Isosmotic hyponatremia from irrigant absorption

Electrolyte Disordersmedium

A 57-year-old woman undergoes a hysteroscopy complicated by uterine perforation and extravasation of irrigant solution. She has a successful surgical repair and is then extubated in the post-anesthesia care unit. Her pain is treated with IV morphine. She has incisional pain and mild nausea. On physical examination, BP is 124/72 mm Hg, heart rate is 92/min, respiratory rate is 14/min, and temperature is 37.6°C. She is no acute distress. There is an expected degree of tenderness at the site of the surgical incision. There is no edema. Laboratory data (1 day preoperative, 1 hour postoperative; reference): sodium 137, 121 mEq/L (136–145); creatinine 0.8, 0.7 mg/dL (0.5–1.1); glucose 86, 75 mg/dL (70–99, fasting); osmolality 289, 282 mOsm/kg H₂O (275–295). Which ONE of the following is the MOST appropriate treatment?

  1. A.Furosemide
  2. B.Hypertonic saline
  3. C.No additional interventionCorrect
  4. D.Isotonic saline

Explanation

No additional intervention is needed at this time for this asymptomatic patient with evidence of irrigant solution absorption. Irrigant solutions containing glycine or sorbitol are used in a variety of endoscopic procedures. Extravasation can result in significant absorption of these effective osmoles, leading to hyponatremia. The effect on serum osmolality depends on the amount and osmolality of the solution absorbed. Glycine and sorbitol irrigant solutions are hypotonic with an osmolality of 200 and 165 mOsm/kg H₂O, respectively. The most common clinical consequences are nausea, hypotension, and reduced urine output, but a variety of cardiovascular and neurologic signs and symptoms has been reported. Severity of presentation appears to correlate with the volume absorbed. In this case, the patient sustained a marked fall in the serum sodium caused by absorption of the irrigant solution but only a slight decrease in the serum osmolality from her baseline and was minimally symptomatic. The differential diagnosis for euvolemic hyponatremia also includes the syndrome of inappropriate antidiuresis (SIAD), for which she is at risk due to exposure to morphine, as well as pain, nausea, and surgical stress, all of which can stimulate antidiuretic hormone secretion. In this case, SIAD is excluded by the absence of hypo-osmolality. Hypertonic saline has been used in patients with neurologic complications and significant hypo-osmolality or in those with a drop in serum sodium level by >5 mEq/L when mental status cannot be assessed due to anesthesia but would not be indicated in this asymptomatic patient. Neither would isotonic saline be indicated in this patient without evidence of hypovolemia. Loop diuretics have been used in patients with irrigant absorption with concomitant volume overload and pulmonary edema, neither of which is present here. In the absence of neurologic symptoms, AKI, or volume disturbance, serum sodium can be allowed to correct without intervention as the retained solute (glycine or sorbitol) is taken up intracellularly, metabolized, and excreted.

Why each option

A.
Loop diuretics are used only when irrigant absorption causes volume overload or pulmonary edema, neither of which is present here.
B.
Hypertonic saline is reserved for neurologic symptoms with true hypo-osmolality; serum osmolality of 282 mOsm/kg means little water shift into the brain.
C.
Correct. Sodium of 121 mEq/L with near-normal osmolality reflects retained glycine or sorbitol, which is metabolized and excreted, so an asymptomatic patient needs no treatment.
D.
Isotonic saline is indicated for hypovolemia, which is absent; her BP, heart rate, and creatinine are stable after surgery.

Reference: Spasovski G, Eur J Endocrinol 2014 (clinical practice guideline on diagnosis and treatment of hyponatraemia); Hahn RG, Br J Anaesth 2006 (fluid absorption in endoscopic surgery)

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