P AEDIATRICS EMC IV 2015

A DULT VERSUS CHILD Anatomy upper and lower airway anatomy. less compliant ventricles in the myocardium. larger skin surface area. poorly formed blood brain barrier. These anatomical differences may then result in a difference in physiology. mike.shannonandmike.net

PHYSIOLOGY Physiologically, neonates have differences in various systems following separation from the placenta. Many of these functions resolve within a few days or weeks following birth, but others only years later (Porter, 2011). This becomes relevant for drug dosing!

PHARMACOKINETICS Absorption- GI changes Distribution- depends on 2 factors: body composition (water, fat and protein) and plasma protein binding. Metabolism - At normal doses some drugs may cause toxicity. Excretion - Immature kidneys, therefore elimination of drugs affected.

(Porter, 2011)

FLUID THERAPY Requirements for children are higher than those for adults for multiple reasons: “the higher metabolic rate of children requires a greater caloric expenditure, which translates into higher fluid requirements.” “children, especially infants, have a much higher body surface area to weight ratio, and this translates into relatively more water loss from skin compared with adults.” “children, especially infants, have higher respiratory rates, and this equates to higher insensible losses from the respiratory tract” (Meyers, 2009). The 3 types of fluid therapy are: Maintenance Deficit Replacement

DRUG-DOSING Drug dosing in children can be done using: Age-based formula- may be ineffective due to the varying growth patterns of children today and does not accurately reflect the pharmacokinetics at that specific developmental age. Weight-based formula- preferred method to calculate a drug dosage. Body surface area-based formula- complex and time- consuming. Allometric scaling- complicated and no longer used.

VOLUME OF DISTRIBUTION Total body weight (TBW) is the actual mass in kilograms weighed on a scale. The ideal body weight (IBW) is an estimation of weight based on sex, height and frame size. The lean body weight (LBW) is the TBW minus the fractional fat mass (measured using skinfold thickness or underwater weighing). The adjusted body weight (ABW) is calculated by adding a correction factor above the IBW to normalize the volume of distribution (Green & Duffull, 2004).

W EIGHT ESTIMATION METHODS Healthcare provider or parent guessing Age-based APLS Leffler’s Luscombe’s Best Guess etc. Length-based PAWPER Broselow Miscellaneous Mercy tape Haftel formula Bavdekar Formula Carroll Technique Mercy Tape- measurement-tapes

PAWPER Tape with body habitus Broselow Tape

REFERENCES Berlin, C., Pharmacokinetics in Children. [Online] Available at: n_children/pharmacokinetics_in_children.html [Accessed 6 June 2014]. n_children/pharmacokinetics_in_children.html Carasco, C., Fletcher, P. & Maconochie, I., Review of commonly used age based weight estimates for paediatric drug dosing in relation to the pharmacokinetic properties of resuscitation drugs. Archives of Disease in Childhood, 97(3), pp.A Fernandez, E. et al., Factors and Mechanisms for Pharmacokinetic Differences between Pediatric Population and Adults. Pharmaceutics, 3(1), pp Green, B. & Duffull, S., What is the best size descriptor to use for pharmacokinetic studies in the obese? British Journal of Clinical Pharmacology, 58(2), pp Meyers, R.S, Paediatric fluid and electrolyte therapy. Journal of Paediatric Pharmacological Therapy. 14 (2), pp Porter, R., Merck Manual. 19th ed. New Jersey: Merck. Tayman, C., Rayyan, M. & Allegaert, K., Neonatal Pharmacology: Extensive Interindividual Variability Despite Limited Size. Journal of Pediatric Pharmacology and Therapeutics, 3(16), pp Wells, M., Weight prediction in children in the emergency department. Master of Science in Medicine in Emergency Medicine, University of Witswatersrand, Johannesburg. Wells, M., Goldstein, L. & Botha, M., Emergency Drug Dosing in Children: A Resuscitation Aid for Paediatric Emergencies. 1st ed. London: Elsevier.