Hi Sarah,
I quite often use the technique of calling a person and then just pushing a button as they turn to look at the camera. In documentary photography, a photographer will often wait for a person to turn and look at the camera without being directed, at which point they push the button; the technique is referred to as confrontation photography and while it is not intended to upset people, it does give us the opportunity to take an uncomplicated look at a person in a photograph. (This particular technique stems from the fact that most people, mean in unfamiliar situations, often reveal quite a bit about themselves by their first glance at a stranger).
The trick to this technique is always to have the camera and the composition ready to go before the person of the camera. In this instance I would have liked to have seen you get slightly lower with the camera and then compose the image more to the left or to the right so that your husband was not directly in the centre of the frame.
I also think this photograph would have been just as good head your husband been looking away from the camera.
I hope your husband's operation goes well and that you get many more opportunities in the future to work on your portrait technique with him.
All the best, Anthony