Hyponatraemia - brain injury from low blood sodium caused by fluid monitoring errors in childbirth

If a mother is allowed to drink too much water during childbirth, her blood can become dangerously short of sodium (salt).  This leaves both the mother and her new baby at risk of serious neurological injury from a condition called hyponatraemia.

Correct fluid management is a basic element of the midwife’s role during her patient’s labour, but failure to prevent this dangerous condition in maternity care is leaving babies with avoidable brain injury.

What is hyponatraemia? 

Hyponatraemia means too little sodium (salt) in the blood. It arises from an incorrect balance between the water in the body and the electrolytes (sodium and potassium). When a patient has hyponatraemia, their fluid has become too diluted.

Mild hyponatraemia may be symptomless and is easily treatable. Severe or acute hyponatraemia is dangerous because when the blood sodium is too low, water is able to leave the bloodstream and enter the brain cells, causing them to swell. Brain swelling (cerebral oedema) can cause permanent damage to the brain and neurological disability.

What causes hyponatraemia?

Causes of hyponatraemia include conditions which disrupt the fluid balance in the body, such as:

• medications, such as diuretics (drugs/substances which increase urination, removing salt and fluid from the body);
• severe diarrhoea;
• severe vomiting;
• intestinal obstruction or fistula;
• heart disease or stroke;
• kidney disease;
• liver disease;
• SIADH (a condition in which the body produces excess antidiuretic hormone, causing water retention and low sodium levels);
• surgery or trauma;
• drinking too much water (dilutional).

Where a patient suffers brain injury from hyponatraemia in hospital, it is usually the result of incorrect fluid management and other mistakes in the patient’s care.

Who is at risk of hyponatraemia?

Anyone can suffer from hyponatraemia but women are at increased risk during pregnancy, labour and after giving birth. Hyponatraemia isn’t caused by pregnancy but a combination of factors in pregnancy and childbirth make women more vulnerable to hyponatraemia at this time.

During normal pregnancy a woman’s circulation naturally increases. This reduces her sodium-to-fluid balance, so from early in the pregnancy she is already at increased risk.  Then in the last three months (third trimester) of pregnancy, many women suffer from urine retention, leaving them less able to excrete water.

During labour, the woman’s body naturally has increased levels of oxytocin, the hormone which stimulates the uterus to contract. Oxytocin is naturally anti-diuretic and causes the labouring woman to retain water. If labour is slow or contractions are weak, women are often given Syntocinon, a synthetic oxytocin drug. This has the same anti-diuretic effect as natural oxytocin. Syntocinon is administered in drip form with IV (intravenous) fluids, further increasing the woman’s fluid intake. 

Labour is hard work and the woman may be encouraged to drink water to prevent dehydration. Research has found that around a quarter (26%) of low-risk mothers who received or drank more than 2.5 litres of fluid in labour were hyponatraemic, compared with only 1% of those who took on less than 1 litre. This was true even where the woman had not received Syntocinon or intravenous fluid.

This type of birth-related hyponatraemia, caused by a woman taking on more low-sodium fluid than she can excrete, is also known as water intoxication. 

What are the signs and symptoms of hyponatraemia?

Hyponatraemia is dangerous for both mother and baby. Maternal symptoms of hyponatraemia depend on the severity and speed of the drop in sodium levels. Mild hyponatraemia may be symptomless, and early signs may be mistaken for other conditions, such as pre-eclampsia. A sharp drop in blood sodium can cause cerebral oedema, leading to permanent brain injury disability and death.

Symptoms and signs of hyponatraemia include:

• nausea;
• lethargy;
• headache;
• agitation;
• confusion or disorientation;
• decreased level of consciousness;
• depressed reflexes;
• abnormal breathing pattern;
• seizures;
• coma;
• death.

As the mother and unborn baby share the mother’s blood circulation, the baby can be affected by the mother’s hyponatraemia even before the mother shows symptoms. Babies born to mothers with hyponatraemia will also suffer the effects of this life-threatening condition. Babies with brain injury from neonatal hyponatraemia may suffer seizures which can be misinterpreted as signs of HIE birth injury (caused by lack of oxygen) and be mistakenly sent for cooling.

Hyponatraemia requires very careful management under senior obstetric and anaesthetic supervision to raise the patient’s blood sodium levels to safe levels. If the blood sodium concentration is increased too quickly it can cause irreversible, severe brain damage. 

Can negligent maternity care cause brain injury from hyponatraemia?

Hyponatraemia from ‘water intoxication’ in childbirth most commonly arises from incorrect fluid management in hospital. Labouring women’s fluid input and output should be monitored and recorded in their records. Imbalances should be  recognised and treated. In a hospital setting, correct fluid management is basic nursing and midwifery care.  If a birthing mother or her baby suffer permanent injury as a result of hyponatraemia during maternity or neonatal hospital care, they may be entitled to claim compensation.

If your child has cerebral palsy or neurological disability as a result of medical negligence, or you have been contacted by HSSIB/MNSI or NHS Resolution, you can talk to a solicitor, free and confidentially, for advice about how to respond or make a claim by contacting us.