@Bbtauer Hi Brenda, and welcome to the JDRF TypeOneNation Forum!
I understand the situation your son is in, especially because he is, like me, slim and using CIQ. I was fortunate when had bi-lateral hernia surgery and had to keep my abdomen clear that I wasn’t using a CGM or CIQ. Seeing that he has planted his G6 on his left arm, and that almost all surgery protocols demand a blood pressure cuff on an arm for intermittent monitoring, I suggest that he place the 6 mm Tandem cannula on the upper side of his left butt; I’m suggesting ‘left side’ so as to free up his right side for the connections to the BP cuff and the 12 lead monitoring system.
As @Joe suggested, the big chore might be educating surgeon and anesthesiologist. I was fortunate that my four surgeons, for different procedures, were mostly understanding when I TOLD them that my insulin pump would remain in place and active before, during, and after surgery and that i would be “in-charge” of my diabetes. I did have to educate a couple of the anesthesiologists and CRN-A.
I hope all goes well for your son; please let us know how he works this out.