A 9-month-old is brought to the emergency center by ambulance. The child had been having emesis and diarrhea with decreased urine output for several days, and the parents noted that she was hard to wake up this morning. Her weight is 9 kg, down from 11 kg the week prior at her 9- month checkup. You note her hea rate and blood pressure to be normal. She is lethargic, and her skin is noted to be "doughy." After confirming that her respiratory status is stable, you send electrolytes, which you expect to be abnormal. You sta an IV. The best solution for an initial IV bolus would be

The description is that of a child with hypernatremia (in this case, the child's sodium was 170 meq/dL); the "doughy" skin is often seen in hypernatremia. The extracellular fluid and circulating blood volumes tend to be preserved with hypernatremic dehydration at the expense of the intracellular volume. Therefore, hypotension may not be observed, and neither are the other signs of circulatory inadequacy that are typical of isotonic or hypotonic dehydration. Signs suggesting involvement of the central nervous system (such as irritability or lethargy) are characteristic of hypeonic dehydration. Slow correction of this hypernatremia (over 24 to 48 h) prevents significant fluid shifts and increased intercranial pressure. Initial bolus therapy should be with isotonic fluid such as normal saline or lactated Ringer's solution. Blood products such as fresh-frozen plasma are not indicated, and hypotonic solutions such as D10W and 1/4 NS could cause rapid fluid shifts, resulting in cerebral edema and death. Hypeonic (3%) saline is used in the event of seizures caused by rapid rehydration, along with other measures typically used to reduce cerebral edema.