Abstract
BACKGROUND: Whilst mild neonatal hyponatraemia is common and relatively harmless, extreme hyponatraemia of 95 mmol per litre has never been reported in a premature baby and such a level could be associated with immediate as well as long-lasting detrimental effects on health. CASE PRESENTATION: Twenty-four days old baby boy born at 28 weeks gestation (triplet one) unexpectedly became moribund with hypovolaemic shock and was found to have blood sodium of 95 mmol per litre. Diagnostic work up revealed a combination of a urinary tract infection, inadvertently low sodium provision with donor breast milk, and weak renin-angiotensin-aldosterone response. Commencement of treatment with intravenous fluids and extra sodium led to unanticipated diuresis and faster than expected increase of sodium level. Ultimately, treatment resulted in clinical recovery and normalisation of sodium level, which subsequently remained normal with no additional sodium supplementation. Follow up revealed mild spastic diplegia. CONCLUSION: Continuous monitoring and daily medical reviews may not be sensitive enough to recognise development of extreme hyponatraemia. Blood sodium levels should be monitored closely and any abnormalities promptly addressed. Treatment of hypovolaemic hyponatraemia should be centred on fluid resuscitation, anticipation of "paradoxical" diuresis, and blood sodium correction rate of 8 to 10 mmol per litre per day.