Under what circumstances would you consider transitioning back to a ventricular peritoneal shunt from a ventricular-pleural shunt?

If a VPleural shunt is working and well tolerated, there is generally no reason to move it, as for many older patients (usually beyond early childhood) these shunt are well tolerated with no long term complications. If there are recurrent issues, such as pleural effusions or a patient with poor respiratory function that does not tolerate the pleural shunt, that is a reason to consider moving it. In that case, you must consider why it isn't currently in the peritoneum. Some patients are not good absorbers in the abdomen, due to prior infections or surgery, and it still might be a poor destination. If you have had a long period of resting the peritoneum, at least months but preferably years, you can try it again, but success is not guaranteed...