Discussion:
Maternal hyponatremia is an important yet unrecognized cause of seizure
during the peripartum period. As discussed above, specific physiological
changes, as well as management practices during the peripartum period
can contribute to maternal and neonatal hyponatremia
Hyponatremia is common during pregnancy and but sodium levels as low as
115 mmol/L are extremely rare. A prospective study in 2008 which
included 287 women at the time of labor determined that approximately
7% of women had a plasma sodium concentration of 130 mmol/L or
lower.[3] The study correlated the hyponatremia to fluid volume
administered during labor and not due to oxytocin or epidural
analgesia.[3] Similar to our patient, the patients’ with
hyponatremia in the study also required device assistance or caesarian
section for delivery. However, unlike our patients, none of them
experienced a grand mal seizure.
In our search, we have uncovered only six other reported cases of severe
hyponatremia in laboring mothers resulting in neurological
sequelae[3] [4][5][6][7][8]. The interesting
issue in our case is that it is the second reported case where fluid
loading contributed to the patient’s hyponatremia was purely via oral
free water intake. Furthermore, this case is only case where oral free
water intake caused multiple grand-mal seizures during the peripartum
period. In the five other cases, fluid supplementation was with oral
intake of water and electrolyte drinks as well as with intravenous fluid
and incidental additional fluid via required oxytocin infusion.
Our patient suffered from seizures due to an acute intoxication of water
causing acute hyponatremia. The patient was advised by the midwife to
increase her water intake as she was getting closer to term “to clean
the baby”. Acute hyponatremia can result in neurological symptoms due
to the water movement into the brain resulting in cerebral edema which
can manifest as seizures, altered mental status, and in severe cases,
even coma and death [9]. These changes are typically brought on less
than 48 hours. In chronic hyponatremia, neurological changes are very
subtle, and patients are typically asymptomatic as the brain adapts to
the changes over a longer duration of time (greater than 48 hours) by
generating ionogenic osmoles [3]. This mechanism protects the brain
by reducing the risk of cerebral edema and therefore, the risk of
seizures.
During labor, water intoxication could also occur due to ADH-like-action
of oxytocin. Oxytocin and ADH are both released from the posterior
pituitary gland are structurally similar which could also result in
water retention as it stimulated the ADH receptors of the kidney
[3]. Oxytocin is primarily given to help augment labor [10].
There have also been cases reported of water intoxication due to
intravenous oxytocin infusion in normal pregnant women that resulted in
severe hyponatremia and a grand-mal seizure [11]. Although our
patient did not receive intravenous oxytocin, there is a natural release
of oxytocin that occurs during delivery which also could have played a
role in this acute hyponatremic setting of our patient that further
exacerbated the hyponatremia.
Although our patient presented with features mimicking eclampsia during
labor, she had no history of pre-eclampsia. Eclampsia is a
life-threatening, pregnancy-related multi-organ disorder that manifests
as unexplained seizures after 20 weeks of gestation due to abnormal
placental development in a patient with a history of pre-eclampsia
[12]. Pre-eclampsia is characterized by a prior history of
hypertension, proteinuria, thrombocytopenia, and liver dysfunction
[12].