Not possible until he is capable of signing one. You would need to seek guardianship.
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I agree with the other attorney that has already answered. If he cannot sign a legal document, then he cannot execute the required paperwork. You need to talk to an attorney that handles estate planning/probate. There are many in your area. Look on this website and on the State Bar of Texas website. I'd also ask friends and family for a referral in your area. I'm sorry that you are going through this horrible experience. All the best to you and your family.
So sorry to hear of your husband's medical condition.
If he is unable to sign a Power of Attorney, or lacks the capacity to do so, you will be unable to go this route.
It seems you might need to seek guardianship over your husband in the probate courts. You should consult with a probate/guardianship attorney in your area.