Lesson 12

Body Water Distribution

• Total body water (TBW) is highest in premature newborns, decreasing with age.

• Changes in body water as a function of age:

  • TBW: Highest at birth, decreases with age.

  • Extracellular fluid (ECF): Highest at birth, decreases with age.

  • Intracellular fluid (ICF): Lowest at birth, increases with age.

Key Values

• Premature Neonate:

  • TBW: 85%

  • ECF: 60%

  • ICF: 25%

• Child:

  • TBW: 60%

  • ECF: 40%

  • ICF: 60%

• Adult:

  • TBW: 60%

  • ECF: 20%

  • ICF: 40%

Signs of Dehydration

• Sunken anterior fontanel

• Weight loss (10% reduction in first week normal)

• Lethargy or irritability

• Dry mucous membranes

• Absence of tears

• Decreased skin turgor

• Increased hematocrit (hemoconcentration) in absence of transfusion

Additional Notes

• In premature and term neonates, ECF is larger than ICF (unlike other age groups).

• Diuresis after birth reduces ECF volume.

• Total body water approaches adult values by approximately one year of age.

• Increased ICF provides a reserve during intravascular volume loss (e.g., from fever, fasting, diarrhea).