You look but you don´t see. A simple urinary catheter and a cognitive error.

This post is dedicated to Daniel Kahneman, who died recently (27 January 2024). He was a psychologist, and economist notable for his work on hedonism, the psychology of judgment, and decision-making. He is also known for his work in behavioral economics, for which he was awarded the 2002 Nobel Memorial Prize in Economic Sciences (wikipedia). 

A cognitive error: How a simple and useful device can deviate your reasoning?

The device that you can see in the image down is called a “urinary collector”, and it is attached to the penis, when it is important to measure the diuresis, but you don’t want to put a catheter into the bladder. The collector is then connected to a bag to measure the amount of urine in certain occasions.

Clinical Case

A doctor went to visit a patient with a diagnosis of a disseminated lung cancer , who was receiving a combination of analgesics, morphine and sedatives, to control the back pain and the shortness of breath. The patient was sedated, without a possibility of a verbal communication. He was calm and relaxed, accompanied by his family.

During the normal basic physical examination, the doctor felt a lump in the hypogastrium, he thought in a urinary retention, but he changed his mind when he saw a catheter with urine going towards a bag.

Final Evolution

After one hour thinking about the situation, he got the answer. Can you suggest the correct one from the following list

  1. The doctor touched an enlarged prostate
  2. The abdominal structure was the stomach
  3. The physician detected a bladder full of urine
  4. It is not so important to clarify the clinical situation

Resolution and explanation

The doctor was really surprised when he detected a lump, when he detected a mass the size of a two-year-old child’s head, located in the hypogastrium, and with a soft palpation. The answer came when the doctor saw the real situation. The urine was not collected with an urethral catheter, but with a “urinary collector”, in a non-alert patient unable to control his own bladder.


When the patient is not alert, never use this type of device because the urine may flow incompletely and the patient may suffer from a retention bladder.

Author: Dr. Lorenzo Alonso Carrión