Tonicity Balance in Patients With Hypernatremia Acquired in the Intensive Care Unit

Background

Hypernatremia is a serious electrolyte disturbance and an independent risk factor for mortality in critically ill patients. In many cases, hypernatremia is an iatrogenic problem that develops in the intensive care unit (ICU).

Study Design

Case series.

Setting & Participants

45 patients were studied in a medical ICU. For inclusion in the study, patients needed to show an increase in serum sodium concentration to greater than 149 mEq/L from an initial concentration of less than 146 mEq/L.

Outcomes

Solute balance, fluid balance, and both. Causes of hypernatremia.

Measurements

The daily mass balance of sodium, potassium, and water over 1- to 3-day intervals was measured while serum sodium levels were increasing.

Results

During the study period, 69 of 981 patients (7%) acquired hypernatremia after admission to the ICU. Of these, 45 had sufficient data for evaluation. Maximum serum sodium levels were 150 to 164 mEq/L. The average duration of hypernatremia was 2 days (range, 1 to 10 days), with an average onset on day 5.9 ± 4.3 of the ICU stay. Patients were classified as having a positive solute balance (n = 17; 38%), negative fluid balance (n = 20; 44%), or both (n = 8; 18%). The most important extrarenal factors contributing to hypernatremia were fever (45%) and diarrhea (18%). Polyuria was observed in 38% of patients and 35% had acute renal failure. Hypertonic solutions were administered to 27% of patients.

Limitations

Retrospective analysis; lack of daily measurement of body weight.

Conclusion

ICU-acquired hypernatremia is associated with multiple factors associated with negative fluid and positive solute balance.

Index Words: Sodium, hypernatremia, pathophysiology, tonicity balance