Sodium and water homeostasis in children with shigellosis

Studies in Bangladesh have shown that the mortality in shigellosis is significantly higher in hyponatraemic (HN) than in normo- (NN) or hypernatraemic children. The aim of this study was to describe the effect of shigellosis on renal haemodynamics and sodium and water homeostasis before treatment was started. Twenty-one moderately ill children infected with Shigella dysenteriae type 1 were studied. Eight of them had a serum sodium concentration below 130 mmol/L. Renal function was determined by glomerular filtration rate measured by clearances of inulin and iohexol. Effective renal plasma flow was estimated by clearance of paraaminohippuric acid. Plasma renin, aldosterone and anti-diuretic hormone were also studied. The HN children had significantly higher haemoglobin and haematocrit levels than the NN group. There was an inverse correlation between serum sodium and haemoglobin, and a direct correlation between serum sodium and urinary sodium and urinary chloride. Direct correlations were found between serum aldosterone and haemoglobin, plasma renin and systolic blood pressure and an inverse correlation between serum aldosterone and serum sodium. Clearances of inulin and iohexol were normal. Detectable levels of ADH were found in both groups, despite low serum osmolalities.

Conclusion : The HN state seems to be triggered by multiple factors. The normal glomerular filtration rate excludes a volume expansion secondary to reduced renal function. Inappropriate or a physiological increase of anti-diuretic hormone secretion may be of importance. The higher sodium losses in stools of the HN children might also be a factor contributing to the HN.