Snuff test that presents brain injury patients with odors can predict recovery


Exposing brain injury patients to an olfactory range may determine whether they will recover, according to researchers behind a ‘sniff test’ study.

Researchers at Cambridge University gave patients scents, including shampoo and rotten fish, and then followed their reactions through a nasal tube.

In the new study, researchers looked at patients with brain injuries who showed very little or no signs of awareness of the world around them.

All patients who responded to the sniff test regained consciousness, and more than 91 percent lived three and a half years after their injury.

The inexpensive and simple test could mean that doctors accurately diagnose and determine treatment for patients with impaired consciousness, the authors claim.

Researchers at Cambridge University gave patients scents, including shampoo and rotten fish, and then followed their reactions through a nasal tube. Stock image

Lead research author Dr. Cambridge University’s Anat Arzi said the accuracy of the sniff test was remarkable.

It is often difficult for physicians to determine a patient’s state of consciousness after a serious brain injury, and errors are made in diagnosis in 40 percent of cases.

A patient who is minimally conscious differs from a patient in a vegetative state and their future results are different.

An accurate diagnosis is critical because it provides information about treatment strategies such as pain management and can influence end-of-life decisions.

Professor Noam Sobel, of the Weizmann Institute of Science in Israel, said that sense of smell is a “very basic mechanism” that relies on structures deep within the brain.

“The brain automatically changes the way we smell in response to different scents,” said Sobel, who was the lead author of the study.

‘If we get an unpleasant odor, for example, we automatically take shorter, shallower breaths.

“In healthy people, the sniffing reaction occurs in both the waking and dormant states of consciousness.”

Scientists conducted their research on 43 serious brain injuries.

The researcher first explained to each patient that different scents would be presented to them in jars and that breathing through their nose would be monitored using a small tube called a nasal cannula.


Investigators had no indication whether the patients had heard or understood.

Then each patient was given a jar with a pleasant fragrance of shampoo, an unpleasant odor of rotten fish or no odor at all for five seconds.

Scientists use a deep mechanism in the brain to make a ‘sniff test’
Our sense of smell is a core and basic mechanism – it depends on structures deep in the brain.

In fact, the brain automatically changes the way we smell in response to different smells.

For more unpleasant smells, such as rotten fish, we breathe shorter and less deeply.

Researchers used this mechanism to make their sniff test in patients who cannot respond in any other way.

They presented patients with an odor in a jar using a nose tube.

The team then measured how much air the patient sniffed in his nose.

Research author Dr. Yaron Sacher of Loewenstein Rehabilitation Hospital in Israel said each jar was presented to the patient at random ten times.

Then they took a measurement of the air volume sniffed by the patient.

Minimally conscious patients inhaled significantly less in response to odors, but did not distinguish between pleasant and unpleasant odors, findings revealed.

Patients also changed their nasal airflow in response to the jar without an odor, indicating jar awareness or a learned anticipation of an odor.

Patients with vegetative status varied. Some did not change their breathing in response to any of the scents, while others did.

Scientists later found 91 percent of patients who had a sniffing reaction shortly after an injury were alive in a follow-up study three and a half years later.

While 63 percent of those who had not responded, died.

The researchers were able to measure how well-rooted brain structures worked by measuring the sniff response in patients with severe brain injuries.

All patients who responded to the sniff test – of both shampoo and rotting fish – regained consciousness three and a half years after their injury with more than 91 percent still alive. Stock image

Within the patient group, they found that the sniff response consistently differed between that in a vegetative state and that in a minimally conscious state, providing further evidence for an accurate diagnosis.

“We found that if patients in a vegetative state had a sniffing reaction, they later switched to at least a minimally conscious state,” Arzi said.

“In some cases, this was the only sign their brain would recover, and we saw it days, weeks, and even months before there were other signs.”

In a vegetative state, the patient may open his eyes, wake up regularly and fall asleep and have basal reflexes, but they do not show meaningful reactions or signs of consciousness.

A minimal conscious state differs because the patient may have periods in which he may show signs of consciousness or respond to orders.

Dr. Tristan Bekinschtein, of the University of Cambridge’s Psychology Department, said that when the sniffle response functions normally, it shows that the patient still has a certain level of consciousness, even if all other signs are absent.

“This new and simple method of assessing the likelihood of recovery should be immediately included in the diagnostic tools for patients with consciousness disorders,” he said.

The findings are published in the journal Nature.

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