thoracic injury is most appropriately defined as multisystemic injury. Multisystem injury is associated with increased mortality.