Reliable electroencephalography (EEG) signatures of transitions between consciousness and unconsciousness under anaesthesia have not yet been identified. Herein we examined network changes using graph theoretical analysis of high-density EEG during patient-titrated propofol-induced sedation. Responsiveness was used as a surrogate for consciousness. We divided the data into five states: baseline, transition into unresponsiveness, unresponsiveness, transition into responsiveness, and recovery. Power spectral analysis showed that delta power increased from responsiveness to unresponsiveness. In unresponsiveness, delta waves propagated from frontal to parietal regions as a traveling wave. Local increases in delta connectivity were evident in parietal but not frontal regions. Graph theory analysis showed that increased local efficiency could differentiate the levels of responsiveness. Interestingly, during transitions of responsive states, increased beta connectivity was noted relative to consciousness and unconsciousness, again with increased local efficiency. Abrupt network changes are evident in the transitions in responsiveness, with increased beta band power/connectivity marking transitions between responsive states, while the delta power/connectivity changes were consistent with the fading of consciousness using its surrogate responsiveness. These results provide novel insights into the neural correlates of these behavioural transitions and EEG signatures for monitoring the levels of consciousness under sedation.

Background. The bispectral index (BIS) has been evaluated as a tool for measuring depth of anaesthesia, but the use of BIS in a paediatric population is still controversial. This study was designed to evaluate the correlation of BIS with end-tidal sevoflurane concentration and age in infants and children. Methods. Eighty-one patients undergoing elective urology surgery were allocated into three age groups; 6 months to 2 yr (n=28), 3–7 yr (n=33), and 8–12 yr (n=20). Sevoflurane was administered to achieve steady-state end-tidal sevoflurane concentrations (ET_sevo) of 2.0, 3.0, and 4.0%; these were achieved consecutively either from the lowest or from the highest concentration. The BIS (version XP) was monitored continuously. Results. In all three groups, BIS decreased significantly when ET_sevo increased from 2.0 to 3.0% but there was a paradoxical increase in BIS values when ET_sevo increased from 3.0 to 4.0%. The non-linear regression analysis showed a significant correlation between BIS and age at each ET_sevo. The younger patients showed the higher BIS values. Conclusions. In children aged 6 months to 12 yr, the BIS increased paradoxically as ET_sevo increased from 3.0 to 4.0%. BIS values showed a wide variation in the same ET_sevo and the age itself was considered to be a factor affecting the BIS values.

Epistaxis is the most common complication of nasotracheal intubation. We compared endotracheal tubes (ETT) obturated with an inflated esophageal stethoscope with normal ETTs with regard to the prevention of epistaxis and navigability, both with and without thermosoftening. Dental surgical patients requiring nasotracheal intubation were randomly allocated into 1 of 4 groups (n = 50 each): Group 1, nonthermosoftened ETTs; Group 2, nonthermosoftened ETTs obturated with an inflated esophageal stethoscope; Group 3, thermosoftened ETTs; and Group 4, thermosoftened ETTs obturated with an inflated esophageal stethoscope. Navigability of ETTs through the nasal cavity and postintubation epistaxis were evaluated. Navigability of ETTs through the nasal cavity was the worst in Group 1 (P = 0.001). Epistaxis was the most severe in Group 1, similar between Groups 2 and 3, and the least severe in Group 4 (P < 0.001). The use of esophageal stethoscope-obturated ETTs was effective, and comparable to thermosoftening, in preventing epistaxis associated with nasotracheal intubation. Thermosoftened, obturated ETTs were more effective than simple thermosoftened ETTs in reducing epistaxis.