In practice, this usually is not significant, since fluid resuscitation is a dynamic process of checking and rechecking the patient's clinical status. In isotonic dehydration, the patient has lost water and sodium in such a way that the serum sodium remains normal. However, some sodium has been lost and must be replaced. This allows you to skip calculations for glucose. This allows you to skip calculations for potassium.
Many practitioners choose to add the potassium only after the patient's first void.
Thus, in the first 8 hours of resuscitation, this patient needs a total of 900 mL of water and 55 mEq of sodium. Thus, in the second phase of resuscitation, this patient needs a total of 1250 mL of water and 66 mEq of sodium. Writing these orders is not enough. Reassess the patient periodically based on clinical appearance and urine output. When the serum sodium is low in a dehydrated patient, the patient has lost more sodium than water.