The Characteristics of Electroencephalogram Signatures in Minimally Conscious State Patients Induced by General Anesthesia.

OBJECTIVE: General anesthesia (GA) is necessary for surgery, even for patients in a minimally conscious state (MCS). The characteristics of the electroencephalogram (EEG) signatures of the MCS patients under GA are still unclear.

METHODS: The EEG during GA were recorded from 10 MCS patients undergoing spinal cord stimulation surgery. The power spectrum, phase-amplitude coupling (PAC), the diversity of connectivity, and the functional network were investigated. Long term recovery was assessed by the Coma Recovery Scale-Revised at one year after the surgery, and the characteristics of the patients with good or bad prognosis status were compared.

RESULTS: For the four MCS patients with good prognostic recovery, slow oscillation (0.1-1 Hz) and the alpha band (8-12 Hz) in the frontal areas increased during the maintenance of a surgical state of anesthesia (MOSSA), and "peak-max" and "trough-max" patterns emerged in frontal and parietal areas. During MOSSA, the six MCS patients with bad prognosis demonstrated: increased modulation index, reduced diversity of connectivity (from mean±SD of 0.877±0.003 to 0.776±0.003, p<0.001), reduced function connectivity significantly in theta band (from mean±SD of 1.032±0.043 to 0.589±0.036, p<0.001, in prefrontal-frontal; and from mean±SD of 0.989±0.043 to 0.684±0.036, p<0.001, in frontal-parietal) and reduced local and global efficiency of the network in delta band.

CONCLUSIONS: A bad prognosis in MCS patients is associated with signs of impaired thalamocortical and cortico-cortical connectivity - as indicated by inability to produce inter-frequency coupling and phase synchronization. These indices may have a role in predicting the long-term recovery of MCS patients.