Try the following approach - anything else is unclean:
private void gridPatients_DoubleClick(object sender, System.EventArgs e)
{
DoStuff();
}
private void gridPatients_KeyDown(object sender, System.Windows.Forms.KeyEventArgs e)
{
DoStuff();
}
private void DoStuff()
{
//do the things that you want to do in KeyDown and DoubleClick
}