Fluids, Electrolytes, Acid-Base Disorders, and Nutrition Support

Hypernatremia: Reflects a deficit of water compared with total body sodium. Therapy should be

adjusted to achieve a serum sodium concentration decrease of 6–8 mEq/L per day; no faster than 10–12

mEq/L per day to reduce the risk of cerebral edema.

Evaluation

Evaluate ECF volume status (increased, normal, decreased). Increased ECF volume is

caused by excessive sodium intake (oral salt tablets, hypertonic saline, 0.9% sodium chloride

solution, lactated Ringer solution, PlasmaLyte/Normosol). This is the least common cause of

hypernatremia. Decreased ECF (hypovolemia, dehydration) results from excessive losses of

both water and sodium.

ii.

Consider urine sodium together with volume status to determine cause and treatment.

Treatment

Hypervolemic hypernatremia – Treated with diuretics, sodium restriction, water replacement,

and/or renal replacement therapy

ii.

Euvolemic hypernatremia – Treated with free water replacement

equation (N Engl J Med 2000;342:1493-9): 0.6 x Wt (kg) x [(serum sodium/140) – 1] (use

0.5 x Wt (kg) for women). Correct deficit over 2–3 days. The equation often underestimates

2013;87:79-85). This is typically accomplished using enteral free water boluses (e.g.,

200–300 mL every 4–6 hours) if the patient has a nasogastric feeding or suction tube.

Administration of high volumes of enteral water boluses should be avoided if the patient

has a post-pyloric tube because it causes cramping and diarrhea. Rare cases of bowel

necrosis post–large water boluses have also occurred when administered directly into the

small bowel (J Parenter Enteral Nutr 2004;28:27-9). If the enteral route is not possible

or the patient is intolerant of enteral water boluses, intravenous dextrose 5% in water or

dextrose 5% in 0.225% sodium chloride can be used.

can be estimated as follows: [sodium concentration of IV fluid (mEq/L) – serum sodium

concentration (mEq/L)] / [TBW + 1] (N Engl J Med 2000;342:1493-9). Refer to Table 5 for

sodium concentration of commonly used intravenous fluids.

iii.

Hypovolemic hypernatremia – Initially treated with volume expansion to restore hemodynamic

stability because total body sodium and volume is low. If hypernatremia is still present once

the patient is hemodynamically stable, free water replacement can be initiated as stated earlier.

iv.

Clinical evaluation during volume repletion is of paramount importance. Serum sodium

should be checked routinely (e.g., every 6–12 hours) to avoid overcorrection. All sources of

excess fluid losses should be monitored and replaced with the appropriate fluid, if indicated.

ECF Volume Status

Hypervolemic

Euvolemic

Hypovolemic

Physiologic findings

See Table 6

Urine sodium (mEq/L)

> 20

Varies

< 20

> 20

Potential etiologies

Excessive sodium

intake from intravenous

or oral, mineralocorti-

coid excess

Extrarenal losses

(insensible losses),

Renal losses

(diabetes insipidus)

Extrarenal

losses (fever,

diarrhea,

respiratory

losses)

Renal losses

(diuretics,

glycosuria,

kidney failure/

injury), diabetic

ketoacidosis,

hyperosmolar

hyperglycemic

syndrome