Hyponatremia in ICU.

Background: Hyponatremia is defined as serum sodium level <135 meq/L. It is the most common electrolyte abnormality seen in hospital admissions worldwide. The proportion is even higher in the ICU setting. A wide variety of factors influence the outcome of the hyponatremic patient. Present study is designed to approach to analyse etiology, clinical features, co-morbid factors, severity of hyponatremia, rate of correction, and impact of treatment on outcome of these diverse group of patients in ICU.

Aims: 1) To find proportion of patients presenting with hyponatremia and requiring medical ICU admission in a tertiary care set up. 2) To study the etiology and clinical features of hyponatremia in patients requiring ICU admission. 3) To compare and study the effect of various factors on the outcome of hyponatremic patients in the ICU.

Methods: This study was a cross-sectional observational study in tertiary care hospital. All indoor general medicine ward admissions over a period of 18 months were screened for the presence of hyponatremia and patients requiring Medical ICU care and satisfying inclusion criteria were studied. Serial serum electrolytes and urine sodium were tested for all patients in the ICU satisfying the inclusion criteria. Type of fluid given and daily correction of serum sodium of all patients were noted. Outcome was measured in terms of mortality, duration of stay in ICU, number of days required for sodium correction and complications of treatment if any. Patients were followed up till hospital discharge or death..

Results: In this study, 5.2% of total admissions had hyponatremia. Among the ICU admissions, the different symptoms attributed to hyponatremia included nausea (69.3%), malaise (80%), drowsiness (61.3%), confusion (41.3%), lethargy (24%), frequent falls (1.3%), convulsions (2.7%), altered sensorium (41.3%) and delirium (9.3%). SIADH was the most common cause of hyponatremia in these patients (32%). Serum sodium levels of patients on admission ranged from 82 - 133 meq/L, with average serum sodium being 124meq/L. Overall mortality among the hyponatremic ICU admissions was 26/75, 34.6%, which was higher than the total ICU mortality of 26% in same duration (p = 0.1). There was a significant increase in duration of stay in ICU in patients with various co-morbidities (p=0.003). There was a significant association between Glasgow Coma Scale (GCS) and serum sodium levels, (p = 0.002). Blood pressure and hydration status did not significantly influence outcome. Lower serum sodium on admission was associated with a lower survival (p= 0.041). Sodium correction of < 5 m eq/day was associated with an increased mortality(p = 0.04), whereas sodium correction of > 10 m eq/day was not associated with increased mortality, but an increased risk of EPM, which was seen in one patient.

Conclusion: Most common cause of hyponatremia in ICU patients is SIADH. Longer duration of stay is seen in the presence of different co-morbidities. A lower GCS and a lower serum sodium on admission is associated with lower survival. Type of fluid used for hyponatremia correction did not influence the outcome. Under correction of hyponatremia in first 24 hours or inadequate correction was associated with a poorer outcome. Overcorrection was not associated with any survival benefit, but was associated with risk of EPM.