Detecting Awareness in the Intensive Care Unit Using Functional Near-Infrared Spectroscopy

Signs of awareness after acute severe brain injury are critical for informing goals-of-care decisions, ranging from the continuation of aggressive life-sustaining therapy to comfort-focused end-of-life measures. However, awareness may go undetected in some critically ill patients when assessed using bedside behavioral neurological examination. Here, we use functional near-infrared spectroscopy to identify covert awareness in acute brain injured patients who are unable to follow behavioral commands.

We conducted a prospective, consecutive cross-sectional study of 32 critically ill patients in a single intensive care unit (ICU). All had acute brain injuries from various causes and lacked behavioral command-following on bedside examination, as determined by using the Coma Recovery Scale-Revised. Using functional near-infrared spectroscopy, an optical bedside neuroimaging technique, we assessed brain activity while patients were instructed to perform a mental imagery task in which a positive response was dependent upon preserved awareness. We referred to this phenomenon as covert awareness.

Of 32 acutely brain injured patients (mean age = 63, ± 12 years, 15 females), 8 (25%) were able to willfully modulate their brain activity when instructed to imagine playing a game of tennis-providing evidence of covert awareness despite no observable behavioral signs that this was the case. We found no association between covert awareness and 3-month functional outcomes using the Glasgow Outcome Scale-Extended.

Functional near-infrared spectroscopy detected preserved consciousness in 25% of patients who lacked behavioral command following in an intensive care setting. This finding highlights the need for further research to assess the use of advanced neuroimaging techniques in the clinical assessment of critically ill patients. Such methods could ensure that goals of care decisions are based on a more accurate understanding of a patient's level of awareness. ANN NEUROL 2025;98:1201-1209.