Critical Importance of Close Monitoring of Sodium and Fluid Balance in Labor and Delivery

Introduction: Hyponatremia (hypoNa) is the most common electrolyte disorder seen in clinical practice; due to its many causes, it can be difficult to diagnose and manage. In this case report, we present a unique case of rapid hypoNa associated with pregnancy and the concurrent use of oxytocin and ketorolac. Oxytocin exerts antidiuretic effects similar to those of vasopressin, leading to water retention and dilutional hypoNa. The risk of oxytocin-induced hypoNa is heightened by concomitant fluid administration, making it a well-recognized but potentially preventable complication in obstetric practice. Ketorolac has also been associated with hypoNa, due to the inhibition of renal prostaglandin synthesis, which affects renal water handling and sodium (Na) balance. Additionally, while healthy women can typically excrete about 900 ml of water per hour, this ability decreases by about 1/3rd in late pregnancy, further complicating the management of fluid balance and hypoNa. Case Description: We present a case of a 35-year-old G1P1 female with a past medical history notable for depression and anxiety who presented 32 weeks pregnant with preeclampsia with severe features. She was started on a magnesium infusion and underwent a cesarian section. During the procedure she had 500 ml blood loss, she received 30 units of oxytocin and 900 ml of lactated ringers (LR). Post procedure she was started on LR at 75 ml/hr and ketorolac every 6 hours for pain control. Eight hours later the patient was found to be lethargic. Stat labs showed a Na of 122 mmol/L (Na was 134 mmol/L on admission). LR was changed to normal saline (NS) and Na further dropped to 119 mmol/L. Urine Na and osmols were 123 mmol/L and 629 mOsm/kg respectively. The patient denied excessive fluid intake and pain. NS and ketorolac were discontinued, and water restriction was initiated. The Na improved to 130 mmol/L within 24 hours. Discussion: This case presents a rare but significant complication of acute hypoNa precipitated by the concurrent administration of oxytocin and ketorolac in a patient population with decreased free water clearance. Prompt recognition and management of hypoNa is vital to prevent serious neurological complications and ensure favorable patient outcomes. This case highlights the need for electrolyte and fluid balance monitoring, particularly in patients receiving medications known to cause hypoNa.