Basic Science and Pathophysiology
There are certain anatomical, physiological and developmental differences between adults and children that influence paediatric toxicological presentations:
Anatomical differences
Body weight: This can vary considerably between children of different ages and nutritional status.
Body surface area (BSA): Children have a larger BSA than adults and will thus have a larger absorptive surface area for agents absorbed through the skin. BSA is also sometimes used to calculate drug dosages instead of body weight. In addition the skin of children is thinner and the keratinised epithelium less well developed.
Airway calibre: The airway calibre of children is much smaller than that of adults. Due to Poiseuille’s law any further reduction either due to constriction (bronchospasm) or obstruction (respiratory secretions or gastric contents) has a significant impact on air flow to the fourth power e.g. halving the radius will cause flow to fall to one sixteenth.
Body water: Children have proportionally greater total body water than adults and this will result in differing volumes of distribution.
Physiological differences
Ventilation: Children have a greater minute volume than adults and so are more susceptible to the effects of gases, vapours and aerosolised agents (carbon monoxide).
Cardiac output: Children increase their cardiac output predominantly by mounting a tachycardia and have limited capacity to increase their stroke volume. They can decompensate quickly if they lose fluid or become bradycardic, an important feature of organophosphorous compounds.
Renal and liver function: Immature renal and liver functioning in children predisposes them to impaired ability to eliminate, and detoxify, toxic substances, respectively.
Glycogen stores: Children have lower glycogen stores within the liver which predisposes them to early hypoglycaemia when they experience a physiological stress e.g. seizures or sepsis.
Blood brain barrier: Toxic agents have a greater potential to gain entry to the central nervous system as children have greater blood brain barrier permeability. In addition the central nervous system of children is still developing and thus at risk of injury from certain exposures (lead) and secondary brain injuries.
Neonates: Some agents (e.g. amphetamines, barbiturates, caffeine, cocaine, opioids and selective serotonin reuptake inhibitors) ingested by the mother in pregnancy will traverse the placenta and can lead to dependence in the foetus which may present as a withdrawal syndrome shortly after birth. Toxic agents may also be transferred by mother to baby in breast milk e.g. aspirin, cocaine and lithium [5].
Developmental considerations
Height: Children have access to, and their attention is drawn to, areas that adults may overlook (under the sink storage).
Developmental milestones: Children between the age of 1 and 5 are adventurous by nature. They will not always appreciate danger and will tend to copy their parents. This is of particular importance when medications are taken in their sight or termed sweets. Some toxic substances have bittering agents added to prevent accidental ingestion.
Learning bite
When considering safeguarding or child protection concerns be sure that the mechanism of ingestion is consistent with that child’s developmental age. Those ingestions under the age of 1 should be carefully assessed before being put down to an accidental ingestion.