"Sniff test" for consciousness may aid in treatment of brain injuries
Assessing the severity of brain injuries in people showing little or no signs of awareness can be a tall order for physicians. A study out of the University of Cambridge has uncovered a possible new tool that could offer a clearer picture and improved treatment plans for these patients, with an inexpensive “sniff test” demonstrating the potential to predict those that will go on to regain consciousness further down the track.
According to the scientists behind the new study, current approaches to determining a state of consciousness in patients suffering from severe brain injuries lead to diagnosis errors in up to 40 percent of cases. This can mean treatment plans that are ill-advised and hamper recovery efforts, and while we are seeing some promising new alternatives, such as advanced EEG scans that reveal “hidden consciousness,” there is a dire need for new solutions.
While small, the new Cambridge study puts forward an interesting possibility that centers on the human sense of smell and the way the brain responds to certain stimuli. Namely, unpleasant stimuli, which prompt the brain to instigate shorter and more shallow breaths, a response exhibited in both waking and sleeping states of consciousness.
The team enlisted 43 patients with severe brain injuries. Different smells in jars were presented to the subjects, and their breathing response was monitored using a small tube via the nose. The smells included a pleasant shampoo, an unpleasant rotting fish, and a neutral smell with no scent at all. Each were presented 10 times in a random order, with the team measuring the volume of air sniffed by the patient in response.
Minimally conscious patients inhaled much less as a response to the smell, although there was no discernible difference in the response between pleasant and unpleasant smells. A difference in their nasal airflow was also detected in response to the neutral smell, which the researchers say suggests an awareness of the jar or a “learned anticipation” of the smell. A variety of responses were observed in vegetative state patients, meanwhile, with some exhibiting altered breathing, while some did not.
The scientists followed up three-and-a-half years later to investigate how the results of their sniff test could be used to help predict patient outcomes. One hundred percent of the subjects who reacted to the sniff test went on to regain consciousness, and 91 percent of those patients were still alive. Sixty-three percent of the subjects that showed no response, meanwhile, had died.
“The accuracy of the sniff test is remarkable – I hope it will help in the treatment of severely brain injured patients around the world,” says Anat Arzi, a researcher in the University of Cambridge’s Department of Psychology and co-leader of the research.
The team consistently observed different responses to the sniff test between patients in a vegetative state, who may open their eyes or have basic reflexes but show no signs of awareness, and those in a minimally conscious state, who may exhibit fleeting signs of awareness. These subtle but important differences further add to the potential of the sniff test as an accurate diagnostic tool, which the team hopes will enter clinical use sooner rather than later.
“When the sniff response is functioning normally it shows that the patient might still have some level of consciousness even when all other signs are absent,” says Dr Tristan Bekinschtein in the University of Cambridge’s Department of Psychology, who was involved in the study. “This new and simple method to assess the likelihood of recovery should be immediately incorporated in the diagnostic tools for patients with disorders of consciousness.”
The research was published in the journal Nature.
Source: University of Cambridge