I'm sorry to read about your husband's situation. This must be a difficult time for you both.
As a nurse-led service not involved in your husband's clinical care we cannot give a medical opinion. This is something only the team involved in his care can tell you.
Sometimes a nephrostomy tube can't be put in safely unless a colostomy is carried out because of a high risk of infection or poor healing. If there is some bowel disease such as a blockage, leakage or infection, bacteria from the bowel can spread and cause a severe infection if a nephrostomy tube is placed. A colostomy diverts stool away, making things cleaner and safer allowing the area to heal and reducing infection risks.
Again the best person to advise you further on all this is your husband's specialist team. If he has a specialist nurse involved in his care then perhaps they can provide you with further information. You often have to call and leave them a message and they will get back to you.
I hope this has been of some help. Give us a ring if you would like to talk anything over. The number to call is Freephone 0808 800 4040 and the lines are open from 9am till 5pm, Monday to Friday.
