A person comes into the emergency room dehydrated after working out in the summe

Question

A person comes into the emergency room dehydrated after working out in the summer sun. His ECF volume is 13 liters and his ECF osmolarity is 340 mOsM. (Ignore ICF in this problem).

a. How many milliosmoles of solute are in his ECF when he arrives at the hospital?

b. An intravenous (IV) infusion of 1 liter of 0.464% NaCl is given. (The molecular weight of NaCl is 58 g/mole). How many milliosmoles of solute are in the IV?

c. Assuming that no water or solutes move out of the ECF, calculate the new ECF volume and osmolarity after the man has been given the IV.

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Explanation / Answer

a. Milliosmoles of solute in ECF = ECF volume × ECF osmolarity = 13 × 340 = 4420 milliosmoles

b. Milliosmoles of solute in IV = IV volume × IV osmolarity = 1 × (0.464/58 × 2 × 1000) = 16 milliosmoles

c. New ECF volume = 13 + 1 = 14 L

New ECF osmolarity = total osmoles/ total volume = (4420 + 16)/ (13 + 1) = 316.85 mOsm

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