Answer:
Heres the advice I would give to Carlos!
Explanation
The most important thing that he can do is just be there for her. Make sure that the wife knows, he's right by her side and he's with her throughout the entire way. Reinforce this by talking to her, "I love you, etc", holding her hand if possible and maintaining eye connection. This will show the wife that she is not alone in this time of pain and her worry levels will be reduced.
Also, Carlos should reassure about what is going to happen. "This is going to be over soon, etc" He should have the wife concentrate on how better everything is going to be when this is all over. When its the end, theres no going to be anymore pain, and you'll be able to feel so much better. Keep reminding her to focus on the end, once its all over, and keep her distracted from the time and what the doctors are doing. "After this, think about how much you gonna be able to do, etc" Stay positive but alert for her, so she knows your looking out.
The last thing could be, again, distracting her but with different ways. Maybe humor, making jokes to make her smile or telling her a story. In any way, give her something her mind can concentrate on instead to her focusing on the scary pain of the procedure. In any way, give a focus point to block out the pain and hang on to something more positive.
Thats all I can say, be there for her, reassure her and distract her. All of these things can reduce her worry and stress!
Hope this helped!! :)