Scientists at Israel’s Weizmann Institute of Science say they have developed a “sniff test” that is able to predict if an unconscious person is likely to regain consciousness,
The study, which examined whether patients reacted to smells with a slight change in their nasal airflow pattern, was conducted by the scientists together with colleagues at the Loewenstein Rehabilitation Hospital, Israel.
According to the findings, published in the journal Nature, all — 100 percent — of the unconscious brain-injured patients who responded to the “sniff test” developed by the researchers regained consciousness during the four-year study period.
The scientists think that this simple, inexpensive test can help doctors more accurately understand the degree of a patient’s brain injury and to what degree the person is conscious or unconscious. Current diagnostic tests can lead to an incorrect diagnosis in up to 40% of cases, the Weizmann Institute said in a statement.
The study also underlines the primal role the sense of smell, “the most ancient part of the brain,” plays in the organization of the human brain and its role in providing an accurate measure of overall brain integrity, the statement added.
After a severe head injury, patients may fall into a comatose state, in which their eyes are closed and they do not have sleep-wake cycles. A coma usually lasts for about two weeks, after which there the patient may either experience a rapid improvement and return to consciousness, undergo a deterioration leading to death, enter a condition defined as “disorder of consciousness.”
When spontaneous eye opening occurs but there is no evidence that the patients are aware of themselves or their surroundings, they are then diagnosed as being in a “vegetative state.”
The gold standard diagnostic tool for assessing the level of consciousness is the Coma Recovery Scale (Revised), which examines responses to various stimuli including eye movements while tracking an object, turning the head toward a sound, and response to pain. Since the rate of diagnosis errors may reach up to 40%, it is recommended to repeat the test at least five times.
“Misdiagnosis can be critical, as it can influence the decision of whether to disconnect patients from life support machines,” said Dr. Anat Arzi, who led the research. With regard to treatment, “if it is judged that a patient is unconscious and doesn’t feel anything, physicians may not prescribe them painkillers that they might need.”
The “consciousness test” developed by the researchers — in collaboration with Dr. Yaron Sacher, head of the Department of Traumatic Brain Injury Rehabilitation at Loewenstein Rehabilitation Hospital — is based on the principle that nasal airflow changes in response to odor; for example, an unpleasant odor will lead to shorter and shallower sniffs. In healthy humans, the sniff-response can occur unconsciously in both wakefulness and sleep.
The study consisted of 43 brain-injured patients in the Loewenstein Rehabilitation Hospital.
The researchers briefly placed jars containing various smells under the unconscious patients’ noses, including a pleasant scent of shampoo, an unpleasant smell of rotten fish, or no odor at all.
At the same time, the scientists precisely measured the volume of air inhaled through the nose in response to the odors. Each jar was presented to the patient ten times in random order during the testing session, and each patient participated in several such sessions.
“Astonishingly, all patients who were classified as being in a ‘vegetative state’ yet responded to the sniff test, later regained consciousness, even if only minimal,” said Arzi in the statement. “In some cases, the result of the sniff test was the first sign that these patients were about to recover consciousness — and this reaction was observed days, weeks and even months prior to any other signs.”
Moreover, the sniff response was able to predict with about 92% accuracy who would survive for at least three years, the statement said.
“The fact that the sniff test is simple and potentially inexpensive makes it advantageous,” Arzi said. “It can be performed at the patients’ bedside without the need to move them — and without complicated machinery.”