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A common misconception of dosing anesthetics in pediatric patients is that children are miniature adults. Although there are substantial physiologic changes with early development and maturation (Table 21–1; Figures 21–1 through 21–3),1-6 they are not rigorously accounted for in published dosing guidelines for pediatric patients. Ideally, dosing recommendations would be based on studies in children at various phases of maturation and characterize drug kinetic and dynamic behavior as a function of age and body composition. Without a scientific basis, anesthesiologists are left to make assumptions and educated guesses when formulating a dosing regimen and then rely on the forgiving nature of most anesthetics that have a wide therapeutic margin.

Table 21–1Body composition, absorption, distribution, metabolism, and renal excretion in young children.1-6
Figure 21–1

Estimated total, intracelluar, and extracelluar water as a percentage of total body weight by age.1-6

Figure 21–2

Body fat as a percentage of total body weight versus age.1-6

Figure 21–3

Glomerular filtration rate (GFR) as a function of age.1-6

A major reason for the paucity of data characterizing anesthetic drug behavior in pediatric patients is drug development cost. Pharmaceutical companies that market drugs in the United States seek approval from the Food and Drug Administration (FDA) for adults but do not pursue approval in children because of prohibitive costs (up to $800 million for one ...

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