What do you do for hipotony in one upper extremity ? Xray ? Wait and see ? Pyhsioterapy   ? Neurology consultation ? Brain surgery consultation ?

If the clinical history is typical (complicated vaginal delivery etc), we don’t do anything investigation apart from clinical assessment. We liberally refer to our physiotherapist for assessment and follow up 

However, if the arm is completely paralytic, then we ask neurology/neurosurgery for advice, but I have not myself been involved in a case that went for nerve suture. But I understand that could be an option.

Brachial plexus injury during difficult delivery usually resolves on it's own. We observe it clinically and if no improvement seen in first week, then we consider physiotherapy and Neurology consult. I didn't had any baby not improving spontaneously for last so many years... all of those babies improved rapidly in their own.