Dear Folks:
    I am inspired to take a trip back into nursing arts by the questions that
have come up about saline.
    Tonicity refers to something about the proportion of molecular weights of
solute/solution in body fluids. When one makes "normal" or "physiologic"
saline, which is 1 teaspoon to a pint of water, the amount of salt per unit
of water is the same as in the body. A hypertonic fluid (like Kathy D writing
about putting salt on slugs) means a high concentration of salt to volume of
water. It pulls water out of the slug to dilute the salt, thus killing the
slug.  A hypotonic solution (less concentration of salt per unit of fluid)
puts water in, bursting cells.
    This is one of the reasons colostrum is so important to give to newborns.
If the baby does have the extremely rare tracheo-esophageal fistula, it is
far better to aspirate a isotonic (or normal or physiologic) solution, rather
than a hypertonic one (like formula) or a hypotonic one (like water).
Colostrum is isotonic; its proportion of salts to fluid is the same as the
baby's. It won't collapse or burst the cell walls.
    Warmly,
Nikki Lee RN, MSN, Mother of 2, IBCLC, CSTP, CIMI
Elkins Park (a suburb of Philadelphia, Pennsylvania,  northeastern USA)

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