I would not delay the case to correct (or begin correcting) this patient's Na. Chronic, documented asymptomatic hyponatremia doesn't put him at risk for sudden brainstem herniation; rapid correction is unnecessary and likely more risky.
As I understand it, central pontine myelinolysis is a far greater risk with rapid correction of chronic hyponatremia than it is when correcting acute hyponatremia. This is the last patient who should get abruptly corrected.
Does 3% vs NS matter? 3% is definitely indicated for initial rapid correction of 4-6 mEq/L in a symptomatic patient, but I don't see any advantage when it comes to the gradual correction to more normal levels.
Also, he doesn't need a central line for his surgery. While you don't HAVE to give 3% through a central line, nurse/floor protocols everywhere I've been would put a halt to 3% through a peripheral IV. Just using NS avoids the central line issue altogether.
I would begin an emergency case in any asymptomatic chronically hyponatremic patient regardless of level, of course with a mind toward probable root causes, careful fluid management, and slow correction.
What's the risk we're afraid of here? Herniation or seizures - not going to happen, he's been <120 forever. In a chronic, asymptomatic patient, I don't see an advantage to preop correction that outweighs whatever makes the case an emergency.
I agree with all of this.