Olfactory sniffing signals consciousness in unresponsive patients with brain injuries.
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Arzi, A., Rozenkrantz, L., Gorodisky, L., Rozenkrantz, D., Holtzman, Y., Ravia, A., Bekinschtein, T., et al. (2020). Olfactory sniffing signals consciousness in unresponsive patients with brain injuries.. Nature, 581 (7809), 428-433. https://doi.org/10.1038/s41586-020-2245-5
It is often difficult to determine state of consciousness following severe brain injury; is the patient vegetative, or perhaps minimally conscious1? and if vegetative, will the patient recover? These diagnoses and prognoses are critical, as they determine therapeutic strategies such as pain management, and can underlie end-of-life decisions. And yet, troublingly, there is up to 40% error in determining state of consciousness in brain-injured patients. Olfaction relies on deep brain structures that are involved in basic mechanisms of arousal6, and therefore we hypothesized that it may serve as a biomarker for consciousness. To test olfaction in brain injured patients we used a non-verbal non-task-dependent measure known as the sniff-response8–11, namely automatic sniff modulations to account for odorant content. By precisely measuring odorant-dependent sniffing we gain a sensitive measure of olfactory function10–15. Here we applied this measure repeatedly over time in 43 severely brain-injured patients. We found that sniff-responses significantly discriminated between vegetative and minimally conscious states at the group level (p < 0.0001, effect-size r = 0.63). More remarkably, at the single patient level, if a vegetative patient had a sniff-response, this indicated future regaining of consciousness at 100% specificity. Finally, olfactory sniff responses predicted long-term survival rates at 92% accuracy (X2 = 14.5, p = 0.0001, Cramer's V effect size = 0.45). These results stress the primality of olfaction in functioning of the human brain, and provide for an accessible bedside tool that signals consciousness and recovery in brain-injured patients.
Humans, Persistent Vegetative State, Brain Injuries, Diagnostic Errors, Prognosis, Sensitivity and Specificity, Survival Analysis, Consciousness, Arousal, Smell, Recovery of Function, Adult, Female, Male, Olfactory Perception, Odorants
External DOI: https://doi.org/10.1038/s41586-020-2245-5
This record's URL: https://www.repository.cam.ac.uk/handle/1810/305055
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