Priority Topic: Dehydration

Key Feature 5: In a dehydrated patient: Identify the precipitating illness or cause, especially looking for non-gastro-intestinal, including drug-related, causes
Skill: Clinical Reasoning
Phase: Hypothesis generation

​Today I encountered a 16 year old female with a history of primary lymphagiectasia (aka lymphagiwhattheheckisthis) who presented to the Children's Emergency Department with sudden onset of incessant vomiting that awoke her suddenly from sleep 3 hours prior to my assessment. On examination she appeared moderately dehydrated (mildly tachycardic with a prolonged cap refill). When I told my preceptor the story, he wasn't convinced that she was dehydrated to a moderate degree, knowing that over such a short timeline of vomiting it would be unlikely to be more than mildly dehydrated. We went in to reassess the patient together, and to his surprise, he agreed that she also appeared moderately dehydrated on assessment. We proceeded to order IV fluids given that she was not able to keep oral fluids down at this point, and then we quickly did some research on her rare disease, to see if her presentation was possibly a complication of it. We learned that one of the complications of this disease was edema and third spacing. Aha! Although we hadn't narrowed down a specific reason for her abdominal pain and vomiting yet, we had a plausible reason for why she was already moderately dehydrated. More than just fluid loss from vomiting, this patient was likely having some third spacing going on. 

When encountering a patient who is hypovolemic, what is the DDx for the hypovolemia? The UpToDate article, Clinical assessment and diagnosis of hypovolemia (dehydration) in children (2018), provides a breakdown:

1. Hemorrhage (A medical adage, "Hypovolemia is from blood loss unless proven otherwise.")
2. Third space loss (Ex: from edema or ascites, which both have their own DDx. Hemorrhage can also occur into a third space, such as is the case with a retroperitoneal hemorrhage)
3. Other
   1. Gastrointestinal (ex: vomiting, diarrhea)
   2. Skin (ex: fever, burns)
   3. Urine (ex: glucosuria, diuretic therapy, diabetes insipidus)
   4. Prolonged inadequate oral fluid intake