The smell test that predicts the return to consciousness of head injured people

The recognition test developed by the researchers from the Weizmann Institute in partnership with Dr. Yaron Sakhar, director of the brain injury rehabilitation department at Beit Levinstein - is based on the principle that our breathing changes in response to a smell; For example, an unpleasant smell will cause our inhalations to become shorter and shallower. These reactions happen even without us being aware of it - whether we are awake or asleep

If an unconscious person reacts to the smell through a subtle change in his breathing pattern - he is expected to regain consciousness. This is the conclusion that emerges from a new study by Weizmann Institute of Science scientists and their partners at the Levinstein Rehabilitation Hospital. According to the research findings, which are published today in the scientific journal Nature, 100% of the head injured unconscious, who responded to the smell test developed by the researchers, regained consciousness during the four-year study period. The scientists believe that this simple and cheap test can help doctors diagnose head injuries and adapt a treatment plan that suits their condition.

After a severe brain injury, it is not always possible to determine the state of consciousness of the head injured person, and the consciousness tests used today may lead to a wrong diagnosis in about 40% of cases. "A wrong diagnosis can have a critical meaning to the point of deciding to disconnect a person from life support devices," says the leader of the study, Dr. Anat Arzi. "Even at the level of routine treatment, if they believe that a person is unconscious and doesn't feel anything, the doctors may not give him the painkillers he so desperately needs." The research began during Dr. Arzi's doctoral studies in Prof. Noam Sobel's research group in the Department of Neurobiology at the Weizmann Institute of Science and continued as part of her post-doctoral research in the Department of Psychology at the University of Cambridge.

The recognition test developed by the researchers - in partnership with Dr. Yaron Sakhar, director of the brain injury rehabilitation department at Beit Levinstein - is based on the principle that our breathing changes in response to a smell; For example, an unpleasant smell will cause our inhalations to become shorter and shallower. These reactions happen even without us being aware of it - whether we are awake or asleep.

In the study, 43 head injured patients hospitalized at Beit Levinstein were examined. The researchers brought jars containing the pleasant smell of shampoo, the smell of stinking fish and a jar with no smell at all to the subjects' noses, and measured with a tube the volume of air they inhaled through the nose in response to the smells; Each jar was presented ten times in random order. "Amazingly, all the patients who were classified as 'plants', but responded to the sniff test, where they subsequently recognized, albeit minimally. In some cases, the result of the smell test was the first sign that the brain of these patients was about to recover - and this reaction was observed days, weeks and even months before other signs," says Dr. Arzi. In addition, approximately 91% of the patients who responded to the sniff test near the brain injury remained alive during the study period, while 63% of the patients who did not respond to the sniff test died.

"The advantage of the smell test is its simplicity, availability and low cost," explains Dr. Arzi. "It can be performed at the patient's bedside, without shaking him - and in fact, hospitals are already equipped with available means for breathing monitoring."

Imagine a tennis match

After a severe head injury, people may enter a state of coma - their eyes are closed and they have no cycles of sleep and wakefulness. A coma usually lasts for about two weeks, after which there may be a rapid improvement and a return to consciousness, a deterioration that leads to death - or beyond the state defined as "impaired consciousness". When the patient opens his eyes spontaneously, but there is no evidence that he is aware of himself or his surroundings, it is customary to classify him as "vegetative". Alternatively, if any consistent signs of consciousness are detected, even if these are weak and unstable signs, the patient will be classified in a state of "minimal consciousness". The currently accepted test for diagnosing the level of consciousness is the Coma Recovery Scale (Revised), which tests responses to various stimuli: following an object with the eyes, turning the head to a sound, response to pain, and so on. Since the rate of misdiagnosis in this test may reach up to 40%, it is recommended to repeat the test five times at least.

However, mistakes also happen when the test is repeated over and over again. "In a well-known study in the field, they put a patient who had a car accident and was defined as a 'plant' into an MRI machine. The researchers asked her to imagine that she was playing tennis, and saw that her brain activity was similar to the brain activity of healthy people when they were asked to imagine playing tennis. Suddenly they realized: 'Wait, she's there. She hears us and responds to our commands. She just has no way to communicate.' There are also well-known stories about people who were classified as plants, but when they regained consciousness, they knew how to tell in detail what happened around them while they were supposedly unconscious," says Dr. Arzi. "This is an important clinical challenge: to diagnose the level of consciousness of a person who has suffered a severe head injury. The smell test we developed may help doctors face this challenge."

for the scientific article

More of the topic in Hayadan:

• Corona detection through self-monitoring of the sense of smell
• Humans' sense of smell creates a kind of "personal fingerprint"
• The scientists of the Weizmann Institute of Science discovered: the degree of pleasantness of smells is the basic scale according to which the perception of smell is organized