A 72-year-old man with a 35g benign prostate gland undergoes TURP under spinal anaesthesia. During the procedure lasting 90 minutes, he develops confusion, bradycardia, nausea, and hyponatraemia (serum Na 118 mEq/L). Visual disturbances are also noted. Which electrolyte/osmolality parameter best distinguishes TURP syndrome caused by glycine absorption from simple dilutional hyponatraemia?
- A Serum osmolality normal or elevated (pseudohyponatraemia due to glycine)
- B Urine sodium > 20 mEq/L suggesting SIADH
- C Serum potassium elevated due to transcellular shift
- D Serum ammonia levels elevated due to glycine metabolism to ammonia ✓
Explanation
TURP syndrome results from systemic absorption of hypotonic glycine 1.5% irrigating fluid. Glycine is metabolised to ammonia (via transamination), causing hyperammonaemia — this explains the encephalopathy (confusion, visual disturbances — glycine is an inhibitory neurotransmitter in the retina) disproportionate to the degree of hyponatraemia. Elevated serum ammonia is a distinguishing feature of glycine-induced TURP syndrome versus simple dilutional hyponatraemia from other causes. Management includes hypertonic saline (3%) for severe hyponatraemia (Na < 120 or symptomatic) and furosemide. Modern practice uses bipolar TURP with normal saline irrigation to eliminate this complication.
Reference: Bailey & Love's Short Practice of Surgery, 27th ed.
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Written and medically reviewed by the StethoPrep medical team.