Correlation of Preoperative Hippocampal Volume Measured with Magnetic Resonance Imaging and Emergence from General Anaesthesia in Elective Neurosurgical Patients: An Observational Study

Background and objectives: The electrophysiological process of emergence from general anesthesia (GA) commences from deeper structures of the brain rather than the cortex. The phylogenetically old parts of the brain (hippocampus) are the first to recover during emergence. Study objectives were to evaluate and predict the effect of preoperative hippocampal volume (HV) measured using MRI with emergence from GA and delayed extubation in patients undergoing elective neurosurgical procedures.

Methods: Patients aged 18-65 years of age scheduled for elective neurosurgical procedures under GA with GCS = 15 were recruited into the prospective cohort. Those who underwent excision of the hippocampus, amygdala, and temporal lobe pathology were excluded. Bilateral HVs and total brain volume were measured preoperatively using MRI brain. GA was induced by thiopentone, fentanyl, and vecuronium and maintained with sevoflurane. At the end of the surgery, sevoflurane was turned off, and a fresh gas flow of 6 L min-1 oxygen was set, allowing patients to wake up by "no contact technique." Time elapsed from turning off sevoflurane till the onset of different phases of emergence was measured. The patterns of emergence were assessed using GCS and Riker Sedation-Agitation Scale.

Results: The complete data of 125 patients of 1192 screened for recruitment were analyzed. The median time for extubation was 13 minutes (IQR 9-16). The average bilateral standardized HV had a statistically significant negative correlation with the time to extubation (r = -0.185; P = 0.039). Average of bilateral standardized HV <2097 mm3 predicts delayed extubation with a specificity: 70.7%, sensitivity: 51.2% and AUC: 0.672, CI 0.524-0.724. Standardized dominant HV <1925 mm3 also predicts delayed extubation with specificity: 78%, sensitivity: 46.4% and AUC: 0.635, CI 0.533-0.738.

Conclusion: Neurosurgical patients with larger average HV might lead to early extubation, vocalization, and faster gaining of orientation after GA.