Measuring Consciousness in the Intensive Care Unit

Abstract

Early reemergence of consciousness predicts long-term functional recovery for patients with severe brain injury. However, tools to reliably detect consciousness in the intensive care unit are lacking. Transcranial magnetic stimulation electroencephalography has the potential to detect consciousness in the intensive care unit, predict recovery, and prevent premature withdrawal of life-sustaining therapy.

Keywords: Coma; Complexity; Consciousness; Transcranial magnetic stimulation electroencephalography (TMS-EEG).

Figure. 1.. Stimulating the brain to determine its capacity for consciousness.

(A) A technologist (left) with expertise in transcranial magnetic stimulation-electroencephalography (TMS-EEG) measures the perturbational complexity index (PCI) in a patient with a severe traumatic brain injury (center), while a physician observes (right). The technician stimulates the right premotor cortex based on precise anatomic guidance provided by the T1-weighted magnetic resonance imaging (MRI) scan on the top of the left screen. A functional MRI connectivity map is used to identify cortical sites to be targeted (e.g., highly connected regions shown in red are likely to have higher PCI values). The turquoise aiming device on the bottom left of the screen provides real-time feedback about the precision of target stimulation. On the right screen, the technologist visually assesses for artifacts and determines the reliability of TMS-evoked potentials recorded by 19 EEG electrodes. In this illustrative patient, the PCI value of 0.48 is above the empirically derived cut-off of 0.31, indicating that the patient’s brain has the same complexity as that of conscious subjects. (B) TMS-evoked EEG waveforms that indicate low (black), moderate (gray), and high (green) potential for recovery of behavioral signs of consciousness. These waveforms are adapted from Casarotto et al. 2016 [19], where low potential for recovery was observed with PCI = 0, moderate potential for recovery with 0 < PCI ≤ 0.31, and high potential for recovery with PCI > 0.31. Abbreviations: A = anterior; I = inferior; L = left; P = posterior; R = right; S = superior.