Children are not little adults

Starting Paediatrics today, its important to realize that the medical approach to children can be incredibly different than that to adults. Children differ from adults physiologically and in their exposure to the environment, here is a list of some important points to consider when dealing with a paediatric patient: 
(this post is based on the WHO document linked here, reference are included within that document)

• Minute ventilation per Kg bodyweight a day is higher in children. It is around 600l in <1year old  which is 3 times the value of an adult, 200l. Therefore environmental toxicants will be delivered to the airways of a child at a higher level than adults. for example: ozone, lead, particulates, nitrogen oxides, mercury, moulds, volatile organic compunds etc. 

• Calorie and water needs are higher in children. Cal/kg/day and ml/kg/day have higher values in younger children, its pretty obvious considering their anabolic state and growth demands. Therefore oral exposures are likely to be higher in children, think of pesticides or mycotoxins that are common in food. I could mention here that a vegan diet may be harmful to children since their calorie demand is so much higher (even though I'm an avid supporter of plant based diets). 

• Gastrointestinal absorption is higher in children and dynamic. For example a child may absorb 70% of ingested lead while an adult around 5-20%. There are microbiome changes throughout childhood, contributing to digestion and absorption. important considering pharmacokinetics, always prescribe drugs in mg/kg not by single doses. 

• Renal function: GFR (glomerular filtration rate) is low at birth (around 10-15ml/min/m2 for a normal full term newborn) and doubles in the first week of life (cirtical period). GFR reaches adult values by around 6-12 months, the general rule is 8 months. tubular function is impaired (secretion) at birth and is normal by 1 year of life. 

• Hepatic function: The activity of phase 1 enzymes are reduced and mature at different rates as child grows. in fact activity of these enzymes can then exceed adult rates between 6-12 years age. phase two enzymes are ready at birth for processes such as conjugation and acetylation. Therefore metabolites of xenobiotics may differ between adults and children, even if rates of metabolism are the same. 

• Transplacental exposures: Many chemicals and drugs cross the placenta, including mercury, lead, substances of abuse, alcohol etc. We all know the story of thalidomide. Also physical factors can affect the baby such as heat and ionizing radiation. important thing to point out here is that maternal exposures do matter!

• Breastfeeding: Breast milk is the safest and most complete nutrition for infants, so mothers should avoid toxic exposures. We use breast milk to spot environmental contaminants, its very likely that you reading this have DDT in your fat because your mother was exposed to it as a child. Lipophilic chemicals are especially good at transferring in breast milk, hence why we don't prescribe quinolones for breastfeeding mothers. 

• Size and surface area: The ratio between skin/surface area to body volume/mass is much higher in children, about 3x for a newborn compared to an adult and 2 times with an infant. therefore dermal exposures may be much higher in children, children also tend to have more skin abrasions/cuts and rashes which make it easier for germs/contaminants to cross the skin barrier. Very important to consider the surface area in children when dealing with burns.

• Organ and system development: the organs in a childs bodie grow and mature throughout childhood. Neuron growth and maturation (myelination and synpatogenesis) continues right the way through puberty, The respiratory system continues linear growth after birth so any exposures to toxic compunds (tobacco smoke! ozone etc.) can have very adverse consequences. The immune system is also actively maturing throughout childhood.

In summary, children have unique and differing-to-adults exposures and a highly dynamic developmental physiology. Combining this with a longer life expectancy and the insidious effects of environmental toxins, it is very important to consider the world/environment we leave behind for children to inherit. 
Children have a completely different pharmacokinetic profile and can be exposed in a variety of ways, so its also important for physicians to be vigiliant in paediatrics pharmo-prescribing. 


Bonus point: Introducing a food early to children does not increase their risk of allergies, NEJM editorial.