Final answer:
In the case of a patient with a traumatic brain injury exhibiting decerebrate posture, the nurse should anticipate an extension of the arms when drawing a blood sample.
Step-by-step explanation:
A nurse caring for a client with a traumatic brain injury who exhibits a decerebrate posture in response to noxious stimuli, such as drawing a blood sample, should anticipate an extension response.
Specifically, the reaction would involve extension of the arms and possibly the legs, which is characterized by stiffening and posturing where the arms are extended out, and the head is arched back.