Final answer:
The nurse would best use a portable ultrasound scanner to assess for bladder retention, as it is a precise and non-invasive method.
Step-by-step explanation:
To assess the bladder for retention after a client who has a history of benign prostatic hypertrophy (BPH) reports having trouble voiding, the nurse would best use a portable ultrasound scanner to scan the bladder. This non-invasive method can quickly and accurately determine the amount of urine remaining in the bladder post-voiding, which is indicative of urinary retention, a common complication of BPH. While palpation for rounded swelling above the symphysis pubis and checking for rebound tenderness can offer some clinical insight, they are less specific and reliable than ultrasound imaging. Insertion of an intermittent urinary catheter could be used to directly measure post-void residual urine and relieve retention but would be more invasive and less preferable as an initial assessment tool.