During surgery in the Trendelenburg position, a sudden drop in urine output is most likely due to which of the following?

During surgery in the Trendelenburg position, a sudden drop in urine output is most likely due to which of the following?

• A. Pooling of urine in the dome of the bladder
• B. Kinking of the urinary catheter
• C. Fluoride toxicity from inhaled anesthetic
• D. Increased antidiuretic hormone production from surgical stimulation

Answer: (A)

When a patient is in Trendelenburg, gravity and the altered orientation can change how urine drains from the bladder. The bladder tilts so its dome becomes the dependent portion, and urine can pool there rather than near the catheter tip at the bladder neck. If urine collects in the dome, the catheter may not drain it efficiently, causing an abrupt apparent drop in measured urine output even though urine production continues. This is a drainage issue caused by positioning, not a true decline in kidney function or a systemic hormonal change. To address it, check that the catheter is patent and not kinked, reposition the patient or adjust the catheter location so urine from the dome can drain, and ensure the collection bag is placed below the bladder to allow gravity drainage. The other options are less likely: catheter kinking is a separate mechanical obstruction that would cause poor drainage regardless of position; fluoride toxicity and increased ADH from surgical stimulation do not explain a sudden, posture-related drop in urine output.

When a patient is in Trendelenburg, gravity and the altered orientation can change how urine drains from the bladder. The bladder tilts so its dome becomes the dependent portion, and urine can pool there rather than near the catheter tip at the bladder neck. If urine collects in the dome, the catheter may not drain it efficiently, causing an abrupt apparent drop in measured urine output even though urine production continues. This is a drainage issue caused by positioning, not a true decline in kidney function or a systemic hormonal change. To address it, check that the catheter is patent and not kinked, reposition the patient or adjust the catheter location so urine from the dome can drain, and ensure the collection bag is placed below the bladder to allow gravity drainage. The other options are less likely: catheter kinking is a separate mechanical obstruction that would cause poor drainage regardless of position; fluoride toxicity and increased ADH from surgical stimulation do not explain a sudden, posture-related drop in urine output.