I also work in a large center that also has a high volume liver transplant service. In these OR cases, our anesthesia team typically places a MAC on the IJ, a couple large bore peripheral IV's, and a RIC (http://spinalist.debunk-it.org/RIC%206.pdf
) in the arm knowing that these are very bloody OR cases that result in large EBL's and multiple transfusions.
That said, placing two central catheters in the same IJ site is acceptable. As an ICU NP, I have placed a triple lumen CVC and a Trialysis catheter (Power-Trialysis* Short-Term Dialysis Catheter | Dialysis Catheters | Bard Access Systems
) in the same IJ site. As Core0 stated, the IJ is typically a large vessel and can accomodate two lines through its diameter. In this age of ultrasound guided line placements, you could actually tell during placement if you can do this just by looking at the size of the IJ on the axial view with the ultrasound probe.
There are many factors taken into consideration when we place lines. Dialysis catheters (such as Trialysis) works well in the Right IJ location best and is preferred especially for patients on CRRT. In the few cases I've placed double lines in the same site, the other IJ site is unusable (clotted, subjected to intervention, etc.), SC sites are contraindicated due to coagulopathy, and femoral sites are not ideal due to a large pannus that could subject the line to infection.
As far as arterial lines, I have placed long femoral catheters in the radial site in a previous setting I worked in. They tend to last longer and same as in Core0's experience, have not seen adverse effects from its long length that would not have happened in the regular length arterial catheter. Our arterial catheters are all Gauge 20's regardless of length if that makes a difference. However, current policy where I work now requires that we only place the short catheters in the radial site. A lot of time, policies are created based on case reports of adverse effects. I would have to dig up the literature on it.