This study is undertaken to compare the effects of general anesthesia and regional anesthesia on olfactory acuity and memory in the postoperative period.

This is an observer blinded randomized study conducted over 164 ASA I- II patients scheduled for elective surgery. They were randomized into four groups to receive regional anesthesia, general anesthesia with sevoflurane or general anesthesia with isoflurane or general anesthesia with propofol. Hindi Mental state Examination (HMSE), olfactory acuity, olfactory memory along with blood sampling to measure serum melatonin levels were tested at 12 h preoperatively (T=0), at 3 h postoperatively (T=1) and at the time of discharge or postoperative day 3 (T=2). Olfactory acuity was tested with successive dilutions of n-butyl alcohol and olfactory memory with the University of Pennsylvania Smell Identification Test.

Olfactory acuity and cognitive function was intact in all patients, before and after anesthesia. Olfactory memory evaluated by UPSIT revealed significantly lower score with patients receiving sevoflurane based anesthesia at 3 hours postoperatively when compared to preoperative and postoperative day 3 value(P = 0.01). Misinterpretation of odours was significantly more in group SEVO than in group RA, ISO and TIVA (P < 0.001) which was accompanied by a significant reduction of plasma melatonin levels in group SEVO.

Sevoflurane is associated with short term olfactory memory impairment.