This is from the 2015 nejm article on cvc complications.
I did a fair share of SC in fellowship. The vein lies in the deltopectoral groove, easy to palpate even in the morbidly obese. Aim for the top of the sternal notch, walk off the bone. Its like any mechanical skill just need enough to get comfortable. Ive used ultrasound and it hasn't been to useful. The morbidly obese are a challenge, for the bmi>50 youre almost diving down at a 45 which can be uncomfortable. I think the super skinny are at more of a risk of pneumo, less space for error. Heres a trick: put them on 100%, when youre walking off the bone ask the circulator to turn the vent to spontaneous