A 39-year-old woman is admitted to the gynecology service for hysterectomy for symptomatic uterine fibroids. Postoperatively the patient develops an ileus accompanied by severe nausea and vomiting; ondansetron is piggybacked into an IV of D5 ½ normal saline running at 125 cc/h. On the second postoperative day the patient becomes drowsy and displays a few myoclonic jerks. Stat labs reveal Na 118, K 3.2, Cl 88 HCO3 22, BUN 3, and creatinine 0.9. Urine studies for Na and osmolality are sent to the lab.
What is the most appropriate next step?
A. Change the IV fluid to 0.9% (normal) saline and restrict free-water intake to 600 cc/dThe patient has acute symptomatic hyponatremia, a life-threatening condition. Although some controversy persists as to whether chronic hyponatremia should be rapidly corrected, acute symptomatic hyponatremia should be rapidly treated with hypertonic saline. This patient is at high risk of seizure and respiratory arrest, the main cause of permanent CNS damage in hyponatremia. ICU care, with frequent monitoring of the serum sodium level and CNS status, is critical. Once the Na has risen 4 to 8 mEq/L and the symptoms have improved, the rate of hypertonic saline infusion can be decreased. Less aggressive methods of treating her free-water overload, such as fluid restriction alone or in combination with furosemide, are not appropriate for this acute emergency. Isotonic fluids such as normal saline and lactated Ringer solution are useful in volume depletion but will not treat this patient’s free-water excess. Postoperative hyponatremia is particularly common in premenopausal women. The nausea and pain sometimes associated with surgery are very potent stimulators of vasopressin (ADH) release by the neurohypophysis. If hypotonic fluids are used at all in this setting, the serum sodium level should be closely monitored, and isotonic fluids used if there is any trend toward free-water retention (ie, hyponatremia).