Hyponatremia complicating labour—rare or unrecognised? A prospective observational study

Abstract

Objective The aim of this study was to investigate the occurrence of hyponatraemia following delivery, with a hypothesis that hyponatraemia has a high prevalence in labouring women.Design Prospective observational study.Setting Consultant-led delivery suite in County Hospital, Kalmar, Sweden.Sample A total of 287 pregnant women at term (37 full gestational weeks).Methods Oral fluids were allowed during labour. Blood samples were collected on admission, after delivery, and from the umbilical artery and vein.Main outcome measure Hyponatraemia defined as plasma sodium £130 mmol/l after delivery.Results Hyponatraemia was found in 16 (26%) of the 61 mothers who received more than 2500 ml of fluid during labour. Twothirds of fluids were orally ingested. Decrease in plasma sodium concentration during labour correlated with duration of labour and the total fluid volume administered. Analysis by multivariate logistic regression showed that hyponatraemia was significantly correlated with fluid volume (P < 0.001) but not with oxytocin administration or epidural analgesia. Hyponatraemia correlated significantly with prolonged second stage of labour, instrumental delivery, and emergency caesarean section for failure to progress (P = 0.002).Conclusions Hyponatraemia is not uncommon following labour. Tolerance to a water load is diminished during labour; therefore, even moderate fluid volumes may cause hyponatraemia. Women should not be encouraged to drink excessively during labour. Oral fluids, when permitted, should be recorded, and intravenous administration of hypotonic fluids should be avoided. When abundant drinking is unrecognised or intravenous fluid administration liberal, life-threatening hyponatraemia may develop. The possibility that hyponatraemia may influence uterine contractility merits further investigation.

Plasma vasopressin, oxytocin, estradiol, and progesterone related to water and sodium excretion in normal pregnancy and gestational hypertension

“…Tolerance to a water load is diminished during labor and hyponatremia is not uncommon often as a result of excessive water intake (24). These observations are important to consider when oxytocin is administered since oxytocin may cause water reabsorption in the kidneys which further dilutes the plasma.…”

Water intoxication following labour and surgery: blaming oxytocin – the easy way out?

“…Moreover, labour itself, blood loss and repeat general anaesthesia also cause significant endogenous release of vasopressin. In a recently published observational study, we found significant reduction of plasma sodium during longer lasting labours in women with an hourly fluid administration of 300 ml 2 . Whatever the source of vasopressin, water intoxication can only develop when free water is present.…”

Hyponatraemia and Brain Oedema in Newborns Following Oral Water Intoxication during Prolonged Labour

“…Moen et al found reduction in plasma sodium to be signifi cantly correlated with duration of labour and total fl uid volume administered during labour. As women drink similar amounts of water per hour a longer duration of labour results in a cumulatively higher fl uid intake [ 6 ] . In the last few years drinking habits seem to change and water intoxication due to excessive oral intake seems to occur more frequently [ 3 , 6 ] .…”

“…While this normally is well tolerated in healthy adults pregnant women have a reduced intrinsic ability to compensate for fl uid overload as water-sparing systems are activated and labour and nausea additionally stimulate ADH secretion [ 7 ] . In addition, oxytocin, structurally similar to vasopressin (ADH), can contribute to water retention by stimulation of the specifi c V2 vasopressin receptors in the kidney [ 6 ] . Babies born after fetal distress or diffi cult delivery, like our 2 patients, have higher circulating ADH concentrations compared to those born uneventfully [ 5 ] and are therefore at risk of exacerbating their hyponatraemia after birth.…”