The answer to this question may indeed turn on the law in the state of Texas and the court's interpretation of the documents involved.  Technically a person appointed as your Medical Power of Attorney has the right to make medical decisions for you in the event that you are not able to do so.  They shouldcarry out your wishes as expressed in your advance directive (DNR - do not resuscitate order, etc.) but if they have to follow them is another story.  I think that you may have to seek an answer in the law in Texas.  I could see the argument being that the medical POA has breached their fiduciary duty to the person for whom the POA was enacted by going against the medical directive.  But unless and until some one challenges it legally the medical POA has the right to make those decisions on the spot.  Good luck.