The nurse cares for a patient who is receiving diphenhydramine for acute rhinitis. The nurse notes that the patient has not voided for the past 12 hours. Which action should the nurse take?

Choice A rationale Diphenhydramine, an H1-receptor antagonist (first-generation antihistamine), possesses significant anticholinergic properties. These properties can cause urinary retention by inhibiting detrusor muscle contraction and constricting the bladder sphincter. Assessing the bladder for distension first will determine the immediate problem and guide intervention, with a normal post-void residual volume being less than 100 mL. Choice B rationale Encouraging increased fluid intake might worsen the patient's condition by increasing bladder volume and potentially exacerbating urinary retention due to the anticholinergic effects of the diphenhydramine. This action should be deferred until bladder emptying status has been accurately assessed, as further filling an already distended bladder is detrimental. Choice C rationale While urinary catheterization may be required for severe retention, it is an invasive procedure with risks like urinary tract infection (UTI). It is premature to request this before performing a non-invasive assessment like palpating or scanning the bladder for distension to confirm the need for intervention. Choice D rationale Requesting an intravenous (IV) fluid bolus would be contraindicated if the patient is experiencing urinary retention. Similar to encouraging oral fluids, a bolus would increase circulatory volume and urine production, placing greater strain on a distended bladder and potentially leading to bladder overstretching or rupture if not addressed.