Constant nausea and retching 8 weeks post esophagastrectomy.

My brother had oesophageal surgery 8 weeks ago and has been readmitted 2x for weight loss and inability to eat in that he feels nauseous 24/7 and eating couple teaspoons food causes severe retching some time later. Currently on TPN IV. He's had all follow up tests and nothing wrong - no narrowing , no leaking just slightly slowed motility. On reglan. Esomeprazole but zofran etc not working so been stopped. Consultant says never seen it before and doesn't know what to do next- GI team stumped as well. Anyone have any suggestions at all? It's worrying the nausea never subsides and he's v low.