Salt I

Hyponatremia, or a low sodium level in the blood, is an interesting problem. If a patient is noted to be hyponatremic, the next clinical question is about their "volume status." Volume status refers to whether a patient is dehydrated, normal, or congested with fluid. Based on that, the diagnostic tests and treatment diverge greatly. It seems like it would be an easy question to answer, but it's really not that simple.

On my last wards rotation, I admitted a patient with a sodium of 120 (normal is 135-145). He had a history of congestive heart failure, a heart attack, diabetes, and arthritis. He was taking no medications. He presented with a couple weeks of nausea, vomiting, and watery diarrhea. He was not eating much. He didn't know whether he had gained or lost weight.

On examination, I easily saw his jugular venous pressure while he was sitting upright. He had edema or swelling in his legs, but not too impressive. His lungs were crystal clear. He had a huge belly but it appeared more obesity than fluid-filled. His labs were remarkable only for some kidney insufficiency. We did a bedside ultrasound which showed an inferior vena cava that was dilated to 2cm with minimal respiratory variation.

The question is simply: is the patient fluid overloaded or dehydrated? It's an interesting question because I had a strong opinion the whole time but the team went back and forth on the right answer, and due to delay, the patient suffered.

In the emergency department, the patient was felt to be hypovolemic. His sodium went to 122 with 2 liters of normal saline. However, I felt very strongly that the patient was fluid overloaded; the gestalt of looking at him and the exam reeked to me of congestive heart failure. I spend a lot of time doing things that are highly subjective such as looking at neck veins, but I convinced myself that they were elevated, not consistent with dehydration. My resident disagreed; she trusted the history more, and with vomiting, diarrhea, and poor oral intake, she thought the patient was dry. She was confused by the bedside echocardiogram but nonetheless wanted to give the patient more normal saline. My argument at the time was that congestive heart failure often presents with nausea, vomiting, and poor PO intake. We agreed to free water restrict that patient and not give more fluids. That first night, I wrote for a baby dose of lasix because I thought it was the right thing to do, though both the ED and the resident disagreed with my clinical assessment. I also added on a BNP (an imperfect laboratory marker for congestive heart failure) to the labs. Although I initially felt the patient needed to be admitted to cardiology, I did not make a strong argument, and so he was admitted to my general medicine team.

More on the case tomorrow.

Image of salt crystals from Death Valley National Park is shown under GNU Free Documentation License, from Wikipedia.