Final answer:
The nurse should position a client who underwent a supratentorial surgery in a semi-Fowler's position, with the head of the bed elevated at around 30 degrees. This helps reduce intracranial pressure and promote adequate cerebral perfusion.
Step-by-step explanation:
After undergoing a supratentorial surgery, the nurse should position the client in a semi-Fowler's position. This position involves elevating the head of the bed around 30 degrees to reduce intracranial pressure and promote adequate cerebral perfusion. The patient's head should be kept in a neutral position, avoiding extreme flexion or rotation, to prevent strain on the incision site and potential complications.