Hypernatremia due to Dehydration in Dementia

Author: V. Dimov, M.D.
Reviewer: S. Randhawa, M.D.

86 yo AAF is admitted to the hospital after she had a seizure while waiting for swallow evaluation as outpatient. Family reports that the patient has baseline advanced dementia, which has been worsening over the last year. She is not verbal.

PMH:
Dementia, HTN, constipation

Medications:
FeSO4, ASA, Colace

SH:
NH resident, totally dependent in ADL/IADL

Physical examination:
VS 36.5-94-14-120/87
HEENT: NC/AT, dry MM
Chest: CTA (B)
CVS: Clear S1S2, tachycardic
Extremities: no c/c/e
Neuro: somnolent, non focal

What do you think is going on?
Seizure can be due to hypernatremia, or less likely, to an intracranial process

Why does she have hypernatremia?
Poor PO intake due to advanced dementia

What would you do?
CBCD, BMP
EKG
CT head w/o contrast

What happened?
BMP showed Na+ 155. IVF were started.


Hypernatremia


Resolution of hypernatremia with D5W

CT of the head revealed no changes since previous exam one year ago:

There is no acute parenchymal hemorrhage or extra axial fluid collection. There is severe, extensive parenchymal volume loss with ex vacuo dilatation of the lateral, third, and fourth ventricles. There are confluent areas of low attenuation in the white matter diffusely, consistent with extensive chronic small vessel ischemic changes. calcifications. There is no mass, mass effect, or midline shift. There are no bony lesions are fractures.

Impression: No change. Extensive parenchymal volume loss. Extensive chronic small vessel ischemic changes.

How much fluid should you order? What type of fluid?
Calculate the water deficit first, by using the standard formula.

Divide the calculated water deficit in half. Add one liter to the number. This is the amount of free water that should be given over the next 24 hours. Do not correct the water deficit completely during the first 24 hours. Only half of it should be replaced.

Remember that the calculated amount is free water, i.e. D5W (not NS = 0.9% NaCl).

The only situation, in which you give NS in hypernatremia, is when the patient is hypotensive. Otherwise the water deficit is always replaced with hypotonic fluid: D5W or 1/2 NS. D5W is the preferred fluid because you need to give less volume to replace the free water. With 1/2 NS, you may end up calculating that the required infusion rate is 400 cc/hr of 1/2 NS. Most of the patients with hypernatremia are elderly with a variable ejection fraction, and giving large amount of IVF can put them in pulmonary edema.

What happened?
The water deficit was replaced with D5W at 125 cc/hr, with a gradual drop in the sodium level to normal. The patient became more alert but continued to refuse food.

What is the next step?
A swallow evaluation was ordered, which indicated that the patient may need alternative means of nutrition.

The family was called and the options were discussed -- hospice or PEG tube placement. The risks of PEG placement were explained, along with the fact that according to studies, the PEG tubes do not prolong life in demented patients.

What happened next?
The family decided to proceed with PEG tube placement. GI consult was called, CBC, PTT/PT were normal, and a PEG tube was placed with no complications. The patient was discharged to a nursing home.

Final diagnosis:
Hypernatremia due to dehydration in a demented patient

What did we learn from this case?
Dehydration is a common cause of hypernatremia in elderly demented patient. Hypernatremia can present with seizures.

The free water deficit needs to be calculated for correct replacement. The best fluid to replace the deficit is D5W.

It is very important to suggest to your patients to formulate an advance directive, detailing the measures that they want implemented in case they become incapacitated, and cannot talk for themselves. This can help to avoid unnecessary and sometimes futile interventions in the future.

References:
MedCalc Formulas: Hyponatremia & Hypernatremia.
Hypernatremia. eMedicine.
Hyponatremia. NEJM 2000.
Hypernatremia. NEJM 2000.
Recurrent Aspiration Pneumonia. NEJM Images in Clinical Medicine, 11/2008.

Related reading:
Ethical Dilemmas: Artificial Feeding. Shrujal Baxi MD, Ethics Section Editor, and Joseph Lowy MD, Medical Director, Palliative Care Service at NYU Hospital.
Hypovolemia versus Dehydration. Renal Fellow Network, 2009.

Published: 3/20/2005
Updated: 04/22/2009