Damian Mc Cormack, M.Ch., F.R.C.S.I., F.R.C.S.(Orth).
Mechanisms of Injury.
Injury to the child may be primary, with direct cellular damage and anatomical disruption, and secondary, from anoxia, hypothermia, impaired perfusion and metabolic upset. The primary injury may be blunt or penetrating. The degree of primary traumatic injury is dependent on several physical laws;
Thus the degree of injury is proportional to the mass of the child or the colliding object, the speed of the child or colliding object, the rate of change of velocity and the focality or diffusion of the transfer of kinetic energy to the body. The response of the body to a collision depends on the tensile strength of the tissues, their elasticity and their compressive strength. High compression, low velocity collision constitutes a crush injury. Low compression but high velocity constitutes a blast injury. Intermediate compression and velocities can produce a variety of visceral injuries. Tissue elasticity is greater in children but tensile and compressive strengths are less that in adults. Shearing injuries are common in children. For instance, the elasticity of the chest wall allows easier transfer of energy to the viscera without rib fracture. Lung contusions are common. Visceral tears and contusions are common. Bowel and vessel disruption and renal injury should be suspected following blunt injury, even in the absence of local fractures.
The different injury mechanisms involved in penetrating trauma should also be recognized. A stab wound may be deceptively small. The potential for injury depends on the anatomical vulnerability of the area and the specific vulnerability of specific areas, such as the neck. Gunshot wounds in children are also occasionally seen. Factors such as bullet type and caliber, impact velocity and range all contribute to the temporary and permanent cavitation which result. Therefore a first step in the assessment of an injured child is an understanding of the injury mechanism and a heightened suspicion for associated injuries.
Special Vulnerability in Children.
The child's head is relatively large, with a thin scalp and delicate epidural vessels. Small epidural venous bleeds are common following blunt head trauma but subdural bleeds are uncommon. The child's brain lacks myelin and the soft cranium allows more movement. These factors reportedly contribute to the coup contrecoup injury mechanism. Most mandible fractures in children involve the condyle whereas the body or angle is vulnerable in adults. Mandibular condyle fractures should be suspected in the presence of a head injury, facial lacerations and a haemotympanum.
The spine is vulnerable in children for several reasons. The large head and relatively weak neck muscles, the flatter facets in the upper cervical spine and ligamentous laxity increase the risk of cervical subluxation. The large head causes the cervical spine to flex when placed on a flat " adult" spine board and therefore care must be taken to avoid this during transport and resuscitation. Some 80% of paediatric cervical injuries occur, and are unstable, in flexion. Only 20% occur in extension. The spine obtains adult characteristics at age 8 years.
The airway is vulnerable because of the relatively large tongue which may easily obstruct the pharynx. The pliable soft tissues are vulnerable to edema. Because the resistance to airflow is proportional to the fourth power of the radius of the airway, hypoxia can rapidly intervene secondary to airway oedema. The larynx is more superior and anterior making more difficult. The thin tissues of the oropharynx and trachea may be more easily injured initially and during attempted intubation.
The chest wall is more compliant and therefore significant energy is transferred to the viscera with few or no rib fractures. Rib fractures therefore imply that a very significant force was involved and the chances of visceral damage are much greater. Similarly the scapula and transverse processes of the thoracic vertebrae are well protected, but if fractured imply life threatening force was involved.
A tension pneumothorax in a child is poorly tolerated, probably because of the elasticity in the mediastinal structures. Severe myocardial contusion and even right atrial rupture with tamponade can occur in high energy trauma.
The abdominal contents are more vulnerable to rupture in a child. The frequency of injury is greater in the kidney, then spleen, liver, pancreas and finally bowel. Usually left sided diaphragm rupture may occur. The liver may absorb the energy on the right side.
Musculo skeletal injuries in children differ for obvious reasons. The thicker periosteum and greater elasticity of bone and the presence of open physes changes the type and management of these injuries.
The relatively large surface area of a child and the lack of ability to shiver has consequences for thermoregulation. Hypothermia is poorly tolerated and can lead to hypoxia, errhythmias and metabolic acidosis. Finally the child is relatively vulnerable because of the psychological effects of trauma. Parental separation is poorly tolerated in the younger child. Children under age 7 may perceive surgical interventions as some form of punishment and require special explanations.
Initial Critical Care Of The Injured Child.
The principles of "ATLS" apply and will not be reiterated in detail. However specific practical aspects of management are discussed.
Airway and cervical spine control
A paediatric spinal board with a recess for the large head should be used. Sand bag and tape are added if a suitable collar is not available. Anyone with a significant injury should be assumed to have a cervical injury until proven otherwise. Some specific indications for spinal immobilization are listed below.
The indications for spinal immobilization are:
· High speed R.T.A.
The principles of airway management are similar to those in the adult. However oesophageal obturator airways are not used in children. In children under 8 years uncuffed endotracheal tubes only should be used.
The indications for endotracheal intubation are:
· Cardiopulmonary arrest
Endotracheal tube size can be calculated by the formula;
An N G tube is necessary after endotracheal intubation because of inevitable gastric distension. An Orogastric tube is placed in the presence of significant facial trauma (possible cribriform plate fracture).
In the event that endotracheal intubation fails a cricothyroidotomy is necessary. A 12 or 14 gauge angiocatheter with a 10 ml syringe is advanced in the midline at the crico thyroid space aiming 450 caudally until air is aspirated. The needle is withdrawn and catheter left in situ for temporary ventilation.
Cervical spine evaluation.
Radiographs of the neck ( lateral film C1 to T1), chest and pelvis are mandatory in the critically injured child.
The following are upper limit guidelines to cervical spine measurements.
The child must be kept warm. His/ her weight in Kg's should be assessed because all drugs and fluids are given " per kg body weight".
Shock is not defined by a specific blood pressure but by impaired tissue perfusion and hypoxia. Most children have a systolic pressure above 80 mmHg. The neonate may have a systolic pressure of 60 mmHg. A fall in blood pressure is a late sign in a shocked child. A rise in diastolic pressure may occur due to vasoconstriction and thus be a sign of ongoing deterioration.
An increase in heart rate is the first sign of circulatory compromise in the child. Up to 25% of blood volume may be lost before any signs of shock appear. Normal nail bed capillary refill time should be less than 2 seconds. A delay beyond 4 seconds in a warm child implies volume loss. Altered mental state and reduced urine output indicate reduced end organ perfusion.
A urine output of 1 ml per Kg per hour indicated adequate renal perfusion.
Normal paediatric vital signs are as follows:
Obtaining vascular access is critical and best achieved with large bore catheters in peripheral veins. Intra osseous infusion in the proximal tibia or distal femur is an acceptable alternative. Blood drawn from the bone can be sent for group and cross match, haematocrit estimation and culture.
The child's total blood volume is about 80 mls /kg or about 8% of body weight. Thus a 10 kg child has a blood volume of only 800 mls. An initial bolus of 20mls/kg of (warm) normal saline or other isotonic crystalloid solution should be given rapidly. This is repeated a second and a third time if necessary until a response is seen in the vital signs. If there is no response after the first two fluid challenges then packed cell transfusion is performed as below. The infusion is continued to "keep vein open".
As a rule replace 1 ml of lost blood with 3 mls of crystalloid.
Whole blood may be given at a rate of 20 mls/kg or Packed RBC's at 10 mls/kg. After every 4 units of blood (during massive transfusion) consider giving;
1 unit of plasma (FFP) at 20 mls/kg,
If more that 50% of the child's blood volume has been replaces an exploratory laparotomy is probably indicated to find the bleeding source. Obviously the presence of long bone fractures and in particular a pelvic fracture may affect this decision. Fractures should be quickly reduced and splinted. The pelvis must be clinically and radiologically assessed. Care should be taken not to loosen or remove trousers or belts before the pelvis is checked and
resuscitation fluids are running. A pneumothorax and cardiac tamponade should be outruled.
The simplest assessment is in terms of "A.V.P.U.", the child being alert, responsive to verbal commands, responsive to pain or unresponsive. The Glasgow Coma Scale has been modified for younger children:
Eye opening response:
The Monroe Kelly hypothesis states that the total volume of the intra cranial contents, Vt, is equal to the sum of its contents;
Vt = Vcsf + V blood + V brain.
Initially after a head injury, with brain swelling or bleeding, the CSF is displaced from the skull. Thereafter a slight increase in volume of one or the other produces rapid increases in pressure. As intracranial pressure approaches blood pressure, cerebral blood flow diminishes and irreversible damage occurs within 3 minutes. Swelling can occur in the brain as a result of extensive peripheral tissue injury and hypoxia, without direct head trauma.
Care therefore must be taken not to over infuse critically injured children because of the risk of cerebral oedema.
Patients with a Glasgow Coma Score of 8 or less are candidates for intracranial pressure monitoring. Those with a G.C.S score greater than 8 may also be candidates if they have large areas of parenchymal disruption, severe impact injuries and multiple contusions or visceral haemorrhage, subdural haematomas or superimposed hypoxia or shock. In the head injured child adequate oxygenation is essential and if necessary administration of Sodium Thiopental, 2 4 mg/kg , is administered to facilitate intubation and hyperventilation. Glucose delivery to the brain is essential because the child has limited glycogen reserve and hypoglycemia must be avoided.
Intracranial pressures are reduced with a combination of fluid restriction, osmotic diuretics such as mannitol, elevation of the head up to 30 degrees from horizontal in the monitored patient, sedation and analgesia and hyperventilation.
Acute care of the injured child differs from that of the adult. Although the principles are the same, with attention to the A,B,C's of resuscitation, the details are different. The specific vulnerabilities of the child when exposed to trauma must be remembered. A high index of suspicion for soft tissue and spinal injury is necessary. The smaller blood volume makes fluid replacement a more exact procedure. The child's sensitivity to hypothermia and the dangers of raised intracranial pressure must be addressed. The skeletal injuries specific to children are described elsewhere. Although it is the skeletal injury which is of most interest to the orthopaedic surgeon, the correct execution of acute paediatric trauma care is a responsibility we share.
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