Background: The most frequent central nervous system illness is acute bacterial meningitis (ABM). It is a fatal condition, especially in newborns and infants (under age of one year). The aim: of this work was to determine the incidence of hyponatremia in ABM in pediatric patients admitted at Aswan University Hospital and to study different factors associated with hyponatremia in bacterial meningitis regarding hospital stay, mortality, and outcomes. Methods: This is a cross sectional study that was carried out on 65 infants and children aged < 5 years admitted at Aswan University hospital, pediatric department from April 2022 to march 2023, all studied patients were subjected to Full history taking and examination, general. Systemic and neurological followed by laboratory evaluation. Diagnosis of bacterial meningitis was done by cerebrospinal fluid (CSF) cytology or antigen detection test &CSF culture. Results: Nearly all the included patients in this study had fever (98%). Convulsions, and status epilepticus were reported in 86.2%, and 20% of the patients respectively, while Headache was found in 3.1% of patients. The most commonly detected neurological complication was hydrocephalous and focal neurological deficit found in 6.2% and 1.5% respectively. As regard the mean serum sodium level at admission it  was 132.1 ± 2.6 meq/L with minimum of 127 meq/L. and maximum of 140 meq/L. At first week it was 133.4 ± 3.9 meq/L. with minimum of 126 meq/L. and maximum of 145 eq/L. At second week, it was 132.7 ± 3.8 meq/L. with minimum of 118 meq/L and maximum of 143 meq/L. At third week, it was 131.6 ± 4.5 meq/L. with minimum of 118 meq/L. and maximum of 137 meq/L.  The majority of participants discharged (89.2%), while only (10.8%) died. There was A statistically significant increase in the serum sodium level at first week, second week and third week when compared with serum sodium level at admission. The mean serum sodium level was reduced among died patients contrasted to patients discharged.
Conclusions: Hyponatremia was mild and was associated with worse outcome, a link was shown between serum sodium level at admission, during hospital  stay and the incidence of complication in  cases of bacterial meningitis, so the serum sodium level is considered as an indicator for outcome of acute bacterial meningitis, the lower the level of serum sodium the worse the outcome (morbidity and mortality).