NHS Resolution: Case story. Understanding the risk of maternal and neonatal hyponatraemia (February 2019)

Summary

This is a case study by NHS Resolution into recognising and avoiding significant maternal and neonatal hyponatraemia.

Content

Key learning points

• All women in labour are at increased risk of hyponatraemia (defined as blood serum sodium < 130 mmol/l), especially dilutional hyponatraemia, which is sometimes referred to as water intoxication.
• This is a result of lower baseline serum sodium in pregnancy, impaired ability to excrete water in the third trimester and exposure to the anti-diuretic effect of oxytocin (synthetic and/or endogenous). Excessive oral or intravenous fluid intake exacerbates this, with potentially serious complications for mother and baby.
• Complications of hyponatraemia include headache, agitation, confusion, seizures and death. Vigilance, diagnosis and active management is therefore imperative.
• Water freely crosses the placenta, lowering the infant’s blood sodium concentration in tandem with its mothers. Seizures secondary to hyponatraemia in the newborn infant are similar to those caused by hypoxic ischaemic encephalopathy (HIE) and they are likely to receive therapeutic cooling as a result.
• In a recent study, 26% of low risk mothers who received or ingested >2500 mls of fluid during labour were hyponatraemic.
• Significant hyponatraemia can be avoided by giving women evidence-based advice on oral fluid intake, careful monitoring of fluid input and output and responding to positive fluid balance.