A 55-year-old woman with chronic obstructive pulmonary disease (COPD) and benign prostatic hyperplasia (BPH) is admitted to the hospital with an acute exacerbation of COPD. She is prescribed ipratropium bromide (an anticholinergic bronchodilator) via nebulizer. On day 3 of admission, she develops acute urinary retention, and the post-void residual volume is >400 mL. Her vital signs are: HR 102/min, BP 145/92 mmHg, temperature 37.8°C, RR 28/min. She is alert and oriented but complains of a dry mouth and blurred vision. What is the MOST likely explanation for her acute urinary retention?