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Severe hyponatremia secondary to water intoxication - an unintended consequence of encouraging oral hydration during labour
Abstract Number: T-58
Abstract Type: Case Report/Case Series
During pregnancy, sodium homeostasis is altered through increased salt appetite and thirst combined with activation of the renin-angiotensin system. Oral hydration is encouraged during labor, and is often supplemented with intravenous fluid. However, excessive fluid intake may result in severe hyponatremia. which can lead to complications in both mother and neonate including seizures, coma and death.
A 33 y/o healthy primigravida at 40+4 weeks presented in active labor and initially attempted a water birth with nitrous oxide for analgesia. During labor she became drowsy with periods of agitation; this was ascribed to labor pain and fatigue. After eight hours she consented to epidural analgesia, but remained agitated despite a bilateral T6 sensory block to ice. Two hours later, the decision was made to proceed to cesarean delivery in view of obstructed labor and non-reassuring fetal heart tracing.
At this point she was reassessed by the anesthesiologist, who found her alertness had deteriorated but she could still be briefly roused. On examination she was afebrile, with no focal neurological signs, pupils were equal and reactive, and blood sugar level was 106.2 mg/dl. Diagnostic tests were ordered, but it was decided that delivery should not be delayed for these investigations. Epidural top-up with 12ml 2% lidocaine with 1:200,000 epinephrine achieved bilateral T4 sensory block and surgery proceeded uneventfully; a vigorous baby was delivered with Apgar scores 9/9.
Post-operatively, laboratory results showed severe hyponatremia, sodium (Na) 116 mEq/L, low urinary Na 5 mEq/L and low urinary osmolality 40 mmol/Kg. Strict fluid restriction successfully restored her Na level and sensorium over the next 24 hours. Upon maternal diagnosis, her baby was also investigated and found to have a corresponding severe hyponatremia (Na 116 mEq/L); hypertonic saline was instituted and the neonate’s serum Na was restored to normal over the next 12 hours.
Collateral history from the family and midwife revealed the patient had been drinking water obsessively based on internet advice to stay well hydrated during labor. A positive fluid balance of 9L was calculated over the preceding 20 hours; based on this, the underlying cause of her altered mental state was diagnosed as hyponatremic encephalopathy secondary to water intoxication.
Hyponatremia is common and under-recognized in pregnancy, as early symptoms (nausea, lethargy and altered sensorium) can be misconstrued as symptoms from protracted labor. Once diagnosis is made, prompt neonatal workup should also be done as maternal hyponatremia can induce fetal hyponatremia via placental equilibration. This case is a reminder of the need for fluid intake monitoring during labor, and that well-intentioned advice can sometimes lead to unintended consequences.
1 Scaife, PJ. et al. Placenta 2017
2. Moen, V et al. Bjog 2009
3. Gude NM, et al. Thromb Res 2004